pioneer venus encounter press kit

8/8/2019 Pioneer Venus Encounter Press Kit

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NASA NewsNational Aeronautics andSpace Administration

Washington. D C 20546AC 20 2 755-8370

PressKitRELEASE NO: 78-181

Contents

For Release IMMEDIATE

Project Pioneer VenusEncounter

GENERAL RELEASE..................................... 1-15

ENCOUNTER TIME LINE................................. 16-22

MISSION PROFILE..................................... 23

ORBITER OPERATIONS.................................. 23-34

MULTIPROBE OPERATIONS............................... 35-43

THE PLANET VENUS.................................... 44-60

MAJOR QUESTIONS ABOUT VENUS......................... 61-62

HISTORICAL DISCOVERIES ABOUT VENUS.................. 63-65

EXPLORATION OF VENUS BY SPACECRAFT.................. 66-67

Mailed:November 28, 1978



ii

THE PIONEER VENUS SPACECRAFT ...................... 68-82

VENUS ATMOSPHERIC PROBES .......................... 82-95

SCIENTIFIC INVESTIGATIONS ......................... 96-116

PRINCIPAL INVESTIGATORS AND SCIENTIFICINSTRUMENTS ...................................... 117-120

MISSION OPERATIONS ................................ 121-122

DATA RETURN. C OMMAND AND TRACKING ................. 123-125

PIONEER VENUS TEAM ................................ 126-128

CONTRACTORS ....................................... 128-131

VENUS STATISTICS .................................. 132



N ! N e w sNational Aeronautics andSpace Administration

Washington, D.C.20546AC 202 755-8370

Nicho las PanagakosHeadquar ters , Washington , D . C .

(Phone: 202/755-3680)

For Release:

IMMEDIATE

P e t e r W al l e rAmes Research Cen te r , Moun ta in V i e w , C a l i f .(Phone: 415/965-5091)

RELEASE NO: 78-181

PIONEER VENUS ENCOUNTER WILL OCCUR I N DECEMBER

The most e x t en s i ve s tud y ev er made of Venus w i l l b e g i n

next month w i t h t h e a r r i v a l a t t h e p l an e t o f P i o n ee r Venus 1

and 2 .

Pioneer Venus 1 w i l l sw ing i n t o o r b i t a ro un d t h e c l o ud -

c o v e re d p l a n e t on D e c . 4 , t a k in g p i c t u r e s and making measure-

men t s fo r one Venus ian year (225 E a r t h d ay s ) o r mo re .

On D e c . 9 , t h e f o u r pr o be s and t r a n s p o r t e r b u s t h a t

comprise P ioneer Venus 2 w i l l p l un g e i n t o t h e V e nu si an

c l o u d s a t w i d e ly s e p a r a t e d p o i n t s f o r d e t a i l e d me as ure me nts

of t h e d en s e a t m o sp h e r e fro m t o p t o b o tt o m.

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The flights may shed new light on some of the most

puzzling questions in planetary science:

0 Why do two planets (Venus and Earth) iith abc t thm

same mass, probably formed out of similar materials and

situated at comparable distances from the Sun, have atmos-

pheres that have evolved so differently that the surface

of Venus is baked by a searing heat, while Earth luxuriates

in a climate”friend1y o life?

The answer to this question depends on an

understanding of the factors that govern the evolution of

a planet’s atmosphere.

Information gathered by the 30 Pioneer experiments on

the composition, circulation and energy balance of Venus’

atmosphere may also help us learn more about the forces that

drive the weather on our own planet.

The flights are the first ones devoted primarily to a

study of the atmosphere and weather of another planet on a

global scale. They employ the largest number of vehicles

ever used in such studies, and will make measurements at

the greatest number of locations.

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The f l i g h t s a l s o seek t o l e a rn more about the charac-

t e r i s t i c s of Venus ' uppe r a tmosphe re and i onos phe re , a s

w e l l a s t h e lower a tmosp here . They w i l l s tu d y t h e i n t e r -

a c t i o n s of these r e g i o n s w i t h t h e solar wind -- t h e c o n t i n -

u ou s s t r e a m o f i o n s an d e l e c t r o n s f l o w i n g o u tw a r d from t h e

Sun -- a nd t h e s o l a r m a g n e ti c and e l e c t r i c f i e l d s .

Pioneer Venus 1 w i l l be t h e f i r s t U . S . s p a c e c r a f t t o

o r b i t V en us , whose s u r f a c e t e m p e r a t u r e ( 4 8 0 degrees C e l s i u s

o r 9 0 0 d e g r ee s F a h r e n h e i t ) , a tm o s ph e ri c p r e s s u r e ( 1 0 0 t i m e s

t h a t of Ea r t h) and permanent c loud co ver have made it a n

enigma among planets .

Launched May 2 0 , t h e O r b i t e r has f lown more th an h a l f

way around t h e Sun on i t s seven-month journey, some 500

m i l l i o n k i l om e t e rs ( 3 0 0 m i l l i o n m i l e s ) , t r a v e l i n g o u t s i d e

t h e E a r t h ' s o r b i t f o r t h e f i r s t t h r e e m o nt hs , an d i n s i d e it

f o r t h e l a s t f o u r m onths.

A t V en us, t h e O r b i t e r w i l l f o l l o w a h i g h l y - i n c l i n e d

2 4-h ou r o r b i t p l a n n ed so t h a t s p a c e c r a f t e v e n ts a r e t im ed

w i t h d a y s on E a r t h .

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At periapsis (orbital low point), the spacecraft will

come as close as 150 km ( 9 0 mi.) to the surface, dipping into

the thin Venus upper atmosphere, sampling its composition and

making radar measurements of the surface elevations and rough-

ness. (That hemisphere of Venus which is visible to Earth

radar shows a basin the size of Hudson Bay, a mountain as

great in extent but not as high as Mars' Olympus Mons -- the

solar system's highest -- and a 1,000-km (600-mi.)-long canyon.

Scientists are anxious to see Venus' unexplored half.) Its

orbital high point (apoapsis) will be 66,600 km (41,000 mi.)

from the planet.

The Pioneer Orbiter will also take daily ultraviolet

and infrared pictures of the thick clouds and atmosphere.

Experimenters will use precise orbital measurements to

chart Venus' gravity field for calculation of planetary shape

and density variations. The 1 2 Orbiter scientific instruments

will make a variety of other remote-sensing and direct measure-

ments of the planet's atmosphere and surrounding environment.

The Orbiter's primary mission has been selected to cover

the time it takes Venus to make one revolution on its axis --

2 4 3 Earth days. During this time, then, Venus will rotate

slowly under the periapsis of the orbit (point of closest

approach) providing closeup radar mapping of the entire

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A l s o , s i n c e V enus c i r c l e s t h e Sun i n 2 2 5 E a r t h d a y s ,

t h e p r i m a r y m i s s i o n m o r e t h a n c o v e r s t h e t i m e needed t o

sample t h e upper a tmosphere and ion osp here a t a l l Sun ang les .

T h e O r b i t e r ' s companion s p a c e c r a f t , Pioneer Venus 2,

t h e M u l t i p r o b e , i s made up of a t r a n s p o r t e r B us, a Large

Probe and t h r e e i d e n t i c a l s m a l l e r pr ob es . Launched Aug. 8 ,

t h e M u l t i p r o b e took a more d i r e c t r o u t e t o Venus than i t s

s i s t e r c r a f t , t r a v e l i n g 350 m i l l i o n km ( 2 2 0 m i l l i o n m i . ) .

T h e p r o b e s w i l l e n t e r t h e a tmosphere a t p o i n t s s p r e ad

1 0 , 0 0 0 km ( 6 , 0 0 0 m i . ) a p a r t o v e r t h e p l a n e t ' s E a r t h- f a c in g

hemisphere . The smal le r p r o b e s a r e named f o r e n t r y l o c a t i o n s .

The Large P r o b e e n t e r s Venu s' a t m o s ph e r e n ea r t h e e q u a t o r

on t h e d ay s i d e . T h e Day P r o b e e n t e r s V en us ' s o u t h e r n hemi-

s p h e r e on t h e p l a n e t ' s d a y s i d e : t h e N ig ht P ro be , t h e n i g h t

s o u t h e r n h e mi sp he re o n t h e n i g h t s i d e : a nd t h e N o r t h P r o b e ,

t h e N o rt h P o l a r v o r t e x , a l s o o n V en us ' n i g h t s i d e . Bus en t r y

i s i n t h e s o u t h e r n h emi s ph e re o n t h e d ay s i d e .

The Bus uses t w o i n s t r u m e nt s t o o b t a i n t h e d a t a on

t h e c o m p o s i ti o n o f t h e u p pe r a t mo s ph e re , f r o m 1 5 0 km down t o

1 1 5 km ( 9 0 m i . down t o 7 0 m i . ) a l t i t u d e , b ef ok e bu r ni n g up

s h o r t l y a f t e r a tm o sp he r i c e n tr y .

C r i t i c a l o p e r a t i o n s a t t h e p l a n e t a re i n j e c t i o n i n t o

o r b i t o f P i o n e e r Venus 1 w h i l e it i s o u t o f r a d i o c o n t a c t

b e h i nd V en us, and t h e e n t r y an d d e s c e n t t h r o u g h t h e atmos-

p h e r e of t h e f o u r p r o b e s a nd B us.

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The sequence o f ev en t s i s as f o l l o w s :

0 On S a tu r da y, D e c . 2 , Ames c o n t r o l l e r s w i l l o r i e n t

t h e O r b i t e r f o r o r b i t i n s e r t i o n a nd t h e n e x t day w i l l l o a d

command memory sequences. A t 8 :06 a.m. PST Monday, D e c . 4 ,

t h e O r b i t e r w i l l p as s b eh i n d Venus and n i n e m i n u t e s l a t e r

t h e command memory w i l l f i r e t h e o r b i t i n s e r t i o n motor f o r

30 s eco n d s , r ed u c i n g v e l o c i t y by 3 , 7 8 0 km/hr (2, 350 mph).

Ten m i n u t e s l a t e r , t h e O r b i t e r em er ges fr om beh i n d V en us ,

and f i v e m i n u t e s a f t e r t h i s , t e l e m e t r y c on fi rm s r e t r o f i r e .

0 F i v e d a y s l a t e r , on D e c . 9 , t h e p r o b e s a re i n p o s i t i on

t o make t h e i r h o u r - l on g d e s ce n t t h r o u g h V enu s' a t m o s ph e r e .

(The fou r p robes and Bus w hich comprise P ioneer Venus 2 w e r e

s e p a r a t ed Nov. 1 5 and 1 9 , w h i l e t h e y w e r e s t i l l some 1 2 m i l -

l i o n km ( 7 m i l l i o n m i . ) from Venus. They have been n e a r l y

d or ma nt and o p e r a t i n g on i n t e r n a l t i m e r s s i n c e t he n i n

o r d e r t o c o n s e r v e b a t t e r y pow er. They w i l l n o t b e h e a rd

from a g a i n u n t i l 1 9 m i n u t e s b e f o r e Venus e n t r y a t 10:26 a.m.

PST .)

0 Three hour s be fo re e n t r y , command sys te ms on board

t h e t h r e e i d e n t i c a l , 90 -k ilog ram (2OO-pound)-North, Day and

N i g h t P r o b e s w i l l t u r n on h ea t e r s t o w a r m up b a t t e r i e s ,

r a d i o s and o s c i l l a t o r s . H alf a n h ou r l a t e r , t h e 320-kg

(700 -lb.) Lar ge Pr ob e' s command syst em w i l l awaken th e c r a f t ,

w arming up b a t t e r i e s an d r a d i o .

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0 A t 10:23 a.m. PST Saturday, D e c . 9 , t h e L a r g e P ro b e

w i l l send i t s f i r s t r a d i o s i g n a l t o E a r t h i n 2 4 days. Then

a t i n t e r v a l s of f i v e , t h r e e a nd f o u r m i n u t e s , t h e N o r t h ,

Day and Night Probes W i l l s i q n a l t o t h e Deep Space Network

(DSN). (T he s i g n a l t a k e s t h r e e m i n u te s t o r e a c h E a r t h . )

0 S e ve n te e n m i n u t e s b e f o r e e n t r y , t h e L a r g e Probe d a t a

sys tem w i l l b e g in o p e r a t i n g a t 256 b i t s p e r s e c o n d ( b p s ) ,

and i t s i n s t r u m e n t s w i l l be w a r m e d up and c a l i b r a t e d .

0 L a r g e P r o b e e n t r y a t 42 , 000 km/hr ( 2 6 , 0 0 0 mph) occurs

a t 10:45 a . m . A t e n t r y p l u s 38 s ec on ds , t h e c r a f t ' s p a r a-

c h u t e d e p l o y s . The h e a t s h i e l d i s j e t t i s o n e d , and 30 s e c o n d s

l a t e r a l l i n s t r u m e n t s a r e o n . F o r t h e nex t 55 min u t e s , t h e

p r o b e w i l l r e t u r n a s t e a d y stream o f d a t a on each l e v e l o f

Venus ' a tmosphere a s it desc ends . Impact on Venus' su r f ac e

w i l l o c c u r a t 11:40 a . m . PST.

0 A f t e r f i r s t r a d i o c o n t a c t w i t h t h e i d e n t i c a l N or th ,

Day an d .N igh t P rob es , d a t a b eg in t o a r r i v e a t 6 4 b p s . I n s t r u -

men t s a re warmed up and ca l i b r a t ed .

a tmosphe re a t 10:50 , 10:53 and 10:56 a . m . PST. One minute

a f t e r e n t ry , windows open, do or s open and booms d e p lo y t o

e xp os e s e n s o rs r e l a t e d t o a t m o sp h er ic s t r u c t u r e and n e t f l u x

( h e a t - s e n s i n g ) e x p e r i m e n t s . F o r t h e nex t 56 minu t e s , a l l

t h r e e p r o b e s w i l l g a t h e r a t m o s p h e r i c d a t a .

The p ro b e s e n t e r t h e

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0 A t 1 6 . 4 m in ut es a f t e r e n t r y , a s Venus ' a tmosphere

t h i c k e n s , t h e d a t a r a t e i s r ed u ced t o 1 6 bps . T h e N o r t h ,

Day and Nig ht Probes impa ct on Venus ' s u r f a c e 1 0 , 0 0 0 k m

( 6 , 0 0 0 m i . ) a p a r t a t 11:47, 11:50 and 11:53 a . m . PST. Though

t h e i r m is s i on s w i l l be o v e r , t h e y may c o n t i n u e b r i e f l y t o

r e t u r n d a t a f r o m t h e s u r f a c e .

A major o p e r a t i o n s p r ob le m i s r e t r i e v a l of p r o b e d a t a .

Dur ing the c r i t i c a l 1 hour and 38 min ute s of p rob e and bus

o p e r a t i o n s a t Venus a l l P i o ne e r s p a c e c r a f t w i l l be t r a n s -

m i t t i n g a t once . T h i s p r e c i o u s d a t a must be recovered. T o

e n s u re t h i s , s p e c i a l e quipm ent h a s been i n s t a l l e d i n t h e

D S N s t a t i o n s a t G o ld s to n e, C a l i f . , a nd C a n be r ra , A u s t r a l i a .

Radio f r e q u e n c i e s of t h e p r o b e s i g n a l s w i l l s h i f t

r a p i d l y d ue t o huge e n t r y d e c e l e r a t i o n s -- f r o m 42 , 000 km/hr

( 2 6 , 0 0 0 mph) t o a b o u t 65 km/hr ( 4 0 mph) -- a n d s i g n a l d i s -

t o r t i o n s caused by Venus ' den se a tmosphere . One consequence

i s t h a t a f t e r t h e 1 0 - t o 15 -s econ d com m un icat io ns b l a ck o u t

d u r in g e n t r y , s i g n a l s w i l l r e a p p e a r a g a i n a t n ew f r eq u en c i e s .

T o a v o i d l o s s of d a t a , b o th D S N s t a t i o n s w i l l use newly-

deve loped rece ivers and recorders w i t h a f r equency band

wide enough t o be c e r t a i n of g e t t i n g t h e f o u r s h i f t i n g s i g -

n a l s . T h e rea l - t ime sys tem w i l l u s e a u to m a t ic t u n e r s , b u t

w i l l l o se s o m e d a t a .

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Scientists believe that the coordinated Pioneer atmos-

pheric data, combined with similar data to Mars, Jupiter

and other planets, will lead to a better understanding of

atmospheric mechanisms in general. Studies of the inter-

actions of temperatures, pressures, composition, clouds and

atmospheric dynamics different from Earth's should provide

insights into important mechanisms which are often prominent

on another planet. Such findings may help us to better

understand the Earth's complex weather machine.

Scientists think Venus may be an unusually good place

to study the mechanics of atmospheres because the planet

rotates very slowly and there are no oceans. The atmosphere

appears to be a relatively "simple" weather machine, and

the basic atmospheric circulation should be a simple hemi-

spheric overturning. Hence, continuous measurements from

orbit, combined with those of the probes from many points

in the atmosphere, could provide at least a broad view of

Venusian weather processes.

Because of its high density, temperature and corrosive

constituents, Venus' atmosphere presents a difficult problem

for entry craft designers.

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High entry speeds of 42,000 km/hr (26,000 mph) add to

the problem, as does the necessity for all instruments to

have either observing or direct sampling access to the

hostile atmosphere.

All four probes are geometrically similar. The main

component of each is a spherical pressure vessel which houses

instruments, communications, data, command and power systems.

The Large Probe weighs 316 kg (698 lb.). It is 1.5 meters

( 5 feet) in diameter, and its seven instruments weigh 28 kg

(62 lb.). The smaller North, Day and Night Probes each

weigh 9 3 kg (206 lb.) . They are 0 .8 m (30 in.) in diameter,

and their three experiments weigh 3 . 5 kg (7.7 lb.).

The transporter Bus is a spin-stabilized, short cylinder

2.4 m (8 ft.) in diameter, housing instruments, communica-

tions, navigation and power systems. The exterior of the

Bus cylinder is covered with power-generating solar cells.

The Orbiter spacecraft, like the Bus, consists prin-

cipally of a spin-stabilized 2.4-m (8-ft.) diameter, short

cylinder containing most spacecraft systems.

Above the cylinder is the narrow-beam, parabolic dish

antenna. The dish is used for high-speed data transmission

and faces toward the Earth throughout the mission, while the

spacecraft spins beneath it.

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Within the cylinder is a thermally-controlled equip-

ment compartment, which houses the 1 2 Orbiter scientific

instruments, a million-bit data memory and the communications

and data-handling systems.

The Orbiter weighs 5 8 0 kg ( 1 , 2 8 0 lb.) with 4 5 kg (100

lb.) of scientific instruments. Weight in orbit after motor

burn is 3 7 2 kg ( 8 2 0 lb.).

The Orbiter's destination, Venus, is the second planet

from the Sun, and the closest one to Earth. Because of its

highly reflective cloud cover, Venus is the brightest object

in the sky after the Sun and the Moon. Its year is 2 2 5

Earth days. Its mean distance from the Sun is 1 0 8 . 2 million

km ( 6 7 . 2 million mi.). This is nearly three-quarters of

Earth's distance from the Sun.

When Venus is closest to Earth, directly between Earth

and Sun, the planet is only 4 2 million km ( 2 6 million mi.)

away.

Since Earth and Venus are almost twin planets, scien-

tists want to know if there is any chance of Earth becoming

a desolate, hell-like world like Venus.

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The atmosphere of Venus appears to be predominantly

carbon dioxide -- about 97 per cent. Only minute amounts

of water vapor have been detected in it. Venus' high

overall density suggests a dense core something like Earth's

nickel-iron core. Venus has no significant magnetic field.

So the planet has no magnetosphere and its unshielded upper

atmosphere interacts directly with the solar wind.

Venus receives almost twice as much solar radiation

as Earth, but it also reflects more than half of this, so

the net solar heat is about the same as Earth's. Venus is

so hot because the atmosphere traps the heat. This trapping

is called a ''greenhouse effect," which means that Venus'

atmosphere allows passage of incoming solar radiation, but

restricts radiation of heat outward.

The temperature at the poles of Venus is only about

10 degrees C (50 degrees F.) less than that at the equator.

Both its day and night hemispheres have about the same tem-

perature. Hence, Venus' massive atmosphere contains cir-

culation mechanisms which distribute solar heat evenly over

the whole planet. In addition to carbon dioxide and water

traces, Venus' atmosphere also has some carbon monoxide,

hydrochloric acid and hydrogen fluoride.

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Venus ' permanent c lo ud s a re v e r y t e n u o u s , s o me th in g

l i k e t e r r e s t r i a l smog. D a t a f r o m S o v i e t V en er a l a n d e r s

s u g g e s t s t h a t t h e y a r e a l m o s t t w i c e a s deep a s E a r t h ' s

c l o u d r e g i o n , a b o u t 1 8 k m (11m i . ) t h i c k , and a re b e l i e v e d

t o be composed ma in ly o f s u l f u r i c ac id d ro p l e t s . Somewhere

be low the bo t t om of t h e main c l o u d l a y e r s , it i s s u g g e s t e d ,

t h e t e m p e r a t u r e becom es g r e a t e no ug h f o r t h e s u l f u r i c a c i d

d r o p l e t s t o e v a po r at e i n t o w a t e r v ap or and s u l f u r i c a c i d

v a p o r . A c l e a r a tm o sp h er e r e s u l t s . Enough s u n l i g h t g e t s

t h r o u g h t h e c l o u d s s o t h a t t h e s u r f a c e a p p e a rs a s b r i g h t

a s o n a n o v e r c a s t da y on E a r t h .

From t h e M ari ne r c lo ud p h ot og ra ph s i n u l t r a v i o l e t l i g h t ,

it a p p e a r s t h a t t h e c l o u d t o p s a r e i n c o n t i n u o us m o ti o n ,

t r a v e l i n g a b o ut 36 0 km/hr ( 2 2 0 mph) and c i r c l i n g t h e p l a n e t

i n f o u r E a r t h d a y s . However, t h e S o v i e t V en er a l a n d e r s

showed t h a t w ind s p e e d s i n t h e d e e p a tm o s p he r e a re e x t r e m e l y

s low. An ab ru p t change i n wind ve lo c i t y app ea r s t o t a k e

p l a c e a b o u t 56 k m ( 3 6 m i . ) a l t i t u d e betw een t h e b a s e of t h e

c l o u d s a nd t h e c l e a r a t m o s p h er e b el ow .

Some m a j or q u e s t i o n s r e l a t i n g t o Ear th and Venus a r e :

a L i k e Venus , the E a r t h ha s a g r e en h o u se e f f e c t wh ic h

may be growing because of i n c r e a s e s i n c a rb on d i o x i d e i n

our a tmosphe re -- due t o l a r g e -s c a l e b u rn in g of f o s s i l f u e l

s i n c e 1 8 5 0 .

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Could the Earth's greenhouse effect become strong

enough to cause a serious, steady rise in temperature?

0 Venus presumably formed as close to the Sun as it

is today, not greatly different from Earth's distance. We

might expect Venusian oceans like our own. Yet there is

almost no water on Venus. Where did the water go, if it

ever existed?

One explanation is that the difference in distance

from the Sun of Venus and Earth at the time they formed

was enough to lead to a big difference in the amount of

hydrated minerals incorporated in the protoplanets. In

this view, Venus has always been deficient in water. Another

proposed explanation is that the water vapor outgassed by

Venus never condensed into a liquid because Venus is too

close to the Sun. In time, the water vapor was split by

sunlight into its constituent hydrogen and oxygen, with the

hydrogen being lost to space.

Cost of the Pioneer Venus spacecraft, scientific

instruments, mission operations and data analysis is about

$175 million.

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-15-

The Pioneer Venus project is managed for NASA's Office

of Space Science by the Ames Research Center, Mountain View,

Calif., and the spacecraft are controlled from the Mission

Operations Center at Ames. The spacecraft were built by

Hughes Aircraft Co., El Segundo, Calif. The scientific

instruments were supplied by NASA centers, other government

organizations, universities and private industry.

The spacecraft are tracked by NASA's Deep Space Net-

work, operated by the Jet Propulsion Laboratory, Pasadena,

Calif., a government-owned research facility managed for

NASA by the California Institute of Technology.

(END OF GENERAL RELEASE. BACKGROUND INFORMATION FOLLOWS.)

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-16-

ENCOUNTER TIME LINE

( A l l t i m e s a r e P a c i f i c S t a n d a r d )

D e c . 2

Midday

D e c . 3

Maneuver t o o r i e n t O r b i t e r f o r i n s e r t i o n . B i t

r a t e lowered (1,024 t o 64 b p s ) ; s w i t c h t o omnia n t e n n a ; s p in -u p h i g h- g a in a n t e n n a ; i n c r e a s e s p i nr a t e t o 30 rpm; d es p i n h igh -ga in an t en na ; r a i s eb i t r a t e (64 t o 1,024 b p s ) .

11:OO p.m. Load b o th O r b i t e r command m e m o r i e s wi th s equencet o f i r e o r b i t i n s e r t i o n motor.

D e c . 4

1:OO a . m . S t a r t command m e m o r i e s t o f i r e o r b i t i n s e r t i o n

m o t o r ( O r b i t e r ) .7:51 a . m . O r b i t e r p a s s e s b e hi n d t h e p l a n e t n i n e m i n u te s

b e f o r e Venus o r b i t i n s e r t i o n ( V O I ) .

8:OO a . m . V O I o c c u r s b e hi nd V enus. S o l i d r o c k e t o r b i t i n s e r -t i o n m oto r b u rn s o u t i n a b o u t 30 seconds and changesv e l o c i t y a b o ut 3,780 km/hr (2,349 mph).

8:lO a . m . O r b i t e r e x i t s f r o m b e h i n d V e n u s .

8:15 a . m . C onfirm O r b i t e r r e t r o f i r e .

8:30 a . m . ( V O I + 30 m in ut es ) I n i t i a l O r b i t e r de sp in t o 1 5 rpm.

9:00 a.m. D e sp in O r b i t e r ' s h i g h - g a in a n t e n n a .

9:00 a . m . t o3:OO p.m. D e te rm i ne o r b i t o f O r b i t e r .

1:OO p.m. ( V O I + 5 ho ur s) Load r a d a r mapper memory f o r f i r s to r b i t .

3:OO p.m. ( V O I + 7 hour s ) Desp in O r b i t e r t o 6 rpm.

4:OO p.m. ( V O I + 8 h o ur s) R e o r i e n ta t i o n o f O r b i t e r s p i n a x i s

t o s o u t h c e l e s t i a l p o l e .

6:OO p.m. ( V O I + 1 0 h o u rs ) O r b i t e r hi g h- g ai n a n t en n a o r i e n t e dt o E ar th and t e l em e t r y swi t ched f rom omni an t enn at o h i g h- g a in a n t e n n a .

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-17-

7 : O O p.m. (VOI + 11 hours) Turn on Orbiter scientificexperiments:

1. Infrared Radiometer (IR), Neutral Mass

Spectrometer (NMS) and Electron Temperature

Probe (ETP) on.

2. Release NMS hat, unlock radar antenna and

deploy ETP boom.3 . NMS calibration sequence, radar calibration

sequence.

8:OO p.m.

1 O : O O p.m.

11:OO p.m.

(VOI + 12 hours) Begin orbit No. 1.

(VOI + 14 hours) Trim spin rate to 5 rpm.

(VOI + 15 hours) Continue turn-on of Orbiterscientific instruments:

1. Magnetometer on.

2. Retarding Potential Analyzer on.VOI sequence complete.

sequence starts. Remaining Orbiter instrumentswill be turned on at various times as requested

by the principal investigators during the firstorbit.

First orbital scientific

Dec. 5

12:OO Noon Start receiving IR weather map of planetatmosphere.

Dec. 6

a.m. Quick looks at solar wind ionosphere interaction

data from Electric Field Detector (EFD); thermalstructure of ionosphere data from ETP; Magnetometerreadings of solar wind and ionosphere; IR weathermaps; IR data on heat balance and distribution;Ultraviolet Spectrometer (WS) maps (Orbiter)

First Orbiter imaging scan by Cloud Photopolarimeter

(CPP)

1:OO a.m.

7 : O O p.m. First Venus image (black and white) received at

Ames from Orbiter CPP.

hours later.*Color image about five

*Experiment result dates and times are estimates and are

tentative.

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-18-

Dec. 7

a.m.

p.m.

Dec. a

Early a.m.

a.m.

p.m.

Daytime

Dec. 9

7 : 5 0 a.m.

8:15 a.m.

a.m.

UVS measures of composition and thermal structure

of hot outermost atmospheric layer: Ion Mass

Spectrometer (IMS) data on distribution and con-

centration of ions in upper atmosphere; NMS read-

ings of upper atmosphere: IR readings of: temperatureprofiles in upper atmosphere, total reflected sun-

light, correlation with ultraviolet markings, watervapor abundance and distribution (Orbiter).*

Second black and white picture received from CPP(color five hours later) *

Data on cloud tops and upper atmosphere from

Orbiter UVS.

Data on temperature profiles of upper atmosphere,total reflected sunlight, correlation with ultra-

violet markings, water vapor abundance and distri-

bution from IR, IR maps: NMS readings of upperatmosphere: IMS readings of ion distribution and

concentration in upper atmosphere; UVS measures ofcomposition and thermal structure of hot outermost

atmosphere layer (Orbiter).*

Gravity anomalies from Orbiter radio science(effects of gravity on orbital path).*

Third planet picture received from CPP.*

Calibrations made: NMS cap released (Bus).

Multiprobe atmosphere entry operations begin.Stable oscillator in radio transmitters of North,

Day and Night probes warmed up by onboard commands.

Command unit on Large Probe initiates warm-up ofbattery and radio receiver.

Final adjustments to Bus' entry angle.


tentative.

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-19-

Dec. 9 (cont'd.)

a.m. Orbiter experiment data continuing daily:IR maps, IR readings of temperature profiles of

upper atmosphere, total reflected sunlight, cor-

relation with ultraviolet markings, water vapor

abundance and distribution; NMS readings of upperatmosphere; I M S readings of ion distribution and

concentration in upper atmosphere; UVS measuresof composition and thermal structure of hot outer-most atmospheric layer (Orbiter) *

p.m. Two planet pictures per day (Orbiter) *

First transmissions from probes:

First Radio First Signal First Data

Signal Received First Data Received

Transmission On Earth Probe Transmission On Earth

10:23 a.m. 10:26 a.m. Large 10 :28 a.m. 10:31 a.m.10:28 a.m. 10:31 a.m. North 10:33 a.m. 10:36 a.m.

10:36 a.m. 10:39 a.m.0:31 a.m. 10:34 a.m. Day10:37 a.m. Night 10:39 a.m. 10:42 a.m.0:34 a.m.

10:45 a.m.

10:50 a.m.

10:53 a.m.

10:56 a.m.

1 0 : 45: 0

a.m.

1 0 : 45:45

a.m.

Begin entry communications blackout. Timer com-

mands data storage (Large Probe).

North Probe begins communication blackout: cables

and weights of despin system deploy to reduce spinrates from 48 to 15 rpm; cables and weights jet-

tisoned immediately after spindown.

Above sequence begins on Day Probe.

Above sequence begins on Night Probe.

Large Probe begins descent phase, deploys parachute

and jettisons forward aeroshell-heat shield.

Altitude of Large Probe is 40 miles; all instru-

ments operating.


tentative.

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-20-

Dec. 9 (cont'd.)

10:51 a.m.

10:54 a.m.

10:57 a.m.

11:02 a.m.

11: 6 : 3 0

a.m.

1 1 : 0 9 : 3 0

a.m.

11: 2: 3 0

a.m.

Dec. 10

a.m.

Noon

Dee. 11

a.m.

Entry and impact times for probes and Bus.

(Entry is at 200 km (125 mi.) altitude,

42,000 km/hr (26,000mph) )

Entry Probe Impact

10:45 a.m. Large 11:40 a.m.

10:50 a.m. North 11:47 a.m.

10:53 a.m. Day 11:50 a.m.1 0 : 5 6 a.m. Night 11:53 a.m.

12:21 p.m. Bus Burns up at 12:23 p.m.

North Probe Nephelometer window opens; AtmosphericStructure and Net Flux Radiometer housing doorsopen, instrument booms deploy on probe, instrument

compartment doors despin probe.

Above sequence begins for Day Probe.

Above sequence begins for Night Probe.

At 45 km (28 mi.) altitude, Large Probe parachute

jettisons.

Data rate of North Probe reduced to 16 bps at29 km (18 mi.) altitude, due to atmosphere

thickening.

Data rate of Day Probe reduced as above.

Data rate of Night Probe reduced as above.

Preliminary cloud location and density data from

all four probe nephelometers.*

Preliminary data on lower atmosphere thermal

structure, all four probes.*

Preliminary Large Probe IR data on heat trapping.*


tentative.

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-21-

Dec. 12

a.m.

a.m.

p.m.

p.m.

Dec. 13

Preliminary data on solar energy deposition fromSolar Flux Radiometer; cloud-layer particle size

from Cloud Particle Size Spectrometer; atmosphere

and cloud components from Atmospheric Composition

Mass Spectrometer (Large Probe).*

Data reduction of Mass Spectrometer measurements

of number density of upper atmosphere; Ion Mass

Spectrometer measurements of upper atmosphere (Bus) *

Reduction of data on Day, Night and North Probe

measurements of heat trapping on Venus from netflux radiometers.*

Thermal structure of ionosphere from Electron

Temperature Probe; Magnetometer readings of iono-

sphere and solar wind fields; Electric Field

Detector readings of solar wind-ionosphere inter-action (Orbiter) *

a.m.

p.m.

Further data reduction on: heat sources and sinks

in atmosphere from Large Probe IR; cloud density

of lower atmosphere from all four probe nephelometers.*

Preliminary data on atmospheric components from

Gas Chromatograph; cloud particle characteristicsfrom 'Solar Radiometer; Solar Radiometer readings

of solar heating in Venus atmosphere (Large Probe) *

p.m. Reduction of upper atmosphere thermal structure

data from four probes.

Dec. 14

a.m. Cloud characteristic data from Large Probe Solar

Flux Radiometer.

Dec. 19 Solar corona turbulence and solar wind velocity

near the Sun from effects on Orbiter radio signal.*

Dec. 2 2 Line-of-sight wind speeds from Multiprobe Doppler

experiment; small-scale turbulence characteristicsof atmosphere from Multiprobe radio science.*

"Experiment result dates and times are estimates and are

tentative.

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- 2 2 -

January Upper atmosphere temperature, pressure and densitydata from Orbiter occultation measurements.*

Small-scale atmospheric turbulence above 35 km(22 mi.), from Orbiter radio science.*

Atmospheric structure characteristics from Multi-

probe radio science.*

Lower atmospheric motion from changing pressureand temperature gradients of Dual Frequency Radio

occultation (Orbiter)

Determination of energy input sources into iono-

sphere from Orbiter Retarding Potential Analyzer.*

Atmospheric drag on Orbiter gives atmospheric

density.

Effects of ionosphere on Orbiter radio signal

during occultation (ionosphere model).*

Venus gravity field model from cumulative small

orbit changes.*

Estimate direction and magnitude of Venus spinvector, magnitude of Venus polar motion, and

improve measurements of Venus-Earth orbits fromOrbiter radio science.*

Venus wind velocities calculated from descent

track of four probes.*


tentative.

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-23-

M I S S I O N PROFILE

The t w o P i on e er f l i g h t s t o Venus w i l l e x p l o r e t h ea tm o sp h er e o f t h e p l a n e t , s t u d y i t s s u r f a c e u s i n g r a d a r

and de t e rmine i t s g l o b a l s ha pe and d e n s i t y d e s t r i b u t i o n .The f i r s t s p a c e c r a f t , P i o n e e r Venus 1, t h e O r b i t e r , w i l lmake e i g h t mon ths o r more o f r emote - sens ing and d i r e c tmeasurement. Pi on ee r Venus 2 , t h e M u l ti p ro b e , s e p a r a t e di n t o f i v e a t mo sp he ric e n t r y c r a f t , e i g h t m i l l i o n m i l e so u t from t h e p l a n e t , w i l l measure t he a tmosphe re f rom to p t ob ott om i n a b o u t two h o ur s a t p o i n t s s p r e a d o v e r t h e e n t i r eE a r t h - f a c i n g h e m i s p h e r e of Venus.

ORBITER OPERATIONS

On D e c . 2 , 1978, t w o d ay s b e f o r e a r r i v a l a t Venus, t h eO r b i t e r s p a c e c r a f t s p i n r a t e w i l l b e i n c r e a s e d t o 30 rpmand t h e O r b i t e r w i l l b e o r i e n t e d w i t h i t s 18,000-N (4,000-lb.)t h r u s t , s o l i d - f u e l e d r o c k e t e n gi ne p o i n t i n g f or wa rd , i n t h ed i r e c t i o n of t r a v e l .

On Dec. 4 , 1 97 8 a t 8:OO a.m. P S T, t h e sp ac ec ra f t commandw i l l command t h e r o c k e t t o i g n i t e f o r t h e 3 0-se co nd

o r b i t - i n s e r t i o n b ur n. T h i s w i l l r ed uc e s p a c e c r a f t v e l o c i t yby 3, 78 1 km/hr ( 2 , 3 4 9 m p h ), p l a c i n g P i o n e e r i n a 2 4-h ou ro r b i t a r ou n d V enus. The p l a n n e d o r b i t w i l l be i n c l i n e d 75d e g r e e s t o V en us ' e q u a t o r , w i t h i t s low p o i n t ( p e r i a D s i s )n e a r 1 8 . 5 d e g re e s n o r t h l a t i t u d e . The o r b i t ' s h i g h p o i n t( a p o a p s i s ) i s e x p e ct e d t o be a t an a l t i t u d e of 6 6 , 0 0 0 km( 4 1 , 0 0 0 m i . ) . P e r i a p s i s i n i t i a l l y w i l l be a t 300 km( 1 8 0 m i . ) , l a t e r r e d uc e d t o a s low a s 1 5 0 km ( 9 0 m i . ) .

W ith in h o ur s a f t e r t h e o r b i t i n s e r t i o n r o c k e t b u rn ,m e m b e r s of t h e O r b i t e r n a v i g a t i o n t eam will have measuredt h e a c t u a l s i z e and s ha pe o f t h e o r b i t . A f t e r s lo w in g t h es p i n r a t e and a d j u s t i n g o r i e n t a t i o n , t h e y w i l l commandf i r i n g o f t h r u s t e r s t o t r i m up t h e o r b i t t o a c c e p ta b l ed imens ions .

D u ri ng t h e 2 43-day p r im a ry O r b i t e r m i s s i o n , t h e o r b i tw i l l have a p e r i o d c l o s e t o 2 4 h o u r s . T h i s means t h a t m os ta c t i v i t i e s w i l l o c c u r o v e r t h e same D S N s t a t i o n e v e ry d ay .

The 24 -h ou r o r b i t h a s b ee n d i v i d . e d i n t o two p e r i o d s ,r e f l e c t i n g t h e ki nd of measuremen ts be in g t ak en . The pe r i -a p s i s ( o r b i t a l low p o i n t ) p e r i o d i s a b o u t f o u r h o u r s l o n g.The a p o a p s is ( o r b i t a l h i g h p o i n t ) p e r i o d i s 2 0 h o u r s l o n g .

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T H E P I ONE E R V E NU S M I S SI ONS

REVERSE

BU S

I ORBITER

' IGHT

PROBE



- 2 5 -

PERSPECTIVE V I EW O F P IO N E E R V E N U S O R B I T



PIONEER VENUS ORBITER

TYPICAL ORB ITAL OPERATIONS

START STORED COMMANDS TO

OPERATE ION MASS SPECTROMETER

(IMS), ULTRAVIOLET SPECTROMETER

(UVS), RETARD1NG POTENTIAL

ANALY ZER (RPA), NEUTRAL MASS

SPECTROMETER (NMS), INF RARE D

RADIOMETER ( I R ) , RADAR MAPPER,

PLASMA ANALYZ ER (PA), ELECTRON

TEMPERATURE PROBE (ETP) DURIN G

CONTINGENCY READ-OUT COMMAND MEMORYCOMMAND

LOAD RADAR

MAPPER MEMORY

1 ORBIT = 24 HOURS

GAMM A BURST DETECTOR, MAGNETOMETER &

ELECTRIC FI ELD DETECTOR OPERATE

CONTINUOUSLY DURING ORBIT

I/ RPA & PASEQUENCES

READ-oUT SEQUENCESDAT A STORAGE

UNITS

/

9 / /

PHOTOPOLARIMETER

OBSERVATIONS AND PLASMA

ANALYZER SEQUENCES




ORBIT INSERTION (EXPERIMENT OPERATIONS)

//

SPACECRAFT BEHIND

PLANET - NO RADIO

COMMUNICATION

\,/ 23

/

1 ORBIT = 24 HOURS

l 8 >17

MAGNETOMETER &

R ET AR D NG POT ENTIA LANALYZER ON

TRIM TO 5 rpm

INFRAR ED RADIOMETER ON;UNLOCK RADAR ANTENNA;RELEASE NEU TRAL MASS

SPECTROMETER (NMS) HAT;DEPLOY ELECTRON TEMPERATUREPROBE (ETP) BOOM; NMS&

ETP ON

TELEMETRY TO HIGH-GAINANTENNA

REOR IENT TO SOUTH6 CELESTIAL POLE

DESPIN 15 TO 6 rpm

MOTOR BURNS I30 secs, CHANGES DESPINVELOCITY 3780 kph HIGH-GAIN

(2349 mph) ANTENNA\

LOAD RADAR MAPPER MEMORYFO R FIRST ORBIT




ORBIT INSERTION (SPACECRAFT OPERATIONS)

0

DEC. 2: ORIENT SPACECRAFTFOR ORBIT INSERTION &

SPIN-UP TO 30 rpm0>/'

,1 P.M. DEC. 3:

LOAD COMMAND MEMORIES

MOTOR

opTO FIRE ORBIT INSERTION ,5p

STARTA.M.OMMANDEC.4:

/p+

L&d\++0EMORIES TO FIRE

ORBIT INSERTION MOTOR

k00

22 21/

SPACECRAFT BEHINDPLANET - NO RADIO

COMMUNICATION\

ORBIT INSERTION:

SOLID ROCKET

MOTOR BURNS30 ecs, CHANGES

VELOCITY 3780 kph

(2349mph)

DESPIN

23

1

1 ORBIT = 24 HOURSBEGINS

TELEMETRY TOHIGH-GAIN ANTENNA

REORIENT TO SOUTHCELESTIAL POLE

c

- 3 TO 6 rpm



- 2 9 -

M i ss io n o p e r a t i o n s w i l l u s e f i v e d a t a f o r m a t s d u r i n gt h e 4-hour p e r i a p s i s p e r i o d . T he sz f o r m a t s a r e d e s ig n e d t op e r m i t s em ph as is i n c e r t a i n i n s t r u m e n ts when d e s i r a b l e ; f o re x a m pl e , o n e p r o v i d e s i n t e n s i v e ae ro no my c o v e r a g e a t p e r i a p -

s i s , a n o t h e r s t r e s s e s o p t i c a l c o v er ag e.

The mapping format g i v e s 4 4 p e r c e n t o f t h e d a t a f l owt o t h e r a d a r m ap pe r f o r Venus s u r f a c e s t u d y , a n d d i v i d e s t h er e s t between t h e u l t r a v i o l e t s p e ct r om e t er and t h e i n f r a r e dr a d i o m e t e r .

N o r m a l l y , c o n t r o l l e r s w i l l u s e o n l y t wo d a t a f o r m a t si n t h e 20 -h ou r a p o a p s i s s eg m en t. The f i r s t of t h e s e w i l lb e f o r t a k in g p i c t u r e s o f t h e whole p l a n e t i n u l t r a v i o l e tl i g h t , which w i l l show t h e f o u r - da y r o t a t i o n o f V e nu s'c l o u d s i n s e q u en c e. Known as t h e i ma g in g f o r m a t , it a l l o -c a t e s 6 7 p e r c e n t o f t h e d a t a s t r e a m t o t h e i ma gi ng a n d

c l o u d p h o t o p o l a r i m e t e r i n s t r u m e n t , and d i v i d e s t h e r e s t amonqt h r e e s o l a r w in d- pl an et i n s t r u m e n t s an d t h e a s t r o n o m i c a l ex-

p e r i m e n t ' s gamma b u r s t d e t e c t o r . The o t h e r f o r m a t , knowna s t h e g e n e r a l f or m at , a l l o c a t e s d a t a r e t u r n among a l l O r -

b i t e r e x pe ri m en ts e x c e p t t h e p i c t u r e - t a k i n g c l ou d p ho to -p o l a r i m e t e r a nd t h e i n f r a r e d r a di o m et e r. A s much a s t h r e e -q u a r t e r s o f t h e t o t a l a po a ps is p e r i od w i l l b e d e vo t ed t oi m ag i ng , w h i ch h a s v e r y l a r g e d a t a r e q u i r e m e n t s .

D uring t h e f i r s t 80 d a y s i n o r b i t , Dec. 5 , 1 97 8 t oFeb. 23, 1979 , t h e O r b i t e r w i l l ? a s s beh ind V enus f o r oc-c u l t a t i o n p e r i o d s o f up t o 23 m i nu te s. T h i s a l lo w s t h er a d i o s c i e n c e team t o m ea su re e f f e c t s of Venus ' a tmosphereo n t h e s p a c e c r a f t r a d i o s i g n a l down t o a p p ro x i m at e ly 50 km( 3 1 m i . ) a l t i t u d e . S i n c e t h e n ar ro w beam s i g n a l i s b e n t

by t h e p l a n e t ' s a t mo sp he re , t h e a n t en n a ' s d i s h r e f l e c t o rw i l l be commanded a s much as 1 7 de gr ee s away from t h e

E a r t h - l i n e t o e x t e n d t h e t i m e o f r e c or d in g t h e s i g n a l as it

i s r e f r a c t e d a ro un d t h e s o l i d p l a n e t .

A l s o , d u r i n g o c c u l t a t i o n s , when c om m u ni ca ti o ns a r e c u to f f , t h e Venus O r b i t e r w i l l s t o r e d a t a i n i t s m i l l i o n - b i tmemory. A f t e r emergence of t h e O r b i t e r , t h e d a t a memoryr e a d o u t w i l l be u se d f o r r e t u r n o f s t o r e d d a t a . A secondo c c u l t a t i o n p e r i o d o c c u r s f ro m May 7-16 , 1 9 7 9 , a l l o w i n ga d d i t i o n a l r a d i o m ea su re me nt s o f t h e u p p er a tm o sp h er e.

D urin g t h e e i g h t months o n o r b i t , h e a l t h o f t h e s pa ce -

c r a f t w i l l be m o n i t o r e d th r o u g h t h e c o n t i n u o u s f l o w o f e n-g i n e e r i n g d a t a . R ed un dan t s y s te m s f o r t h e m os t c r i t i c a l

f u n c t i o n s ( s u ch as command and d a t a r e t u r n ) w i l l be u se d i f

needed.

- more -



ORBIT CHANGES SHOW VENUS'

INTERIOR DENSITY DISTR IBUTlON

//

/

/

G R A V I T Y ,'S IG N A TU R E

----_-r

I

\

\\ BETA

\

' V O L C A N

,: FEATURI

I

I

I

I

I

I

IIII

I



-31-

Mission Opera t ions e n g i n e e r s a l s o w i l l t r i m t h e o r b i ta b o u t every 1 0 d ay s e i t h e r t o l o w e r p e r i a p s i s a l t i t u d ewhich i s g r a d u al l y r a i s e d by s o l a r g r a v i t y p e r t u r b a t i o n so r t o a d j u s t t h e o r b i t a l p e r io d when it d r i f t s f rom th e

d e s i r e d v a l u e .

The pr i m a ry m i s si o n e n d s a f t e r 2 4 3 d a ys . S h o r t l y a f t e r -w a r d s , t h e O r b i t e r a n d Venus w i l l be b e h i n d t h e Sun andcommunicat ions w i l l b e g ar b l e d o r c u t o f f for s e v e r a l d a y s.A f t e r e me rg en ce f ro m s o l a r b l a c k o u t , t h e o p p o r t u n i t y w i l lb e a v a i l a b l e f o r e x te n d ed m i ss i on o p e r a t i o n s .

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- 3 2 -

RADAR MAPPER SCANS ON VENUS' SURFACEINSTRUME NT SCANS A BAND 55" WIDE AROUND THE PLANET FROM 10"

SOUTH LATITUDE TO 45" NORTH LATITUDE



LL 0 I

IK 2



-



- 3 5 -

MULTIPROBE O P E R A T I O N S

On D e c . 9 , 1978, a t about 10:45 a . m . PST, t h e f o u r p r o b e sw i l l a r r i v e a t Venus and en t e r t h e a tmosphe re . The La rgeProbe w i l l descend t o V en us' s u r f a c e i n 5 5 m i n u t e s an d t h e

Nor th , Day and Nigh t p rob es i n abo u t 57 minu t e s .

La rge P robe En t ry Even t s

A t 2.5 h o u rs b e f o r e e n t r y ( t i m e o f e n t r y i s d e f i n e d a st i m e a t 200 km ( 1 2 0 m i . ) a l t i t u d e ) , t h e L a rg e P r o b e ' s commandu n i t w i l l o r d e r warmup o f t h e b a t t e r y a nd r a d i o r e c e i v e r .Twenty-two m inu t e s be fo re en t r y , t h e p robe w i l l b e g i n t r a n s m i s s i o no f r a d i o s i g n a l s t o E a r t h . A t e n t r y m i n u s 1 7 m i n u t e s , t h ep ro be b e g in s t r a n s m i t t i n g d a t a a t 256 b ps . The command u n i ti n i t i a t e s warmup of t h e s ev en s c i e n t i f i c i n s t r u m en t s a b oa rd ,p l u s i n s t r u m e n t c a l i b r a t i o n . F i v e m i nu t es b e f o r e t h e p eake n t r y d e c e l e r a t i o n p u l s e o f 320 G , t h e p r o b e w i l l be t r a v e l i n g

4 1 , 6 0 0 km/hr ( 2 6 , 0 0 0 mph).

The t i m e r w i l l command d a t a s t o r a g e f o r t h e a t m o s p h e r i cs t r u c t u r e e x p e r i m en t d u r i n g e n t r y c om mu ni ca ti on s b l a c k o u t .

T h i r t y - e i g h t s e c o n d s a f t e r e n t r y , t h e 316-kg ( 7 0 0- l b .)p r o b e b e g i n s t h e d e s c e n t p h a s e , d e p l o y s i t s p a r a c h u t e a n dj e t t i s o n s i t s f o rw a rd a e r o s h e l l - h e a t s h i e l d . F o r t y - t h r e es ec on ds a f t e r e n t r y , a t a n a l t i t u d e of 66 km ( 4 0 m i . ) , a l li n s t r u m e n t s s h o u l d b e o p e r a t i n g . S e v e nt e en m i n u te s l a t e r ,

a t a n a l t i t u d e of 4 7 km ( 2 8 m i . ) , t h e p a r ac h u te i s j e t t i s o n e d ,and t h e a e r o dy n am i ca ll y s t a b l e p r e s s u r e vesse l d e s ce n d s t ot h e s u r f a c e i n 39 m i n u te s , i m pa c ti ng 5 5 m i nu t es a f t e r e n t r y .

T h e p r o b e j e t t i s o n s i t s p a r a c h u t e t o s p e ed i t s d e s c e n t t h r o u g hVenus' ve r y dense a tmosphe re , so t h a t i t r e a ch e s t h e s u r f a c eb e f o r e h e a t d e s t r o y s it.

D u r in g d e s c e n t , t h e L ar g e P r o b e ' s s e v e n i n s t r u m e n t s w i l lh av e o b t a i n e d d a t a t o d e t er m i ne a l t i t u d e a n d c o m po s it io n o fc l ou d l a y e r s , a tm o sp he re c o n s t i t u e n t s , t e m p e r a t u re , p r e s s u r e ,d e n s i t y , w ind f l o w and v a r i a t i o n s of h e a t f l o w i n t h e a t mo s ph e re .

Large Probe w i l l i m p a c t t h e s u r f a c e a t a b o u t 36 km/hr( 2 2 mph). (None of t h e pr ob es i s r e q u i r e d t o s u r v i v e i m p a c t,b u t t h e y may r e t u r n some s u r f a c e d a t a , e s p e c i a l l y t h e t h r e es m a l l e r p r o be s , which r e t a i n t h e i r h e a t s h i e l d s . )

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- 3 6 -

P I O N E ER V E N U S A T M O S P H ER E

P RO B ES S E P A R A T I O N

. . .. . .. . .. . .. . . .. . .. . e .- - :.e . .: . .. . . .

. . . ... . .. . . .* . * .. .. . ... .

I .

SOUNDE R

PROBE

D A Y

PROBE

The transporter Bus releases the Sounder Probe 11.1 million km (6.9 million m i) from Venus on Nov. 15.

Four days later, the Bus releases the three identical North, Day, and Night Probes, 9.3 million km (5.8

million m i) from Venus.



eENTRY

L A R G E P R OB E D E S C E N T S E Q U E NC E

9

?\

eF IR E MORT AR

4!I

EPLOY PILOT CHU TE / \

eELEASE AFT COV ER

EXTRA CT CHUTE BAG I \

DEPLOY MA IN CHUTET

T%

RELEASE

CHUTE

AEROSHELL/PRESSURE VESSEL

SEPARATION



- 3 8 -

North, Day and Night Probe Events

The 91 kg (200 lb.) North, Day and Niqht probes also will

enter the planet's atmosphere at about 4 1 , 6 0 0 km/hr (26,000 mph).However, the angles of their flight paths into the atmospherevary greatly. This means that entry heating and durations

of maximum deceleration pulses vary widely. Peak decelera-tion forces vary from 200 G to 5 6 5 G . Entry times also

differ by 11 minutes. A s with the Large Probe, entry isdefined as occurring at an altitude of 200 km (120 mi.).

Three hours before entry, the stable oscillator in the

radio transmitter for one-way Doppler tracking and the batteryon each smaller probe are warmed up by commands from theonboard command units. Twenty-two minutes before entry, each

probe begins transmission of radio signals to Earth.

Seventeen minutes before entry, the smaller probes begintransmitting data at 64 bps. The command unit initiates

warmup and calibration for the three instruments on each of

the probes.

Five minutes before entry, two cables and weights ofthe yo-yo despin system are deployed to reduce the spin ratesof each probe from 48 to 15 rpm. The high spin rates imparted

by the Bus earlier were needed to disperse the probes to entrypoints widely spaced over the planet. However, this widedispersion a l s o means that the smaller probes enter Venus'

high upper atmosphere somewhat tilted o f f their flight paths.The "spindown" of the probes is needed to make it easier for

aerodynamic forces to line up the axes of the probes with the

flight paths. This must occur quickly before heating at the

edges of the probes' conical heat shields becomes serious.Cables and weights are jettisoned immediately after spindown.

Five minutes before the peak deceleration pulse ofatmospheric entry, the command unit orders the "blackout"

format for storage of spacecraft data, plus heat shieldtemperature and accelerometer measurements for the atmos-pheric structure experiment. This is to assure no l o s s ofdata during the 10-to-15-second communications blackout atentry.

Within the first minute (18 to 4 6 seconds) after entry,

the nephelometer window on each Probe is opened, and the

atmospheric structure and net flux radiometer housing doorsare opened and instrument booms deployed.

At this time, the upper descent phase begins, with thethree probes in the altitude range of 72 to 65 km ( 4 3 to

39 mi.) and all instruments operating. The instrumentcompartment doors on each side of the smaller probe after-

bodies serve to despin the probes.

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-40-

A small vane on the pressure sensor inlet prevents thespin rate from falling to zero rpm, enabling instruments to

make observations over a full rotation of the probe.

At entry plus 16.4 minutes, as the thickening atmosphere

interferes with radio transmission, the data rate is reducedto 16 bps. This occurs at an altitude of 30 km (18 mi.).

From this point, the North, Day and Night probes descendinto Venus' increasingly dense lower atmosphere, impactingon the surface at 36 km/hr (22 mph) 57 minutes after their

entry times. Unlike the Large Probe, the smaller probesretain their heat shields to the surface. The density ofthe atmosphere is so great that the drag of these aero-

dynamic surfaces slows the probes to the desired descentspeed.

Bus Events

Eighty-eight minutes after all probes have entered theVenus atmosphere, the Bus will enter on the day side of the

planet at a high latitude in the southern hemisphere. TheBus has no heat shield for high-speed entry, and is expected

to burn up two minutes after entry. However, the Bus carriestwo experiments on the composition of the atmosphere, an ionand a neutral mass spectrometer. These instruments measureconstituents of the ionosphere and upper atmosphere from

200 km (120 mi.) down to 115 km (71 mi.). These are the

missions' only atmospheric composition measurements between

150 and 115 km (93 and 71 mi.), a region that contains themaximum density of the Venusian ionosphere. The Bus, with

i t s more powerful transmitter, returns this data to Earthat 1,024 bps before its destruction.

Entry Data Return--Probes, Bus and Orbiter

The four probes and the Bus will return their data

during a critical 1-hour, 38-minute-period on Dec. 9.

This will extend from Large Probe entry at 10:45,a.m. PSTto Bus burnup at 12:23 p.m. PST.

The probes and Bus will return data almost simultaneously.

All the spacecraft radio data directly to Earth. This means

that Deep Space Network stations must find, receive and recordfive entry craft data signals plus Orbiter data, all at thesame time. To make sure of getting this critical data, the

two D S N 64-m (210-ft.) antennas at Canberra, Australia, andGoldstone, Calif., will receive and record all incomingsignals simultaneously.

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-41-

F r e q u e n c i e s of t h e p ro be s i g n a l s w i l l s h i f t w i d e l yb e c a u s e of t h e a b r u p t s p a c e c r a f t v e l o c i t y c ha ng es a t e n t r y - -from 4 1 , 6 0 0 km/hr ( 2 6 , 0 0 0 m p h ) down t o a b o u t 6 5 km/hr

( 4 0 mph)-- a nd s i g n a l d i s t o r t i o n s by V en us ' d e n s e a t m o s ph e r e .To f u r t h e r co m p l ic a te s i g n a l r e c e p t i o n s , t h e r e i s a 10- to -15

second communica t ions b lackout a t peak e n t r y d e c e l e r a t i o n .For a s h o r t t i m e t h e r e i s n o s i g n a l a t a l l , and when t h es i g n a l d oe s resume i t s f r e q u e n c y h as s h i f t e d . T o a s s u r eg e t t i n g d a t a streams from t h e f i v e e n t r y c r a f t , g ro un dr e c e i v e r s w i t h b a n d w i d t h s s u f f i c i e n t t o c ov er a l l p o s s i b l e

f re qu en cy s h i f t s w i l l r e c e i v e and r e c o r d t h e i n c o m in gs i g n a l s .

The DSN's rea l - t ime rece iver s y st em s a t b o t h G o ld st on eand Canber ra w i l l s e r v e a s b a ck u ps t o t h e wide-band record inga r r a y s . F or t h i s r e a l - t i m e r e c e p t i o n of t h e s i g n a l s , t h e

DSN h a s a c q u i r e d s p e c i a l a u t o m a t i c t u n i n g e qu ip me nt t o

e n a b l e o p e r a t o r s t o s t a y l o ck e d o n p ro be s i g n a l s d u r i n g a s

much of t h e p ro b e e n t r y an d d e s c e n t p e r i o d s a s p o s s i b l e ,d e s p i t e s h i f t s i n s i g n a l f r e qu e n c ie s .

S c i e n t i s t s w i l l c a l c u l a t e a tm o s ph e ri c wind v e l o c i t i e sa n d d i r e c t i o n s f r o m measurements of c h a n ge s i n p r ob et r a j e c t o r i e s ( v e l o c i t i e s ) , t h r ou g h t r i a n g u l a t i o n m e as ur em en tsi n v o l v i n g f o u r s t a t i o n s . Two S T D N s t a t i o n s a t Guam a n dS a n t i a g o , C h i l e , w i l l r e c o r d Bus an d p r o b e d a t a , a l o n g w i t ht h e D S N s t a t i o n s a t Canber ra and Golds tone .



PROBE DATA RETURN

During flight through the atmosphere of the Sounder, North, Day and Night probes and the Bus, NASA's

Deep Space Netw ork must hand le data from six spacecraft at once. A ll Pioneer Venus spacecraft transm it

directly to Earth from the planet.



5 0 %



- 4 4 -

THE PLANET V E N U S

Venus is the planet most similar to Earth in size, mass

and distance from the Sun. But its surface is much hotter,

its atmosphere much denser, and its rotation much slower than

that of Earth.

The diameter of Venus is 1 2 , 1 0 0 km ( 7 5 1 9 mi.), compared

with Earth's 1 2 , 7 4 5 km ( 7 9 2 0 mi.). The mass of Venus is

0.81 times that of the Earth. The mean density of Venus is

5 . 2 6 grams per cubic cm compared with Earth's 5 . 5 grams per

cubic cm.

Because Venus is closer to the Sun, it receives abouttwice as much energy as Earth. However, it is more reflective

than Earth because of its cloudy atmosphere. As a result of

these two competing factors, Venus absorbs about the sameamount of solar energy as Earth. Thus Venus would be expected

to have a temperature very similar to Earth's. In fact, thesurface of Venus is very hot, about 480 degrees 2 ( 9 0 0 degrees F).

This theory for the high temperature of Venus assumes that

the atmosphere allows the passage of the incoming solar radiationto the lower atmosphere and the surface. However, the atmosphere

restricts the passage of heat radiation from the surface and thelower atmosphere back into space. The heat is trapped. Earthhas a modest greenhouse effect that raises its surface temperature

by about 35 degrees C (95 degrees F.),but in some parts of the

infrared spectrum heat can escape by direct radiation from theEarth's surface to space. Because of its density, compositionand clouds, the Venus atmosphere is very thick, and because it

is mostly carbon dioxide, it is essentially opaque to outgoingheat radiation at all important wavelengths.

One of the most puzzling aspects of Venus is its lack ofwater. If Venus is as dry as it seems, where did the oceans ofVenus go, if any ever existed? One speculation is that the

water rose into the upper atmosphere and was dissociated by

solar ultraviolet radiation into hydrogen and oxygen. Thehydrogen escaped into space from the top of the Venus atmosphere,

and the heavier oxygen diffused down to the oxidized crust.Detailed analysis shows that it might not be Practical for Venus

to have lost an ocean of water by such a route.formed close enough to the Sun so that the temperature prevented

water from being incorporated into the solid material that formedthe planet. If so, Venus would never have had enough water

within its rocks to form early deep oceans like those of Earth.

Direct measurements of gases within the Venus atmosphere maypoint toward one of two alternatives: Either that water was

not incorporated into Venus as much as on Earth, or that wateroutgassed and was subsequently lost.

Perhaps Venus

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- 4 5 -

O r b i t an d R o t a t i o n of Venus

T h e r o t a t i o n of Venus i s v e r y slow a nd i n a r e t r o g r a d ed i r e c t i o n , t h a t i s , o p p o s i t e t o t h e d i r e c t i o n o f t h e p l a n e t ' sr e v o l u t i o n a b o u t t h e Sun and t o t h e r o t a t i o n o f m o s t o t h e rp l a n e t s .

a round the Sun a r e i n o p p os i t e d i r e c t i o n s , t h e l e n g th of a s o l a rday on Venus i s 1 1 7 E a r t h d a y s ( 5 8 . 5 E a r t h d a y s of " d a y l i g h t "58 .5 E a r t h d ay s o f n i g h t ) .

V enus tu rn s on i t s a x i s o nc e i n 2 43 .1 E a r t h d ay s .

S i n c e V en us' r o t a t i o n o n i t s a x i s a nd r e v o l u t io n i n o r b i t

The o r b i t s of Ear th and V enus a r e t i l t e d t o e ac h o t h e ra b o u t 3 .5 d e g r e e s . V en us ' a x i s i s t i l t e d a b ou t 6 d e g r e e sf r o m p e r p e n d i c u l a r t o t h e p l a n e of t h e p l a n e t ' s o r b i t .co mpares w i t h E a r t h ' s a x i a l tilt of 23.5 degrees which produceso u r s e a s o n s . T hu s, s e a s o n a l e f f e c t s o n Venus a re smal l .

T h i s

Some s c i e n t i s t s b e l i e v e t h a t Venus' p e r io d o f r o t a t i o ni s t i e d

t ot h e r e v o l u t i o n o f t h e E a r t h an d Venus a r ou n d t h e

Sun. Venus p r e s e n t s t h e same hem isphere toward E a r t h a t each

c l o s e s t a p p r o a c h ; t h a t i s , e a c h t i m e t h e p l a n e t p a s s e s b e tw ee nSun and E a r t h . I f t h e r o t a t i o n of Venus i s l o c k e d t o t h e c lose

a p p r o a c h e s o f E a r t h a nd Venus, t h e n t h e i n t e r n a l d i s t r i b u t i o n ofmass w i t h i n Venus s h o u l d b e s l i g h t l y asymmetric.

Why does V e n u s r o t a t e s o slowly when m o s t o t h e r p l a n e t sr o t a t e i n p e r io d s of h o u r s r a t h e r t h a n m on th s? One s p e c u l a t i o ni s t h a t a l a r g e b ody h i t Venus and s topped i t s r o t a t i o n . T h isl a r g e bo dy m ig h t ha v e be e n c a p t u r e d a s a s a t e l l i t e i n t o ar e t r o g r a d e o r b i t a nd l a t e r impacted wi th Venus t o s t o p i t sn or ma l r o t a t i o n a nd r o t a t e it s lo w ly i n a n o p p o s i t e d i r e c t i o n .

It c o u l d be t h a t Venus was formed f r o m l a r g e f r a g m e n t s ,and a s a r e s u l t of t h e combined im p ac t s o f t h e s e f r a g m e n t s n e v e rhad much ro ta t i o n . A ccord ing t o a n o t he r s u g g e st i o n , s o l a r t i d a le f f e c t s i n V en us ' d e n s e a t m o s ph e r e may have slowed r o t a t i o nand t h e n " t u rn e d t h e p l a n e t o v e r " , a c c o u nt i n g f o r i t s backwardr o t a t i o n .

Radar as tro no me rs have mapped a n area o n t h e E a r t h - f a c i n g

s i d e of t h e p l a n e t a s l a r g e a s A s i a and have found w ha t app ea r st o be a r u gg e d s u r f a c e . A c c or d in g t o t h e r a d a r r e s u l t s , t h e re

a re huge sha l low c r a t e r s a s w e l l a s an enormous volcano whichmay be as l a r g e i n a r e a , t h o u g h n o t a s h i g h , a s Olympus Monson Mars ( t h e s o l a r s y s te m ' s l a r g e s t d i sc o v e re d so f a r ) . Radara s t r o n o m e r s a l s o d e t e c t e d wh at a p p e a r s t o be an enormous canyon.T h i s chasm i s 1 4 0 0 k m ( 8 7 0 m i . ) l o n g , 1 5 0 k m ( 9 5 m i . ) w i d e , andsevera l k i l o m e t e r s d e e p .

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-46-

VENUS' CLOUD CIRCU LAT ION

Ultraviolet picture of Venus' clouds taken at 720,000 k m (450,000mi ) by Mariner 10. This

ph oto consists of a mosaic of several T V frames. The dark markings of the clouds appear to

rotate in about four days in a retrograde direction.



- 4 7 -

Venus' I n t e r i o r and Absence of Magnet ic F i e l d

U n li ke t h e E a r t h , V enus h a s no s i g n i f i c a n t m a gn e ti c f i e l d .

C on ve ct io n c u r r e n t s i nT h e g e n e r a t i o n of E a r t h ' s f i e l d i s a t t r i b u t e d t o a s e l f - s u s t a i n i n gdynamo i n t h e f l u i d core o f t h e p l a n e t .t h e co re g i v e r i s e t o e l e c t r i c c u r r e n t s t h a t p ro du ce t h e e x t e r n a l

m a g n e t i c f i e l d . T h i s t h e o r y , w hic h a l s o seems t o a pp ly t oJ u p i t e r , p r e d i c t s t h a t s lo w -s p in n in g p l a n e t s l i k e Venus shouldno t have magne t i c f i e l d s .

Venus i s a p la n e t whose shape cou ld be v e ry c l o s e t o asph e re acc o rd ing t o r a d a r measu remen t s. They show i t s e q u a t o rt o be a l m o s t a p e r f e c t c i r c l e . B ec au se t h e p o l e s d o n o t r o t a t ei n t o view a s d o p o i n t s on t h e e q u a t o r , c i r c u l a r i t y aro un d t h ep o l e s c a n n ot b e m ea su re d. The l a c k o f i r r e g u l a r i t i e s i nshape , and of a s a t e l l i t e makes it d i f f i c u l t t o d e t er mi ne t h ei n t e r n a l d e n s i t y d i s t r i b u t i o n of t h e p l a n e t . Most models oft h e i n t e r i o r a r e based on i t s s i m i l a r i t y t o E a r t h , c o n s i s t i n gof a l i q u i d c o r e , a s o l i d m a n tl e and a s o l i d c r u s t . B ut t h e

t r u e n a t u re o f t h e i n t e r i o r of t h e p l a n e t i s ve ry much i nd o u b t b e c a u s e s c i e n t i s t s d o n o t k n o w V e n u s ' t h e r m a l s t r u c t u r eo r t h e n a t u r e of t h e m a t e r i a l s which make up i t s mass.

The Atmosphere of Venus

Carbon d iox ide i s t h e d o m in an t g a s i n t h e V e nu s ia na tmosphe re . T h e r e a re a l s o t r a c e s of w a t e r , carb on monoxide ,h y d r o c h l o r i c a c i d and hy dr og en f l u o r i d e . Free oxygen has neverbeen found.

T h e c l o u d s w hi ch o b s c u r e t h e s u r f a c e of V e n u s c o n s i s t of

t h i c k h a ze s of d r o p l e t s b e l i e v e d t o be made o f s u l f u r i c ac i d .Venus ' c louds a re p a l e y e ll o w a nd v e r y r e f l e c t i v e , r e t u r n i n gi n t o s p a c e s o m e 75 p e r c e n t o f t h e s u n l i g h t f a l l i n g on them.

Space prob e measurements have shown t h a t t h e r e a r e d i s t i n c tc l o u d l a y e r s much h i g h e r t h a n t e r r e s t r i a l c l o u d s . P h o t o g r a p h st a ke n i n u l t r a v i o l e t l i g h t r e ve a l a f o u r - d a y r o t a t i o n of t h e

m ar kin gs i n t h e s e c l o u d s . T h i s r o t a t i o n i s l i k e t h a t of t h ep l a n e t , i n a r e t r o g r a d e d i r ec t i o n . Unusua l dynamics o f t h ea tmosphe re a r e r e q u i r e d t o a c co u nt f o r t h i s high-speed c loudmot ion .

The g e n e r a l l y a c c e p t e d f i g u r e f o r a tm o sp h er ic c a r bo nd i o x i d e on Venus i s 9 7 p e r c e n t . However , measurements made

by e a r l y Vene ra s p a c e c r a f t (USSR) d i f f e r from r a d i o o c c u l a t i o nmeasuremen t s sugges t i ng t h e p r e s e n c e o f a b o u t 7 0 p e r c e n tc a rb o n d i o x i d e i n t h e Venusian atmo sphe re. And, i f t h e r ei s much a rgon i n t h e a tmosphe re , t h e amount of carb on d i ox id ec o u l d be as l o w a s 2 5 p e r c e n t .

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Adding to the uncertainty is the fact that the percentagesdetermined by the Veneras were obtained by sampling the

atmosphere in regions where there are sulfuric acid droplets.

The presence of the acid may have contaminated these measurements.

It is therefore possible to argue that the carbon dioxide is

considerably less than 9 7 per cent, with the remainder being

made up by some combination of nitrogen and argon.

The amount of carbon dioxide is important because it plays

a major role in the interpretation of the microwave spectrum

of the planet. If the atmosphere is 9 7 per cent carbon dioxide,the microwave observations permit the presence of as much as

0.1 per cent water below the clouds. Some instruments on the

most recent Veneras 9 and 10 indicated that water vapor

constituted about 0.1 per cent of the atmosphere below the

main clouds. At the cloud tops it is only 0.0001 per cent,

however. But, if there is another gas in the atmosphere of

Venus that is not a good microwave absorber, the planet's

atmosphere might contain more water than is now believed.

Carbon dioxide is also important to theories about theevolution of the atmosphere of Venus, and to the radiative

properties of the present atmosphere and its dynamic

characteristics.

The atmospheres of both Venus and Earth are assumed to

have originated from gases that were released from the interiors

of the planets which were hot when the planets first formed. In

the case of Earth, most of the outgassing may have occurred soon

after formation, from the heat of formation. Venus may neverhave had much water to outgas in the first place if it was

formed from parts of the solar nebula that were poor in water.Or it may be that Venus formed with as much water as the Earth,but this water has now been lost.

The Earth holds its water in its oceans because it is muchcooler than Venus and there is a "lid" on its atmosphere. This

lid is the very cold tropopause where the temperature riseswith altitude. This prevents heated water vapor from rising

by convection to cooler heights where it could be,dissociated

by solar ultraviolet radiation. But if Earth were moved to

the same distance from the Sun as Venus, conditions could

change drastically. The additional solar energy would be

sufficient to evaporate all of Earth's oceans.

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If Venus had been formed from the same mix of materialsas Earth and then outgassed its volatiles, we would expect it

to have an atmosphere about 350 times as massive as Earth's.Carbon dioxide would account for a surface pressure of about100 atmospheres, and water vapor would account for about 150

atmospheres. On Earth most of the 100 atmospheres of carbon

dioxide is tied up in carbonate rocks which are chemicallystable at terrestrial temperatures, but unstable at Venus

temperatures. Earth's oceans, if vaporized, would result in

an atmospheric pressure of about 250 atmospheres. Venusdoes indeed have nearly 100 atmospheres of carbon dioxide,

but the water is apparently absent. There are no oceans,

and the atmospheric water vapor is a minor constituent.

One of the major questions to be answered by Pioneer Venusis just how much water vapor is present. Water vapor would

be broken down by solar ultraviolet radiation into oxygenand hydrogen. The hydrogen would escape into space leavingthe oxygen behind. Effectively the oceans would be leaking

into space.

This could have happened to Venus. If the primitive

atmosphere of Venus consisted mostly of steam (because theplanet is closer to the Sun than Earth), the resulting

convective atmosphere could not have had a barrier to

convection. The water vapor would have dissociated into

hydrogen and oxygen. Calculations suggest that withinabout 30 million years perhaps 90 per cent of the water

could have been lost to the planet, but all could not be

lost in this way.

Furthermore, there is no easy way to explain what

happened to the leftover oxygen other than that it reacted

with the surface rocks. Yet without running water tocontinually expose fresh rocks for oxidation, the process

might be insufficient to remove all the oxygen.drift might be a possible mechanism to expose fresh rocks.

There is a question, too, of what happens to the oxygen nowreleased in the upper atmosphere by photodissociation ofcarbon dioxide to produce the carbon monoxide observed

spectroscopically. The incorporation of oxygen with sulfurto form the sulfuric acid droplets does not seem to account

for all the missing oxygen.

Continental

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0

Ue

w

U3

I-E

W e

2

Uw

I-I

I-Uw

v2

7w > a

a I



-51-

On Venus, because of the high surface temperatures,

reactions between rocks, minerals and the atmosphere are

expected to be much faster than on Earth. However, on Earth

the action of running water constantly exposes new rocks to

the action of the atmosphere and aids oxidation and otherreactions between the rocks and the atmosphere. This is not

happening on Venus. If fresh rocks are not being exposed bysome other mechanism, the atmosphere of Venus may not haveachieved equilibrium with surface materials.

The Venus atmosphere can be divided into three distinctregions:

the ionosphere and the exosphere; a region of clouds; and a

region from the base of the clouds to the surface.

a region above the visible cloud tops which includes

Upper Atmosphere

The upper atmosphere of Venus has an ionosphere which is

different from that of Earth. Because Venus does not have asignificant magnetic field, the solar wind interacts directly

with the upper atmosphere and the ionosphere of the planet.

Among the atmospheric regions of Venus, the upper atmosphereabove the cloud tops is best understood. It has been investigated

from Earth and from flyby and orbiting spacecraft. Above 150 km

( 9 0 mi.) it is more rarefied than the atmosphere of Earth at the

same height. Like Earth's atmosphere, it is ionized by incoming

solar radiation to produce positively-charged ions and free

electrons of an ionosphere, which is thinner and closer to the

surface of the planet than Earth's ionosphere. Like Earth's

ionosphere, the ionosphere of Venus has layers at which the

number of electrons per cubic centimeter (electron density)peaks. In Earth's ionospheric layers, the peak electron density

is about 100,000 to 1,000,000 electrons per cubic centimeter, and

occurs at an altitude of about 250 to 300 km (150 to 180 mi.).

The major ion is singly-charged carbon dioxide.

Mariner 10 found two clearly defined layers in the nighttime

ionosphere: a main layer at 142 km ( 8 7 mi.) altitude and a

lesser layer at 124 km ( 7 6 mi.). The peak intensity of the latter

was about 7 8 per cent of the higher layer. On the dayside there

was one main layer at 142 km ( 8 7 mi.) and several minor layers,

including one at 128 km ( 7 8 mi.) and another at about 1 8 0 km

(110 mi.). The Venera 9 and 10 orbiters obtained similar results,

but single layers seem to be the most common.

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SOLAR WIND - VENUS INTERACTIONS

BOW SHOCK

T R A N S I T I O NR E G O N

_ -/- -- R A R E F A C T I O N.---

$JOLAR



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From a practical standpoint, Venus has no intrinsic

magnetic field. The field of Venus is less than 1/10,000 ofEarth's field. There is a region of rarefaction (lessened

density) of the solar wind flow at Venus, and the characteristics

of the plasma there indicate that Venus absorbs part of the flux

of the solar wind. On the dayside of Venus, there is a sharpboundary to the ionosphere at 350 to 500 km ( 2 1 0 to 305 mi.).

This is believed to be caused by the interaction of the solar

wind with Venus' atmosphere. On the night side of the planet,

the ionosphere extends high into space and probably into a

plasma tail stretching away from the Sun.

Temperatures have been measured in regions above the visiblecloud layers by radio occultation. The temperature of theexosphere (region where particles escape the planet) was derivedfrom density variation with altitude found by the ultraviolet

experiments of spacecraft. From observations of the ultraviolet

radiation from hydrogen and helium atoms, it is calculated that

the temperature of the exosphere of Venus when Mariner10

flewpast the planet was about 1 2 7 degrees C ( 2 6 0 degrees F). At such

a temperature, the thermal escape of helium gas would be negligibleAccordingly it is thought that if helium outgassed from the rocks

of Venus as it did on Earth the gas might have accumulated in

the upper atmosphere of Venus.about 800 km (480 mi.) and contains up to 10,000 atoms per

cubic centimeter.

A corona of hydrogen begins at

Haze Layers

At least two tenuous layers of haze can be seen in high

resolution pictures of the limb (edge of the disc) of Venus.They extend from equatorial regions to higher latitudes. They

may be associated with temperature inversions in the highatmosphere, and may result from processes similar to those in

Earth's atmosphere which produce layers of aerosols in thestratosphere. Aerosols are solid or liquid particles suspended

in an atmosphere. The stratified layers of haze are in the

region 8 0 to 90 km (50 to 5 6 mi.) above the surface of Venuswhere the atmospheric pressure is between 50 and 0.5 millibars.

(Pressure at Earth's surface is 1000 millibars). These haze

layers are extremely tenuous. At the topmost haze layer, if

the atmosphere is mainly carbon dioxide, the temperature shouldbe - 7 5 degrees C. However, temperatures determined from

occultations differ appreciably above 60 km ( 3 7 mi.)t suggestingtemperature inversions that separate the haze layers from thetopmost convective cloud deck as well as the upper from thelower haze layers. In the region above 50 km (30 mi.), the

daytime atmosphere is about 15 degrees C ( 5 9 degrees F)warmer than the temperature at night.

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The Cloud Layers

Below the upper atmosphere is the 18-km (11-mi.)-thick

region containing the clouds of Venus visible from Earth. While

the clouds of Venus look extremely opaque, they are in fact very

tenuous. Veneras 9 and 10 determined that visibility within the

clouds is between 1 and 3 km (0.6 to 1.8 mi.). They are morelike thin hazes than terrestrial clouds. The particles makingup the clouds of Venus are spherical and about one to two

microns in diameter. These droplets apparently consist ofsulfuric acid, with concentrations varying from 50 to 500

per cubic centimeter.

The presence of sulfuric acid clouds explain the extremedryness of the Venus upper atmosphere. Nearly all the water

has chemically bound up in the sulfuric acid droplets. The

density of Venus' atmosphere at this level is about one-tenththe density of Earth's atmosphere at sea level. Sulfuric acid

clouds remain as clouds over a wider range of temperature than

water clouds, although high temperatures cause some of thewater to evaporate from the droplets. There is evidence of

the presence of fluorine in the Venus atmosphere. This element

probably combines with water into the extremely stable and

corrosive fluorosulfonic acid. But none of these acids can

account for the absorption of ultraviolet radiation by the

clouds. There must be an unknown ultraviolet absorber in theclouds which gives rise to the dark markings seen in ultravioletpictures of Venus.

One speculation is that the dark regions seen in ultraviolet

light are oxygen-depleted regions where a significant amount ofultraviolet-absorbing sulfur is being produced. There appears

to be a whole series of compounds of sulfur, oxygen and halo-qens that enter into the chemistry of the atmosphere of Venus.

The Pioneer Venus measurements of the constituents of theatmosphere of Venus with a mass spectrometer and gas chromatographshould contribute greatly to our understanding of these chemicalprocesses that are responsible for the Venusian clouds and theirmarkings.

The dark markings of the clouds, seen in ultraviolet light,

have characteristic forms that have been studied from Earth.

There are horizontal Y-shaped features which sometimes have atail. There are features that look like a reversed letter C.

The features in the form of a reverse letter C appear moreoften on the evening terminator than on the morning terminator.

Other features are like a reversed C with a bisecting bar.Sometimes there are two parallel equatorial bands. The

patterns are a l s o almost always symmetrical about the equator

of Venus. The arms of these features are always open in the

direction of their retrograde motion which varies between

180 and 470 kph (112 to 2 6 5 mph).

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E

I-ILuI

Y

2

VENUS ATMOSPHERE

M A I N

IONIZATION140

WEAKLY

IONIZED

. . . . . . . LAYERS

TROPOPAUSE

60 CLOUDS

WIND

SHEARILOW HAZES

A €ROSOLS

DUST

CLEAR

20

V ATMOSPHERE

I SURFACE

o - & w l RUST

UPPERATMOSPHERE

C L O U D S

LOWERATMOSPHERE

25 50 75 100

WIND SPEED m/s



- 5 7 -

S

a

In the upper atmosphere the effects of solar heating are

ignificant, and the C-bar, C- and Y-shaped features are all.ssociated ith the sub-solar point, which is the point where

the Sun shines down on the Venus atmosphere from directlyoverhead. However, the features move around the planet and

are not fixed with respect to the sub-solar point.

A big question about Venus' atmosphere is whether the

apparent motions of the ultraviolet markings are a result ofactual movement or merely a wave motion. The evidence today

points to an actual movement of mass: i.e., winds. But there

is some evidence of wave motions, diurnal tides and parallelequatorial belts.

The division between the high wind velocities of the

stratosphere, and the near calm of the dense surface atmosphere

seems to come at about the 56 krn (36 mi.) level. The big change

in wind velocity thus appears to take place at the bottom of the

clouds where there must be a shear zone. Thus, the cloud bottomsare expected to be extremely ragged.

The Soviet probes measured the amount of solar radiationdown to the surface. Above 50 km (31 mi.), scattering appears

to be by the cloud particles. Below about 25 km (15 mi.), thescattering is Rayleigh scattering; i.e., by much smaller air

molecules. At the surface, with the Sun's position about 30

degrees from overhead, the integrated flux was measured as

being about equal to that on an overcast day on the Earth at

sea level in mid-latitudes.

The high velocity winds in the Venus atmosphere might arise

because the planet has such a massive and deep atmosphere. Large-scale eddies containing a lot of energy could transport momentum

from low to high altitudes with a high amplification. The ionwind speeds in the dense lower atmosphere produced by the heat

from the Sun and the rotation of the planet are amplified intothe thin upper atmosphere.

Lower Atmosphere

The penetration of Veneras 9 and 10 into the lower atmosphereproduced new information about this region. At about 50 km (30 mi.)altitude, the wind velocity appears to be about 130 kph (80 mph).

At the landing site of Venera 9, the local wind velocity variedfrom 1.2 to 2.5 kph (.9 to 1.4 mph); at the Venera 10 site, itvaried from 2.9 to 4.7 kph (1.8 to 9.2 mph). The two landers

thus confirmed a low wind velocity c lose to the surface, as well

as little dust content in the low atmosphere.

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T h e r e a re s t i l l many u n r e s o l v e d q u e s t i o n s a b o u t t h ea tm osphere of Venus t h a t need t o be answ ered , such a s :

0 H o w does t he V enus weather m a c h i n e r e a l l y work?

0 I t i s r e a l l y a greenhouse e f f e c t t h a t makes Venusso h o t compared w i t h t h e E a r t h ? O r i s t h e re adynam ic cause?

Did Venus once have a more moderate s u r f a c et e m p e r a t u r e ?

0 What c a u s e s t h e d a r k m a rk in g s i n t h e Venus c louds?

0 What are t h e c o n s t i t u e n t s of t h e Venus a tm osphere?

Therm al em iss ion from t h e u pp er a t mo sp h er e d i f f e r s v e r y

l i t t l e between ni g h t and day and between l o w and h i g h l a t i t u d e .

T h i s i n d i c a t e s a dynam ic a c t i v i t y w i t h i n t h e a tm osphere , ands u g g e s t s t h a t h e a t i n s u b s t a n t i a l amounts i s b e in g t r a n s f e r r e da ro un d t h e p l a n e t h o r i z o n t a l l y . T here a r e dynamic a c t i v i t i e sa t all l e v e l s b e c a u s e s p a c e c r a f t h a ve d e te r m in e d t h a t t h e s o l a rr a d i a t i o n p e n e t r a t e s t h ro ug h t h e c l o u d s a nd , t h e r e f o r e , a f f e c t st h e atmosphere down t o t h e s u r f a c e . D i r e c t s o l a r h e a t in g i smost i m p o r t a n t a bo ve 56 km ( 3 4 m i . ) ; dynamic e f f e c t s b e l o w t h a t .

Over t h e w hol e of t h e p l a n e t t h e r e i s a l s o t h e e f f e c tof t h e a t m o s p h e r e a t t h e e q u a t o r r i s i n g a s it i s warmed by

s u n l i g h t , a n d s i n k i n g n e a r t h e P o l e s , as it c o o l s .

T h e S u r f a c e o f Venus

Radar h a s revealed l a r g e - s c a l e f e a t u r e s t h a t su g g es tt e c t o n i c s a nd i m p a c t m o ld in g of V e n u s ' t o p o g r a p h y . D e t a i l so f t h e s u r f a c e have b e en p r o v i d e d b y t h e t w o S o v i e t l a n d e rs p a c e c r a f t .

The r a d a r o b s e r v a t i o n s r e v e a l a l a r g e - s c a l e g r a n u l a rs t r u c t u r e , s u g g e s t i v e of a r o ck - st r ew n d e s e r t . L ar ge b u ts ha l l ow c i r c u l a r f e a t u r e s , m o s t l i k e l y c r a t e r s , a r e f o un d i ne q u a t o r i a l re g i o n s . Some a re a s o f h i g h r a d a r r e f l e c t i v i t y a r ei n t e r p r e t e d a s e x t e n s i v e l a v a f l o w s a n d m o u n t a i n o u s a r e a s . A

major chasm s t r e t c h e s 1 4 0 0 k m ( 8 7 0 m i . ) n o r t h a nd s o u t h a c r o s s

t h e e q u a t o r.

A t f i v e d e g r e es s o u t h l a t i t u d e and 320 d e g r e e s l o n g i t u d ei s t h e h i g h mounta in B e t a w i t h a c r a t e r e d t o p l i k e t h e l a r g e

M a r t i a n v o l c a n o e s . T h e r e a r e a l s o a r c u a t e r i d g e s . One is a tl e a s t 800 k m ( 4 8 0 m i . ) l o n g . T h e r e a re mounta inous a r e a s whichmay be v o l c a n i c o r a r e s u l t o f c r u s t a l p l a t e m ovements.

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- 59 -

Pho tographs from one S o v i e t l a n d e r s p a c e c r a f t c on fi rm ad r y ro ck y s u r f a c e t h a t h a s been f r a c t u re d and moved abo u t byunknown p r oc es se s . The second l a nd e r p roduced a p i c t u r e ofr o c k s w i t h r ou nd ed ed g e s a nd p i t t e d s u r f a c e s . The fo rm s o ft h e s e rocks may be e x p la i ne d by v o l c a n i c a c t i v i t i e s ha vi ng

t a k en p l a c e on the s u r f a c e .

T h e e x i s t e n c e o f c r a t e r s o n Venus s u g g e s t s t h a t i t s s u r f a c eh a s n o t b ee n s u b j e c t e d t o t h e m a jo r t e c t o n i c c h an g es e x p e r i e n ce don E a r t h , b u t t h a t it has p r o b a b l y e v o l v e d s o m e w h a t a l o n g t h esame l i n e s a s Mars. Some o l d c r a t e r e d t e r r a i n i s p r e s e r v e dw h i l e o t h e r p a r t s h av e be en m o d i f i e d by t e c t o n i c s and vo l can i sm.

Venus migh t , i ndee d , have evo lved t o a s t a g e b etw ee n t h a t ofMars and t h a t o f t h e E a r t h .

Venera 9 l a n d e d a t 33 degrees n o r th l a t i t u d e . I t s p i c t u r eshows heaps o f ro ck s , m os t l y abou t 30 c m ( 1 2 i n . ) o r more i n

s i z e , and w i t h r a t h e r s h a rp edges. The f o r m a t io n o f t h e s e r oc ksi s b e l i e v e d t o be a s s o c i a t e d w i t h t e c t o n i c p r o c e s s es . T h e l a n d e ri s b e l i e v e d t o b e on t h e s i d e of a h i l l i n which t h e r e i s somedownward movement of t h e rocks . The s ha rp edges and l a c k ofround ing of t h e r oc ks a t t h i s s i t e s u g ge s t t h a t t h e y w e r eformed from breakage of h a r d , l a y e r e d rocks , p o s s i b l y a l a v af low.

Venera 1 0 l anded a t 1 5 d eg re es n o r t h l a t i t u d e , i n a n a reaw i t h a much smoother s u r f a c e . T h i s i s b e l i e v ed t o be a p l a t e a uo r p l a i n o f g r e a t e r r e l a t i v e a g e t ha n t h e s i t e of Venera 9 .

T here a r e s o m e r o c k y e l e v a t i o n s which a r e c o v e r e d w i t h ar e l a t i v e l y d ar k , f i n e - gr a in e d s o i l . T h i s i m p l i e s t h a t t h e

rocks have been weathered , p o s s i b l y by c h em i c a l a c t i o n w i t ht h e a t m o s p h e r e . It i s u n l i k e ly t h a t t h e g e n t l e w in ds a t t h es u r f a c e c o u ld h av e be en r e s p o n s i b l e for t h e w e a th e r in g .G e n e r a l l y a t t h i s s i t e t h e m a t e r i a l of t h e V e nu si an s o i l i sd a r k , b u t t h e r e a re o u t c r o p s of l i g h t e r - c o l o r e d rock p e n e t r a t i n gt h e s o i l . Some o f t h e d a r k s o i l f i l l s d ep r e s s i on s o f t h eo u t c r o p s . T h i s s u r f a c e i s i n t e r p r e t e d a s being much o l d e r andmore weathered t ha n t h e s u r f a c e s e en a t t h e Venera 9 s i t e . T h e

w e a t h e r i n g p r o c e s s may be a c h e m ic a l i n t e r a c t i o n b et we en t h eh o t r o c k s an d t h e a t m os p h er e , p o s s i b l y by m i n e r a l a c i d s andwater v a p o r .

Measurements made by t h e s p a c e c ra f t in d i c a t e t h a t t h e

s u r f a c e rocks have a de n s i t y between 2 . 7 and 2 . 9 grams perc u b i c c e n t i m e t e r , w hich i s t y p i c a l of t e r r e s t r i a l b a s a l t i cr o c k s .

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- 6 0 -

Surface temperatures appear to be high enough to makeportions of the surface glow a dull red. They are high enough

to melt zinc, but not most common rocks. The Venus rocks at

the two landing sites are about as radioactive as terrestrial

lavas and granites. This suggests that Venus, like Earth,has differentiated by heating to form a dense core and a

lighter crust.

Though it has dramatic major features, the surface issmoother than that of Earth and Mars. Radar-measured minimum

to maximum height differences are 10 km (6 mi.) -- the height

of Mt. Everest. This compares with 20 km (12.4 mi.) on theEarth, from the bottom of the Mariannas Trench to the top

of Everest. It compares with 30 km (18.6 mi.) on Mars, from

the floor of the Hellas basin to the peak of Olympus Mons.Craters on Venus seem to be shallower than on the other worldsof the inner solar system.

On the Moon and Mercury, and to a somewhat lesser extent

on Mars, the ratio of craters diameter to depth is about 10to 1. On Venus, according to the radar surveys, the ratiois more like 100 to 1. The craters on Venus seem to beextremely shallow; the reason is not known. It could result

from plastic deformation of the hot surface or from someweathering process.

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-62-

0 What a r e t h e r o l e s of g l o b a l c i r c u l a t i o n and l o c a lt u r b u l e n c e i n s t a b i l i z i n g t h e u pp er a tm os ph er e?

0 What a r e t h e e f f e c t s of t h e n e u t r a l p a r t i c l e s o n io no -

s p h e r e c o m p o si t io n ?

0 How h i g h d oe s s u p e r r o t a t i o n ( fo u r- da y r o t a t i o n ) of t h ec l o u d t o p s e x t e n d ?

0 S i n c e V enus h a s no m a g n e t i c f i e l d , t h e s o l a r w i n d i n t e r -a c t s d i r e c t l y w i t h t h e uppe r a tmosphe re . What mechani smsd oe s t h i s c r e a t e , and do th e y a f f e c t t h e lower a tmosphe re?

0 Where di d Venus ' a tmo sphe re c o m e f rom and where i s i t

go ing?

The main sources of Venus ' a tmosphe re p robab ly a r e o u t -

g a s s i n g from t h e i n t e r i o r , g a s e s from t h e o r i g i n a l s o l a rn e b u l a an d some s o l a r wind p a r t i c l e s .

e Where i s t h e water t h a t may ha ve on ce been on Venus?

The o b v i o us an s we r s a r e t h a t it e i t h e r " l ea k ed " t o s p a c eb e c a u s e o f h i g h Venus h e a t i n g , o r it w a s n e v e r t h e r e .Bu t numerous q ue s t i o ns r ema in .

0 Why does Venus ' a tmosphere d i f f e r s o much f rom t h a t ofi t s ' 't w in " p l a n e t , E a r t h ?

0 I s a l l V enus t e r r a i n r e l a t i v e l y low co mp are d t o E a r t h a n dM a r s o r does V en us ' " i n v i s i b l e h e mi sp h er e " c o n t a i n h i g hmounta ins and deep canyons comparable t o t h o s e o n E a r t hand Mars?

0 I s V enus a s c l o s e t o a p e r f e c t s p he re a s t h e e q u a t o r ia lmeasurements sugges t?

0 Does V enus' i n t e r i o r c o n t a i n l a r g e c o n c e n t r a t i o n s o f h ig hd e n s i t y m a t e r i a l .

T he l o c k i n g o f 1 7e nu s' r o t a t i o n t o E a r t h ' s o r b i t s u g g es t ss u c h m as s c o n c e n t r a t i o n s .

0 What i s t h e s u r f a c e t o po gr ap hy ?

0 What i s t h e c o m p o s it i on of t h e s u r f a c e ?

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-63-

HISTORICAL DISCOVERIES ABOUT VENUS

684 BC

1 6 1 0

1 7 6 1

1 7 9 2

1807

1890

1 920

1 9 2 2

1932

1 9 4 2

1 955

1 956

1 9 57

Ninevah t a b i e t s r e c o r d o b s e r v a t i o n s o f V e nu s.

U si ng t h e n ew l y- in v en te d t e l e s c o p e , G a l i l e of i n d s t h a t V e n u s e x h i b i t s p h a s e s l i k e t h o s e of

t h e Moon.

M i k h a i l V . Lomonosov ( U . S .S . R ) i n t e r p r e t s o p t i c a l

e f f e c t s ob se rv e d d u ri n g t r a n s i t o f V enus a s duet o a n a t m os ph er e o n t h e p l a n e t .

Johann H . S c h ro te r (Germany) con clud es Venus h a s

a n a t m o sp h e re b e c a u s e t h e c u s p s a t t h e c r e s c e n tphase ex t e nd beyond t h e g e o m e t ri c a l c r e s c e n t .

Joh ann Wurm (Germany) de te rm in es t h e dia me te r oft h e v i s i b l e d i s c o f Venus a s 12 ,2 93 km (7 ,6 39 m i . ) .

S c h i a p a r e l l i c o nc lu d es from h i s o b s e rv a t io n s t h a t

V enus r o t a t e s i n 2 25 d a ys .

Edward S t . John ( U . S . ) a n d S e t h B . N i c h o l s o n( U . S . ) s u g g e s t t h a t Venus i s a d r y , d u s t y wo rl d

b e ca u se t h e y c a n n o t d e t e c t a ny water v a po r i n i t sa tmosphe re .

L y ot m ea su re s t h e p o l a r i z a t i o n o f s u n l i g h t re -

f l e c t e d fro m t h e c l o u d s o f Venus a nd i n t r o d u c e sa new m eth od o f i n v e s t i g a t i n g t h e s i z e a n d n a t u r eo f p a r t i c l e s i n i t s c l o u d s .

Walter S . Adams ( U . S . ) and Theodore Dunham ( U . S . )

d e t e c t c a r b o n d i o x i d e i n t h e a t m o sp h e re o f V en us .

R u p e r t W i l d t (U .S .) shows t h a t t h e h i g h s u r f a c et e m p e r a t u r e of Venus could a r i s e f r o m a g r e e n -h ou se e f f e c t i n a n a tm os ph er e w i t h a h i g h p r o p o r -t i o n of c a rb o n d i o x i d e .

F r e d H o yl e ( U n i t e d Kingdom) s u g g e s t s t h a t t h eVenus c louds a r e a photochemica l hydrocarbon smog.

R a d i o waves a t 3-cm wavelength a r e d e t e c t e d f r o m

V enus a n d show t h a t t h e s u r f a c e t e m p e r a t u r e isv e r y h i g h ; a b o u t 330 d e g r e e s C ( 62 5 d e g r e e s F . ) .

C h a r l e s B oy er ( F r a n c e ) d i s c o v e r s a fou r -day r o t a -t i o n p e r io d o f t h e u l t r a v i o l e t m ark ing s i n t h ec lo ud s o f Venus.

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- 6 4 -

1 9 6 0

1 9 6 0

1 9 6 2

1 9 6 2

1 9 6 2

1 9 6 7

1 9 6 7

1 9 6 8

1968

1 969

1 9 7 1

A douin D o l l f u s ( F r a n c e ) d e t e r m i n e s p r e s s u r e a tc l o u d t o p s a s 9 0 m i l l i b a r s , u s i n g p o l a r i m e t r y .

C a r l Sagan ( U . S .) c a l c u l a t e s h e a t i n g i n atmos-p h e r e w i t h l a r g e a mo un ts o f c a r b on d i o x i d e a nd

w a t e r v a p o r , c o n c l u d e s s u r f a c e t e m p e r a t u r e c a nb e r a i s e d by g re e nh o u se e f f e c t t o a bo ve t h e b o i l -i n g p o i n t of w a t e r , 1 0 0 d e g r e e s C ( 2 1 2 d e g r e e s F . ) .L o w r a d a r r e f l e c t i v i t y o f Venus r u l e s o u t anyp o s s i b i l i t y o f t h e r e b e i n g l a r g e b o d ie s of w a t e ron t h e p l a n e t ' s s u r f a c e .

R a d a r o b s e r v a t i o n of Venus e s t a b l i s h e s r o t a t i o na s r e t r o g r a d e i n a p e r i o d o f a p p r o x i m a t e l y 2 4 0d a y s .

M a r i n e r 2 f l y b y c o n f ir m s h i g h s u r f a c e p r e s s u r e( a t l e a s t 75 a t m o s p h e r e s ) a n d t e m p e r a t u r e ( a b o u t650 degrees K) a n d show s no s u b s t a n t i a l m a g n e t i cf i e l d .

M a r i n er 5 f l y b y u s e s r a d i o o c c u l t a t i o n t o measures t r u c t u r e o f u p p er a tm o sp he re a nd l o c a t e h e i g h to f c l o u d s ab o ve s u r f a c e ; d i s c o v e r s i o n o s p h e r e a ndf i n d s t h a t c a rb o n d i o x i d e i s major compound ofa tmosphe re .

James P o l l a c k ( U . S . ) a nd S ag an c a l c u l a t e g r e e n-h o u s e e f f e c t f o r m a s s i v e V enus a t m o s ph e r e , show-

i n g t h a t s o l a r e n erg y a lo n e c a n h e a t s u r f a c e t oabove 450 de gr ee s C ( 8 45 d e g r e e s F . ) .Radius of Venus s u r f a c e de t e rm ined f rom ra d a rt o be 6 ,050 km (3 ,750 m i . ) w i t h u n c e r t a i n t y ofl e s s t h a n 5 km ( 3 m i . ) .

S u r f a c e t e m p e r a t ur e s a n d p r e s s u r e s a r e e s t i m a t e dfrom r a d i o a n d r a d a r d a t a a s 477 d e g r e e s C (890d e g r e e s F . ) and 9 0 a t m o s p h e r e s .

U.S.S.R. probes ,Vene ra 5 and 6, s u c c e s s f u l l y l a ndo n s u r f a c e , d e t e r m i n e a c c u r a t e t e m p e r a t u r e ( 7 50

d e g r e e s K) a n d p r e s s u r e ( 9 0 a t m o s p h e r e s ) , a l s os t r u c t u r e o f l o w e r a tmosphe re .

A n a l y s is of p o l a r i z a t i o n d a t a by James Hansena nd A l b e r t A r k in g ( U . S .) shows t h a t t h e c l o u dp a r t i c l e s a r e s p h e r i c a l w i th a r e f r a c t i v e i nd exof 1 . 4 4 , r a d i u s of 1 . 0 5 pm and a l o c a t i o n a t a

p r e s s u r e l e v e l o f 50 m i l l i b a r s .

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- 6 5 -

1 9 7 2

1 9 7 2

1 9 7 3

1973

1 9 7 3

1 9 7 4

1 9 7 4

1 9 7 6

1 9 7 6

1 9 77

A . T . Young and G . S i l l (U.S.) i n d e p e n d e n t l yc o n c l u d e t h a t t h e p o l a r i z a t i o n d a t a im ply t h a tVenus c louds are composed o f s u l p h u r i c a c i dd r o p l e t s .

U . S . S . R . Venera 8 l a n d e r m ea su re s r a d i o a c t i v e

c o n t e n t of s u r f a c e r o c k s , c o n c l u d es Venus i sd i f f e r e n t i a t e d . A ls o d e te rm in e s t h a t s u n l i g h t( a few p e r c e n t ) p e n e t r a t e s t o s u r f a c e .

O b s e r v at i o n s o f c a rb o n d i o x i d e a b s o r p t i o n s i nVenus atmosphere show a 2 0 p e r c e n t f l u c t u a t i o no v e r a f ou r -d a y p e r i o d , i n t e r p r e t e d a s upwardand downward motions of cloud de c k p l a n e t w i d e .

R a da r s c a n s o f Venus r e v e a l hu ge s h a l l o w c r a t e r son t h e p l a n e t ' s s u r f a c e .

Po l l ac k m akes ob se rv a t io ns o f V enus f rdm h igh-

f l y i n g a i r c r a f t and c on c lu d es t h a t c lo u d s a r ed ee p h a ze s o f s u l f u r i c a c i d d r o p s .

R i c h a r d G o l d s t e i n (U S .) produces h i u k ? s o l u -t i o n r a d a r im ag es of s m a l l a re a s of t h e p l a n e t ' ss u r f a c e s ho win g many t o p o g r a p h i c f e a t u r e s .

M a r i n e r 1 0 ( f l yb y ) o b t a i n s d e t a i l e d L l t r a v i o l e tp h o to g r ap h s o f c l o u d s , d e te r m in e d c i r c u l a t i o np a t t e r n s i n up p er a t mo s ph e re .

U.S.S.R. Venera 9 and 1 0 l a n d e r s p h o t o g r a p hs u r f a c e a t two l o c a t i o n s , s ho wi ng e x p os e d r o c k s

a nd e v i d e n c e o f e r o s i o n p r o c e s s e s .

A r v y d a s K l i o r e ( U .S .) a nd c o l l e a g u e s c o n c l u d efrom r a d i o o c c u l t a t i o n d a t a t h a t a d d i t i o n a ld i s c r e t e c l ou d l a y e r s e x i s t below t h e main s u l -f u r i c a c i d c l o u d s .

R ad ar i m ag e s w i t h t h e u p g r ad e d A r e c i b o r a d a r

i n d i c a t e l a r g e v o lc a n oe s and c r a t e r s o n p l a n e t .

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E X P L O R A T I O N OF VENUS BY SPACECRAFT

V enus ha s been exp lo re d by 1 3 s p a c e c r a f t of w h i c h t h r e ew e r e American and 1 0 w e r e R u ss ia n . F i v e o f t h e s e s p a c e c r a f tw e r e f l y b y s a nd e i g h t w e r e l a n d e r s . S e v e r a l o f t h e R u s s ia ns p a c e c r a f t c o n s i s t e d o f b o t h o r b i t e r s a n d l a n d e r s which s ep a-

r a t e d on a r r i v a l a t Venus. The re co rd i s a s f o l l o w s :

Venera 1 ( U . S . S . R . ) A f l y b y s p a c e c r a f t ; p a s s ed VenusMay 1 9 6 1 . No s c i en ce d a t a werer e t u r n e d , a c co r di n g t o r e p o r t s .

M a r i n e r 2 ( U . S . ) A f l y b y s p a c e c r a f t : p a s s e d VenusDecember 1 9 6 2 . Discovered t h a t t h et e m p e r a t u r e a v e r a g e s 426 d e g r e e s C

( 7 9 9 d e g r e e s F . ) o n b o t h n i g h t a n dd ay he m is p he r es , a nd t h a t t h e p l a n e th a s v i r t u a l l y n o m ag n et ic f i e l d andno r a d i a t i o n b e l t s .

Venera 2 (U.S.S.R.) A f l y b y s p a c e c r a f t ; p a s s ed VenusF e b r u a r y 1 9 6 6 . An a t t e m p t t o p h o to -g r a p h Ven us a p p a r e n t l y w a s n o ts u c c e s s f u l .

Venera 3 (U .S .S .R. ) A l a n d e r s p a c e c r a f t : e n t e r e d t h eatmosphere March 1 9 6 6 . N o r e p o r t so f any s c i e n t i f i c d a t a b e in g r e t u r n e d .

phere o f V enus O c tober 1 9 6 7 , andr e t u r n e d d a t a d u r i n g d e s c e n t t o a

few a tm osp heres . D e te rmined th ea tm osphere i s m a in l y c a r b o n d i o x i d e .

Venera 4 (U.S.S.R.) A l a n d e r s p a c e c r a f t ; e n t e r e d atmos-

M a r i n e r 5 ( U . S . ) A f l y b y s p a c e c r a f t ; p a ss e d October

1 9 6 7 . P r o v i d e d t e m p e r a t u r e a ndp r e s s u r e p r o f i l e s t o 527 degrees C

( 9 8 1 d e g r e e s F . ) and 1 0 0 a tm ospheresa t t h e s u r f a c e . D et er mi ne d t h e d e-t a i l e d s t r u c t u r e of t h e io n o sp h er e ,a n d d i s c o v e r e d t h e a t o m i c h y d r o g e nc o r o n a .

Venera 5 ( U . S . S . R . ) A l a n d e r s p a c e c r a f t : d e s c e n t c a p s u l e

e n t e r e d t h e a t mo s ph e re i n May 1 9 6 9 .M ea su re d t e m p e r a t u r e , p r e s s u r e a nda t m o s p h e r i c c o m p o s i t i o n .

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Venera 6 ( U . S . S . R . ) A l a n d e r s p a c e c r a f t : c a p s u l e e n t e r e dt h e a tmosp here May 1 9 6 9 . Determined

low w a t e r v a p o r c o n t e n t : s u g g e s t e dp r e s en c e o f n i t r o g en . M easu red c a r -

b o n d i o x i d e a s 93 t o 9 7 p e r c e n t o fa tmosp here , and oxygen l e s s t h a n 0 . 4p e r c e n t : s u r f a c e p r e s s u r e o f n e a r l y1 0 0 a tmospheres .

Venera 7 ( U . S . S . R . ) A l a n d er s p a c e c r a f t ; e n t r y c a p s u lepe ne t r a t ed th e a tmosphere December1 9 7 1 ; d a t a were t r a n s m i t t e d f o r 23m i n u t e s f ro m t h e s u r f ac e . M easu reda s u r f a c e t e m p e r a t u r e o f 543 d e g r e e s C( 1 , 0 0 9 d e g r e e s F . ) and a p r e s s u r e o f9 0 a tmospheres .

Venera 8 ( U . S . S . R . ) A l a n d e r s p a c e c r a f t : c a p s u l e la nd edJ u l y 1 9 7 2 , a nd t r a n s m i t t e d s u r f a c ed a t a f o r 1 0 7 minu tes . De te rminedamounts of u ran ium, thor ium and po ta s-

sium i n s u r f a c e m a t e r i a l s and showedt h e y w e r e s i m i l a r t o amounts i n t e r -

r e s t r i a l rocks . Measured a s u r f a c et em p e r a t u r e o f 530 d eg r ee s C (986d e g r e e s F . ) .

Mar iner 1 0 (U.S.) Mercury-bound s p a c e c ra f t : pass ed VenusF eb r u a r y 1 9 7 4 . O bta ine d f i r s t p i c -t u r e s from s p a c e c r a f t . R ev ea le d t h es t r u c t u r a l d e t a i l s of t h e c l o u ds i nu l t r a v i o l e t l i g h t . C onfirmed t h e c - ,y- and ?s i - shaped c loud mark ing s ,and f o u r- d ay r o t a t i o n o f t h e s e mark-i n g s . Found s i g n i f i c a n t am ounts o fh e l iu m and co n f i rm ed t h e p r e s en c e o fh yd ro gen i n t h e u p p e r a t m o s p h e re .P ho to gr ap he d h i g h - a l t i t u d e h a z e l a y e r s .

Venera 9 (U.S.S.R.) A l a n d e r s p a c e c r a f t . C a p s ul e r e ac h eds u r f a c e O ct o be r 1 97 5 a t 33 degrees N .

l a t i t u d e , 293 d e g r ee s l o n g it u d e . R e -

t u r ne d f i r s t p i c t u r e from t h e s u r f a c eof Venus. Measured wind sp ee ds , p r es -s u r e , t e mp e ra t ur e and s o l a r r a d i a t i o n

f l u x t h r o u g h o u t t h e a t m o s ph e re t o t h e

s u r f a c e . O r b i t e r s u rv e ye d p l a n e t .

Venera 1 0 ( U . . . . ) A l a n d er s p a c e c r a f t ; c a p s u le reached

s u r f a c e O c t o b er 1 97 5 a t 1 5 d e g r e e s N .

l a t i t u d e , 295 d e g r ee s l o n gi t u d e . R e -

t u r ne d s ec on d s u r f a c e p i c t u r e . O r b i t e r

s u r v ey e d p l a n e t a nd l o ok e d a t s u r f a c ew i t h b i s t a t i c r a d a r . D eterm ined s u r f a c ee l e v a t i o n s d i f f e r e d b o n ly a f e w k i l o -meters a lo ng o r b i t e r T ra ck .



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THE P I O N E E R V E N U S SPACECRAFT

The Pi on ee r Venus mi ss ion w i l l be ac com plis hed by two

s e p a r a t e s p a c e c r a f t , t h e 9 r b i t e r and t h e M u lt ip ro be . T heO r b i t e r , c a r r y i n g 1 2 s c i e n t i f i c i ns t r u m en t s , w i l l g l o b a l l ysu rv ey Venus' a tmosphe re and su r r oun d ing env i ronmen t . I t

w i l l s t u d y t h e V e n us ia n s u r f a c e and p e r fo r m o ne a s t r o n o m i c a le x p e r i m e n t .

The Mul t iprobe w i l l d i v i d e i n t o f i v e a tm os ph ere e n t r yc r a f t as i t approa ches Venus f rom Ea r th . These a r e t h et r a n s p o r t e r B us , t h e L a r ge a nd t h r e e S m a ll P r o b e s . Thef o u r p r ob e s w i l l measure Venus ' a tmosp here f rom i t s t e n u o u sb e g i nn i n g s down t o t h e d e ns e s u p e r h e a t e d r e g i o n s a t t h e s u r -f a c e . A f t e r l a u n c hi n g t h e p r o b e s , t h e B us, t o o , w i l l e n t e rand measure com pos i t ion of Venus ' upper a tmosphere .

T o ge th er t h e f i v e a tm o s ph e ri c e n t r y c r a f t w i l l c a r r y1 8 s c i e n t i f i c i n s t r u m e n t s . The L ar ge P ro be c a r r i e s s e ve ni n s t r u m e n t s ; t h e S m a ll P r o b e s , t h r e e e a c h , and t h e B us, tw o.

T o m e e t t h e P i o n e e r Venus r e q u i r e m e n t f o r tw o r e l a t i v e l ys i m p l e an d low c o s t s p a c e c r a f t , d e s i g n e r s c ho s e s p i n n i n g ve -h i c l e s . S p in n in g c y l i n d r i c a l s p a c e c r a f t p ro v id e s t a b i l i t yw i t h minimum we igh t , good s o l a r c e l l deployment , v iewingf o r e xp er im e nt s i n a f u l l c i r c l e and s p i n s c a n f o r t h eimag ing sys t em.

The B a s i c Bus

The Venus O r b i t e r a n d Venus M u l t i p r o b e s p a c e c r a f t s h a r ea ' ' b a s i c b us'' d e s i g n . T h r ee q u a r t e r s of t h e s y s te m o n t h eb a s i c b u s e s a r e common t o b o t h s p a c e c r a f t . I n t h e M u l t i-p r ob e d e s i g n , t h e f o u r a t mo s ph er e e n t r y p r o b e s a r e mountedon t h e f l a t s u r f a c e w hich i s t h e t o p o r f o r w ar d e nd of t h eb u s c y l i n d e r .

The common sys t ems on t h e b a s i c bus f o r bo tf i s p a c ec ra f ti n c l u d e a t h e r m a l l y - c o n t r o l l e d e q u i p m e n t a n d e x p e r i m e n t s c o m -p a rt m en t ; s o l a r - e l e c t r i c p a n e l s , b a t t e r i e s and power d i s -t r i b u t i o n sys t em; fo rward and a f t "omni" an t enn as ; communi-

c a t i o n s sy s te m ; d a t a - p r o c e s s i n g s y st e m ; Sun a nd s t a r s e n s o r sf o r o r i e n t a t i o n r e f e r e n c e d u r i n g c r u i s e and ma ne uv ers ; hy-d r a z i n e p r o p e l l a n t t a nk s ; and t h r u s t e r s f o r o r i e n t a t i o n ,c o u r s e ch an g es an d s p i n - r a t e c o n t r o l .

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S t r u c t u r e

T h e b a s i c bu s p o r t i o n s o f b o t h s p a c e c r a f t a re t h e i rmain b o d i es , f l a t c y l i n d e r s , 2 .5 m ( 8 . 3 f t ) i n d i am e te r and1 . 2 m (4 f t . ) h ig h.

The bus es p ro v id e a s p i n - s t a b i l i z e d p l a t f o r m f o r

s c i e n t i f i c i n st ru m e nt s , s p a c e c r h f t s ys te ms and i n t h e caseo f t h e M u l ti p ro b e , t h e f o u r p r ob e c r a f t . A c i r c u l a r e qu ip -ment s h e l f w i t h a n a r e a o f 4 . 3 7 sq . m ( 5 0 sq . f t . ) i s l o c a t e di n t h e u p p er o r f ow a rd e n d o f t h e b u s c y l i n d e r . The s h e l fi s mounted on t h e f o rw a r d e nd of t h e t h r u s t t u b e , t h e r i g i d

s t r u c t u r e w hich c o nn e ct s t h e s p a c e c r a f t t o t h e l a un c h ve-h i c l e . T w e l v e e q u a l l y s p ac ed s t r u t s s u p p o r t t h e e qu ip me nts h e l f p e r i m e t e r from t h e ba s e of t h e t h r u s t t ube . Thec y l i n d r i c a l s o l a r a r r a y i s , i n t u r n , a t t a ch e d t o t h e e q ui p-m en t s h e l f w i t h 24 b r a c k e t s .

T he rm al l o u v e r s ( f i f t e e n on t h e O r b i t e r an d e l e v e n ont h e M u lt ip ro b e) a t t a c h e d t o t h e l ow er s u r f a c e of t h e e q u i p -ment s h e l f , o pen and c l o s e ( w i t h h e a t - s e n s i t i v e - b i m e t a l l i cs p r i n g s ) t o c o n t r o l h e a t r a d i a t i o n from t h e e q uip me ntcompar tment . La rge h e a t p ro duc e r s , such as r a d i o a m p l i -f i e r s , a r e l o c a t e d o v e r s e v e r a l o f t h e s e l o u v e r s .

Maneuver System

The maneuvering sys tem of t h e b a s i c b us c o n t r o l s s p i nr a t e s , makes c o u r se a nd o r b i t c o r r e c t i o n s , and m a i n ta i n ss p i n a x i s po s i t io n -- u su a l l y p e r p en d i c ul a r t o t h e e c l i p t i cfor b o t h s p a c e c r a f t .

Benea th t he equ ipmen t compar tmen t , a l s o a t t a ch e d t o t h et h r u s t t ub e , a re t w o c o n i c al - h em i s p h er i c p r o p e l l a n t ta n k s ,3 3 c m . ( 1 2 . 8 i n . ) i n d i am e t er . The t a n k s s t o r e h y d ra z in ep r o p e l l a n t f o r two a x i a l and f o u r r a d i a l t h r u s t e r s . T hesecan chan ge s p a c e c r a f t o r i e n t i a t i o n , s p i n r a t e o r v e l o c i t y .

The maneuver sys te m ha s one mid- range Sun se ns or , twoe x t e nd e d - ra n g e Sun s e n s o r s , a nd a s t a r s e n s or t o s e n s es p a c e c r a f t o r i e n t a t i o n and p r o vi d e a r e f e r e n c e f o r f i n d i n gs p i n - a x i s a n g l e . The s t a r s e n s o r i s mounted on t h e equi p-m ent s h e l f a n d h a s a l o o k a n g l e of a b o u t 57 d e g r e e s t o t h es p i n a x i s . S u n s e n s o r s a r e a l l a t o ne p o i n t on t h e e q u ip -

m ent s h e l f p e r i m e t e r . They look r a d i a l l y t h ro u g h a n op en-i n g i n t h e s o l a r a r r a y and see t h e Sun on e a ch r o t a t i o n .

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- 7 0 -

R ed un dant d a t a p r o c es s o r u n i t s f o r m a t t h e Sun an ds t a r s e n s or o u t p ut s f o r t e l em e t r y t r a n s m is s i o n t o t h e E a r t h ,t o c a l c u l a t e s p a c e c r a f t o r i e n t a t i o n . T hese d a t a p r o ce s s o rsa l s o p r o v i d e s e q ue nc ed f i r i n g commands t o t h e t h r u s t e r s t omake o r i e n t a t i o n , v e l o c i t y

w i t h t h e s p i n a x i s , and a r e l o c a t e d a t t op and bo t tom o ft h e b us c y l i n d e r , d i a g o n a l l y o p p o s i t e e ac h o t h e r . They p o i n ti n o p p o s i t e d i r e c t i o n s , and t o t u r n t h e b us s p i n a x i s ,b ot h f i r e i n p u l s e s i n o p po s i t e d i r e c t i o n s . T o speed up o rs lo w down t h e b us a l o n g t h e d i r e c t i o n o f i t s s p i n a x i s , o n l yo ne t h r u s t e r i s p u l se f i r e d a t t w o p o i n t s 1 8 0 d e g r e e s a p a r ta round the c i r c l e of b us r o t a t i o n . E i t h e r t h e t o p o rb o tt o m t h r u s t e r c an be p u l s e d d e p en d in g on d e s i r e d d i r e c -t i o n o f v e l o c i t y c ha ng e.

and s p i n r a t e c h a ng es .

T h e s y s t em ' s t w o a x i a l t h r u s t e r n oz z le s a r e a l i g n e d

The O r b i t e r h a s a t h i r d a x i a l t h r u s t e r . T hi s i s l o c a -t e d o n t h e b o t t om of t h e bu s c y l i n d e r an d a l l o w s c o n t i n u o us

f i r i n g o f two bo tt om t h r u s t e r s t o make t h e moves i n an ax i a ld i r e c t i o n n eeded f o r o r b i t c h an ge s.

The f o u r r a d i a l t h r u s t e r s a re a r r a ng e d i n two p a i r s ,w i t h t h e p a i r s p o i n t i n g i n o p p o si t e d i r e c t i o n s . They a re

mounted app ro x imate ly i n a p l an e p e r p e n di c u la r t o t h e s p i na x i s , and t h i s p l a ne p a s s e s t hr o ug h t h e c e n t e r o f g r a v i t y .The r a d i a l t h r u s t e r s c ha nge t h e v e l o c i t y i n a d i r e c t i o np e r pe n d i cu l a r t o t h e s p i n a x i s .

T he se r a d i a l t h r u s t e r s a l s o h av e b ee n p l a c e d a t f o u re q u i d i s t a n t p o i n t s a r ou nd t h e p e r i m e t e r o f t h e b us c y l i n d e r .T h i s h a s t h e e f f e c t of p o i n t i n g them a t o p p o s i te a c u t e a n-

g l e s t o t h e c i r c l e o f r o t a t i o n . The r e s u l t i s t h a t f i r i n gtwo of them 1 80 d e g r e e s a p a r t , t o g e t h e r , w i l l slow downt h e s p i n r a t e . The o t h e r two w i l l speed it up.

Power System

The bus s o l a r power s ys t em p ro v id es 28 -vo l t DC e l e c -t r i c power t o O r b i t e r and Mu lt ip ro be s c i e n t i f i c i n s tr u m e n tsa nd s p a c e c r a f t s ub sy st em s . Seven r e s i s t i v e s h u n t l i m i t e r sho ld th e maximum vo l t ag e a t 30 .8 v o l t s . When th e vo l t a ged ro ps below 27.8 v o l t s , t h e b a t t e r i e s s t a r t t o s h a r e t h el o a d t hr ou gh d i s c h a r g e c o n t r o l l e r s . S ma ll s o l a r a r r a y s re-

c ha rg e t h e b a t t e r i e s .

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-71-

A s w i tc h p r o t e c t s t h e m a i n pow er bus f rom c u r re n to v e r l o a d s o r u n d e r v o l ta q e by a u t o m a t i c a l l y t u r n i n g

o f f i n s t r u m e n t s , s w i t ch e d l o a d s , and t r a n s m i t t e r b u se s .Th e s y s t e m 's a r r a y of s o l a r c e l l s i s s l i g h t l y s m al l e r f o rt h e M u l t ip r o be bu s t h a n f o r t h e O r b i t e r bu s b e ca u s e o f t h e

h i gh er pow er demands o f O rb i t e r ' s 1 2 exper im en t s . -The O r b i t e r

s o l a r a r r a y h a s 7 . 2 sq . m (77 . 8 sq . f t . ) of 2 x 2 cm ( . 8 x . 8 i nc e l l s . When a t r i q h t a n g l e s t o t h e S un l i n e , t h e s e p r o v i d e 226

w a t t s n e a r E a r t h and 3 1 2 w a t t s a t V enus . The M ul t i p rob e s o l a ra r r a y h a s 6 . 9 sq. m ( 6 5 . 7 sq. f t . ) of c e l l s a n d p r o v i d e s 2 1 4w a t t s n e a r E a r t h and 2 4 1 w a t t s a t Venus.

The power sy s t em 's two 7 .5 ampere-hour n ickel -cadmiumb a t t e r i e s p ro v id e a t o t a l o f 252 w a t t h ou rs of e l e c t r i c a le n e r g y . Power i s p r o v i d e d t o i n s t r u m e n t s fro m t h e s c i e n c epower b u s t h r o u g h r e d u n d a n t b u s e s i n t h e power i n t e r f a c eu n i t . O n-of f pow er sw i t c h i ng i s p e r fo r m e d i n t h e i n d i v i -d u a l i ns t r um e nt s f o r f l e x i b i l i t y i n s t e a d of c e n t r a l i z e ds w i t c hi n g i n t h e power i n t e r f a c e u n i t . The poweri n t e r f a c e u n i t p r o v i d e s o n- of f s w i t c h in g f o r p r o p ul s i o n

h e a t e r s .

- .

Communications System

The com m unica t ions sys t em fo r t h e t w o b u s e s c a n r e c e i v ecommands f r o m E a r t h i n any s p a c e c r a f t o r i e n t a t i o n t hr ou ght w o r e d u n d a n t S-band t r a n s p o n d e r s , c o n n ec t ed t o tw o omnid i r e c t i o n a l a n te n na s . (A t r a n s p o n d e r i s a r a d i o s y st e m

which receives i n c o m i n g s i g n a l s a n d t u n e s t h e o u t g o i n gt r a n s m i t t e r t o a f r equency w hich i s a t a c o n s t a n t r a t i ot o t h e in co min g s i g n a l . ) T h i s means t h a t D oD ple r s h i f ti n r a d i o f r e qu e n cy d ue t o s p a c e c r a f t m o ti on c a n be measuredp r e c i s e l y o n r a d i o t r a n s m is s i o n s f r o m b o t h E a r t h t o s pa ce -c r a f t and s p a c e c r a f t t o E ar th -- be ca us e f r e q u e n c i e s , b o t hl e a v i n g t h e E a r t h and a r r i v i n g a t t h e E a r t h a re known pre-c i s e l y . T h is a l lows s p a c e c r a f t v e l o c i t y m ea su re me nt s a c -c u r a t e t o .003 kph.

a d d r e s s a b l e ( re sp o nd s o n ly t o c e r t a i n f r e q u e n c i e s , andt h e r e c e i v e r s a re a u t o m a t i c a l l y r e v e r s e d by t h e command pro-c e s s o r l o g i c i f no command i s r e c e i v ed f o r 3 6 hours . H ence ,i f one f a i l s t h e o t h e r t a k e s over . T h e two r e c e i v e r o u t -p u t s a re c ro s s- co n ne c te d t o r e du n da n t e x c i t e r s , e i t h e r ofw h i c h c a n b e s e l e c t e d by ground command, T h e t r a n s p o n d e rp r o v i d e s e i t h e r a f i x e d - r a t i o in co min g t o ou t g oi n g c a r r i e rf r e q u e n c y , o r a f ix e d- fr eq u en c y c a r r i e r s i g n a l i n case off a i l u r e o f t h e two-way system.

The r e c e i v e r p o r t i o n of e a c h t r a n s p o n d e r i s f r equency-

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- 7 2 -

The s p a c e c r a f t - t o - E a r t h r a d i o l i n k i s prov ided by anS-band t r a n s m i t t e r , w h ic h c a n r a d i a t e a t 10 o r 2 0 w a t t s , w i t hr e d u n c a n t power a m p l i f i e r s o p e r a t i n g t h r ou g h e i t h e r t h efo r e o r a f t I'omni" an t enn as . The omnis cove r a hemisphe rel o o k i n g f o r w a r d o r a f t . B o t h O r b i t e r and Mul t i p robe space -c r a f t h a ve , i n a d d i t i o n t o t h e two Bus om nis, s p e c i a l i z e dan t ennas wh ich w i l l be d e s c r i b ed i n s e c t i o n s o n t h i e r com-

munica t i ons . E i t he r omni an t en na can be s e l e c t e d by g roundcommand. One omni an t en n a i s c o n n e c t e d t o o n e o f t h e two

r e d u n d a n t r e c e i v e r s , and t h e o t h e r omni ( o r o t h e r s p a c e c r a f tan t en na d es ig na te d by command) i s c on ne ct ed t o t h e o t h e rre ce iv e r . Th is a r rangemen t can be rev er se d by commarid.

Command Sys e m

The b a s i c bu s command s y s t e m accepts incoming commandsf r o m t h e bus r a d i o r e ce iv e r s . Command demodu la to r s t u rn ont h e sy st em , c o n v e rt t h e s i g n a l t o a u s a b l e b i n a r y b i ts t r e a m , a n d p a s s i t on t o c ross -c onne c ted command pr oc es so rs .Commands a re e i t h e r s t o r e d f o r l a t e r ex e c ut i on , o r e x ec ut edimmedia t e ly . Sp ac ec ra f t u n i t s r e ce iv e commands f rom re -

dun da nt command o u t p u t modules . The command sy st em a c c e p tsa pulse-code-modulated/frequency-shift-keyed/phase-modulated(PCM/FSK/PM) d a t a s t r e a m a t f o u r b i t s p e r se co nd .

Each command word c o n s i s t s of 48 b i t s i nc lu d in g 1 3b i t s f o r s y n c h r o n i z a t i o n , w hich g i v e s a one - in - a -mi l l i onp ro b ab i l i t y o f a f a l s e command. The sys t em has a t o t a l o f1 9 2 pulse commands and 1 2 mag nit ude commands. The commandmemory can s t o r e up t o 1 2 8 commands ( r ed un da nt ly ) f o r l a t e re x e c u t i o n .

Data Handl ina Svstem

The t e l e m e t r y p r o c e s s o r f o r t h e b us d a t a h a n d l i n g s y st ems am p le s s c i e n t i f i c a nd e n g i n e e r i n g m ea su re men t s o u r c e s i nsequence . I t t r a n s m i t s an i n s t r u c t i o n word t o t h e P i o ne e rCommand Module (C M) encode r wh ich add res ses a data modulet o r ea d o u t t h e s e l e c t e d channe l .

The i n t e r r o g a t e d c h a nn e l can be e i t h e r a n a l o g , i e r i a ld i g i t a l o r b i n a r y o n e - b i t ( y es -n o ) i n f o r m a t i o n . The PC M

e n c o d e r s h i p s t h e e nc od ed m ea su re me nt t o t h e t e l e m e t r y p r o -c e s s o r , w h e r e it i s f r a m e - f o r m a t t e d , c o n v o l u t i o n a l l y coded

and used t o b i p h a s e m o d ul at e a s u b c a r r i e r . The s u b c a r r i e rt h e n p h a s e m o d u l a t e s t h e o u t g o i n g c a r r i e r s i g n a l .

T h e t e l e m e t r y p r o c e s s o r s and PCM e n c o de r s a r e c r o s s -c o n n ec t ed a nd f u l l y r e d un d a n t.

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-73-

C r i t i c a l t e l e m e t r y m ea su re me nts a r e a s s i g n e d d a t a c han -n e l s o n t w o d i f f e r e n t d a t a m o d u l e s . The d a t a h a n d l i n gsys tem s c a n a c c e p t up t o 256 c h a n n e l s of d a t a .

A l l P i o n e e r Venus t e l e m e t r y d a t a a r e b i n a r y ( a s e r i e s

of ones and z e r o e s ) , and a l l d a t a " wo rd s" c o n s i s t o f e i g h to n e s and z e r o es a r r a ng e d i n t h e o r d e r d et e rm i n ed by t h e i n -f o r m a ti o n t h e y c a r r y . A nalog d a t a a r e c o n v e rt e d t o e i g h t -b i t w ord s. D at a i n p u t s a r e m u l t i p l e x e d and f o rm a t t ed i n t o

f r am es o f 6 4 e i g h t - b i t s w o rd s. Of t h e 6 4 w or ds , t h r e e a r e re -

q u i r e d f o r s y nc h r o n iz a t i on and i d e n t i f i c a t i o n , and t h r e ea r e su bco mm uta ted f o r s p a c e c r a f t h o u se k e ep i ng d a t a .

The ou tpu t of t h e d a t a s y st em i s an 8 t o 2 048 b i t p e rsecond PCM/PSK c o n v o l u t i o n a l l y co ded d a t a s t r e a m , b i p h a s emodulated on a 16384 Hz s u b c a r r i e r .

The O r b i t e r S p a c e c r a f t

The Venus O r b i t e r s p a c e c r a f t i n c o r p o r a t e s t h e b a s i c P i o n e e rB u s . I t a l s o c o n s i s t s of a d e sp u n, h i g h - g a i n d i s h a n t en n a on a3- m ( 1 0 - f t . ) m a s t t o r e t u r n t h e l a r g e volume of

O r b i t e r e x p e r im e n t s an d i ma gi ng d a t a t o E a r t h . The O r b i t e rc a r r i e s 1 2 s c i e n t i f i c i ns t ru m e nt s , a m i l l i o n - b i t d a t amemory t o s t o r e o b s e r v a t i o n s (when t h e s p a c e c r a f t i s b e h i n dVenus, o r t h e y c a nn ot be t r a n s m i t t e d t o E a r t h f o r o t h e rr e a s o n s ) , and a s o l i d - f u e l r o c k e t motor f o r i n s e r t i o n i n t o

o r b i t a t t h e p l a n e t .

The Q r b i t e r , i n c l u d i n g an t e n n a m a st , i s n e a r l y 4 . 5 m( 1 5 f t . ) h i g h . The b a s i c b u s c y l i n d e r m ak in g up i t s

main body i s abou t 2 . 5 m ( 8 . 3 f t . ) i n d i a m e t e r , a n d 1 . 2 m(4 f t . ) h i g h . Launch w e i g h t o f t h e O r b i t e r i s about 582 kg( 1 2 8 0 l b s . ) w i t h 45 kg ( 1 0 0 I b s . ) of s c i e n t i f i c i n st r um e n ts .

Weight a f t e r o r b i t a l i n s e r t i o n i s 368 kg ( 8 1 0 l b s . ) .

T h r e e i n s t r u m e n t s ( t h e m ag ne to me te r e l e c t r o n t e m p e r a t u r eprobe and e l e c t r i c f i e l d d e t e c t o r ) h ave s e n s o r e l emen t smounted on booms. The magnetometer s e n s o rs a r e mounted on

t h e t h r e e - s e c t i o n , d e pl o ya b le 4 . 7 m ( 1 5 .5 f t . ) boom. A

s i n g l e s e n so r i s m ounted abou t tw o- th i rds o f t h e way ou tfrom t h e b us c y l i n d e r , and a p e r p e n d i c u l a r p a i r a r e mounted

a t th e boom's end. The boom is d e p lo y e d a f t e r l a u n c h byf i r i n g p y r o t e c h n i c d e v i c e s , and e x te n d s r a d i a l l y from t h eupper r i m o f t h e c y l i n d e r . T h e b o o m p o s i t i o n s t h e sensors

a t a p o i n t o f m i n i m u m m a g n e t ic i n t e r f e r e n c e fro m t h e s p ac e -c r a f t .

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O RB ITER SPACECRAFT

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ORBIT INSERT1



- 7 5 -

The b a l l - l i k e s e n s o r s ( a n te n n a s) f o r t h e e l e c t r i c f i e l dd e t e c t o r s p r i n g o u t 0 . 6 m ( 2 6 i n . ) a f t e r j e t t i s o n of t h el au n ch f a i r i n g . The e l e c t r o n t e m p e r a tu r e p r ob e u s e s t w o

sensor e lements mounted a t r i g h t a n g le s t o on e a no t h er .The a x i a l s e n s o r i s m o u n t e d p a r a l l e l t o t h e s p i n a x i s a nde x t e n d s t h ro u g h t h e t h er m a l t o p co v e r. The r a d i a l s e n s o ri s on a 1 . 0 m ( 4 0 i n . ) boom, d e plo ye d a f t e r o r b i t i n s e r t i o n .

The gamma r ay b u r s t d e t ec to r u se s two de t e c t o r s mountedon t h e e q u i p m e n t s h e l f a b o u t 1 8 0 d e g r e e s a p a r t . T h i s a l -lows complete coverage of t h e c e l e s t i a l s p h er e f o r a l l po-s i t i o n s o f s p a c e c ra f t r o t a t i o n .

O r b i t e r S c i e n t i f i c I ns tr um en ts

A l l 1 2 s c i e n t i f i c i ns tr um en ts a r e mounted d i r e c t l y ont h e t o p s i d e o f t h e e qu ip men t s h e l f . E i g h t o f t h e i n s t r u -m en ts v ie w t h e p l a n e t t h r o u g h e i t h e r t h e s i d e o r t o p of

t h e b u s c y l i n d e r . Of t h e e i g h t , two ( t h e c l o u d P ho to -p o l a r i m e t e r an d t h e r a d a r ma pp er ) e mp loy s c a n n i n g se n so r swhich move th ro ug h a r a n g e o f 1 4 0 d e q re e s i n a p l a n e p e r -p e n d i c u l a r t o t h e bu s e x pe ri m en t s h e l f .

O rb i t e r An tenna Svst ems

A b a s i c p a r t o f t h e O r b i t e r sy stem , n o t p a r t of t h eb a s i c b u s, i s t h e d es pu n, h ig h -g a in p a r a b o l i c - r e f l e c t o ra n t e n n a , w h ic h f o c u s e s a 7 . 6 degree-wide r a d io beam on t h eE a r t h t h r o u g h o u t t h e m i s s i o n . The a n t e n n a d i s h i s 1 0 9 c m

(4 3 i n . ) i n d ia m e t e r , and a m p l i f i e s t h e O r b i t e r r a d i o s i g -

n a l 3 1 6 t i m e s . Venus and t h e O rb i t e r w i l l be 2 0 3 m i l l i o n k m( 1 2 6 m i l l i o n m i . ) f a r t h e r f ro m E a r t h a t t h e en d o f t h e243-day O r b i t e r p r im a r y m i s s i o n t h a n a t P l a n e t - a r r i v a l .The antenna i s n ee ded t o r e t u r n d a t a a t h i g h r a t e s o v e rt h e s e d i s t a n c e s . The h i g h- g a in a n t e n n a d i s h , a s l e e ved i p o l e a n t e n n a , an d t h e f o rw a r d r ro mn i" a n t e n n a a r e a l lmounted on t h e despun 2 . 9 - m ( 9 . 8 - f t. ) m a st F r o j e c t i n g upa l o n g t h e s p i n - a x i s f r o m t h e t o p of t h e O r b i t e r c y l i n d e r .The s leeve d i p o l e a n t e n n a b r o a d c a s t s a r a d io beam whichforms a p a n ca k e -l ik e p a t t e r n ar ou nd t h e s p a c e c r a f t , p e r-p e n d i c u l ar t o i t s s p i n a x i s . T h i s p r o v i d e s a b a c k u p f o r

t h e narrow -beam d i s h a n t e n n a i n c a s e of f a i l u r e o f t h e d e s p i ns y st em . The b u s a f t omni a n t e n n a p r o v i d e s t h e f o u r t h O r -

b i t e r a n te n n a . The o mn is b r o a d c a s t i n a h e m i s p h e r ic p a t -t e r n , f or wa rd o r a f t .

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S i n c e t h e O r b i t e r d i s h a n t e nn a d oe s n o t s p i n , as doest h e s p a c e c r a f t be lo w i t , it c o n s t a n t l y f a c e s E a r t h , b o t h o nc r u i s e a nd o r b i t . The d es pu n c o n d i t i o n o f t h e an t enna andi t s m a s t i s m a i n t a i n e d by b e a r i n g , e l e c t r i c motor , ands l i p - r i n g a r r a n g e m e n t .

A q u a d r i p o d s t r u c t u r e , m o u n t e d o n t h e upper end of t h e

b us t h r u s t tu b e , s u p p o r t s t h e Bear ing and Power TransferAssembly ( B A P T A ) w h i c h m e c h a n i c a l l y d e s p i n s t h e a n t e n n a s .The m a s t i s a t t a c h e d t o t h e d es pu n f l a n g e o f t h e b e a r i n gassembly. The t h r e e a n t e n n a s o n t h e m a s t a r e c o n n ec te d t ot r a n s m i t t e r s a n d r e c e ive r s by a s e r i e s of t r a n s f e r s w i t c h e sth rough t h e d u a l f r e q u e n c y r o t a r y j o i n t . P u l s e commandsfro m E a r t h t o t h e s e s w i t c h e s a re p r o v i d e d t h r o u g h t h e B A P T A

s l i p r i n g s and b ru s he s .

The c o n t r o l s y s te m p r o v i d e s r e d u n d an t d e s p in c o n t r o le l e c t r o n i c s t o d r i v e o ne G f two redundant BAP TA m o t or s t od e s p i n a n d p o i n t t h e h igh-ga in an t en na t oward t h e E a r t h .The d e s p i n c o n t r o l s ys t em f u n c t i o n s as a c l o s e d l o o p ,

au tonomous ly ope ra t i ng t h e s y st em t o m a i n t a in a n t en n ap o i n t i n g .

Motor to rq ue commands a r e ge ne ra te d by t h e desp in con-t r o l e l e c t r o n i c s b a se d upon Sun o r s t a r s e n s o r and B A P T Am a s t e r i n d e x p u l s e s . An e l e v a t i o n d r i v e m a i n t a i n s a n t e n n ap o i n t i n g d u r i n g o c c u l t a t i o n s .

F o r t h e o c c u l t a t i o n e x p e r i m e n t s , t h e O r b i t e r c a r r i e s ane x t r a 7 5 0 m i l l i w a t t X-band t r a n s m i t t e r , w hose s i g n a l f r e -quency i s a lw ay s m a i nt a in e d a t a r a t i o of 1 1 . 3 t o t h a t oft h e main S-band t r a n s m i t t e r . B o t h S and X-Band s ig n a l s a r et r a n s m i t t e d by t h e d i s h a n t e n n a , w h ic h c a n b e moved 1 5 de-

grees from t h e E a r t h l i n e a s t h e O r b i t e r pa ss es behind. Venus.T h i s p e r m i t s k e ep i n g t h e r a d i o beam t o b e a i m e d ' a t V en us'

jupper a tmosphere f o r a l o n g e r t i m e . R e f r a c t i o n by t h e a t -mosphere bends t h e nar row-beam s i q n a l a round t h e p l a n e t soi t r e a ch e s E a r t h d e s p i t e t h e s e p o i n t i n g a n g l e s .

The X-band s i g n a l cannot be modula ted , and i s o n l y f o rs tu dy o f a tmosphe re e f f e c t s on r a d i o s i g n a l s a t two,wave-l e n g t h s . The X-band beam w id t h i s 2 . 2 degrees compared w i t h

the S-band 7 . 6 d e g r e e s .

Ground commands co n t r o l t h e an t en na po i n t i n g an g l e .The e l e v a t i o n d r i v e f o r t h e a n te n na d i s h c o n s i s t s of amoto r -d r iven j acksc rew. E l e c t ro n i c s con ve r t commands i n t od i s c r e t e p u l s e s t o c o n t r o l t h e m o t o r .

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O r b i t e r D a t a S t o r a q e

F o r p e r i o d s when t h e s p a c e c r a f t i s be hi nd Venus and ra -dio communicat ion i s c u t o f f , t h e d a t a memory c a n s t o r e up

t o a m i l l i o n d a t a b i t s . O c c ul t a t io n s l a s t up t o 2 6 m i n u t e s ,and a m i l l i o n - b i t memory a l l o w s d a t a t o be t a k e n a t a min-

i m u m r a t e o f ab o u t 700 b i t s p e r second i n t h i s t i m e . Thed a t a s t o r ag e c ap ac i t y can a l s o h e l p when D eep S p ace N etw ork(DSN) s t a t ions a r e n o t l i s t e n i n g t o t h e O r b i t e r f o r v a r i o usr e a s o ns . S t o r e d d a t a a r e p l ay ed b ack a t a minimum r a t e of1 7 0 b p s , and t h e O r b i t e r can p l a y b ac k d a t a w h i l e t a k i n g

and t r a n s m i t t i n g new d a t a .

O rb i t e r Da ta-Hand ling Sys tem

The O r b i t e r s p a c e c r a f t d a t a -h a n d li n g s ys te m u s e s t h e

bus da ta sys t em component s , p lu s i t s mil l ion -b i t memory . I t

a c c e p t s i n f o r m a t i o n fr om s p a c e c r a f t s ys t em s an d t h e 1 2s c i e n t i f i c i ns t r um e nt s i n s e r i a l d i g i t a l , a n a l og and one-b i t b i n a r y ( ye s- no ) form . I t co n v e r t s an a l o g an d ye s- noi n f o r m a t i o n t o s e r i a l d i g i t a l f or m, a nd a r r a n g e s a l l i n f o r -m at io n i n f o rm a ts f o r t r a n s m is s i on . T h i s c o n s i s t s of acon t inuo us sequence o f majo r t e l e me t r y f r a mes , eac h composedo f 6 4 minor f rame s. Each minor f rame co nt a in s 6 4 e i g h t -

b i t words ( 512 b i t s p e r m i no r f r a m e ) . The w ord s i n a minorf r a m e a r e a r r a ng e d i n t o on e of 1 3 preprogrammed formats,s e l e c t a b le by command. Each minor fr ame co n t a i n s w i t h i nit:

e H i gh - ra t e s c i e n c e o r e n g in e e r in g d a t a ( i n one

o f t h e 1 3 f o r m a t s ) ;

Sub-commutated d a t a f o r m a t s :0 S p a c e c r a f t d a t a ; a nd

e Frame s y n c h r o n i z a t i o n d a t a .

The t h r e e sub -commuta ted d a t a fo rmat s i n each mino rf ra me c a r r y d a t a whi ch c a n b e r e p o r t e d a t low r a t e s . Onei s f o r l o w - ra t e s c i e n c e a nd s c i e n c e h o us e ke e p in g d a t a , a ndt h e t wo o t h e r s a r e f o r l o w- ra te s p a c e c r a f t e n g in e e r in g d a t a .

The O r b i t e r ' s 1 3 h i g h - r a t e d a t a f o r m a ts i n c l u d e s e v ens c i e n c e f o r m at s f o r u s e on o r b i t . The o t h e r h i g h - r a t e f o r -m a t s a re D a t a memory pla ybac k ( c o nt a in in g some r e a l - t i m e

s c i e n c e ) , D at a memory r ead o u t ( s t o r e d d a t a o n l y ) , Launch-c r u i s e , E n gi n ee r in g -o n ly f o r m a t, A t t i t u d e c o n t r o l s y st e mfo rm at ( f o r ma ne uv ers ) , and Command memory r ea do ut for ma t .

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The d a t a s y s te m o p e r a t e s i n r e a l - t i m e f o r t e l e m e tr ys to r age mode . I t s memory s t o r e s b o t h s c i e n c e an d e n g i n e e r i n gd a t a . T welv e t e l e m e t r y s t o r a g e p l a y b a c k an d r ea l - t im e d a t ar a t e s be tw ee n 8 an d 2048 b p s a r e a v a i l a b l e . A r a t e o f1 0 2 4 bps i s u se d d ur i n g i n t e r p l a n e t a r y c r u i s e .

Of t h e s e ve n s c i e n c e f o rm a t s u se d on o r b i t , f i v e a re f o rt h e c l o s e - i n p e r i a p s i s s e c t i o n of t h e o r b i t . Two a re f o rt h e f a r - o u t a p oa p si s p o r t i o n of t h e o r b i t .

Of t h e f i v e c l o s e - i n f o r m a t s , t w o e m p h a s i z e a c q u i s i -t i o n o f aeronomy da t a . A t h i r d g e n e r a l f or ma t a l l ow s d a t at a k i n g by v i r t u a l l y a l l e xp er im e nt s.

T h e f o u r t h c l o s e - i n f o r m at , t h e O p t i c a l , i s f o r j u s tt w o i n s t r u m e n t s . I t a l l o c a t e s 73 p e r c e n t o f t h e d a t astream t o t h e i n f r a r e d r ad i o m e te r , t h e r e s t of t h e p h o t o -p o l a r i m e t e r . T h e l a s t fo rm a t , t h e Mapping fo rma t , g iv es

4 4 p e r c e n t of t h e d a t a s t re a m t o t h e r a d a r m ap pe r, and t h er e s t i s d i v i d e d among f o u r o t h e r " ma pp in g" t y p e i n s t r u m e n t s .

Of t h e two s c i e n c e f o r m a t s f o r t h e f a r - o u t a p o a p s i so r b i t a l s eg m en t, t h e I ma gin g f o r m at p r o v i d e s 67 p e r c e n t oft h e d a t a s t ream f o r c l o u d p ho t o p ol a r im e t e r p i c t u r e s o fVenus ' c l o ud s , and t h e r e s t f o r f o u r s p a c e e nv i ro n m en t i n -s t r u m e n t s . The G e n er a l f o rm a t f o r a p o a p s i s c a r r i e s d a t a f o ra l l i n s t r u m e n t s e x c e p t t h e i n f r a f e d a nd im a gi ng i n s t r u m e n t s ,b u t makes b i g a l l o c a t i o n s t o t h e s p a c e e n v i r o n m en t m ea su re -m e nt s o f t h e m a g ne t om e te r , s o l a r w in d i n s t r u m e n t a nd t h egamma r a y b u r s t d e t e c t o r .

O r b i t a l I n s e r t i o n R ocket

The o r b i t a l i n s e r t i o n m otor r e du c es O r b i t e r v e l o c i t yby 3 ,816 kph (2 ,366 mph) f o r o r b i t a l cap tu re by Venus .I t i s a s o l i d p r o p e l l a n t e n gi n e, a t t a c h e d t o t h e bu s t h r u s tt u be be low th e equ ipment compar tmen t. The eng ine ha s1 8 , 0 0 0 Newtons ( 4 0 0 0 l b s . ) of t h r u s t , and t h e i n s e r t i o n r o-c k e t bu r n r e d u c e s O r b i t e r w e ig h t by 1 8 1 kg ( 3 9 8 l b . ) .

T h e M u l t i p r o b e S p a c e c r a f t

The f i r s t si m u l ta n e o u s m u l t i p l e - e n t r y c r a f t m ea su re -ments of t h e a tm o sp h er e o f a n o t h e r p l a n e t w i l l be accompl i shedby th e Venus Mu l t ipro be .

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The f ou r p robes w i l l be l aunched f rom the Mul t ip ro heBus 1 3 m i l l i o n km ( 7 . 8 m i l l i o n m i . ) from t h e p l a n e t a ndw i l l t he n f l y t o t h e i r e n t r y p o i n t s , two on t h e d ay s i d eand two on the n i g h t s i d e of Venus.

The M u l t i p r o b e s p ac ec r a f t w e i gh s 9 0 4 kg ( 1 , 9 9 0 l b . )and c a r r i e s 5 1 kg ( 1 1 2 l b s . ) o f s c i e n t i f i c i n st ru m en t s. The

s p a c e c r a f t c o n s i s t s o f t h e P i o n e e r Venus b a s i c bu s m od i fi e dt o c a r r y t h e f o u r a tm os ph er e p r o b es . I t s d i a m e t e r i s t h a to f t he Bus, 2 .5 m ( 8 . 3 f t . ) . From t h e b o tt om o f t h e Bus t ot h e t i p o f t h e m ain p ro b e, it i s 2 . 9 m ( 9 . 5 f t . ) h iq h .

D ur in g t h e f l i g h t t o Venus, t h e f o u r p r ob e s a r e c a r r i e don t h e Bus by a l a r g e i n v e r t e d c on e s t r u c t u r e a nd t h r e eeq u a l l y - s p a ced c i r c u l a r c lamp s s u r r o u n d i n g t h e con e. T hesea t ta c hm e n t s t r u c t u r e s a r e b o l t e d t o t h e Bus t h r u s t t u b e ,t h e s t r u c t u r a l l i n k t o t h e lau n ch v e h i c l e . The L a rg e P r ob ei s c e n t e r e d o n t h e Bus s p i n a x i s , and i s launched towardVenus by a p y r o t ech n i c - s p r i n g s e p a r a t i o n s y s tem . The r i n gs u p p o r t c la mp s a t t a c h i n g t h e S m a l l Probes a re h inged . Fo rl au n ch o f t h e Sa r n l l P r o b e s , t h e c la mp s o pe n by t h e f i r i n go f ex p l o s i v e n u t s . When o p en , t h ey a l l o w t h e p r o b es t os p i n o f f t h e Bus i n a t a n g e n t i a l d i r e c t i o n due t o Bus ro-t a t i o n . C o n t r o l l e rs i n c r e a s e Bus s p in f rom 15 t o 4 8 rpmf o r S m a ll P r o b e l a u n c h .

The Mu l t i p r ob e ' s fo rward omni an tenna ex ten ds above t heto p o f t h e Bus c y l in de r , and an a f t omni ex t end s down belowit. B ot h omni an t en n as have h em i s p h e r i c r ad i a t i o i - p a t t e r n s .A t t a ch e d t o t h e e qu ip me nt s h e l f i s an a f t -po in t ing , med ium-g a i n ho rn a n t e n n a , f o r u se d u r i n g c r i t i c a l maneuvers whent h e a f t e n d o f t h e s p a c e c r a f t i s p o i n t e d t o w a r d t h e E a r t h ,

a s it i s when th e probe s a r e lau nched toward Venus.

T h e r em a i n i n g s y s t em s o n t h e M u l t i p ro b e s p a c e c r a f t a r et h o s e c a r r i e d o n b o t h O r b i t e r and M u l t i p r o b e b u s e s . T h ese c o m -mon bus systems a r e : The instr ume nt-e quip men t compartment andb a s i c b us s t r u c t u r e : t h e s o l a r a r r a y , b a t t e r i e s and power d i s -t r i b u t i o n s y st em ; t h e S un an d s t a r s e n s o r s , p r o p e l l a n t s t o r a g et a n k s an d t h r u s t e r s o f t h e b u s m an eu ve rin g an d s t a b i l i z i n g s y s -t e m . Ot he r Bus sys tems a r e t h e t r a n s m i t t e r s , r e k e i v e r s and p ro -c e ss o rs of t h e bus communicat ions , command and d a t a ha ndl ing s ys tem.

These s y st e ms a l l o w t h e Bus t o p r o v i d e f o r t h e M u l t i -p ro be s p a c e c r a f t , a s i t d oe s f o r t h e O r b i t e r , a s t a b l e , r o -

t a t i n g p l a t f o r m and a p r o t e c t i v e , t e m p e r a t u r e - c o n tr o l l e de nv ir on me nt f o r t h e s c i e n t i f i c i n s t r um e n t s and s p a c e c r a f tsys t ems .

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They a l s o p r o v i d e e l e c t r i c power, make maneuvers, re-ce i v e commands, p r o c es s ex p e r i m en t d a t a , and t r a n s m i t d a t at o B a rt h.

Mul t ip ro be Data System

The d a t a s y st e m f o r t h e M u l t ip r ob e s p a c e c r a f t u s e s t h es t an da rd bus componen ts . However, d a ta fo rmat s a r e o r -g a n i ze d t o m e e t r e q u i r e m e n t s o f t h e M u l t i pr o b e m i s s i o n .T h e M u l t i p r o b e d a t a s y s t em h an d l e s d a t a fro m b o t h Bus andp r o be s b e f o r e p r ob e la u n c h. A f t e r p r ob e l a u n c h , i t h a n d l e sBus d a ta on l y . The p robes have t h e i r own da ta sys t ems .(See s e c t i o n s d e s c r i b i n g t h e s e . )

The M u l t i pr o b e d a t a s y s t em acce p t s en g i n ee r i n g andm i s s i o n o p e r a t i o n s i n f o r m a t i o n f ro m t h e f o u r p r o be s a b o a r dt h e s p a c e c r a f t , u n t i l pr ob e la u nc h , a s w e l l as f rom theM u lt ip ro be bu s i t s e l f . I t a l s o h a n d l e s d a t a f ro m t h e t wo

e x p e ri m e n ts c a r r i e d o n t h e M u l ti p r ob e b u s. A s on the O r -b i t e r , t h e sys tem a c ce p ts d a t a i n s e r i a l d i g i t a l , a na logand o n e - b i t b i n a r y s t a t u s ( ye s- no ) form. I t c o n v e r t s t h ea n a l o g d a t a t o s e r i a l d i g i t a l b in a r y from an d a r r an ge s a l li n f or m a t io n f o r t r a n s m i s s i on t o E a r t h i n t h e s t a n d a r d P i -

oneer Venus s e r i e s of majo r t e l em et ry f r ames , each composedof 6 4 minor f rames.

Each minor frame i s composed of a s e r i e s of 6 4 e i g h t -b i t w o rd s. The w or ds i n a m i no r fr am e a r e a r r an g ed i ns e v e r a l f o r m a t s . Each m in or f ra me c o n t a i n s h i g h - r a t es c i en ce o r en g i n ee r i n g d a t a , p l u s sub -com mu ta ted f o r m a t s ,s p a c e c r a f t d a t a , and f ra me s y n c h r o n i z a t io n d a t a . One sub-

commutated format c a r r i e s l o w - r a t e s c i e n c e a n d s c i e n c ehousekeep ing da ta ; two a re f o r lo w -r a te s p a c e c r a f t i n f o r -m ak io n. T welve r ea l - t i m e ( no d a t a s t o r ag eo n t h e M u l t i -p r ob e ) d a t a t r a n s m i s s i o n r a t e s b e t w e e n 8 and 2 0 4 8 b p s canb e u s ed . L i k e t h e O r b i t e r , t h e M u l t ip r o be a l s o h a s h i g h-d a t a - r a t e f o r m at s f o r A t t i t u d e c o n t r o l ( us ed d u r i n g maneu-v e r s ) , f o r E ng in eer i ng d a t a o n l y , and f o r command- memoryr e a d o u t . A s i n g l e f o rm a t f o r a tm os ph er e e n t r y t r a n s m i t sh i g h - r a t e s c i e n c e d a t a . Assuming t h e e x pe c t e d d a t a r a t eo f 1 0 2 4 bps a t e n t ry , d a t a r a t e f o r t h e t w o Mult iprobe Busex p e r i m en t s w i l l b e 256 b p s f o r t h e n e u t r a l mass s p e c t r o -m e t e r , and 1 1 2 b ps f o r t h e i o n mass s p e c t r o m e t e r .

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Multiprobe Bus Experiments

After launch of its four probes 20 days out fromVenus, the Multiprobe Bus becomes a probe itself, providing

the mission's only high upper atmosphere composition

measurements. These operate as the Bus enters but beforeit starts to burn up at 115 km (71 mi.) altitude.

These two mass spectometer instruments are attached to

the equipment shelf with their inlets projecting abovethe flat top of the Bus cylinder.

VENUS ATMOSPHERIC PROBES

Because of its high pressures (nearly 100 times Earth's),high temperaturesatmosphere presents a difficult problem for flight designers.

The high entry speeds of about 41,600 kph (26,000 mph) addto the problem.

The Large and Small Probes are geometrically similar.The main component of each is a spherical pressure vessel,

which houses the scientific instruments and the following

spacecraft systems: communications, data, command and power.

The Large Probe weighs about 316 kg (698 lbs.); the SmallProbes, 93 kg (206 lbs.) each.

Conical aeroshells provide stable flight paths and heat

protection for all four probes during atmospheric entry.heat shield-carrying aeroshells are 45-degree cones with spheri-

cally blunted tips, whose radii are equal to half the base radii

of the cones.

All instruments within the pressure vessels of all fourprobes require either observing or direct sampling access tothe hostile Venusian atmosphere. This access is one of the

hardest problems of the mission.

sealed penetrations of several types. Each Small Probe has

seven. Pressure vessel penetrations for all probes include15 sapphire and one diamond window.

and corrosive constituents, Venus'

The

The Large Probe has 14

The Large Probe

The Large Probe weighs about 316 kg (695 lbs.) and isabout 1.5 meters (5 feet) in diameter. It returns data at

256 bps. Its seven scientific instruments weigh 28 kg

(62 lbs.). These include two instruments to identify atmos-

phere components. The other five instruments will measurethe clouds, atmospheric structure, energy distributioncirculation.

of the planet.

andThe probe enters at the equator on the day side

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Large Probe Structure

The Large Probe consists of the forward aeroshell-heat

shield, the pressure vessel and the aft cover. Both aero-shell and aft cover are jettisoned at main chute deployment.

The spherical pressure vessel is 7 3 . 2 cm ( 2 8 . 8 in.) indiameter, and is made of titanium for light weight and high

strength at high temperatures. Because it is jettisoned atrelatively cool, high altitudes, the aeroshell can be made

of less heat-resistant aluminum.

The weight limits on interplanetary spacecraft and the 14hull penetrations required that the pressure vessel be designedwith great care and machined with precision for both lightness

and strength. The flight vessel has been tested successfully

under Venus-like conditions of 100 Earth atmospheres of pressure

and 470 degrees C (900 degrees F) temperatures. Test vesselshave withstood higher pressures.

The vessel is made in three pieces, joined by flanges,

seals and bolts. Sections are the aft hemisphere, a forwardcap and a flat ring section between the two. The vessel has14 sealed penetrations (one for the antenna, four for electri-

cal cabling, two for access hatches and seven for scientific

instruments). Four instruments use nine observation windows

through four of the hull penetrations. Eight windows are of

sapphire, and one of diamond. These materials admit light or

heat at the wavelengths being measured, while withstanding

Venusian heat and pressure. The solar flux radiometer has

five windows through one hull penetration; the nephelometer,

two windows and the infrared and cloud particle instruments,

one window each.

Three vessel penetrations are inlets for direct atmosphere

sampling by three instruments--mass spectrometer, gas chroma-tograph and atmosphere structure experiment. At its aft pole

the spherical vessel has a hemisphere pattern antenna for

communication with Earth. Two four-inch arms on one side holdthe reflecting prism for the cloud particle instrument. Asingle arm on the other side has a temperature sensor at its tip.Three parachute-shroud towers are mounted above aerodynamic drag

plates, spaced equally around the equator of the sphere. The

vessel has an electronics access port for system checkout, anda cooling port used in ground tests.

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L A R G E PROBE

RADIO

TRANSPARENT WINDOW

PR ESSUR E

V ESSE L/DEC EL MOD

UMBl LlCALCABLE CUTTER

PARACHUTE TOWER

CLOUD PARTICLE

SPECTROMETER

WINDOW

SOLAR FLUX DESCENT MODULERADIOMETER

WINDOW

PYROTECHNIC

CONNECTOR

PRESSURE VESSEL

SEPAR ATI N ASSE MB LY

NEUTRAL

MASS SPEC. INLET

AERO FAIRING

CUT OUT FOR

TEMPERATURESENSOR

ATMOSPHERE

STRUCTURE

PILOT CHUTEUAND MORTAR

PROBE/BUS IN FLIGHTEC ELER A T ONMODULE DISCONN ECT



LA RG E PROBE PRESSURE VESSEL

ACCESS HATC H

PRESSURE VESSEL

ACCELEROMETER

P Y R O T E C H N I C

C O N TR O L U N ITSA E R O FA IR IN G

PRESSURE VESSEL

D E R



-86-

Flight Sequence

About 2 0 minutes before atmospheric entry, with the probetraveling at speeds of about 41,600 kph (26,000 mph), timer

commands turn on and warm up the Large Probe instruments and

systems. The craft establishes its radio link with Earth.

At an altitude of about 120 km ( 7 5 mi.), significant

atmospheric braking has begun, and three-axis accelera-

tions and heat shield temperature data are being storedfor later playback (providing spacecraft flight data for

use by the atmospheric structure experiment). Entry

occurs with peak deceleration of 3 2 0 G at about 78 km (49mi.). As deceleration forces slack off, a G-switch starts

a timer, ending data storage and starting a timing sequence

for aeroshell and heat shield jettison.

Just below 68 km ( 4 2 mi.), when the Large Probe has slowed to

about 680 kph (420 mph), the pilot chute is mortar-fired

from a small compartment in the side of the aeroshell. This

small parachute is attached by lines to the aft cover which

is separated by an explosive nut and pulled free. The cover,

in turn, is attached to the main parachute. The pilot chutethen extracts the main chute from its compartment within the

conical aeroshell. The main chute then opens. After vehicle

stabilization, mechanical and electrical ties to the aeroshell

are severed by explosive nuts, or by cable cutters, and the

main chute pulls the spherical pressure vessel out of its

surrounding aeroshell. The aeroshell falls away.

Once the pressure vessel is freed of the aeroshell and aft

cover, the scientific instruments have full access to Venus'

atmosphere, and the parachute has slowed its descent rate to

2 7 0 kph (165 mph). Seventeen minutes later, at 47 km (28 mi.)

altitude, the main chute is jettisoned, and the aerodynamically

stable pressure vessel descends to the surface in 3 9 minutes.

Flight Systems

Thermal protection during atmosphere entry is provided

by the carbon phenolic heat shield covering the forward facing

conical aeroshell, and by coating all other surfaces of the

aeroshell and aft cover with a low density elastomeric material.The conical aeroshell is a one-piece aluminum structure with

integrally-machined stiffening rings. The ablative carbon

phenolic heat shield is bonded to this structure. The aeroshellcone has a base diameter of 142 cm (4.7 ft.) .

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- 8 7 -

The 4 . 9 meter ( 1 6 . 2 f t . ) - d i a m e t e r d a c r o n ma in p a r a c h u t e i s

of t h e c o n i c a l r i b b o n t y p e . L o ca te d i n a curved compar tmenton one s i d e o f t h e a e r o s h e l l , t h e m or ta r -dep loyed dacron p i l o t

c h u t e i s 7 6 crn ( 2 . 5 f e e t ) i n d i am et er . A f t e r s e p a r a t i o n oft h e a e r o s h e l l , a f t c o v er a nd main c h u t e h av e o c c u r r e d , t h e

p r e s s u r e vesse l d e s c e n ds t o t h e s u r f a c e . The m o ti on i s s t a -b i l i z e d by l o c a t i n g t h e c e n t e r o f g r a v i t y o f t h e p r e s s u r e

v e s s e l w e l l f o rw a rd a nd by a n a i r f l o w s e p a r a t i o n r i n g a ro un dt h e s p h e r e ' s e q u a t o r . Drag p l a t e s on t h e f lo w s e p a r a t i o n r i n gs l o w t h e d e s c e nt r a t e , and vanes a t t a c h e d t o t h e a i r f l o w r i n gm a i n t a i n s p i n f o r c o n t i n u o u s v ie w in g i n a f u l l c i r c l e by thee x p e r im e n t s d u r i n g d e s c e n t . A f a i r i n g c ov e rs t h e fo rw ardhem i sphe re of t h e p r e s s u r e v e s s e l , p r o v id i n g a smooth aerody-na mic s u r f a c e d u r i n g d e s c e n t .

H e a t P r o t e c t i o n

The L a rg e P ro b e p r e s s u r e v e s s e l i s made of t i tanium f o rh e a t r e s i s t a n c e . W it hi n t h e s p h e r i c a l v e s s e 1 , i n s t r u m e n t s a nd

s y s t e m s a re mounted on t w o p a r a l l e l s h e l v es made o f b e r y l l i u mt o se rve a s h e a t s i n k s . E quipm ent i n s i d e t h e v e s s e l i s f u r t h e rp r o t e c t e d f r o m h e a t by a 2 . 5 c m (1 i n . ) - t h i c k k a pt on b l a n k e t ,

which c o mp le te ly l i n e s t h e i n t e r i o r .

S c i e n t i f i c I n s t r um e n ts

The s ev en s c i e n t i f i c i n s t ru m e n t s on t h e L a r g e P r o b e i n c l u d et h e g a s c h r o m a t o g r a p h a n d mass s p e c t r o m e t e r , w hi ch measure t h e

c o m p o s i t i o n of V enu s' a tm o sp h er e d i r e c t l y . The o t h e r f i v e i n s t r u -ments e i t h e r "look o u t " w indows o r s e n s e v e h i c l e m o t io n s a nd /o r t e m p e r a t u r e w i t h a c c e l e r o m e t e r s an d a w i r e - c o n n e c t e d h e a t

s e n s o r , r e s p e c t i v e l y .

The i n f r a r e d r a d i o m e t e r r e q u i r e s a d ia mo nd window becausediamond i s t h e o n l y m a t e r i a l t r a n s p a r e n t t o t h e a p p r o p r i a t e

w a ve le ng th s an d a b l e t o w i t h s t a n d t h e h i g h t e m p e r a t u r e s a ndp r e s s u r e s of t h e atmos phere . T hi s window i s a b o u t t h r e e -

q u a r t e r s o f a n in c h i n diamete r a nd a n e i g h t h of a n i n c h t h i c k( ab o ut t h e s i z e o f a q u a r t e r ) . I t w ei ghs 1 3 . 5 c a r a t s and w a sshaped by diam ond c u t t e r s i n The N e t he r l and s f rom a 20 5-ca ra ti n d u s t r i a l g r a d e r o ug h dia mo nd . T h e n e p h e l o m e t e r ( c l o u d - s e n s o r )us es tw o s ap ph i r e window s. The c lo ud p a r t i c l e i n st ru m e nt d i r e c t s

a l a s e r beam t h r o u g h a s a p p h i r e window t o a n o u t s i d e r e f l e c t i n gpr i sm and back t o i t s s e n s o r . T h e s o l a r f l u x ra d io m e te r h a s f i v e

sa pp h i re w indow s.

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- 8 8 -

Communications System

S c i e n t i f i c i n s tr u m e n t and s p a c e c r a f t s y s t e m s d a t a a r er e t u r n e d by t h e c om m un ic at io n s s y s t em . S p a c e c r a f t d a t a i n -c l u d e i n t e r n a l t e m p e r a t u r e a nd p r e s s u r e m e as u re m en ts , e l e c -

t r i c a l c u r r e n t f l o w a nd v o l t a g e a nd o n -o r -o f f s t a t u s o fs y s t em s a nd i n s t r u m e n t s .

The p r o b e’ s s o l i d s t a t e t r a n s m i t t e r and h e m i s p h e r i c a lc o v er a ge a n t e n n a r e t u r n a 256-bps d a t a s t re a m t o E a r t h . T h e

s y st e m u s e s f o u r 1 0 - w a t t s o l i d s t a t e a m p l i f i e r s p r ov id in g at r a n s m i t t e r power of 4 0 w a t t s .

A t r a n s p o n d e r r e c e ive s an S-band c a r r i e r wave a t 2 . 1 GHz,and s e t s t h e p r o b e t r a n s m i t t e r t o s e n d a t 2.3 GHz. The t r a n s -p o n d e r r e c e i v e r i s u s e d o n l y f o r two-way Doppler t r a c k in g .The i nc om in g s i g n a l c a r r i e s no i n f o r m a t i o n , a nd t h e p r o b e d o e snot rece ive commands .

Command System

Once t h e L a r ge Probe h a s s ep a r a t ed from t h e Bus, onboarde le c t r o n ic s p ro v i de a l l p robe commands. The command sys temc o n s i s t s o f a command u n i t , a p y r o te c h n i c c o n t r o l u n i t an dt h e s e n s o r s t o s e r v i c e t h e command u n i t .

The s y s t e m ca n p r o v i d e 6 4 s e p a r a t e commands f o r s p a c e c r a f ts ys te m s a nd s c i e n t i f i c i n s t ru m e n t s. I t c o n t a i n s t h e c r u i s et i m e r ( t h e on l y o p e r a t i n g u n i t d u r i n g t h e 24-day pe r iod be-

tween Bus s e p a r a t i o n an d e n t r y ) , a n e n t r y s e qu e n ce programmerand a command d e c o d e r . Commands a re i n i t i a t e d by a cl o ckg e n e r a t o r o r a G - s w i t c h t o s e n s e d e c e l e r a t i o n fo rce s . A t e m -p e r a t u r e s w i t c h p r o v i d e s b ac ku p f o r t h e t i m e r a t p a r a c h u t ej e t t i s o n .

T h e p y ro t ec h n ic c o n t r o l u n i t i s made up of 1 2 s q u i b d r i v e r s

which p r o v i d e c u r r e n t t o f i r e e x p l o s iv e n u t s f o r s e p a r a t i o nof t h e a e r o s h e l l , t h e a f t c o v e r an d m ain c h u t e ; a nd a c t u a t o r sf o r t h e cab le c u t t e r , p i l o t c h u t e mortar and m a s s s p e c t r o m e t e ri n l e t cover.

Data Handling System

The Large Probe d a t a h a n d l i n g u n i t ca n a c c e p t 36 a n a l o g ,1 2 s e r i a l d i g i t a l , and 2 4 o n e - b i t ( ye s- no ) s t a t u s c h a n n e ls ’ f ro m

s c i e n t i f i c i n s t r u m e n t s and p r ob e s y st em s . The u n i t c o n v e r t st h e a n a l o g an d y es -n o d a t a t o s e r i a l d i g i t a l form and a r r a n g e sa l l d a t a i n major t e l e m e t r y frames composed of 1 6 minor frames

f o r t im e - mu l ti p le x e d t r a n s m i s s i o n t o E a r t h . Each minor f ramei s composed of a s e r i e s of 6 4 e i g h t - b i t w o r d s ( 5 1 2 d a t a b i t sp e r m i n o r f rame) .

- m o r e -



- 8 9 -

The data handling system provides for two data formats:

blackout and descent. A storage capacity of 3 0 7 2 bits is pro-

vided by a data memory, for use during entry blackout.the blackout period, the stored data will be read out of the

memory and telemetered in the descent format. Data are stored

at 1 2 8 bps. In the descent format, transmission will be at2 5 6 bps. Allocation of this bit rate among the seven Large

Probe experiments will range from 16 to 44 bps per experiment.Only the atmospheric structure and nephelometer experiments

will use the entry blackout storage format at 72 bps and 4 bps,respectively. Two subcommutated formats for lowrate phenomena

also provide housekeeping data, and additional data for theatmospheric structure, nephelometer, cloud particle spectro-

meter and solar flux radiometer experiments.

Following

Power Svs em

The power system uses a silver-zinc battery, providing4 0 ampere hours of energy at 2 8 volts. The system consists

of a battery, a power interface unit and a current sensor.

The power interface unit controls power and contains fuses

and power switching relays for vehicle systems. Power forprobe checkout and heating is provided by the Bus prior toprobe to probe separation. During this time, the batteries

are open-circuited by switches in the power interface unit.

The Small Probes

Atmosphere entry points for the Small Probes are spread

over the face of Venus--two on the night side at high northernand mid-southern latitudes, and the third at mid-southern lati-

tudes on the day side.

Like the Large Probe, each of the Small Probes consistsof a forward heat shield, a pressure vessel and an afterbody.

The three small probes are identical. Each is 0 .8 m ( 3 0 in.)in diameter and weighs 9 0 kg ( 2 0 0 lb.). Each carries three

scientific instruments, weighing 3 .5 kg (7.7 lb.). The three

Small Probe instruments return less detailed information than

the seven on the Large Probe. But except for the atmosphericcomposition measurements, made only by two Large Probe instru-

ments, Small Probe atmosphere measurements are in many respectscomparable to Large Probe data.data at 6 4 bps during flight down to 30 km (18 mi.) altitudeand 1 6 bps from there to the surface.

The Small Probes transmit

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-90-

Neither forward aeroshell nor afterbody of the Small

Probes ever separates from the pressure vessel, nor is a para-chute used for deceleration as with the Large Probe. TheSmall Probes are slowed entirely by aerodynamic braking, and

instruments gain access to the atmosphere through doors in theintegral afterbody. Both aeroshell and pressure vessel aremade of titanium for light weight and strength at high tempera-

tures. The afterbody is made of aluminum.

Small Probe Structures

The pressure vessel nests into the aeroshell and is

permanently attached to it. The afterbody also is permanentlyattached to the pressure vessel, and its shape closely follows

the contours of the vessel's aft hemisphere, protecting it from

atmosphere heat. As in the case of the Large Probe, the pres-

sure vessels for the three small probes had to be very careful-

ly designed and machined because of weight limitations, the seven

hull penetrations required and the strength requirements at high

Venusian pressures and temperatures.

The pressure vessels are fabricated in two hemispheres

and joined with flanges, bolts and seals. The flight vesselswere tested at Venus surface temperatures and pressures, and

the test vessels tested even under more severe conditions.

Three doors in the afterbody open after entry heating

at about 7 0 km altitude (44 mi.), providing access by the threeinstruments to the atmosphere.from each of two protective housings--one for the atmospheric

structure and the other for the net flux radiometer instrument.

These housings project like ears from each side of the pres-

sure vessel sphere. The temperature sensor and atmosphericpressure inlet for the atmospheric structure instrument extend

10 cm (4 in.) from the door of one housing, and the nex flux

radiometer sensor extends similarly on the opposite side.

Two of these doors.open out

When the doors to these two housings open after atmospheric

entry at 7 0 km (44 mi.) altitude, they are retained, rather than

jettisoned, and serve to slow spacecraft spin rate. A vane, lessthan one square inch, is attached to the pressure sensor inletto assure that the vehicle will spin throughout the descent,so that instruments can see in a full circle as the probe

rotates. The cloud sensor (nephelometer) cover opens andfolds down. As with the Large Probe, a hemispherical-pattern

antenna is mounted at the aft pole of the pressure vesselsphere.

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-91-

SMALL PROBE

N E T F L U X A TM O SP HE R E

RADIO M E TE R S TRUCTURE DO O R

ATMOSPHERE

S TRUCTURE

TE M P E RATURE

I N L E T A N DS P IN CO NTRO L V A NE

NE P HE LO M E TE R/u0 - Y0/CABLE

(S I

CABLE

CARBO N P HE NO LIC

R I N G F O R S E P A R A T IO N H E A T S H I E L DCLAM P

D E C E L E R A T IO N M O D U L E



- 9 2 -

Each Small Probe pressure vessel has a total of seven

sealed penetrations: one for the antenna, one for the two

sapphire nephelometer windows, one for the atmospheric pres-

sure inlet and a hatch for ground test cooling and systemscheckout. The other three vessel penetrations are feed-

throughs for electrical cables. Each external radiometersensor on each small probe has two diamond windows.

Flight Sequence

For the three Small Probes, atmospheric entry speeds

are about 4 2 , 0 0 0 kph (26,000 mph), and peak decelerations vary

in entry flight path angles.

Twenty minutes before entry, all systems and instruments

are activated and communications with Earth are established.Just before entry, spin rates are cut about three times from48 to 14 rpm, The 48-rPm spin rate imparted by spin-off

launch from the Bus disperses the probes over the planet to

desired entry points. But it also means that the probesenter the upper atmosphere somewhat tilted to their entryflight paths. With the slower 15-rpm rotation, aerodynamic

forces quickly line up the axes of the probes with their entry

heating damage could occur on the edges of the probes conical

heat shields.

A yo-yo system spins down the probes. Two weights are

cut loose by a pyrotechnic cable cutter, and probe spin

swings the weights out on 2.4 m (8-ft.) cables. With thisweight moved radially outward, rotation rate must slow to

maintain the same rotational momentum. Weights and cablesare then jettisoned.

In order to save weight and also because a longer stay-time at upper altitudes is not needed, the small probes do

not use parachutes. On the large probe, more time is needed

for measurements of atmosphere and cloud composition. Thesmall probes do not carry atmospheric composition instruments.

As with the Large Probe, heat shield temperature and

probe acceleration data are stored for the atmospberic struc-ture experiment during the entry communications blackout. A

G-switch ends data storage after blackout.

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I .



-93-

Flight Systems

Thermal protection during entry is provided by ablativecarbon phenolic heat shields, which are 45-degree cones with

the same geometry as the Large Probe heat shield. For fur-ther heat protection, the entire afterbody is coated with

a low-density elastomeric material. The heat shield material

is bonded to the Small Probe titanium aeroshell. Base diameterof the aeroshell heat shield cone is 76 cm (30 in.).

The conical aeroshell provides aerodynamic braking and flight

stability, as does location of the probe center of gravity well

forward in the vehicle. Designers chose the aeroshell conestructure primarily for flight through the searing heat and

extreme deceleration of atmosphere entry. However, the conealso provides stable flight and substantially slows descent

rate in Venus' thick lower atmosphere.

Heat Protection

A s with the Large Probe, heat protection for the small

probes is provided by a kapton blanket completely lining the

interior of an 45 cm (18-in.) diameter spherical titanium pressure

vessel. It, too, has two shelves which carry all equipmentand scientific instruments, and are made of beryllium to

serve as heat sinks. Since the aeroshell descends to

the surface with the pressure vessel, it, too, is made of

light-weight, heat-resistant titanium.

Scientific Instruments

The three scientific instruments on the small probes

measure atmospheric structure (pressure, temperature andacceleration from which altitude and density are determined),

cloud particles and layers, and heat distribution in the

atmosphere. These measurements, and claculations basedon them, will allow characterization of Venus' atmosphere.

For the atmospheric structure experiment, the outside

inlet for the pressure sensor, and the arm carrying the harp-

like temperature sensor both extend from the experiment housing.

The pressure sensor itself and temperature-sensor electronics

are internal, as are the accelerometers used for density cal-

culations.

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- 9 4 -

T h e c l o u d s e n s o r i n s t r u m e n t ( n e p he l o m e te r ) i s e n t i r e l yi n s i d e t h e p r e s s u r e v e s s e l , a nd l o o k s o u t t h r o u g h t w o s a p p h i r ewindows. For t h e n e t f l u x r ad io m e te r (h ea t d e p o s i t i o n i n s t r u -m e n t ) s e n s o r s a r e co m p l e t e l y ex t e r n a l , m ounted on a s m a l l boomex t e n d i n g f ro m t h e ex p e r i m en t h o u s in g . The r ad i o m e t e r s e n s o rw i t h i t s t w o diam ond window s t u r n s co n s t a n t l y i n a h a l f c i r c l e ,f i r s t l o o k i n g up a nd t h e n down. I n s t r u m e n t e l e c t r o n i c s a r ei n t e r n a l .

Communications

Communicat ions systems f o r t h e S m a l l probes c o n s i s t o fs o l i d s t a t e t r a n s m i t t e r s and h e m i s p h e r i c a l c o ve r ag e a n t e n n a s ,i d e n t i c a l w i t h those f o r t h e L a r g e Probe. Each t r a n s m i t t e rh a s one 10- W a t t , s o l i d s t a t e a m p l i f i e r . T h i s compares wi th40 w a t t s f o r t h e L a rg e P ro be . T h i s sy s te m c a n t r a n s m i t d a t a

t o t h e D S N ' s 6 4 - m (210- foo t ) a n t e n n a s a t a r a t e of 64 bps above30 km ( 1 9 m i . ) a l t i t u d e a nd 1 6 b p s be lo w t h a t t o impact . TheS m a ll Pr o b e s do n o t c a r r y a r e c e i v e r f o r two-way Dopple r t r a c k -

i n g as d o es t h e L ar g e P r o be , and D o p pl e r t r a c k i n g i s done us ingan o s c i l l a t o r ( s t a b l e t o a p p r o x i m a t e l y o n e p a r t i n a b i l l i o n )

on t h e p r o b e s a s a r e f e r e n c e f r eq u en c y f o r gro un d t r a c k i n gcomDutat ions .

D a t a r e t u r n e d i n c lu d e s c i e n t i f i c a nd e n gi n ee r in g i n f o r -mat ion . T h i s i n c l u d e s i n t e r n a l t e m p e ra t u r e and p r e s s u r e m ea su re -men t s , e l e c t r i c a l c u r r e n t fl o w a nd v o l t a g e s , a nd o n- of f s t a t u sof i n s t r u m en t s an d p r o be s y s t em s .

Command System

t h a t on t h e L a rg e Pr o be . I t p r o v i d e s 6 4 commands, a l l o r i g i -n a t e d o n b o a rd t h e p r o b es b y t i m e r s , programmers, G-switchesand o t h e r l o g i c s a nd d e v i c e s .

The command s ys te m on t h e S m a l l P r o b es i s i d e n t i c a l t o

Data Handl ing System

Components o f th e d a ta han d l in g sys t em on th e S m a l l

P r o b es a re i d e n t i c a l t o t h o s e f o r t h e L a r g e Pr o b e . The d a t a -h a n d l i n g u n i t c an a c c e p t 36 a n a l o g , 1 2 d i g i t a l and 24 one-b i t c h a n n e l s f ro m i n s t r u m e n t s a nd s y s t em s . L o gi c of d a t af o r m a t s a l s o i s i d e n t i c a l .

- m o r e -



- 9 5 -

The s y s t em f o r e ach S m a l l Probe p r ov id e s f o r t h r e eh i g h - r a t e d a t a f o r m a t s : u p p e r d e s c e n t , l o w e r d e s c e n t a n de n t r y b l a c k o u t . As w i t h t h e L a rg e P ro b e, a s t o r a g e c a p a c i t yo f 3072 b i t s i s prov ided by t h e da ta memory. Fo l lowing th een t r y co m m u n i ca t i o n s b l ack o u t , s t o r e d d a t a w i l l b e p l a y e dback and t e l e m e t e r e d i n t h e u p p e r d e s c e n t f or m a t a t 6 4 bps .R e a l t i m e t r a n s m i s s i o n w i l l o c cu r i n i t i a l l y a t 6 4 bps i n t h e

u p p e r d e s c e n t format , chang ing t o 1 6 b p s a t 30 km ( 1 9 m i . )

a l t i t u d e ( lower d e s c e n t f o r m a t ) . Data r a t e a l l o c a t i o n amongt h e t h r e e S m a l l Probe i n s t r u m e n t s r a n g e s f r o m 6 t o 20 bps i nt h e upper for mat and 1 . 5 t o 7 .2 5 b p s i n t h e l o w er f o r m a t .

Power Sys e m s

S m a l l Probe power systems a re s i l v e r - z i n c b a t t e r i e sw h i c h p r o v i d e 11 ampere-hours of en e r g y a t a normal 2 8

v o l t s . The s y st e m i n c l u d e s a b a t t e r y , power i n t e r f a c e u n i ta n d c u r r e n t s e n s o r . O t h e r components a r e i d e n t i c a l t o t h o s e

f o r t h e L a rg e P ro b e.

- m o r e -



- 9 6 -

S C I E N T I F I C I N V E S T I G A T I O N S

O r b i t e r

C l o u d P h o t o p o l a r i m e t e r -- T h i s i n s t r u m e n t m e a su r es t h ev e r t i c a l d i s t r i b u t i o n o f c l o ud and ha ze p a r t i c l e s and ob-s e r v e s u l t r a v i o l e t a tm o s ph e ri c m ar ki ng s a nd c l o u d c i r c u l a -t i o n s . U l t r a v i o l e t images p r o v id e t h e v i s u a l r e f e r e n c e f o rd a t a from o t h e r O r b i t e r e xp er im e nt s and f o r t h i s i n s t r u m e n t ' sp o l a r i z a t i o n r e a d in g s .

A 3.7-cm ( 1 . 5 - i n . ) t e l e s c o p e w i t h a r o t a t i n g f i l t e r

w he el o b s e r v e s t h e p l a n e t a t f i x e d a n g l e s , u s i n g t h e O r b i t e rr o t a t i o n f o r s ca ns ac ros s t h e p l a n e t a nd m o ti on a l o n g t h es p a c e c r a f t t r a j e c t o r y a ro u nd V enus f o r c o mp le te p l a n e t a r ym ap pi ng . T he a n g l e o f t h e t e l e s c o p e may b e v a r i e d b y g r ou n dcommand f o r s e l e c t o b s e r v a t i o n s from a ny p o i n t i n o r b i t .

The i n s t ru m e n t u s e s a n u l t r a v i o l e t ( U V ) f i l t e r ( f o rmaximum c o n t r a s t ) t o t r a c k t h e p u z z l i n g f a s t -m o v in g UV

a b s o r b i n g m a r k in g s . F i v e p l a n e t a r y im ag es c a n b e made i ne ac h s p a c e c r a f t o r b i t . The f i e l d o f v iew i s a b o u t o n e - h a l fm i l l i r a d i a n , c o rr e sp o n di n g t o a r e s o lu t i o n of abo u t 30 km(19 m i . ) d i r e c t l y be low t h e O r b i t e r .

The i n s t r u m e n t m e as ur es s c a t t e r e d s u n l i g h t p o l a r i z a t i o nb a se d o n c l o u d an d h a ze p a r t i c l e s i z e , s h a p e a n d d e n s i t y .V e r t i c a l d i s t r i b u t i o n of c lo u d and h az e p a r t i c l e s i n r e l a -

t i o n t o a t m o s ph e r i c p r e s s u r e i s e x t r a c t e d from t h i s d a t a .

W hile t h e O r b i t e r i s a t p e r i a p s i s t h e i n s tr u m e n t o b s e r ve s

i n v i s i b l e l i g h t t h e hi gh -h az e l a y e r s of t h e a tm os ph er e.These " l imb scans ' ' have a r e s o l u t i o n a s s m a l l a s . 5 km ( . 3 m i . ) .The i n s t r um en t we ighs 5 kg (11 l b . ) a nd u s e s 5 .4 w a t t s .

S ur fa ce Radar Mapper - - The r a d a r mapping exper imentmakes f o r t h e f i r s t t i m e s t u d i e s of l a r g e p o r t i o n s of t h ep l a n e t ' s h e mi sp h er e n o t v i s i b l e from E a r t h . T h i s e x p er im e n tw i l l p r ov i de t h e o n l y d i r e c t o bs e r v a t i on s of t h e s u r f a c e t ob e o b t a i n e d fro m t h e O r b i t e r . From o b s e r v i n g t h e e c h o o fs e v e r a l r a d i o f r e q u e n c i e s , e x p er im e n te r s d e r i v e s u r f a c eh e i g h t s a lo n g t h e o r b i t a l t r a j e c t o r y t o a n a c c u r a c y o f 1 0 0 m( 3 0 0 f t . ) o r b e t t e r , g i v i n g a good e s t i m a t e o f g l o b a l to p o-

g r a p h y a n d s h a p e . S u r f a c e e l e c t r i c a l c o n d u c t i v i t y c an a l s ob e d e r i v e d from t h e r a d a r d a t a .

A l o w power ( 2 0 w a t t s peak p u ls e power) S-band (1 .757G H zlr ad ar s ys te m o b s e r v e s t h e s u r f a c e f o r o n e o u t o f e v e ry1 2 s ec on ds o f s p a c e c r a f t r o t a t i o n .

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O R B I T E R E X P E R I M E N T S

M A G N E T O M E T E R M A G N E T O M E T E R

SENSOR BOOM

R E T A R D I N G\/ niJE LE C TR IC F IE LD

SPECTROMETER

U L T R A V I O L E T

SPECTROMETER

TE MP E R A TU R E

N E U T R A L M AS SSPECTROMETER GAM MA BURST

DETECTOR ON

S H E LF N O TVISIBLE

R A D IO ME TE R \ R A D A R MA P P E R A N TE N N A



- 98 -

Measurements a r e made whenever th e Or b i t e r i s below3 , 0 0 0 km (1 ,860 m i . ) , s u b j e c t t o c o n s t r a i n t s s e t b y t h er e v o l v i n g r a d a r a n t e n n a an d by c o m p e t i t i o n w i t h o t h e r e x-p e ri m en ts f o r t h e l i m i t e d t e l e m e t r y c a p a c i t y . The i n s t r u -m ent a u t o m a t i c a l l y c om p en sa te s f o r D op pl er s h i f t c a us e dby t h e r a d i a l mo ti on of t h e O r b i t e r .

T e a m s c i e n t i s t s s u b t r a c t t h e o b se rv ed d i s t a n c e betw eent h e O r b i t e r and t h e s u r f a c e from t h e s p a c e c r a f t ' s o r b i t a lr a d i u s ( o b t a i n e d from DSN t r a c k i n g ) t o f i n d a b s o l u t e top o-g r a p h i c a l m ea su re me nts . S u r f a c e r e s o l u t i o n i s b e s t a t a p e r i a p s i sa l t i t u d e o f 200 km ( 1 7 4 m i . ) : 20 k m ( 1 2 m i . ) l ong and 1 6

k m ( 9 . 6 m i . ) a c r o s s t h e s u b o r b i t a l t r a c k . Data g a t h e r e dby t h e i n s t r u m e n t a nd te lemetered t o E a r t h w i l l be computer-a s se m b le d i n t o r a d a r maps o f t h e p l a n e t .

R e s o l u t i o n i s comparable t o t h e Ea r th - ba s ed r a d a rs t u d i e s ; enough t o d i s c e r n m a jo r s u r f a c e f e a t u r e s .

The in s t r um en t weighs 9 . 7 kg ( 2 1 . 3 l b . ) a nd u s e s 1 8

w a t t s .

I n f r a r e d R a d i o m e t e r -- T h i s i n s t r u m e n t m ea s ur e s t h e" h e a t " ( i n f r a r e d r a d i a t i o n ) e m i t t e d by t h e a tm os ph er e a tv a r i o u s a l t i t u d e s f rom 60 k m (36 m i . ) a t t h e t o p of t h ed e ns e c l o ud l a y e r s o u t t o 1 5 0 km ( 9 0 m i . ) . I n a d d i t i o n ,t h e i n s tr u m e nt s e a r c h e s f o r w a t e r v ap o r abo ve t h e c l o u dl a y e r s , m ea su re s t h e s i z e o f h e a t t r a p p i n g c lo u d l a y e r sand m ea su re s t h e p l a n e t a r y s o l a r r e f l e c t a n c e ( a l b e d o ) .The r a d i o m e t e r ' s d a t a y i e l d s a v e r t i c a l t e m pe ra tu re p r o f i l eo f t h e upper a tmosphere a s w e l l a s a h o r i z o n t a l t e m p e r a t u r e

p r o f i l e a l on g t h e s u b o r b i t a l t r a c k . Such i n fo r m a ti o n i si m p o rt a n t i n u nc ov er in g t h e e x t e n t a n d d r i v i n g f o r c e s o ft h e seemi ng f o u r- d ay c i r c u l a t i o n o f t h e up p er a tm o s p h er e .

The i n s t r u m e n t f e a t u r e s e i g h t d e t e c t o r s , e ac h s e n s i t i v et o a d i f f e r e n t f r a c t i o n of t h e i n f r a r e d s pe ct ru m. F i v ed e t e c t o r s m ea su re t h e i n f r a r e d e m i s s io n s a t f i v e s e l e c t edw av e l en g t h s o f t h e p n ( m i c r o m e t e r s ) , a b s o r p t i o n b an d o fcarbon d i ox id e . Each wave leng th samples a s p e c i f i c d e p thi n t h e a t m o sp h er e , d ep en di ng o n h e a t a b s o r b i n g c h a r a c t e r -i s t i c s o f t h e C 0 2 m o le c ul e an d t h e v a r i a t i o n o f t e m p er a t ur ew i t h a l t i t u d e . One d e t e c t o r e x c l u s i v e l y d e t e c t s an d mapst h e d i s t r i b u t i o n of water v ap or ( i f i t e x i s t s ) i n t he

u p p e r a t m o sp h e r e. A n o t he r d e t e c t o r m eas u re s t h e s i z e ands h a p e o f c l o u d l a y e r s , a nd t h e l a s t d e te c to r m eas u r e s t h e

t o t a l s o l a r r e f l e c t a n c e .

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V E N U S O R B I T E R IMAGING SYSTEM

PE R IAPSISCLOSEST

' PERlAPSlS

The Cloud Photopolarimeter uses motion along the Orbiter's flight path around Venus, and spacecraft

rotation for picture scanning of the planet in ultraviolet light. The .instrument can make five planetary

images in each spacecraft orbit. It has a resolution of about 30 km (19 miles). It also measures cloud

particle characteristics, and will make pictures of haze layers a t the planet edge with a resolution of 15 km

(0.3 mile).



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A 48-mm-ape rtu re t e l e sc op e m i r ro r f e e ds a l l e i g h tc h a n n e l s . The t e l e s c o p e i s s e t a t 45 d e g r e e s t o t h eO r b i t e r s p i n a x i s so t h a t s ca ns a re made b y s p a c e c r a f tro t a t i o n . When l ook ing a t o n e p l a n e t ' s l im b t h e n ar ro wf i e l d of v iew g i v e s v e r t i c a l r e s o l u t i o n o f 5 km ( 3 m i . )a t p e r i a p s i s . When t h e O r b i t e r i s i n b e s t p o s i t i o n f o r

l im b s c a n ni n g o f t h e p l a n e t ' s a t m o sp h e r ic " ed ge , I' t h ei n s tr u m e nt o b t a i n s a d d i t i o n a l d a t a o n cl o u d l a y e r s a n dt h e v e r t i c a l d i s t r i b u t i o n of w a t e r v a p o r .

The i n s t ru me n t we ighs 5.9 kg ( 1 3 l b . ) a nd u s e s 5 . 2w a t t s .

A ir gl ow U l t r a v i o l e t S p e c t r o m e te r -- The u l t r a v i o l e ts p e c t r o m e t e r o b s e r v e s t h e num erous a t m o s p h e r i c m a r k in g sw hich c a n b e s e e n o n l y th r ou g h u l t r a v i o l e t ( U V ) f i l t e r s .The i n s t r u m e n t t r a c k s t h e UV abso rb ing masses wh ich r o t a t ei n f o u r d a y s, m e as ur es t h e e s c a p e r a t e of atomic hydrogenfrom t h e o u t e r a tm o sp he re an d m e as ur es t h e u l t r a v i o l e t

s c a t t e r i n g p r o p e r t i e s of t h e c l o u d t o p s a n d ha z e s a t a b o u t80 km (50 m i . ) a l t i t u d e .

A b s o r p t i o n o f UV r a d i a t i o n i n t h e u pp er a tm os ph er ep ro d uc es o p t i c a l UV emiss ions known a s t h e " a i r g l o w " .V a r i ou s a i r g l o w e m i s s i o n s a r e c au se d by d i f f e r e n t p h y s i c a lp r o c e s s e s (e . g . , s p l i t - u p o f m o le c ul es i n t o e l e c t r o n i c a l l ye x c i t e d a to m s ) . By v iewing day and n i g h t a i rg low a t wave-l e n g t h s b e t w e e n 1 , 1 0 0 Angstroms and 3,400 Angstroms, t h es p e c t r o m e t e r c a n t h u s i d e n t i f y t h e mechanism w hi ch e x c i t e st h e g a s e s o f t h e u p p e r a t m o sp h e r e. The t e m p e r a t u r e s o ft h e u p p e r a t m o s p h e re a t v a r io u s a l t i t u d e s c an a l s o b ei n f e r r e d f ro m d a t a f ro m l im b s c a n s a t t h e a t m o s p h e r e ' s

edge , a t s e le c te d w a v e l e n g t h s .

The i n s t r um en t measu res t h e Lyman Alpha co rona t o f i n dh yd ro ge n e s c a p i n g f rom t h e f a r t h e s t r e a c h e s o f V e nu s'a t m o sp h e r e. T h e s e d a t a a r e i m p o r t a n t b e c a u s e e s c a p i n ga tomic hydrogen i s t h e l a s t s t e p when a p l a n e t i s l o s i n gwater .

The s p e c t r o m e t e r f e a t u r e s a 125-mm t e l e s c o p e and mono-chroma to r t o r e s t r i c t (upon ground command) t h e vi ewi ngspec t rum t o any UV w a v el en g th . P h o t o m u l t i p l i e r t u b e s co n-v e r t t h e i m pi ng in g W r a d i a t i o n t o e l e c t r i c a l i m p u l s e s ,which a re t h e n t e l e m e t e r e d t o E a r t h f o r c o n s t r u c t i o n i n t o

u l t r a v i o l e t p l a n e t a r y maps.

The i n s t r um en t we ighs 3 . 1 kg ( 6 . 9 l b . ) a nd u s e s 1 . 7

w a t t s .

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-101-

N e u t r a l Mass S p e c t r o m e t e r -- T h i s i n s t r u m e n t m ea s u re st h e d e n s i t i e s of n e u t r a l i o n i z e d a t o m s a nd m o l e c u l e s i n

Venus ' uppe r a tmos phere be tween 150 km ( 9 0 m i . ) a t p e r i -a p s i s and 200 km ( 1 2 0 m i . ) . F i n d i n g t h e v e r t i c a l and h o r i -

z o n t a l v a r i a t i o n s i n t h e n e u t r a l g a s m ol ec ul es w i l l h e l pd e f i n e t h e c h em ic al s t a t e of t h e u p p e r a t m o s p h e re . V a r i a -

t i o n s o f h yd ro ge n an d he li um c o n c e n t r a t i o n s w i l l t e l l t h ee x t e n t o f g a s e s c a p e f ro m t h e a t m os p h er e . R e s e a r c h e r s w i l lf i n d t h e h e i g h t o f t h e ho mo pau se ( a bo v e w hi ch a t m o s p h e r em ix in g s t o p s ) by co mp ari ng t h e d e n s i t i e s o f i n e r t g a s e s a tt h e O r b i t e r a l t i t u d e s w i t h m e as ur em en ts made by t h e L a r g eP r o b e a nd Bus n e u t r a l mass s p e c t r o m e t e r s b e l o w 1 5 0 km ( 9 3 m i . ) .

N ob le g a s e s , o t h e r n o n - r e a c t i v e g a s e s an d c h e m i c a l l y

a c t i v e g a s e s up t o 4 6 atomic mass u n i t s a r e i d e n t i f i e d a ndm easu red . Gas molecules a re f i r s t i o ni ze d and t he n d e f l e c t e dby a m a g n e t ic f i e l d a c c o r d i n g t o t h e i r m a s s . The ave ragev e r t i c a l s pa ci ng of s a m p l e p o i n t s i s a p p r o x i m a t e l y 400 m

( 2 4 0 f t . ) a t 500 km ( 3 0 0 m i . ) a l t i t u d e w hi l e t h e h o r i z o n t a l

s p a c i n g f o r s am pl in g a l o n g t h e O r b i t e r p a t h i s a b o u t 2 km( 1 . 2 m i . ) .

The i n s t r umen t weighs 4 . 5 kg ( 9 . 8 l b . ) a nd u s e s 1 5 w a t t s .

I o n Mass S p e c t r o m e t e r -- The i o n m a s s s p e c t r o m e t e rm ea su re s t h e d i s t r i b u t i o n a nd c o n c e n t r a t i o n of p o s i t i v e l yc h a r g e d i o n s i n t h e V en u si an u p p e r a t m os p h er e fr om 1 5 0 km

( 9 0 m i . ) t o t h e i o n o sp h e r e . The in s t r u m e n t d i r e c t l y mea-s u r e s io n s i n a m a s s r a n g e f ro m h y dr og e n i o n ( p r o t o n ) t oi o n s of i r o n , c o r r e sp o n d i n g t o f ro m 1 t o 56 a to mi c massu n i t s . Such d a t a a r e i m p o r ta n t i n u n d er s ta n d in g t h e b a s i cn a t u r e of t h e i o n o s p h e r e an d i t s r e l a t i o n w i th t h e s o l a r wind.

The in s t r um en t m akes f i r s t a n e x p l o r a t o r y sweep o f 1 . 5

s e c o n d s , d u r i n g w hic h a s e a r c h i s made f o r up t o 1 6 d i f -f e r e n t i o ns . I t then makes a s e r i e s o f s w e e p s , r e p e a t i n gt h e s a mp li ng of t h e e i g h t m os t p ro m in e nt i o n s i d e n t i f i e dd u r i n g t h e e x p l o r a t o r y s we ep . ( Th e Bus i n s t r u m e n t i s i d e n -t i c a l t o t h e O r b i t e r v e r s i o n e x c e p t t h a t t h e s e o p e r a t i n gs e q u e n c e s c a n n o t b e modified by ground command a s t h e y c a non t h e O r b i t e r . )

I n f l i g h t , a s e ns o r i s e x po s ed t o a s t r e a m of atmos-p h e r i c i o n s , w h ic h f l o w i n t o a n aluminum c y l i n d e r e n c l o s i n ga s e r i e s of p a r a l l e l w i r e g r i d s . Each i o n s p e c i e s i s a c c e l -

e r a t e d by a s p e c i f i c v o l t a g e a p p l i e d t o t h e g r i d s so t h a tt h e i o n s i m pi ng e o n a c o l l e c t o r a t t h e r ea r o f t h e s e n s o rc y l i n d e r . The i o n s t r e a m ' s a c c e l e r a t i n g v o l ta g e w i l l y i e l di t s i d e n t i t y and i t s a m p l i t u d e w i l l r e v e a l i t s c o n c e n t r a t i o n .

T he i n s t r u m e n t w e ig h s 3 kg ( 6 . 6 l b . ) a nd u s e s 1 . 5 w a t t s .

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S o l a r Wind P l a s m a A n a l y z e r -- T h i s i n s t r u m e n t m e a su r esp r o p e r t i e s of t h e s o l a r wind and i t s i n t e r a c t i o n s w i t hV e nu s ' i o n o s p h e r e a n d u p p e r a t m o s p h e re . T he i n s t r u m e n tm e as ur es v e l o c i t y , f l ow d i r e c t i o n an d t e m p e r at u r e of t h es o l a r w in d. Such f i n d i n g s s h o u l d h e l p e x p l a i n h o w t h e

i o n o s p h e r e r e a c t s w i t h t h e s o l a r w in d an d p o s s i b l y t h er o l e t h e s o l a r w ind p l a y s i n V en us ' weather p a t t e r n s .

The r e g i o n a r o u nd V en us , t h e c a v i t y "shadowed" b y t h es o l a r w in d, i s d e te r m in e d t o t h e e x t e n t a ll o w ed b y t h es p a c e c r a f t o r b i t . The i n s t r u m e n t s e a r c h e s f o r streams ofs o l a r p a r t i c l e s i n t h i s r e g i o n .

The p lasm a ana lyze r i s a n electrostatic/energy-per-u n i t c h ar g e s p e c t r o m e t e r . The s o l a r wind f l u x ( r a t e off l o w of t h e s o l a r wind) i s m ea su re d by t h e d e f l e c t i o n o fi n - r u s h i n g p a r t i c l e s by an e l e c t r o s t a t i c f i e l d be tw ee ntw o m e t a l p l a t e s . I f t h e p a r t i c l e s a re w i t h i n t h e e n er gy

r a n ge d et er m in ed by t h e p l a t e s ' v o l t a g e d i f f e r e n c e s , t h eye x i t be tween t h e p l a t e s , h i t t i n g o ne o f f i v e d e t e c t o r s .Which t a r g e t th e p a r t i c l e s h i t d e t e r m i n e s t h e s o l a r windd i r e c t i o n . By v a r y i n g t h e v o l t a g e b et we en t h e p l a t e s , t h ei n s tr u m e n t y i e l d s a c o m p l e t e p a r t i c l e s p e c t r u m of t h e s o l a rwind.

T h e i n s t r u m e n t w e ig h s 3 .9 kg ( 8 . 6 l b . ) a nd u s e s 5 . 2

w a t t s .

Magnetometer -- T h e m a gn e to m et er s t u d i e s V e nu s ' m a g -n e t i c f i e l d and t h e i n t e r a c t i o n of t h e s o l a r w i n d w i t h t h ep l a n e t . I t " s ea r ch e s ". f o r s u r f a c e - c o r r e l a t e d m a gn et ic fea-

t u r e s , s u ch a s r e g i o n s of c r u s t ma gn et iz ed i n t h e p a s t p e r -haps when Venus had much s t r o n g e r m a g n e t ic p r o p e r t i e s . Themeasurements of t h e m a gn e ti c f i e l d of E a r t h ' s s i s t e r p l a n e tmay s h e d l i g h t on w h a t i n t e r n a l f l u i d m o ti on s pr od uc e p la n e -t a r y m a g n e t i c f i e l d s . ( I t i s s t i l l not known what mot ionsa r e r e s p o n s i b l e f o r E a r t h ' s m a gn e ti c f i e l d s . )

I t a p p e a r s V en us h a s a v e r y weak m ag n e ti c f i e l d ; y e t ,it may p l a y a n i m p o r t a n t r o l e i n t h e i o n o s p h e r e - s o l a r w in di n t e r a c t i o n . T h e m a gn e to m et er s h o u l d f i n d whether it i st h e weak i n t r i n s i c m ag ne ti c f i e l d , a n i n d u c e d m a g n e t i cf i e l d o r t h e i o n os p he re i t s e l f w hich d e f l e c t s t h e s o l a rwind.

The i n s t r u m e n t c o n s i s t s of t h r e e s e n s o r s on 4.7-m( 1 5 . 5 - f t . ) booms, long enough t o i s o l a t e t h e m from mucho f t h e s p a c e c r a f t ' s own m a g ne t ic f i e l d . The inboard s e n s o r ,t i l t e d 45 d e g re e s t o t h e s p i n a x i s e x c l u s i v e l y m e as u re st h e O r b i t e r ' s m ag ne ti c f i e l d , w hich w i l l be s u b t r a c t e d f r o mt h e o u tb o a rd s e n s o r s ' r e a d i n g s .

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Each s e n s o r c o n s i s t s of a r i n g a r o u n d which i s wrapped

a r i b b o n of perm eab le metal . Any e x t e r n a l ma g n et ic f i e l dc a u s e s t h e core t o p r o d u c e a n e l e c t r i c a l s i g n a l . A f e e d -

b ack s i g n a l t he n c a n c e ls t h e e x t e r n a l f i e l d so t h a t t h em a gn e to m et er a l w ay s o p e r a t e s i n a z e r o f i e l d c o n d i t i o n .The s t r e n g t h of t h e f e ed b ac k s i g n a l i s a measure of t h ee x t e r n a l m ag ne ti c f i e l d .

T h e i n s t r u m e n t weighs 2 kg ( 4 . 4 l b . ) a nd u s e s 2 . 2w a t t s power.

E l e c t r i c F i e l d Detec tor=- - T h i s i n s t r u m e n t w i l l h e l pa n sw e r q u e s t i o n s c o n c e r n i n g the c h a r a c t e r i s t i c s o f t h e i n t e r -a c t i o n s betw een Venus and t h e s o l a r wind, t h e m i l l i o n - m i l e -

an-hour i o n i z e d g a s t h a t c o n t i n u a l l y streams outward fromt h e S un t o t h e s o l a r s y st em .

T h e d e t e c t o r w i l l d e te r m in e t h e k i n d s o f i n t e r a c t i o n sbetween th e plasma ( t h e mass of i o n s a nd e l e c t r o n s ) of

V en us ' i o n o s p h e r e a n d t h e s o l a r w in d, t h e e x t e n t t o whichth e s o l a r w ind i s d e f l e c t e d around Venus , t h e e x t e n t t owhich the s o l a r wind h e a t s t h e i o n os p he r e, t h e e x t e n t ofi o n i z a t i o n c a u se d by e x o s p h e r e- s o l a r w ind i n t e r a c t i o n an ds o l a r w i n d t u r b u l e n c e . T h e i n s t r u m e n t a l s o searches f o r

" w h i s t l e r s " -- e l e c t r o m a g n e t i c d i s t u r b a n c e s which t r a v e la l o n g a p l a n e t ' s m a gn e ti c f i e l d l i n e s .

T h e i n s t r u m e n t m e as u re s e l e c t r i c components of plasmawaves and r a d i o e m i s s io n s i n th e f r e q u e n c y r e g i o n f r o m1 0 0 t o 1 0 0 , 0 0 0 H e r t z w hi ch i n d u c e a c u r r e n t i n t h e i n s t r u -m ent ' s V - type e l e c t r i c d i p o l e a n te n n a. T h e c u r r e n t i sa m p l i f i e d an d t h e i n f o r m a t i o n p r o ce s s e d a nd r e l a y e d b a ck

t o E a r t h . Four 30 p e r c e n t b an d wi dt h c h a n n e l s a re employed;each i s u s e f u l a t d i f f e r e n t p o i n t s a lo ng t h e O r b i t e r t r a -j e c t o r y , as i t p a s s e s t h r ou g h v a r y i ng d e n s i t i e s of t h es o l a r w in d . T he 0.6-m ( 2 6 - i n . ) - l o n g a n t e n n a i s d e s i g n e dt o l e a n on t h e O r b i t e r s h r o u d a n d d e p l o y a u t o m a t i c a l l ywhen th e sh roud i s e j e c t e d .

T h e i n s t r u m e n t w e ig h s 0 . 8 kg (1.74 l b ) a n d u s e s 0 . 7w a t t s of power.

E l e c t r o n T e m p e ra t u re P r o b e s -- T h e p r o b e s m e a su r e t h et h e r m a l c h a r a c t e r i s t i c s of V e n u s ' i o n o s p h e r e : e l e c t r o nt e m p e r a t u r e a nd c o n c e n t r a t i o n a nd i o n p la sm a mass and con-c e n t r a t i o n , a s well a s t h e s p a c e c r a f t ' s own e l e c t r i c a l

p o t e n t i a l . S uc h m e as ur em e nt s w i l l h e l p s c i e n t i s t s under-s t a n d t h e h e a t i n g m ec ha nism s of V en us ' i o n o s p h e r e , c u r r e n t l yb e l i e v e d t o i n c l u d e h e a t i n g a t h i gh e r a l t i t u d e s by t h e s o l a rwind and a t low er a l t i t u d e s by s o l a r u l t r a v i o l e t r a d ia t i o n .

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T w o c y l i n d r i c a l probes 7 c m ( 3 i n . ) b y 0 . 2 5 c m ( 0 . 5

i n . ) a r e use d. One pro be i s mounted p a r a l l e l t o t h e space -c r a f t s p i n a x i s on a 0 . 4 - m (16-in. ) boom, and t h e o t h e rp r o b e i s m o u n t e d p e r p e n d i c u l a r t o t h e s p i n a x i s on a 1-m( 4 0 - i n . ) boom. (The booms a r e long enough t o p l a c e t h ese ns or s beyond m uch of t h e p h o t o e l e c t r o n c l o u d an d i o n

s h e a t h s u rr o un d in g t h e s p a c e c r a f t w h i c h m i g h t d i s t o r t read-i n g s . ) T h e l o n g e r boom a l l o w s measurement of e l e c t r o n c o n -t e n t a n d t e m p er a tu r e f o r c o n d i t i o n s of v e r y l o w e l e c t r o nc o n c e n t r a t i o n s .

E a c h p r o b e h a s i t s own power g e n e r a t o r w h i l e s h a r i n gi n f l i g h t d a t a a n a l y s i s c i r c u i t r y . A s a w t o o t h v o l t a g e s w ee pseach p r o b e t w i c e p e r s e c o n d a nd i s e l e c t r o n i c a l l y a da pt ed t om atch t h e e x i s t i n g e l e c t r o n d e n s i t y an d te m p e r a tu r e b e i n gmeasured.

T he i n s t r u m e n t w e i gh s 2 . 2 kg ( 4 . 7 6 lb.) a n d u s e s 4 . 8

w a t t s of power.

Charqed P a r t i c l e R e t a r d i n g P o t e n t i a l A na ly ze r -- T h i s

i n s t r u m e n t m e a su r es t h e t e m p e r a t u r e , c o n c e n t r a t i o n a n d v e l o -c i t y of t h e m o s t a bu n da nt i o n s i n t h e i o n o s p h e r e ( p r e s u m a b l yc a r b o n d i o x i d e an d ox yg en i o n s . ) I t a l s o m e a s u r e s t h e c o n -c e n t r a t i o n , t e m p e ra t u re an d e n e r g y of s u r r o u n d i n g p h o t o -e l e c t r o n s i n t h e i on o sp he re .

T h e i n s t r u m e n t i s d es ig ne d s p e c i f i c a l l y f o r d e t e c t i n gt h e l o w e ne rg y pla sm a p a r t i c l e s i n V en us ' i o n o sp h e r e , a sopposed t o t h e much more h i g h l y e n e r gi z e d s o l a r wind par-t i c l e s . However, t h e a n a l y z e r s h o u ld p r o v i d e d a t a c on c er n-i n g t h e s o l a r w in d- io no sp he re i n t e r a c t i o n a t a n a l t i t u d e o f

400 t o 500 k m ( 2 4 0 t o 300 m i . ) a t t h e p o i n t where t h e s o l a rwind streams i n t o t h e i o n o sp h er e .

By v ar yi ng e l e c t r i c a l p o t e n t i a l s , c o l l e c t o r g r i d s of6 c m ( 2 .5 i n . ) d i am e te r s e l e c t i v e l y allow v a r i o u s i o n o s p h e r i cp a r t i c l e s t o s t r i k e a d e t e c t o r . C u r r e n t i nd uc ed i n t h e de-

t e c t o r i s a m p l i f i e d by a n e l e c t r o m e t e r .

Measurements a r e t a k e n a t i n t e r v a l s a 1 on g .a 120-km ( 7 2 -

m i . ) o r b i t s eg me nt t h r o ug h t h e i o n o s p h e r i c pla sm a r e g i o n .O n b o a r d a n a l y s i s s e l e c t s t h e optimum p o i n t i n t h e s p a c e c r a f t

r o t a t i o n a t which t o sample t h e i o n o s p h e r i c plasma, s o t h a teach s c a n i s c o m pl e te d i n a small f r a c t i o n of a s p i n p e r i od .

The i n s t r u m e n t a c h i e v e s a 20-km ( 1 2 - m i . ) r e s o l u t i o n f o rt o t a l i o n c o n c e n t r a t i o n .

T he i n s t r u m e n t w e ig h s 2 . 8 kg ( 6 . 3 l b . ) a nd u s e s 2 . 4w a t t s of power.

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G a m m a R a y B u r s t D e t e c t o r -- T h e gamma r a y b u r s t d e t e c t o ro b s e rv e s t h e i n t e n s e s h o r t d u r a t i o n ( on e -t e nt h s ec on d t o a

f e w t e n t h s of s e c o nd s ) " b u r s t s " of h i g h en e r q y p r o t o n s f ro mo u t e r s p a c e . T h i s phenomenon w a s n ' t d i s c o v e r e d u n t i l 1 97 3,a nd t h e n a t u r e a nd o r i g i n o f t h e s o u rc e s a r e s t i l l unknown.T h e gamma ray b u r s t s occ ur randomly i n t i m e ( r o u g h l y 1 0 p e ry e a r ) a nd a pp e ar t o o r i g i n a t e from random p o i n t s i n t h e u n i -v e r s e . T he gamma r ay b u r s t d e t e c t o r i s t h e o n l y ex p e r i m en ton Pi on ee r Venus which i s n o t i n vo lv ed i n t h e d i r e c t s tu dyof Venus and i t s e n v i r o n s .

The Venus O r b i t e r , s e p a r a t e d f r o m E a r t h b y r o u g h l y o n ea s t ro n o m ic a l u n i t ( 1 4 9 m i l l i o n km o r 93 m i l l i o n m i . ) p r o v i d e sa means t o o b t a i n a " f i x " o n t h e s t r a n g e b u r s t s , by c o r r e l a -t i n g i t s o b s e r v a t i o n s w i t h t h o s e made by o r b i t i n g E a r t hs a t e l l i t e s . Measurements of t h e gamma r a y so ur ce s w i l l b emade w i t h a n a c c u r a cy of l e s s t h a n o n e a r c m i n u t e , p r e c i s eenough f o r a n a t t e m p t a t o p t i c a l i d e n t i f i c a t i o n of t h e s o ur ce s .

Two sodium i o d i d e p h o t o m u l t i p l i e r d e t e c t o r u n i t s s en -s i t i v e t o p ho to ns i n t h e 0 . 2 t o 2 . 0 m i l l i o n e l e c t r o n v o l t s( M e V ) e n e r g y r a n g e p r o v i d e a co n t i n u o u s t i m e h i s t o r y f o rt h o s e b u r s t s i n t e n s e enough t o be d e t e c t e d a n d g i v e a c o a r s ep r o f i l e of t h e gamma b u r s t energ y range . A memory u n i t of

2 0 , 0 0 0 " b i t s " f o r s t o r i n g d a t a f o r l a t e r r e a d o u t i s r e q u i r e dt o accom modate t h e v e r y h i g h d a t a r a t e s t h a t o cc u r d u ri n g a

b r i e f b u r s t .

The in s t r um en t weighs 2 . 8 kg (6.35 l b . ) a n d u s e s 1 . 3

w a t t s of power.

O r b i t e r Rad io Sc ience

I n t e r n a l D e n s i ty D i s t r i b u t i o n E xp er im en t -- T h i s e x p e r i -m en t d e t e r m i n e s V e n us 's i n t e r n a l m a s s d i s t r i b u t i o n , t h e pro -cesses which have p ro du ce d t h a t d i s t r i b u t i o n , t h e p l a n e t ' sg l o b a l s ha p e a nd t h e r e l a t i o n s h i p b etw ee n V enu s' s u r f a c ef e a t u r e s and t h e i r c o r re sp on di ng i n t e r n a l d e n s i t i e s . R e -s e a r c h e r s h op e t o c o n s t r u c t a model of t h e p h y s i c a l p r o c e s s e sw hi ch go v er ne d V en us ' p l a n e t a r y e v o l u t i o n w i t h t h e h e l p o ft h i s e x pe r im e n t ' s d a t a .

S c i e n t i s t s u s e t h e two-way D op pl er t r a c k i n g o f t h eO r b i t e r , w h i c h i s also u se d f o r n a v i g a t i o n , t o f i n d v e ry

s m a l l ch an g es i n i t s o r b i t . They u s e t h e s e o r b i t c ha ng est o c h a r t V enus ' g r a v i t y f i e l d . T h i s g r a v i t y i n f o rm a ti o nc a n t h e n b e used t o c a l c u l a t e v a r i a t i o n s i n p l a n e t d e n s i t y .

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An S-band s i g n a l of 2 . 2 G H z i s t r a n s m i t t e d f r o m a D S N

a n te n na , r e c e i v e d by t h e O r b i t e r s p a c e c r a f t and r e t r a n s -m i t t e d back t o t h e DSN an t en n a . D o p p l e r s h i f t s i n f re qu en cyof these s i g n a l s mean c h an ge s i n s p a c e c r a f t v e l o c i t y . Mostof th e v e l o c i t y c h a n g e s a r e due t o t h e r e l a t i v e o r b i t a l

mo t ions of E a r t h , Venus and t h e Pi on ee r Venus O r b i t e r . How-e v e r , l o c a l a no ma li e s i n t h e i n t e r n a l mass d i s t r i b u t i o n ofVenus i n d u c e a d d i t i o n a l v e l o c i t y c h an g es . A n a l y s i s of t h ev e l o c i t y c ha ng es t h e r e f o r e p ro v i d e s i n f o r m a t i o n on t h e i n -t e r n a l m a s s d i s t r i b u t i o n of Venus.

Comparison of t h i s d a t a w i t h t h e r a d a r mapping d a t amay s u p p o r t t h e e x i s t e n c e of b a s i c o n- go in g p h y s i c a l p r o -cesses , s u ch a s E a r t h - l i k e p l a t e t e c t o n i c s ( t h e movementof m a ss iv e c r u s t a l p l a t e s s l o wl y p a s t o ne a n o t h e r ) . Thed a t a a l s o w i l l i n f e r t h e l i k e l y co m p o s it i o n a nd t e m p e r a t u r eo f V enus' i n t e r i o r .

C e l e s t i a l Mechanics Exper iment -- T h e c e l e s t i a l mechanicse x pe r im e n t s t u d i e s V en us ' g r a v i t y f i e l d , l e a d i n g t o c a l c u -l a t i o n s of i t s g l o b a l s h a p e a nd i n f e r e n c e s a b o u t t h e d y na mi csof t h e p l a n e t ' s u p p e r a t mo s ph e re a nd i o n o s p h e r e . T he e x p e r i -ment a l s o m ea su re s t h e d i r e c t i o n of V en us ' s p i n a x i s , r o t a -t i o n o f t h e p l a n e t ' s p o l e s , d e n s i t y of t h e u p p er a t m o s ph e r e ,r e l a t i v i s t i c e f f e c t s of s o l a r g r a v i t y on t h e O r b i t e r t r a c k i n gs i g n a l and improves ou r knowledge of t h e e x a c t p l a n e t a r y t r a -j e c t o r i e s of Venus and E a r t h .

S c i e n t i s t s u s e Do pp le r t r a c k i n g t o c h a r t t h e p l a n e t ' sg r a v i t y f i e l d . A DSN an t en n a o n E a r t h t r a n s m i t s a r a d i os i g n a l of 2 . 2 G H z t o t h e O r b i t e r , w hich r e t r a n s m i t s t h a t

s i g n a l , m u l t i p l i e d by 2 4 0 / 2 2 1 ( t o d i s c r i m i n a t e o ut g o in g fromi nc om in g s i g n a l s ) . U ne xp ec te d f r e q ue n c y s h i f t s i n t h e s e

s i g n a l s mean c h an ge s i n s p a c e c r a f t p o s i t i o n . T h e s e changesa r e cau s ed b y t h e m a s s and g r a v i t a t i o n a l f i e l d of Venus,g r a v i t y f i e l d of t h e Sun and Venus ' own atm os ph ere , w h i c h

e x e r t s a d r a g o n t h e O r b i t e r . More d e t a i l e d s t u d i e s of t h ea tmosphere a r e p o s s ib l e j u s t b e f o r e and a f t e r t h e o c c u l t a -t i o n s of t h e O r b i te r by Venus , when t h e r a d i o s i g n a l mustp a ss q u i t e c l o s e t o t h e p l a n e t s u r f a c e on i t s way t o E a r t h .

D i s t o r t i o n s ( s c i n t i l l a t i o n s ) of t h e O r b i t e r s i g n a l d u ri n gthese p e r i o d s r e v e a l v a r i a t i o n s i n up pe r a tm os ph er e d e n s i t y .

S i m u l t an eo u s r a d i o t r a c k i n g of the O r b i t e r w i t h e x t r a -g a l a c t i c r a d i o s o ur c es w i l l a l l o w v e r y p r e c i s e d e t e r m i n a t i o nof t h e o r b i t s of E a r t h a n d V enus w i t h r e s p e c t t o t h e s e e x t r a -g a l a c t i c o b j e c t s .

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D u al F r eq u e nc y R a d io O c c u l t a t i o n E x p er im e n t -- T h i se x p e r i m e n t s t u d i e s t h e a tmos phere of Venus by obse rv inghow O r b i t e r X- a nd S -b and r a d i o s i g n a l s p e n e t r a t e V en us 'atmosphere on t h e way t o r e c e i v e r s o n E a r t h . T h e 4 0 o c c u l -t a t i o n s w i t h Venus which t h e O r b i t e r t r a j e c t o r y e n c o u n t e r s

o v e r i t s m i s s i o n l i f e t i m e w i l l produce 80 p r o f i l e s of t h es i g n a l d i s t o r t i n g p r o p e r t i e s of t h e p l a n e t ' s lower and upper

a t m o s p h e r e a n d i o n o s p h e r e .

By an a l yz in g t h e s c i n t i l l a t i o n s i n r a d i o s i g n a l s c au se dby v a r i o u s a t mo s ph e ri c l a y e r s , i n v e s t i g a t o r s c a n i n f e r t h er e f r a c t i o n , t e mp e ra tu r e , p r e s s u r e a nd d e n s i t i e s of t h e atmos-p h e r e f r o m 3 4 k m ( 2 0 m i . ) a l t i t u d e u p t hr ou gh t h e i o n o s p h e r e .A s t h e r a d i o s i g n a l s p i e r c e t h e i o no s ph e re , i n v e s t i g a t o r sc an me as ur e s i g n a l d i s t o r t i o n d ue t o v a r y i n g e l e c t r o n d en -s i t i e s i n t h i s b ar el y- kn o wn r e g i o n . S i n c e m o s t of t h e se

measurements a re made o n V e n u s t : n i g h t s i d e , d a t a i s p r o v i d e don t h e r e p o r t e d l y v a r i a b l e V e nu sia n n i g h t t i m e i o n o s p h e r e .

T h e O r b i t e r hi g h- g ai n a n t en n a i s s p e c i a l l y aimed d u r i n go c c u l t a t i o n s s o t h a t t h e r e f r a c t e d r a d i o s i g n a l i s o p t i m a l l yaimed a t E a r t h . D S N s t a t i o n s on E a r t h a r e e qu ip p ed w i t hs p e c i a l r e c e i v e r s t o t r a c k t h e i n c o m i n g s i g n a l s a s t h e i rp h a se a nd f r e q u e n c i e s a r e m o d i f ie d d u r i n g t r a n s m i s s i o nthrough Venus I s atmosphere.

Atmospher ic and S o l a r Wind Turb ulen ce Exper imen t -- T h ee x p e r im e n t o b s e r v e s t h e s m a l l s c a l e t u r b u l e n c e ( l e s s t h a n 1 0

km o r 6 m i . ) i n t h e Venus ian a tmosphe re above 3 5 k m ( 2 2 m i . )a l t i t u d e . I t w i l l r e v e a l t h e v a r i a t i o n of a t m o s p he r i c t u r -

b u le n ce w i t h l a t i t u d e , l o n g i t u d e an d a l t i t u d e c h an ge s d u r in g

t h e 40 o c c u l t a t i o n s w hen O r b i t e r s p a c e c r a f t s i g n a l s m us tp a s s t h r o u g h V e nu s ' a t m o s p he r e o n t h e i r way t o E a r t h t r a c k -i n g s t a t i o n s . B ec au se t h e s i g n a l s t r a v e l t hr ou g h t h e i ono-s p h e r e a s w e l l , f l u c t u a t i o n s i n e l e c t r o n d e n s i t y ca n a l s o b e

i n f e r r e d from t h e d a t a .

F o l l o w i n g c o n c l u s i o n of t h e n or ma l m i s s i o n l i f e t i m e(a round Augus t 19791, t h e O r b i t e r w i l l p r o v i d e d e n s i t y an dv e l o c i t y m e a s u r e m e n t s of t h e s o l a r wind near t h e Sun. Venusw i l l t h e n a p pr o ac h s u p e r i o r c o n j u n c t i o n ( E a r t h a nd Venus

w i l l b e on o p p o s i t e s i d e s of t h e S u n ) . T h i s i s a n i d e a lt i m e t o i n v e s t i g a t e t h e s o l a r wind , t h e s t ream of i o n i z e dp a r t i c l e s c o n s t a n t ly s w i r l i n g o f f t h e Sun . Because t h e s o l a r

wind i s s o c h a n g e a b l e , r e p e a t e d O r b i t e r o b s e r v a t i o n s of t h es o l a r w in d n e a r t o a nd f a r f rom t h e Sun w i l l p r o v i d e n e e d e di n f o r m a t i o n a b o u t s o l a r wind d e n s i t y , t u r b u l e n c e a nd v e l o c i t yu n i f o r m i t y . T w o D S N s t a t i o n s w i l l a n al y ze t h e f l u c t u a t i o n s( s c i n t i l l a t i o n s ) i n the O r b i t e r S- and X-band s i g n a l s a s t h e yp a s s t h e s o l a r w ind o n t h e i r way t o E a r t h .

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Atmospher ic Drag Exper iment -- T h i s i n v e s t i g a t i o n t a k e sd r a g m easurement f o r t h e f i r s t t i m e of a n o t h e r p l a n e t ' s a tm os -p h e r e , a s t h e a tm o sp he re " f r i c t i o n " o f Venus s l o w s t h e O r b i-t e r . E x p e r i m en t e r s w i l l us e d r ag measu remen ts th roughou tt h e O r b i t e r m i ss i on t o s e a r c h f o r a ny v a r i a t i o n s i n a tmos-p h e r i c d e n s i ty t h a t c o r r e l a t e w i t h s o l a r w ind a c t i v i t y c h a ng e si n s o l a r u l t r a v i o l e t r a d i a t i o n and d i f f e r e n c e s i n d e n s i t y on

t h e p l a n e t ' s n i g h t s i d e . I n a d d i t i o n , p r o j e c t s c i e n t i s t s a r el o o ki n g f o r e vi d e n ce t h a t t h e s ee ming f ou r- da y r o t a t i o n o f t h el o wer a t m o sp h e r e ex t en d s i n t o t h e u pp e r a t m o s p he r e .

D S N s t a t i o n s a n a l yz e t h e D o pp le r e f f e c t on t h e s pa ce -c r a f t ' s X- an d S-band r a d i o s i g n a l , c au s ed b y a t m o s p h e r i cd r ag -i n d u ced ch an g e i n t h e O r b i t e r ' s d i r e c t i o n a nd s p ee d .

The e n t i r e s p a c e c r a f t , e s s e n t i a l l y t h e s ha pe of a c y l i n -d e r , a c t s a s t h e t e s t i n s t r u m e n t . A t mo sp he ri c d e n s i t y i sd et er mi ne d b e s t i n t h e v i c i n i t y of p e r i a p s i s ( be tw ee n 1 5 0

and 250 km o r 9 3 and 1 5 5 m i . ) , w he re t h e d ra g e f f e c t i s muchg r e a t e r t h an e l s ew h er e a l on g t h e O r b i t e r t r a j e c t o r y . A s t h e

p e r i a p s i s a l t i t u d e c ha ng es , v a r i a t i o n s of a t m o s p h e r i c d e n s i t yw i t h a l t i t u d e c an be p l o t t e d .

Knowledge o f a tmo sphe r i c d e n s i t y a i d s i n t e r p r e t a t i o n o fm a s s s p e c tr o m e te r f i n d i n g s , i n f e r s t h e c om p os it io n a nd t e m -p e r a t u r e of t h e u p pe r at mo sp he re a nd a i d s i n c o n s t r u c t i n g amodel of Venus ' upper a tmosp here .

Large P robe Exper imen t s

N e u t r a l Mass S p e c t r o m e t e r -- T h e n e u t r a l mass s p e c t r o -m e t e r m eas u r es t h e a t m o s p h e r i c co m p o s i t i o n o f t h e l o w e r 60 km( 3 6

m i . ) of Venus' a tm osp here ( l a r ge1 y t h e a tmosphere belowt h e ma s si v e c l o u d l a y e r s ) a s t h e L a r g e P r ob e d e s cen d s b yparachute . Knowledge of t h e r e l a t i v e a bu nd an ce s of g a s e sw i l l h e l p a ns we r q u e s t i o n s a b o ut t h e e v o l u t i o n , s t r u c t u r ea nd h e a t b a l a n c e of Venus.

The i n s t r u m e n t d e t e r m i n e s t h e v e r t i c a l d i s t r i b u t i o n andc o n c e n t r a t i o n o f n o n - r e a c t i v e g a s e s , c h e m i c a l l y g c t i v e g a s e s

and r a t i o s of i n e r t ga s i s o to p e s . Water v ap or ( i f i t e x i s t s )i s a l s o measured .

T h e i n s t r u m en t i s m ounted i n s i d e t h e L a r g e Pr o be p r e s -s u r e v e s s e l . I t r e c e i v e s a co n t i n u o u s f l o w o f a t m o s p h e r i c

g a s t h r o u g h t w o u n i q u e ceramic i n l e t t ub es t h a t p r o t r u d et hr ou gh t h e p r e s s u r e v e s s e l w a l l . The i n l e t tu b e s a re c a l l e dC e r a m i c Micro Leaks (CMLS) and a r e made t o g r e a t l y l i m i t t h eamount of g a s e n t e r i n g t h e i n s tr u m e nt , w i t h o u t c he m i ca l lya l t e r i n g it.

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The C M L s a r e p a s s i v e d e v i c e s a nd t h e a mount of g a sf l o w in g t h r o u gh t hem i n c r e a s e s w i t h i n c r e a s i n g a t m o s p h e ri cp r e s s u r e . T o p r e v e n t " f l o o d i n g " of t h e i n s t r u m e n t , o n e CML

i s sea l ed when t h e a t m o s p h e r i c p r e s s u r e i s a b o u t 1 . 5 b a r s .

A f t e r e n t e r i n g t h e i n s tr u m e nt , t h e a t m o s p h e r i c g a s i s f i r s ti o n i z e d a n d t h e s e p a r a te d i o n s s o r t e d o u t f o r m a s s andq u a n t i t y o f each c o n s t i t u e n t by t h e i r d i f f e r e n t d e f l e c t i o n si n p a s s i n g t h ro u gh m a g n et ic f i e l d s .

The spec t rometer c an i d e n t i f y g a s e s w i t h masses up t o208 atomic m a s s u n i t s , b e l ie v e d t o be a l a r g e e n o u g h m a s sr an g e f o r a l l m o le cu le s l i k e l y t o b e e n c ou n te r ed i n t h el ow e r a tm o sp h er e. S e n s i t i v i t y i s o ne p a r t p e r m i l l i o n .

S i x t y a t m o s p h e r i c s a m p l i n g s a re p l a n n e d , w i t h a mass spec t rumt a k i n g 6 4 s e c o n d s . An o n b o ar d m i c r o p r o c e s s o r c o n t r o l s t h ei n s t r u m e n t a n d a c c u m u l a t e s d a t a f o r t e le m e t r y t o E a r t h .

The i n s t r um en t we ighs 1 0 . 9 kg ( 2 4 l b . ) a n d u s e s 14 w a t t s .

G a s Chromatograph -- T h e ga s ch roma tograph measures t h eg a s e o u s c o m p o s i t i o n of Venus ' l o w e r atmosphere. B y f i n d i n qt h e m a j o r s o u r c e s o f i n f r a r e d o p a c i t y ( t h o s e gases t h a t t r a ph e a t ) , s c i e n t i s t s s ho uld b e t t e r un de rs ta nd why Venus h as 480-d e g r e e C (900-degree F . ) s u r f a c e t e m p e r a t u r e s . From t h em e as ur em e nt o f g a s e s pr od u ce d b y r a d i o a c t i v e d e c ay , s c i e n -t i s t s c a n i n f e r t h e d e gr ee of d i f f e r e n t i a t i o n w i t h i n V enus'i n t e r i o r . E x p e r i m e n t e r s w i l l a l s o b e a b l e t o d e d u c e t h es i m i l a r i t y of t h e c om p os it io n o f t h e s o l i d p a r t s of Venusa nd E a r t h by t h e i d e n t i f i c a t i o n of v a r io u s s u l f u r i c g ases .

T h e i n s t r u m e n t s a m p l e s t h e lower a t m o s p h e r e t h r e e t i m e sd u r i n g t h e L a rg e P r o b e ' s d e s c e n t . T h e a tmosphe re f l o w s i n t oa t u b e p e n e t r a t i n g t h e e x t e r i o r of t h e L a r g e P r o b e a nd i n t oa hel ium g a s s t ream, w h i c h sweeps t h e s a m p le i n t o t w o chroma-tog ra ph co lumns. Atmosphe r ic ga se s a re i d e n t i f i e d by t h et i m e it t akes t hem t o f l ow th rough t h e co lumns. As a c a l i -b r a t i o n c h e c k , t w o sam ples o f f r e o n ( a g a s n o t l i k e l y t o be

e n c o u n t e r ed i n t h e a t m o sp h er e) a r e added t o t h e t h i r d sample ,and t h e i r r e s o l u t i o n n o te d .

T h e i n s t r u m e n t w e i g h s 6 . 3 kg ( 1 3 . 8 l b ) a n d u s e s 4 2w a t t s , t h e m o st of any P io nee r Venus i n s t ru me n t .

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S o l a r F l u x R a d io m e te r - - Th is i n s t r u m e n t m e a s ur e s w h er es o l a r ene rgy i s d e p o s i t e d i n t h e l ow e r V e nu si an a tm o s ph e re ,g i v i n g a v e r t i c a l p r o f i l e of s u n l i g h t i n p u t . I t r e v e a l show much sunlight i s abs orbe d by t h e c lo ud s and how muchs u n l i g h t r e a c h es t h e s u r f a c e , i m p o rt a n t i n f or m a t i o n f o r re -so lv in g whe the r Venus ha s a greenho use wea the r mach ine ande x p l a i n i n g w h y i t s s u r f a c e i s s o h o t .

The i n s t r u m e n t c o n t i n u a l l y m e as ur es t h e d i f f e r e n c e i ns u n l i g h t i n t e n s i t y d i r e c t l y a bo ve a nd below t h e Large Probeh o r i z o n a s t h e pro be d r i f t s t o t h e p l a n e t s u r f a c e . F i v eq u a r t z l e n s e s of 3 mm ( 1 / 8 i n . ) d ia m et er i n s i d e f i v e f l a tsapphi re windows c o l l e c t t h e l i g h t a n d t r a n s m i t it b y q u a r t zr o d s t o a n e l e c t r o n i c l i g h t d e t e c t o r . S u n l i g h t i n t e n s i t y i sd e t ec t e d i n t h e s p e c t r a l r a ng e of 0 . 4 t o 1 .8 p m ( m i c r o m e t e r s ) ,t h e w a ve le n gt h r a n g e f o r m os t s o l a r e n e r g y . V e r t i c a l r e s o -l u t i o n i s 700 t o 1,000 m ( 2 , 3 0 0 t o 3 , 3 0 0 f t . ) . L e n s e s a r ep o s i t i o n e d b o t h u p a n d down t o f i n d t h e a m o u n t of s o l a re n e r g y absorbed i n l a y e r s o f t h e a t m os ph er e. T o a v o i d h a v i ngt h e p r ob e o r i t s p a ra c hu te i n t h e f i e l d o f v iew , t h e r a d io -

m e t e r s a mp l es s u n l i g h t i n na rr ow 5 -d eg re e f i e l d s o f v ie w .

The i n s t ru me n t we ighs 1 . 6 kg ( 3 . 5 l b . ) a n d u s e s 4 w a t t s .

I n f r a r e d R a d i o m e t e r -- The i n f r a r e d r a d i o m e t e r me a su r est h e v e r t i c a l d i s t r i b u t i o n o f i n f r a r e d r a d i a t i o n i n t h e atmos-phe re f rom Large P robe pa ra ch u t e dep loymen t a t 6 7 km ( 4 0 m i . )down t o t h e s u r f a c e . I t a l s o d e t e c t s c lo ud l a y e r s a nd w a t e rva po r , bo th of which may w e l l be t rapping enormous amountso f h e a t an d p r e v en t i ng t h e i r r e r a d i a t i o n b ac k i n t o s p a c e.F i n d i n g major h e a t s o u r c e s ( a nd t r a p s ) i s e s s e n t i a l t o prov ingVenus has a greenhouse hea t i ng mechan i sm.

S i x p y r o e l e c t r i c i n f r a r e d d e t e c t o r s were c h o s e n b e c a u s et h e y do n o t need s p e c i a l c o o l i n g eq ui pm en t f o r t h e i r u s e i nt h e e xt r e m e a t m o s p h e r i c h e a t . Each d e t e c t o r v ie w s t h e a tm os -p h e r e v i a r o t a t i n g l i g h t p i p e s t hr ou gh a d i f f e r e n t i n f r a r edf i l t e r b etw een 3 and 50 mic rons . The v i ews o f t h e d e t e c t o r si s d i r e c t e d a t 4 5 d e g r e e s a b o v e a nd b el ow t h e p r o b e h o r i z o nt h r o u g h a diamond window heated t o p r e v e n t p a r t i c l e c on tam i-n a t i o n d u r i n g p as s a g e t h ro u gh c l o u d s . T h e d i f f e r e n ce i n i n f r a -r e d r a d i a t i o n , c l o u d o p a c i t y and water vapor between t h e t w ov i e w i n g a n g l e s i s t e l e m e t e r e d t o E a r t h e v e r y 6 s e c o n d s , g i v i n ga v e r t i c a l i n f r a r e d s p a t i a l r e s o l u t i o n of 250 m (8 25 f t . ) o rb e t t e r .

Two of t h e s i x d e t e c t o r s m o n it o r t h e t em p e ra t ur e an do p t i c a l u n i f o r m i t y o f t h e d ia mo nd v i e w i ng window , t w o d e t e c -t o r s d e t e c t a n d m e a s u r e w a t e r v a p o r , o n e d e t e c t o r measuresc l o ud o p a c i t y a nd t h e r e m ai n in g d e t e c t o r me as ur es t h e i n f r a r e d

i n t e n s i t i e s of t h e a tm o s ph e ri c l a y e r s t h e L ar ge Pr obe p a s s e st h r o u g h .

The i n s t r um en t weighs 2 . 6 k g ( 5 . 8 l b . ) a nd u s e s 5 . 5 w a t t s .

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Cloud P a r t i c l e S i z e S p e c tr o m e te r -- T h i s i n s t r u m e n t

measures t h e p a r t i c l e s i z e an d s ha p e a nd d e n s i t y of V enus'c lo ud s i n t h e lower a tmosphe re from 67 k m ( 4 0 m i . ) down t ot h e s u r f a c e .

Through measurements of p a r t i c l e s i z e and m a s s , t h e

i n v e s t i g a t i o n p ro v i de s a v e r t i c a l p r o f i l e of p a r t i c u l a t ec o n c e n t r a t i o n f o r 3 4 d i f f e r e n t s i z e c l a s s i f i c a t i o n s , r a n g i n g

f r o m 1 t o 500 m i cr o ns i n d i am e t e r ( a micron i s o ne m i l l i o n t hof a m e t e r o r r o u g h l y t w o t e n - t h o u s a n d t h s of a n i n c h ) . Suchmeasurements w i l l g i v e c l u e s t o b a s i c c l o ud f o r m a t i o n p r o-

cesses a nd c l o u d - s u n l i g h t i n t e r a c t i o n s on V en us.meter a l s o d i f f e r e n t i a t e s i c e c r y s t a l s -- i f any a re p r e s e n t-- from o t h e r c r y s t a l l i n e p a r t i c u l a t e s by d e te rm in in g t h ei c e ' s c h a r a c t e r i s t i c " a s p e c t r a t i o " -- t h e r a t i o of p a r t i c l e

t h i c k n e s s t o s i z e .

The s p e c t r o -

T h e i n s t r u m e n t d i r e c t s a l a s e r beam o n t o an e x t e r n a lm i r r o r s u p p o r t e d 1 5 c m ( 6 i n . ) from t h e p r e s s u r e v e s s e l ' s

o u t e r s u r f a c e . T h e m i r r o r d i r e c t s t h e beam b ac k i n t o ab a c k s c a t t e r d e t e c t o r . A s a p a r t i c l e e n t e r s t h e i n s t r u m e n t ' sf i e l d of view, i t s shadow i s imaged onto a p h o t o d i o d e a r r a yd e t e c t o r , w h e r e i t s shadow s i z e i s measured and recorded .

The i ns t ru me n t weighs 4.4 kg ( 9 . 6 l b . ) a nd u s e s 2 0 w a t t s .

Larqe and S m a l l P r o b e I n s t r u m e n t s

A t m os p he ri c S t r u c t u r e E x p e ri m e n ts -- T h e s e i n v e s t i g a t i o n s

d e t e r m i n e V en us ' a t m o s p h e r i c s t r u c t u r e f ro m 200 km ( 1 2 0 m i . )

t o impac t a t f o u r e n t r y s i t e s w e l l s e p a r a t e d from o n e a n o t h e r .

T em p er at ur e, p r e s s u r e a nd a c c e l e r a t i o n s e n s o r s on a l l f o u r

p r o b e s y i e l d d a t a on t h e l o c a t i o n a nd i n t e n s i t i e s of atmos-p h e r i c t u r b u l e n c e , t h e v a r i a t i o n of t e m p e r a t u r e s w i t h pres-

s u r e and a l t i t u d e , th e a v e r a g e a t m o s p h e r i c m o l e c u l a r w e i g h tand the r a d i a l d i s ta n c e t o t h e c e n t e r o f V enus. I f t h eP r ob e s s u r v i v e i mp a ct ( a remote p o s s i b i l i t y ) , t he y w i l l re -

v e a l a n y se i smic a c t i v i t y i n t h e c r u s t of t h e p l a n e t .

Each h as o n e f r e e w i r e e le m en t p r o t r u d i n g i n t o t h e a tm o sp he ref o r maximum s e n s i t i v i t y and one e l emen t bonded t o t h e s u p p o r tframe f o r maximum s u r v i v a b i l i t y .r a n g e p e r m i t s it t o r e c o r d t e m p e r a t u r e s f r o m b e l o w f r e e z i n gt o 4 70 d e g r e e s C ( 9 0 0 d e g r e e s F.).

T h e t e m p er a tu r e s e n s o r s a re d u a l resistance.thermometers.

I t s e x t r e m e t e m p e r a t u r e

P r e s s u r e s e n s o r s a r e m u l t i p l e r an ge , m i n i a t u re s i l i c o n

d iaphragm se ns o r s . The w i d e r ange needed f r o m 30 m i l l i b a r st o 1 0 0 b a r s p r e s s u r e i s a c h i e v e d b y 1 2 s e n s o r s of o v e r l a p p i n gs e n s i t i v i t y . T h i s a l s o p r o v i d e s r e d u nd a nc y i n case of a

s e n s o r m a l f u n c t io n .

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on e

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A c c e l e r a t i o n s e n s o r s ( f o u r o n t h e l a r g e r pr o b e, o nech of t h e s m a l l p r o b e s ) h a v e p e n d u l o u s mass, main-

t a i n e d i n n u l l ( z e r o ) p o s i t i o n by t h e i n t e r a c t i o n of ac u r r e n t i n a c o i l i n s i d e t h e m a s s w i t h a m a gn e ti c f i e l d .The n u l l i n g c u r r e n t i s t h e measure of a c c e le r a t ion .

An e l e c t r o n i c s p a ck a ge d i s t r i b u t e s power t o a l l sen-s o r s , s am ple s t h e i r o u t p u t , c ha ng es t h e i r r a n g e s a n d s t o r e s

d a t a .

T he i n s t r u m e n t s o n t h e L a r g e P r o b e w ei gh 2 . 3 k g ( 5 . 1l b . ) a nd u s e 4 . 9 w a t t s . On each o f t h e Sm al l P rob es t h ei n s t r u m e n t s w ei gh 1 . 2 kg ( 2 . 7 l b . ) a nd u s e 3 .5 w a t t s .

Nephelometer -- The n e p he l om e t er s e a r c h e s f o r c l o u d

p a r t i c l e s ( s o l i d o r l i q u i d ) i n t h e l o w e r atmosphere f rom6 7 k m ( 4 0 m i . ) t o t h e s u r f a c e . By p r o v i d i n g a l l f o u r p r o b e sw i t h n e p he l om e t er s , i n v e s t i g a t o r s can d e t e r m i n e w h e t h e r

c l o u d l a y e r s v a r y fro m l o c a t i o n t o l o c a t i o n o r a re u n i f o r m l yd i s t r i b u t e d a c r o s s t h e p l a n e t .

A l i g h t e m i t t i n g d i o d e (LED) of 9 , 0 0 0 A n g s t r o m s t o g e t h e rw i t h a p l a s t i c F r e s n e l l e n s f o r f o cu s i ng t h e l i g h t i l l u m i n a t et h e a t m o s p h e r e t h r o u g h a window mounted i n t h e p ro b e p r e s s u r e

vesse l . The t r a n s m i t t e d l i g h t beam i s p r o j e c t e d a d i s t a n c eb ey on d t h e t u r b u l e n t a t m os p h er e s u r r o u n d i n g t h e p r o b e s a st he y descend . Through a second window, a r ece ive r m easurest h e i n t e n s i t y of l i g h t b a c k s c a t t e re d ( a bo u t 1 7 5 d e g r e e s ) b ya t m o s p h e r i c p a r t i c l e s . B ot h windows a r e p r o t e c t e d f ro m t h es e a r i n g t e mp e r at u re s of t h e Venusian a tmosphere and f roms t r a y l i g h t .

I n v e s t i g a t o r s w i l l u s e t h e backw ard l i g h t s c a t t e r i n g

p r o p e r t y of c l o u d s an d h a z e s t o c o n s t r u c t a v e r t i c a l p r o -f i l e o f p a r t i c l e d i s t r i b u t i o n i n t h e l ow er a tm osphere . I n

a d d i t i o n , t h e t w o s m a l l p r o b e s d e s c e n d i n g i n t h e s u n l i ts i d e w i l l b e m ea su rin g t h e v e r t i c a l d i s t r i b u t i o n of s o l a r

s c a t t e r e d l i g h t a t 3,500 Angstroms and 5,300 Angstroms.

T he i n s t r u m e n t w e ig h s 1.1 kg ( 2 . 4 l b . ) a nd u s e s 2 . 4w a t t s .

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S m a l l Probe ExDer iments

N e t F l u x Radiometer -- T h i s i n s t ru m e n t maps t h e p la n e-t a r y p o s i t i o n s of s o u r c e s a nd absorbe rs of r a d i a t i v e e n e r g y

and t h e i r v e r t i c a l d i s t r i b u t i o n . T h e d i s t r i b u t i o n of r a d i a -t i v e e n er gy ( h e a t a nd s u n l i g h t ) p ow er s t h e a t m o s p h e r i c c i r -

c u l a t i o n o n V e n u s a s w e l l a s E a r t h . T h e i n s t r u m e n t d a t a w i l lb e r e l a t e d t o t h e o b s er v e d a t m o s p h e r i c m o t i o n s , t e m p e r a t u r es t r u c t u r e and c lo u d c h a r a c t e r i s t i c s f r o m o t h e r P i o n e e r V e n u se x p e r i m e n t s t o g a i n a more a c c u r a t e p i c t u r e o f V en us ' w e a -t h e r m a ch in e .

The i n s t r u m e n t s o n each of t h e t h r e e S m a l l P r o b e s a r e

i d e n t i c a l a nd c a n o p e r a t e e qu a l ly i n e i t h e r day o r n i g h th e m i s ph e r e s . F o l l ow i n g d e s c e n t i n t o t h e lower a tm ospherebelow 72 km ( 4 5 m i . ) t h e i n s t r u m e n t ' s s e n s or i s dep loyedf r o m a p r o t e c t i v e e n c l os u r e t o a p o s i t i o n l o c a t i n g it beyond

t h e t u r b u l e n c e n e a r t h e b a s e of t h e h e a t s h i e l d . Data col-l e c t i o n c o n t in u e s u n t i l i mp ac t.

The i n s t r u m e n t ' s f l u x p l a t e i s o r i e n t e d p a r a l l e l t o t h ep l a n e t ' s s u r fa c e . A d i f f e r e n c e be tween upward and downwardr a d i a n t e ne rg y f a l l i n g o n t h e two s i d e s of t h e p l a t e p ro du ce sa t e m p e r a t u r e g r a d i e n t t h r o u g h it , w hich indu ces an e l e c t r i c a l

c u r r e n t . The p l a t e i s f l i p p e d 1 8 0 d e g r e e s e v e r y s e co n d t oa s s u r e e ve n d a t a c o l l e c t i o n .

The i n s t r u m e n t w e ig hs 1.1 kg ( 2 . 4 l b . ) a n d u s e s 3 . 8 w a t t s .

MultiDrobe Bus ExDeriments

N e u t r a l Mass S p e c t r o m e t e r -- T h e n e u t r a l m a s s s p e c t r o -m e t e r m e a s u r es t h e v a r i o u s co mp on en ts (atoms a n d m o l e c u l e s )of t h e a t m o s p he r e s a nd t h e i r v e r t i c a l d i s t r i b u t i o n f r o ma b o u t 1 , 0 0 0 km ( 6 0 0 m i . ) t o 130 km (8 0 m i . ) , em phas iz ingt h e a l t i t u d e r an ge 1 5 0 t o 1 2 0 km (90 t o 75 m i . ) w h i c h n e i t h e rt h e O r b i t e r n o r t h e f o u r p r o b e s reach . ( T h e Bus i s e x p e c t e dt o b u r n u p a t a n a l t i t u d e of a b o u t 1 2 0 km ( 7 5 m i . ) .

From t h e i n s t r u m e n t d a t a , i n v e s t i g a t o r s c a n d e r i v e t h eh e i g h t o f th e t u r b op a u s e ( t h e r e g i o n a bo ve w hi ch a t m o s p h e r i cg a s e s do n o t m i x ) , f i n d t h e r a t i o s of a t m o s p h e r i c i s o t o p e sa nd d e r i v e eddy d i f f u s i o n c o e f f i c i e n t s (mathematical e x p r e s -

s i o n s d e s c r i b i n ghow

r a p i d l y t h e a tm o sp h er e i s m i x e d ) .T h e

c o m p o s i t i o n of t h e i o n o s p h e r e ' s maximum d e n s i t y c a n a l s o b e

d e t e r m i n e d , a s w e l l a s t h e t e m p e r a t u r e o f t h e e x o s p he r e, t h eo u t e rm o s t f r i n g e of Venus ' a tm osphere .

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T he i n s t r u m e n t i o n i z e s a t m o s p h e r i c co mp on en ts u p t o 4 6

a t o m i c mass (hydrogen t o i r o n ) by e l ec t r o n bombardment. I tt h e n s e p a r a t e s them a c c o r d i n g t o t he i r masses by how f a rt h e y a re d e f l e c t e d by a m a g n e t i c f i e l d . The i n s t r u m e n t f e a -t u r e s a f a s t d a t a s am p li ng an d t e l e m e t e r i n g c a p a c i - ty t o copew i t h t h e 3 km-per-second ( 1 1 0 mph) Bus d e sc en t sp ee d. One

d ay b e f o r e Venus e n c o u n t e r , a known amount of g a s i s r e l e a s e di n t o t h e i n s tr u m e n t f o r i d e n t i f i c a t i o n a nd measurem ent, t o b eused a s a r e f e r e n c e f o r t h e s pe c t ro m e t er ' s s e n s i t i v i t y .

T he i n s t r u m e n t w e ig h s 6 . 8 kg ( 1 5 l b . ) a nd u s e s 5 w a t t s .

I o n Mass S p e c t r o m e t e r -- The ion mass s p e c t r o m e t e rm ea su re s t h e d i s t r i b u t i o n an d c o n c e n t r a t io n of p o s i t i v e l yc h a r g e d i o n s i n t h e u p p e r Venus a t m o s ph e r e fr om 1 2 0 km ( 75m i . ) up t h r o u g h t h e i o n o s p h e r e .

(See O r b i t e r I o n Mass S p e c tr o m e te r f o r i n s t r u m e n td e s c r i p t i o n . )

M u l t i p r o b e R a d io S c i e n c e E x p e ri m e n ts

D i f f e r e n t i a l Long B a s e l i n e I n t e r f e r o m e t r y -- T h i si n s t r u m e n t m e as ur es t h e v e l o c i t y a nd d i r e c t i o n o f V en us 'winds a s t h e f o u r p r o b e s d e sc e nd t h r o u g h t h e a t m o sp h e re .By c om p ar in g t h e d e s c e n t p a t h s o f t h e p r o b e s w i t h s i m u l -t a n e o u s m e as ur em e nt s o f a t m o s p h e r i c t e m p e r a t u r e a n d p r e s -s u r e fro m p r ob e s e n s o r s , i n v e s t i g a t o r s c a n a ss e mb l e a b e t t e rmodel of V enus ' a t mo s ph e ri c c i r c u l a t i o n , p a r t i c u l a r l y i nr e g a r d t o wind speeds .

W h il e t h e f o u r p r o b e s d e s c en d t o t h e s u r f a c e , t h e Busf o l l o w s a b a l l i s t i c t r a j e c t o r y i n t h e up pe r atm os ph ere .T h i s t r a j e c t o r y s e r ve s a s a r e f e r e n c e . P r o b e v e l o c i t i e sc a n b e r e c o n s t r u c t e d and mea su re d v e r y a c c u r a t e l y r e l a t i v e

t h e b u s , an d a b s o l u t e p ro b e v e l o c i t i e s c an b e r e c o n s t ru c t e df ro m t h e known b u s v e l o c i t y .t i o n s of t h e p ro b e t r a j e c t o r i e s fro m a n a t m o sp h e r el e s sma thema t i ca l mode l a r e c a u s e d by a t m o s p h e r i c w in d s .

I n v e s t i g a t o r s assume d e v i a -

Two w i d e l y s e p a r a t e d D S N s t a t i o n s s im u l t a ne o us ly t r a c k i n ga l l s p a c e c r a f t d et er mi ne t h a t p a r t o f t h e v e l o c i t y v e c t o ra l o n g t h e E arth -V en us l i n e o f s i g h t . D i f f e r e n t i a l l on g -b as edi n t e r f e ro m e t r y u se s t h r e e D S N s t a t i o n s t o f i n d t h e o t h e r two

c om po ne nts of t h e v e l o c i t y v e c t o r t o t r i a n g u l a t e o r g e t a" f i x 1 ' i n t h r e e d im e ns io ns o n t h e c o n s t a n t l y c h an g in g p a t h sof t h e f a l l i n g p r ob es .

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Atmospher i c P ro pa ga t io n Exper imen t -- T h i s i n v e s t i g a -t i o n a t te m p t s t o g l e a n in f o rm a t i on a b o u t V enus ' s u r f a c ea nd a tm o sp h er e by t h e e f f e c t s o f t h e a t m os p he r e o n t h ep r o be s ' r a d i o s i g n a l s . A s t h e p r ob e s d es c e nd , P i o n e e rs c i e n t i s t s s e a r c h f o r e v id en ce of a v e r y weak s i g n a l t h a tt r a v e l s downward, r e f l e c t s o f f t h e s u r f a c e of Venus and

t h e n b o u n ces t o E ar t h . S u ch a d i s t o r t e d s i g n a l i s Dopplers h i f t e d away fr om t h e pr o b e s i g n a l of 2 , 3 0 0 M H z ( m i l l i o nHe r t z ) by l e s s th a n Hz and i s a lm os t u n d e te c t a b l e . I f t h i ss i g n a l i s d i s c o v e r e d , i t s h o u ld r e v e a l i n f o r m a t i o n a b o u tt h e V e nu si an s u r f a c e -- h en ce , a i d i n t h e i n t e r p r e t a t i o no f t h e r a d a r m ap pin g d a t a .

The descend ing p robe s a l s o r e v e a l i n f or m a t io n a b o u tt h e a t m o s ph e r e . P r o b e r a d i o s i g n a l s weaken w i t h d e c r e a s i n ga l t i t u d e due t o C 0 2 a b s o r p t i o n , a tm o sp he re r e f r a c t i o n a nda d d i t i o n a l a b s o r p t i o n from c l o u d l a y e r s o r some o t h e r a b-s o r b e r . The s t r e n g t h o f t h e p r ob e s i g n a l s s h o u ld r e v e a lth e unknown ab so rbe r : i f i t i s a c l ou d l a y e r , i n v e s t i g a t o r sc a n m ea su re t h e h e i g h t and t h i c k n e s s o f t h e l a y e r .

Atmospher i c Turbu lence Exper imen t s -- T h i s i n v e s t i g a -t i o n s t u d i e s t h e t u r b u l e n c e i n t h e Ve nu si an a tm o sp he re , t h u sa i d i n g i n t h e u n d e r s t a n d i n g o f t h e d yn am ic s o f V en us 'p h er e c i r c u l a t i o n .t h e i r t r a n s m i t t i n g s i g n a l s w i l l l i k e l y be d i s t o r t e d by s m a l lr e g i o n s o f t u r b u l e n c e c a u s e d b y t e m p e r a t u r e , p r e s s u r e andv e l o c i t y f l u c t u a t i on s . D S N r e c e i v i n g s t a t i o n s o n E a r t h w i l la n a l yz e t h e s i g n a l s f o r d i s t o r t i o n c a u se d by a t m os p he r ic t u r -bu le nce . The p robe d a t a com pl em en ts a t m o s p h e r i c t u r b u l e n c ed a t a a b o v e 35 km ( 2 1 m i . ) t a ke n by t h e O r b i t e r .

atmos-A s a l l f o u r p r ob es d es ce nd t o t h e s u r f a c e ,

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PRINCIPAL INVESTIGATORS AND SC IENT IF IC INSTRUMENTS

O r b i t e r S p a c e c r a f t

D r . James Hansen

Goddard I n s t i t u t e o f S p a c eS t u d i e s

D r . G ordon P e t t e n g i l l( T e a m L e a d e r ) , M a s s a c h u s e t t sI n sti u t e o f T e ch n ol og y

D r . F r e d r i c T a y lo r

J e t P r o p u l s i o n L a b o r a t o r y

D r . I a n S t e w a r tU n i v e r s i t y o f C o l o r a d o

D r . Hasso NiemannG od da rd S p a c e F l i g h t C e n t e r

H a r r y T a y l o rG od dard S p a c e F l i g h t C e n t e r

D r . J o h n W o l f e

A m e s R e s e a r c h C e n t e r

D r . C h r i s t o p h e r R u s s e l l

U n i v e r s i t y of C a l i f o r n i a ,L o s A nge le s

D r . F r e d e r i c k S c a r fTRW, I n c .

L a r r y Br ace

Goddard Space F l i g h t C e n t e r

D r . W i l l i a m KnudsenLockheed M i s s i l e s an d

S p a c e C o .

D r . W . D . Evans

Los A l a m o s S c i e n t i f i cL a b o r a t o r y

C loud P o l a r i m e t e r , I m a g ing

Exper im en t

Radar Mapper

T e m p e r a t u r e S o u n d i n g

I n f r a r e d R ad io m ete r

U l t r a v i o l e t S p e c t r o m e t e r

N e u t r a l Mass S p e c t r o m e t e r

Ion Mass S p e c t r o m e t e r

So l a r W ind /P l a s m a A n a l y z e r

Magnetometer

E l e c t r i c F i e l d De te c to r

E l e c t r o n T e m p er a tu r e P r o b e

R e t a r d i n g P o t e n t i a l A n a l y z e r

G a m m a Ray B u r s t D et ec t o r

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O r b i t e r R a d i o S c i e n c e

R a d io s c i e n c e e x p e r im e n t s m ea su re i n t e r a c t i o n ofs p a c e c r a f t r a d i o s i g n a l s w i t h V enus a nd i t s a tmosphe re ,u s i ng t h e O r b i t e r a n d f i v e pr ob e c r a f t a s i n s t r u m e n t s .D r . Gordon P e t t e n g i l l , M a s sa c hu s et ts I n s t i t u t e of Tech-

nology, i s team l e a d e r .

D r . R og er P h i l l i p s Venus I n t e r n a l D e n s i tyJ e t P r o p u l s i o n L a b or a to r y D i s t r i b u t i o n

D r . I . I . S h a p i r oM a ss ac hu se tt s I n s t i t u t e

of Technology

C e l e s t i a l Mechanics

D r . A rv yd as K l i o r e R ad io O c c u l t a t i o nJ e t P r o p u l s i o n L a b o r a t o r y

D r . Thomas C r o f t R a d io O c c u l t a t i o n

S t a n f o r d Research I n s t i t u t e

D r . R i c h a r d Woo Atmospher i c and S o l a r CoronaJ e t P r o p u l s i o n L a b o r a t o r y

D r . G e r a l d K e a t i n gL a n g l e y R e s e a r c h C e n t e r

Atmospheric Drag

M u l t i p r o b e S p a c e c r a f t ( L ar g e P r ob e )

D r . John Hoffman Mass S p e c t r o m e t e rU n i v e r s i t y of Texas , D a l l a s

Vance OyamaAmes Research C e n t e r

A l v i n S e i f fAmes R e s e a r c h C e n t e r

D r . M a r t i n TomaskoU n i v e r s i t y of A r i z o n a

R o b e r t B o eseAmes R e s e a r c h C e n t e r

G a s Chromatograph

A t m o s p h e r e S t r u c t u r e

S o l a r Flux Radiometer

I n f r a r e d R a d i o m e t e r

D r . R o b e r t K n o l l e n b e r g Cloud P a r t i c l e S i z eP a r t i c l e Measur ing Sys tems , I n c . S p e c t r o m e t e r

D r . B o r i s RagentAmes Research C e n t e r

D r . Jacques Blamont

U n i v e r s i t y of P a r i s

N e p he l om e te r ( c l o u d s e n s o r )

Nephelometer

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M u l t i p r o b e S p a c e c r a f t (Three S m a l l P r o b e s )

A l v i n S e i f f

Ames R e s e a r c h C e n t e r

D r . B o r i s R a ge ntA m e s R e s e a r c h C e n t e r

D r . Jacques BlamontU n i v e r s i t y of P a r i s

A t m o s p h e r e S t r u c t u r e

Nephelometer

Nephelometer

D r . V e r n e r Suomi N e t F l u x R a d i o m e t e r

U n i v e r s i t y o f W i sc o ns i n

M u l t i p r o b e S p a c e c r a f t (B us )

D r . Ulf von ZahnU n i v e r s i t y of Bonn,W e s t Germany

Mass Spec t rometer

H a r r y T a y l o r I o n M a s s S p e c t r o m e t e r

Goddard S p ac e F l i g h t C e n t e r

M u l t i p r o b e R a di o S c i e n c e ( A l l Probes )

D r . C h a r l e s C . C ou nse lm an D i f f e r e n t i a l L o n g- B a se l in eM a s sa c hu s et ts I n s t i t u t e of I n t e f e r om e tr y

Technology

D r . Thomas C r o f t A t m o s p h e r i c A t t e n u a t i o n

S t a n f o r d R es ea rc h I n s t i t u t e

D r . R i c h a r d Woo Atm osp heri c Tu rb ul en ce

J e t P r o p u l s i o n L a b o r at o r y

I n t e r d i s c i p l i n a r y S c i e n t i s t s

I n t e r d i s c i p l i n a r y s c i e n t i s t s hav e b een se lec ted f o rb o t h t h e Mul t ip robe and O r b i t e r M i s s i o n s t o p r o v i d e a s s i s -t a n ce i n a n a l y se s of t h e Venus ian a tmosphe re . They are :

D r . S i e g f r i e d B a u e rG od dard S p a c e F l i g h t C e n t e r

D r . Thomas Donahue

U n i v e r s i t y of Michigan

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-120-

D r . R ic ha r d G oody

H a r v a r d U n i v e r s i t y

D r . Dona ld HuntenU n i v e r s i t y of A r i z o n a

D r . James P o l l a c k


Nelson S p e n c e r

G od dard S p a c e F l i g h t C e n t e r

H a r o l d M a s u r s k y

U .S. G e o l o g i c a l S u r v e y

D r . G e or ge M c G i l l

U n i v e r s i t y of M a s s a c h u s e t t s

D r . Andrew NagyU n i v e r s i t y of M i c h i g a n

D r . G e r a ld S c h u b e r t

U n i v e r s i ty o f C a l i f o r n i a , L o s A n g e l e s

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M I S S I O N OPERATIONS

F o r Pioneer V en us , m i s s i o n c o n t r o l l e r s w i l l be o p e r a t -i n g s i m u l t a n e o u s l y t w o d i f f e r e n t s p a c e c r a f t on t w o d i f f e r e n tm i s s i o n s . T h e O r b i t e r a n d M u l t i p r o b e w e r e l a u n c h e d w i t h i n

t h r e e m on th s of e a ch o t h e r to a r r i v e a t t h e p l a n e t l e s st h a n a week apar t .

D u ri n g t h e Venus e n c o u n t e r p e r i o d , l a u n c h o f t h ef o u r p ro b es from t h e t r a n s p o r t e r Bus t o t h e i r a t m o s p h e r i ce n t r y p o i n t s w i l l be accom pl i shed ; th e Bus w i l l b e r e t a r -g e t ed f o r i t s e n t r y : t h e O r b i t e r w i l l be p l a c e d on i t s

24-ho ur, h i g h - i n c l i n a t i o n , h i g h l y e l l i p t i c a l o r b i t . F i ved ay s a f t e r O r b i t e r e n c o u nt e r , p ro be e n t r y w i l l be moni-t o r e d , and t h e c r i t i c a l p ro be d a t a r e c e i v e d and s t o r e df o r l a t e r a n a l y s i s .

W ith c o m p le t i o n o f t h e M u l t ip r o b e m i s si o n - - a f t e r i m -

p a c t o f t h e p r o b e s on t h e s u r f a c e an d b u rn -u p o f t h e Busc o n t r o l l e r s w i l l c o n t i n u e t o o p e r a t e t h e O r b i t e r f o r t h e

e i g h t m on th s o f i t s pr im ary m iss ion . C o n t ro l l e r s may makes i g n i f i c a n t changes i n t h e o r b i t d u r i n g t h i s e xt en de dm i s s i o n p e r i o d .

c r a f t , m i s si o n o p e r a t i o n s o f t e n r e q u i r e 24-hour-a-dayc o n t r o l and c a r e f u l a n a l y s i s a nd p la n ni n g i n s h o r t t i m e

s p a n s. G r ou n d- c on t ro l le d s p a c e c r a f t p r o v id e f l e x i b i l i t yf o r c h an g in g p l a n s and o b j e c t i v e s . They a l s o o f f e r e co n-o mies i n s p a c e c r a f t d e s i g n and c o n s t r u c t i o n .

S i n c e a l l P i o n e e r s a r e r e l a t i v e l y u n au to ma te d sp a ce -

P i o n e e r Venus c o n t r o l an d s p a c e c r a f t o p e r a t i o n s w i l l

be a t t h e P i o n e e r M i s s i o n O p e r a t i o n s C e n t e r ( P M O C ) , Ames

R esea rch C en te r , M ounta in V i e w , C a l i f . , fro m t h e t i m e b o t hs p a c e c r a f t s e p a r a t e from t h e i r l au nc h v e h i c l e s t h ro ug ht h e e nd of t h e O r b i t e r m is s i on .

P i o n e e r Venus o p e r a t i o n s w i l l be made somewhat morecom plex by t h e c o n t i n u e d o p e r a t i o n a t t h e PMOC o f t h ep r e v i o u s l y l a un c he d P i o n e e r s p a c e c r a f t . P i o n e e r s 6 t o 9c o n t i n u e t o c i r c l e t h e Sun and r e t u r n i n t e r p l a n e t a r y d a t a .P i o n e e r 1 0 c o n t in u e s t o e n t e r p r e v i o u s l y u ne xp lo re ds p a c e o n i t s way o u t o f t h e s o l a r s y st e m (it s now ap-p r a c h i n g U ra nu s' o r b i t ) . P i o n e e r 11 i s descend ing backto war d t h e e c l i p t i c and ma n's f i r s t e n co u nt e r w i t h S a t u rni n September 1 9 7 9 .

The PMOC i s t h e c e n t r a l mi s si o n c o n t r o l c e n t e r . I t

i s u nd er o p e r a t i o n a l d i r e c t i o n of t h e F l i g h t D i r e c t o r .T h i s a r e a will o r i g i n a t e a l l command i n f o r m a t i o n a nd re-

ce ive and d i s p l a y t e l e m e t r y d a t a r e q u i r e d f o r m i s s io n c on-t r o l . A l t h o u g h a l l commands a re o r i g i n a te d i n t h e PMOC,emergency p roced ures in c l ud e backup command gen er a t io n a tt h e D S N s t a t i o n s , i f n e c es sa ry .

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The PMOC h a s c om pu ti ng c a p a b i l i t y b o t h f o r commandingt h e two s p a c e c r a f t and f o r i n t e r p r e t i n g t h e d a t a s t r e ama s it i s r e c e i v e d f r o m t h e D S N s t a t i o n s f o r u se by f l i g h tc o n t r o l l e r s m o n i t or i n g s p a c e c r a f t p er fo rm an ce .

S e v e r a l g r o u p s of s p e c i a l i s t s d i r e c t an d s u p p o r t l a u n chi n t e r p l a n e t a r y , o r b i t a l a nd at m os p he r ic e n t r y o p e r a t i o n s .

T h e P i o n e e r M i ss i o n O p e r a t i o n s t ea m c o n s i s t s o f p e r -s o n n e l f rom g ov er nm en t an d c o n t r a c t o r o r g a n i z a t i o n s , ando p e r a t e s u nd er c o n t r o l of t h e P r o j e c t Manager and Mi ssi onOperat ions System Manager.

B ecause P ion ee r V enus i nc lu de s two m i ss io ns , t w of l i g h t o p e r a t i o n s g r ou p s h av e be en named fo r each- -an O r -

b i t e r group and a Mult ipro be group. Both groups have t h e

same e l e m e n t s . The Sc i en ce A n a ly s i s Team i n each groupi s composed o f s c i e n c e o p e r a t i o n s p e o p l e f ro m t h e p r o j e c t

and t h e p r i n c i p a l i n v e s t i g a t o r s (o r t h e i r r e p r e s e n t a t i v e s )f o r each exper im en t on boa rd t h e O r b i t e r and M ul t ip robe .They determine t h e s t a t u s o f ea ch s c i e n t i f i c i n st r u me n t ,and fo rm u la t e command sequences f o r th e ins t ru m e nt s .

Both groups a l s o have Sp ac ec ra f t Pe r form ance A na ly -s i s teams, made up of e n g i n e e r in g s p e c i a l i s t s on s pa ce -c r a f t s y st em s s uc h as : communicat ions , t h e r m a l c o n t r o la nd p ow er. T he se t ea ms a n a l y z e a nd e v a l u a t e s p a c e c r a f tp e r fo r m a n ce a nd p r e d i c t s p a c e c r a f t r e s p o n s e s t o commands.

A t h i r d o r g a n i z a t i o n s e r v es b ot h s p a c e c r a f t . T h i s i st h e N av ig a t ion and Maneuver s g roup , which h a n d l e s space-

c r a f t n a v ig a t io n and o r i e n t a t i o n i n s pa ce ; o r b i t a l i n j e c -t i o n , t r i m , and c h an g es a nd p r o b e - t a r g e t i n g a nd l a u n c h .T h i s group is made up o f e n g in e e r i n g s p e c i a l i s t s i nsp a c e c r a f t o r i e n t a t i o n g eo m et ry , t r a j e c t o r i e s , and maneu-v e r s . The J e t P r o p u l s i o n L a b o r a t o r y , u nd er c o n t r a c t t oAmes, does c om p ut er a n a l y s i s o f D S N t r a c k i n g i n f o r m a t i o nt o d et er mi ne s p a c e c r a f t t r a j e c t o r i e s .

The M iss ion O p era t io ns Team a l s o i n c l u d e s a l a u n chs p e c i a l i s t , a h ar dw ar e e x p e r t and a computer sys tems de-

v e lo p me n t an d o p e r a t i o n s g r o u p .

S u p p o r t g r o u ps a t Ames a n d o t h e r 3ASA f a c i l i t i e s a s-

s i s t t h e m i s s i o n o p e r a t i o n s t ea m t o per fo rm com pute r so f tya red ev el op m en t, m i s s i o n c o n t r o l and o f f - l i n e d a t a p r o c e s s i n g .

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DATA RETU RN, COMMAND AND TRACKING

N A S A ' s Deep S pac e Network ( D S N ) w i l l t r a c k a n d re -

c e i v e d a t a d i r e c t l y from a l l s i x P i o n e e r Venus s p a c e c r a f t( t h e O r b i t e r , t h e Bus a nd t h e f o u r p ro b e s ) . Commands a r e

t r a n s m i t t e d t o s p a c e c r a f t f ro m t h e P i o n e e r M i s si o n Ope ra-t i o n s C o n t r o l C e nt e r th r o u g h t h e D S N s t a t i o n s .

T r a c k i n g w i l l b e by t h e DSN's g l o b a l n e tw or k o f 2 6 - m( 8 5 - f t . ) and h i g h l y s e n s i t i v e 64-m ( 2 1 0 - f t . ) a n t e n n a s . The 6 4 s

w i l l be u s e d d u r i n g c r i t i c a l p h a s e s of t h e m i s s io n s u c h a sr e o r i e n t a t i o n , v e l o c i t y c o r r e c t i o n s , o r b i t i n s e r t i o n , and

e n t r y of t h e f o u r p ro b e s i n t o Ve nu s' a tm o sp h er e -- as w e l la s f o r s p e c i a l s c i e n c e e v e n t s s uc h a s o c c u l t a t i o n . A t t h ee nd o f t h e O r b i t e r p r im a r y m i s s i o n , Venus w i l l be 2 0 3

m i l l i o n km ( 1 2 6 m i l l i o n m i . ) f a r t h e r from E a r t h t h an a tO r b i t e r a r r i v a l .

D u r i n g t h e c r i t i c a l two-hour p e r io d o f a tm osphe r i ce n t r y by t h e Bus a nd f l i g h t s down t o t h e s u r f a c e by t h ef o u r p r o b e s , b o t h t h e 6 4 - m ( 2 1 0 - f t . ) a n t e n n a s a t G o l d s t o n e ,C a l i f . , and a t C a nb e rr a , A u s t r a l i a , w i l l be used t o re-

ce iv e and reco rd Venus a tm osphere da ta , com ing i n s im ul -t a n e o u s l y f r o m a l l f i v e p ro be c r a f t .

The Deep Space N e t w o r k w i t h f a c i l i t i e s l o c a t e d a ta p p r o x im a t e l y 1 2 0- de g re e i n t e r v a l s a r ou n d t h e E a r t h , w i l ls u p p o r t t h e P i o n e e r Venus s p a c e c r a f t . The p r i m a r y m i s s i o n

o f t h e O r b i t e r i s 1 5 , m o n t h s : s i x months i n t r a n s i t and e i g h tmonths i n o r b i t . A s t h e O r b i t e r and M ul t ip robe " s e t " a tone s t a t i o n due t o t h e E a r t h ' s r o t a t i o n , t he y w i l l r i s e

a t t h e n e x t o ne .

The D S N , o p e r a t e d by t h e J e t P r o p u l s i o n L a b o r a to r y( J P L ) , P as ad en a, C a l i f . , h a s s i x 26-ml ( 8 5 - f t . ) p a r a b o l i c - r e -f l e c t o r d i s h a n t en n as , t w o a t G old sto ne , i n C a l i f o r n i a ' sMojave D e s e r t ; two a t Madrid , S pai n and t w o a t C anber ra .

T h e r e a re a l s o t h r e e 64-m ( 2 1 0 - f t . ) a n t e n n a s , o ne e a c h a t Gold-s tone , M adr id and C anber ra .

R ad io s c i e n c e e x p e r i m e n t e r s w i l l e s t im a te wind speeds

a nd d i r e c t i o n s i n t h e Venus a t m os p h er e by c om pu ti nq t h et h e e x a c t f l i g h t pa t h s of t h e f o u r p ro be s u s in g D S N d a t a .I n a d d i t i o n t o t h e G ol ds to n e and C an b er ra s t a t i o n s , two

NASA S T D N s t a t i o n s a t Guam an d S a n t i a g o , C h i l e , w i l l sup-p o r t t h i s e f f o r t . Radio i n t e r f e r o m e t r y i n a t r i a n g u l a t i o np r o c e s s w i l l be u se d i n t h i s c o mp u ta ti on . (See M u l t i p r o b eExper im en t s - R a d i o S c i e n c e . )

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PIONEER VENUS COMMUNICATIONS NETWORK

GOLDSTONE,

DEEP SPACE MA DR ID,NETWORK (DSN)

/

SANTIAGO, SPACECRAFT G U ~ M ,C A N B ER R A ,

T R A C K IN G A N D D A T A S T D N D S NN ET WO R K ( ST D N )



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At all times, incoming telemetry data from the spacecraftis formatted at DSN stations for high-speed transmission toAmes computers. These computers will check for unexpected or

critical changes in data and provide information for analysisby specialists in the spacecraft, experiments and ground sys-

tem. Their analyses will be used for spacecraft control. Out-

going commands are verified by Ames computers and sent to DSN

stations where they are reverified by computer and then trans-mitted. Navigation data and trajectory computations for the

Pioneer spacecraft are furnished by JPL's Navigation System

Section under contract to Ames. They do computer analysis ofDSN Doppler and range tracking information to provide spacecraft

trajectories for calculation of Venus orbit and planetary

targeting.

For Pioneer Venus, the DSN has made a number of special

modifications. Added receivers are needed to handle the fivedifferent data streams at once of the four probes and Bus.

Special wideband recorders are required to cope with the largefrequency shifts which will happen with the changes in velocity

at entry -- and atmospheric effects on signal propagation asthe probes descend to Venus' surface. To save all of the one-

change-only data, due to variances outside the predicted range

of frequency changes, the DSN has provided special equipment toautomatically tune the receivers to the signal transmitted by

each probe.

Incoming telemetry is formatted at DSN stations for trans-

mission via NASA Communications System (NASCOM) high-speed cir-cuits to the pioneer Mission Computing Center (PMCC). There it

is processed to supply various types of real time display infor-

mation on spacecraft and instrument status.

In addition to use of telemetry for providing missionoperations and quick-look data, all telemetry will be processed

at the PMCC to provide data records for the individual experi-menters in the form of Experimenter Data Records. Provided to

principal investigators, it becomes the raw material for use by

them in producing mission findings.

For all of NASA's unmanned missions in deep space, the DSN

provides tracking information on course and direction of theflight, velocity and range from Earth. Its global stations

also receive engineering and science telemetry and send com-

mands. All communications links are in S-band frequency (though

Venus Orbiter occultation experiments are X-band carrier only).

No telemetry data are sent.

DSN stations relay spacecraft Doppler tracking to JPL. High

speed data links allow real time transmission of all data from

spacecraft directly to the PMCC at Ames. Throughout the mission,

scientific data recorded on magnetic tape will be sent from DSN

stations to Ames for processing.

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NASA H e a d q u a r t e r s

D r . N o e l H i n n e r s

Andrew J. S t o f a n

- 1 2 6 -

P I O N E E R VENUS TEAM

A . Thomas Young

D r . G e o f f r e y A . B r i g g s

F r e d D . Kochendor f e r

P a u l T a r ve r

D r . R o b e r t E . Murphy

J o h n F . Y a r d l e y

J o s e p h B . Mahon

F . R o b e r t S c h m i d t

D r . W i l l i a m C . S c h n e i d e r

A r n o l d C . B e l c h e r

Maurice E . B i n k l e y


C . A . S y v e r t s o n

D r . Dean R . Chapman

C h a r l e s F . H a l l

A s s o c i a t e A d m i n i s t r a t o r

f o r Space S c i e n c e

Deputy Asso c i a t e A d m i n i s -t r a t o r f o r S p ac e S c i e n c e

D i r e c t o r , P l a n e t a r y P r o g r a m s

D e pu ty D i r e c t o r , P l a n e t a r yP r o g r a m s

P i o n e e r Venus Program Manager

Deputy P i o n e e r Venus Pr ogr a m

Manager

P i o n e e r Venus Pr ogr a m

S c i e n t i s t

Asso c i a t e A d m i n i s t r a t o r f o rS p a c e T r a n s p o r t a t i o n S y s t e m s

V e h i c l e P r og ra m sD i r e c t o r , Expe nda b l e La unc h

Manager , A t l a s C e n t a u r

Assoc ia te A d m i n i s t r a t o r f o rS p a c e T r a c k i n g a n d D a t a

S y s t e m s

N e t w o r k O p e r a t i o n s

N e t w o r k S u p p o r t

Direc to r

Di rec to r o f A s t r o n a u t i c s

Pioneer Venus P r o j e c t Manager

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-127-

Ames R e se a rc h C e n t e r ( c o n t ' d . )

D r . Lawrence C o l in P io ne e r Venus P r o j e c t

S c i e n t i s t

Ralph W . H o l t z c l a w S pa ce c r a f t Sys tems Manager

J o e l S p e r a n s Exper iment Sys e m s Manager

R o b e r t U . H o f s t e t t e r M i s s io n O p e r a t i o n s M anager

Henry Asch R e l i a b i l i t y and Q u a l i t yAssurance

E r n e s t J . I u f e r M a g n e t i c s

J e t P r o p u l s i o n L a b o r a t o r y

D r . Bruce C . Murray

R i c h a r d B . M i l l e r

Eugene S . Burke , J r .

L e w i s R e s e a r c h C e n t e r

D r . John McCarthy

D r . Seymour C. H i m m e l

Lawrence J . R o s s

C a r l B . Wentworth

Edwin Muckley

Direc to r

Track ing and Data Sys temsManager

S u p e r v i s o r , D S N O p e r a t i o n sPlanning Group

D i r e c t o r

A s s o c i a t e D i r e c t o r

C h i e f , V e h i c l e s E n g in e e r i n gD i v i s i o n

C h i e f , P r o g r a m I n t e g r a t i o nD i v i s i o n

M i ss io n P r o j e c t E n g in e er

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-128-

Kennedy Space C e n t e r

D r . L e e R . S c h e r e r

G e r a l d D . G r i f f i n

D r . Walter J . Kapryan

George F . Page

J o h n D . G o s s e t t

Donald C . Sheppard

C . A . Terhune

B a r r y O l t o n

Hughes A i r c r a f t C o .

S . D . Dorfman

D i r e c t o r

Deputy Di r e c t o r

D i r e c t o r o f S p a c e V e h i c l eO p e r a t i o n s

D i r e c t o r , Expendab le V eh ic le s

Manager, C e n t a u r O p e r a t i o n s

M anager , S pa ce c r a f t andS u p p o r t O p e r a t i o n s D i v i s i o n

C h i e f E n g i n e e r , A t l a s C e n t a u r

KSC P r o j e c t E n g i n e e r f o r

P i o n e e r Venus

P i o n e e r Venus P r o j e c t Managerf o r Hughes

CONTRACTORS

Hughes A i r c r a f t C o .

Space and Communications GroupE l Segundo, C a l i f .

( P r i m e c o n t r a c t o r ) S p a c e c r a f t

and Radar Mapper

H u g h e s A i r c r a f t C o .

D a t a S y s t e m s D i v i s i o nC u l v e r C i t y , C a l i f .

Genera l E l e c t r i c C o .

P h i l a d e l p h i a , P a .

Motorola, I n c .Phoen ix , A r i z .

Thiokol Chemical Co .El kt on , Md.

D a t a S t o r a g e U n i t

De c e l e r a t i on Modules

T r a n s p o n d e r s

O r b i t I n s e r t i o n M otor

B a l l B r o t h e r s R e s e a rc h C o rp .B o u l d e r , Colo.

S t a r S e ns o rs

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- 1 2 9 -

N or th rop C orp .L o s A n g e l e s , C a l i f .

Thermal Louvers

S t a b l e O s c i l l a t o r sr e q u e n c y E l e c t r o n i c s , I n C .

N e w Hyde Park, N . Y .

Nickel-Cadmium Battery C e l l se n e r a l E l e c t r i c Co .

G a i n e s v i l l e , F l a .

S i l v e r - Z i n c B a t t e r y C e l l sa g l e - P i c h e r I n d u s t r i e s , I n c .Jo p l i n , Mo.

S o l a r C e l l s and Coversp e c t r o l a b , I n c .S y l m a r , C a l i f .

P r e s s u r e V e s s e l F o r g i n g sr c t u r n s M a n u f a c t u r i n g C o .

O x n a r d , C a l i f .

P r e s s u r e V e s s e l Machiningewbrook Machine Corp.S i l v e r C re ek , N . Y .

Southw es t R esea rch I n s t i t u t eSan A nton io , Texas

P r e s s u r e V e s s e l T e s t i n g

I n p u t B u f f e r si l i c o n i x , I n c.S a n t a C l a r a , C a l i f .

La rge Probe N e u t r a l MassS p e c t r o m e t e r

U n i v e r s i t y of Texas a tD a l l a s

L a r g e a n d S m a l l Pr obe Atmos-p h er e S t r u c t u r e I n s t r u m e n t s ,O r b i t e r P l a s m a A nalyze r

Western A e r o s p a c e L a b o r a t o r i e sG a r d e n a , C a l i f .

La rge and S m a l l P r o b eAccelerometers

Sys ron-DonnerC o n c o r d , C a l i f .

L a r g e P r o b e S o l a r F l u xR adiom ete r Sensor

U n i v e r s i t y o f A r i z o n aTucson, A r i z .

L a r g e Probe S o l a r F l u xRadiometer E l e c t r o n i c s

M a r t i n Ma r i e t t a Corp.Denver, Colo.

Large P r o b e I n f r a r e d R a d i o m e t e rand Cloud P a r t i c l e S i z eS p e c t r o m e t e r

B a l l B r o t h e r s R e s e ar c h C o rp .B ou lde r , C o lo .

L a r g e P r o b e G a s Chromatograph,Large and S m a l l Pro be Nephelo-meters, O r b i t e r E l e c t r i c

F i e l d D e t e c to r

TRW Systems GroupT RW, I n c .Redondo Beach, C a l i f .

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-130-

U n i v e r s i t y o f W is c o n s in

Madison, W i s . R a d i o m e t e r

S m a l l P r o b e N e t Flux

A ik en I n d u s t r i e s , I n c .C o l l e g e P a r k , Md.

M u l t i p r o b e Bus a nd O r b i t e rIon Mass S p e c t r o m e t e r s

Lockheed Missi l es and Space Co.

S u nn y va l e, C a l i f . A n al y ze r

O r b i t e r R e t ar d i ng P o t e n t i a l

IPWF r e i b u r g , W e s t Germany

U n i v e r s i t y of C o lo r a d oB o u l d e r , C o l o .

O r b i t e r R e ta r d in g P o t e n t i a l

O r b i t e r U l t r a v i o l e t S p e c t r o m e t e r

A n a ly z e r S e n s o r

U n i v e r s i t y o f C a l i f o r n i a a t O r b i t e r Magnetometer

L o s Angeles

Wes t inghouse , I n c .B a l t i m o r e , Md.

J e t P r o p u l s i o n L a b o r a t o r yP a s a d e n a , C a l i f .

M a s s a c h u s e t t s I n sti u eof Techno log y

Cambridge, Mass.

O r b i t e r M a g n e to m e te r

O r b i t e r I n f r a r e d R ad io me te r

M u l t i p r o b e a n d O r b i t e r G r o u n dB a s e d R a d io S c i e n c eE x p e r im e n t s

P a r t i c l e Measur ing Sys tems , I n c . L a r g e P r o b e C lo u d P a r t i c l e

B o u l d e r , C o l o . S i z e S p e c tr o m e te r

DC A R e l i a b i l i t y L ab or at or y

Mountain V i e w , C a l i f . a nd S c r e e n i n g

B e nd ix F i e l d E n g i n e e r i n g C o rp .

S u n n y v a l e , C a l i f . S o f tw a r e D e ve lo p me nt

E l e c t r o n i c P a r t s P r o c u r e m e n t

Miss ions O p e r a t i o n s a nd

General DynamicsC o n v a i r D i v i s i o nSan Diego, C a l i f .

L o s A l a m o s S c i e n t i f i c

L o s A l a m o s , N . M .

L a b o r a t o r y

S a n d ia L a b o r a t o r i e sAlbuquerque , N . .

Launch Vehic les

O r b i t e r G a m m a Ray B u r s t

De te c to r

O r b i t e r G a m m a R a y B u r s tD et ec t o r

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-131-

S an t a B a r b a r a R es ea r ch

S a n t a B a r ba r a, C a l i f .C e n t e r

U n i v e r s i t y of MinnesotaMinneapol is , Minn .

U n i v e r s i t y of BonnBonn, Germany

J e t P r o p u l s i o n L a b o r at o r yPasadena , C a l i f .

SR I In t e r na t i 0na 1.

Menlo P a r k , C a l i f .

O r b i t e r C lo ud P h o t o p o l a r i m e t e r

M u l t i p r o b e B u s N eu t r a l MassS p e c t r o m e t e r

M u l t i p r o b e Bus N e u t r a l Mass

Spe c t r omete r

M u l t i p r o b e and O r b i t e r GroundB a s e d R a d i o S c i e n c eExper imen t s

M u l t ip r o b e an d O r b i t e rGround Based Radio ScienceExper imen t s

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VENUS STATISTICS

O r b i t a l

. 7 2 3 a s t r o n o m i ca l u- ...t s1 0 8 . 2 m i l l i o n k m

6 7 . 2 m i l l i o n m i .

Mean d i s ta n c e f rom Sun:

I n c l i n a t i o n of o r b i t t op l a n e of e c l i p t i c : 3 . 3 d e g r e e s

S i d e r e a l p e r io d ( r e l a t i v et o s t a r s ) : 225 Ea r t h days

1 2 6 , 1 8 0 km/hr78,408 mph

Mean o r b i t a l v e l o c i t y :

C l o s e s t approach t o E a r t h : 4 2 m i l l i o n km

26 m i l l i o n m i .

P l a n e t a r y

D i a m e t e r ( s o l i d s u r f a c e) : 1 2 , 1 0 0 km7,519 m i .

D i a m e t e r ( t o p of c l o u d s ) : 1 2 , 2 4 0 km7 , 6 0 6 m i .

0 .815 Ear th massesass:

5.26 gm/cm3en s i t y :

pioneer venus encounter press kit

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