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Variations in the Radiation Environment

J. L. BarthNASA/GSFC

C. D. GorskySGT, Inc.

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Introduction

A programmatic methodology for enabling COTS and emerging technology use in radiation environments requires an accurate definition of the environment with appropriate design margins.

Variations in the environment are presented. Limitations of radiation environment models

are presented with methods of extending their functionality.

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The Radiation Environment

Solar Protons&

Heavier Ions

Galactic Cosmic Rays

Trapped Particles

Nikkei Science, Inc. of Japan, by K. Endo

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Components of the Natural Environment

Transient» Galactic Cosmic Rays

Protons & Heavier Ions

» Solar Particle Events Protons & Heavier Ions

Trapped» Electrons, Protons, & Heavier Ions

Atmospheric & Terrestrial Secondaries» Neutrons

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Radiation Effects

Total Ionizing Dose» Trapped Protons &

Electrons» Solar Protons

Single Event Effects» Protons

Trapped Solar

» Heavier Ions Galactic Cosmic Rays Solar Events

» Neutrons

Displacement Damage» Protons» Electrons

Spacecraft Charging» Surface

Plasma

» Deep Dielectric High Energy Electrons

Background Interference on Instruments

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Programmatic Methodologyref: LaBel et al. IEEE/NSREC 1998

Define the hazard Evaluate the hazard (e.g., dose-depth curves) Define requirements Evaluate parts lists Test unknowns or perform radiation lot acceptance tests

(RLATs) on non-RH guaranteed devices Evaluate test data and predict performance Work with designers on alternate device selection or

mitigation options/validation Refine above as necessary

» 3-D analysis of shielding rather than dose-depth curves» Select harder part

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Environment Definition for Programmatic Methodology

Total Ionizing Dose» Dose-Depth Curves or Spacecraft

Specific Dose Levels Trapped Protons & Electrons Solar Protons Secondary Bremsstrahlung

Single Event Effects - Average & Peak Conditions» LET Spectra

Galactic Cosmic Ray Heavy Ions Solar Heavy Ions

» Energy Spectra Solar Protons Trapped Protons

Displacement Damage» Energy Spectra

Shielded Solar Protons Shielded Trapped Protons

Charging/Discharging» Surface - Plasma Electrons» Deep-dielectric - High Energy Electrons

Instrument Interference» Primary Particles» Secondary Particles - Shielding

Analysis

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Sun:Dominates the Environment

Trapped Particles

Heavier Ions

Protons

Source

SunModulator

Galactic Cosmic Rays

AtmosphericNeutrons

Trapped Particles

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Solar Flares

0

50

150

200

250

100

300 Cycle 19 Cycle 20 Cycle 21 Cycle 22

Cycle 18

Solar Activity:Cyclic Variation

Sunspot Cycle Discovered in mid 1800s Coronal Mass Ejections

» Increase in Solar Wind Velocity» Solar Particle Events - Proton Rich

Solar Flares» Increase in Solar Wind Density» Solar Particle Events - Heavy Ion Rich

Holloman AFB/SOON

Su

nsp

ot

Num

bers

Yearsafter Lund Observatory

Sunspot Cycle

Coronal Mass Ejections

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The Magnetosphere

Defined by Interaction of:Earth’s Magnetic Field - Solar Wind

Solar Direction: Compressed to ~ 10 ER Anti-Solar Direction: Stretched into Long

Magnetotail ~ 300 Earth Radii Open at the Poles Bar Magnet Representation Accurate to

4 - 5 Earth Radii

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Magnetosphere

CuspBow Shock

Solar Wind

Central Plasma Sheet

Magnetopause

Heikkila (Color by University of Washington)

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Particle Penetration of the Magnetosphere

Most Solar Wind Particles Are Deflected (99.9%)» Some Become Trapped & Energized

Galactic Cosmic Ray & Solar Particle Penetration Depends on:» Particle Energy» Ionization State

Galactic Fully Ionized Solar & Anomalous Component of GCRs Have Lower Ionization

States

Measured with Magnetic Rigidity in Units of GV

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Magnetic Rigidity

2 3 4 5 6 7

Total Energy Required to Penetrate the Magnetosphere

H

Z > 1

Magnetic Equator 2900 MeV

12 MeV/n

23 MeV/n46 MeV/n

109 MeV/n

313 MeV/n1147 MeV/n

87 MeV173

MeV284 MeV987

MeV

48 MeV

momentumcharge

after Stassinopoulos

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Magnetic Storms / Space Weather

“Gusty” Solar Wind Disturbs the Current Systems

Major Storms Probably the Result of CMEs» Must Be Pointed Toward Earth» Strongest Arrive with Interplanetary Magnetic

Field Oriented South Can Have Severe Effects

» Power Blackouts on Earth» Disruption of Communications Satellites» Loss of Satellites - ANIK-E1, Telstar 401

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Sunspot Cycle with Magnetic Sunspot Cycle with Magnetic StormsStorms

An

nu

al N

um

ber

of

Days

wit

h A

p>

4

Sunspots & Magnetic Storm Days

An

nu

al Su

nsp

ot

Nu

mb

erSunspot Number# of Days with Ap > 4

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1 6 11 16 21 25 311 6 11 16 21 25 31

Solar Wind Velocity (IMP-8 MIT) SAMPEX Electrons E > 1 MeV

Time of ANIK Failure

ANIK E1: Magnetic Storm

January 1994

Velo

city

(km

/s)

Cou

nts

/s (

x1

0)

8

1

2

3

4

5

6

7

0200

300

800

700

400

500

600

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Trapped - Van Allen Belts Omnidirectional Components

» Protons: E ~ .04 - 500 MeV» Electrons: E ~ .04 - 7(?) MeV» Heavier Ions: Low E - Non-problem for Electronics

Location of Peak Levels Depends on Energy Average Counts Vary Slowly with the Solar Cycle Location of Populations Shifts with Time Counts Can Increase by Orders of Magnitude During Magnetic

Storms» March 1991 Storm - Increases Were Long Term

Radiation Effects» Dose & Degradation» Single Event Effects - Protons only

Models - AP8/NOAAPRO & AE8

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Van Allen Belts

Inner Belt

Outer Belt

High Latitude Horns

Slot Region

BIRA/IASB

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Proton & Electron Average Models

1 2 3 4 5 6 7 8 9 101234

L-Shell

AP-8 Model AE-8 Model

Ep > 10 MeV Ee > 1 MeV

NASA/GSFC

#/cm2/sec #/cm2/sec

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Protons Fairly Stable

Cyclic Modulations Due to the Solar Cycle ~ 2» Lowest Levels Are at Peak of Solar

Maximum» Highest Levels Are at Lowest Point in

Solar Minimum» Rate of Change ~ 6%/year

Geomagnetic Field Shift Changes Location» ~ 6 ° westward / 20 years

Anisotropy at Inner Edge (300-500 km) 2 ~ 7

Particle Increases at Outer Edge - New Belts» Geomagnetic Storms

Cyclic Modulation Due to the Solar Cycle ~ 2» Highest Levels Are at Peak

of Solar Maximum» Lowest Levels Are at Lowest

Point in Solar Minimum Inner Zone - Fairly Stable Outer Zone - Dynamic 102 ~

106

» Solar Cycle Variations Are Masked

» Local Time Variations Due to Magnetic Field Distortion

» 27-Day Variation Due to Solar Rotation

» Magnetic Storms & Sub-Storms

Electrons

Trapped Particle Variations

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TIROS/NOAA Trapped ProtonsP

roto

n F

lux

(#/c

m2 /

s)

Date

Solar Cycle Variation: 80-215 MeV Protons

L=1.20

L=1.18

L=1.16

L=1.14

B/Bmin=1.0

Rad

io F

lux

F 10

.7

Huston et al.

1976 1980 1984 1988 1992 1996

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March 1991 Magnetic StormNew Proton Belt

CRRES - AF Phillips Laboratory, SPD/GD

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Activity in the Slot Region - SAMPEX

Day (1992)

L-Sh

ell

190 250 310 370 430 490 550

5

3

11

9

7

1

SAMPEX/P1ADC: Electrons E > 0.4 MeV

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Magnetic Storms - Hipparcos

L-Sh

ell

4-Day, 9-Orbit Averages

Star Mapper - Radiation Background

Daly, et al.

March1990 1991 1992

2

4

6

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Protons in SAA - 800 km

Longitude (deg)

Lati

tude (

deg)

Longitude (deg)

Lati

tude (

deg)

Longitude (deg)

Lati

tude (

deg)

Protons in SAA - 1300 km Protons in SAA - 3000 km

Proton Flux Contours

Variations with Altitude

» At 800 km, SAA is an oval

shape

» At 1300 km, the size of the oval shape increases

» At 3000 km, Van Allen “belt” structure of proton flux contours

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AP8 - MAX Spectra

Energy Range» .04 - 500 MeV

Range in Al:» 30 MeV ~ .17

inch Effects:

» Total Dose» Single Event

Effects» Solar Cell

Damage

Energy (>MeV)

Flu

en

ce (

#/c

m2/d

ay)

Integral Proton Fluences

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AE-8 - MAX Spectra

Energy Range» .04 - 7 MeV

Range in Al:

Effects:» Total Dose» Surface

Charging» Deep Dielectric

Charging» Solar Cell

Damage

Energy (>MeV)

Flu

en

ce (

#/c

m2/d

ay)

Integral Electron Fluences

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Single Event Effects - Proton Rates

0 100 200 300 400 500100

101

102

103

104

105

106

Peak Counts in SAAAveraged Over Worst Case SAA PassDaily Average

Trapped proton exposure in LEO depends on where satellite passes through the SAA

Calculate SEE rates for» Proton daily average» Worst case SAA pass» Peak proton counts in

SAA Implications for

memory scrub rates & other spacecraft operations

Energy (>MeV)

I=90 deg, H=1000/1000 km, Solar Minimum

Pro

tons

(#/c

m2/s

)

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Particle Variations

Protons and Photons

»extremely penetrating

»difficult to shield against

Electrons

»lower energies make them less penetrating

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Dose Variation with Altitude0 degree inclination

Total Dose at the Center of Solid Aluminum SpheresCircular Orbits, I=0 deg, Solar Maximum

0.1

1

10

100

1000

10000

100000

2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000

Altitude (km)

Do

se

(k

rad

s-s

i/1

yr)

20 mils

50 mils

100 mils

150 mils

200 mils

250 mils

300 mils

500 mils

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Dose Variation with Altitude90 degree inclination

Total Dose at the Center of Solid Aluminum SpheresCircular Orbits, I=90 deg, Solar Maximum

0.1

1

10

100

1000

10000

100000

2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000

Altitude (km)

Do

se

(k

rad

s-s

i/1

yr)

20 mils

50 mils

100 mils

150 mils

200 mils

250 mils

300 mils

500 mils

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Total Dose at the Center of Solid Alumium Spheres for 1 year MissionSolar Maximum, AP-8 & AE-8 Models

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1 10 100 1000

Aluminum Shield Thickness (mils)

To

tal

Do

se

(k

rad

s-s

i)

I=0deg, H=3000/3000 km

I=18deg, H=360/36000 km

I=0deg, H=6000/6000 km

I=90deg, H=3000/3000 km

I=90deg, H=1000/6000 km

I=90deg, H=6000/6000 km

I=98 deg, H=705/705 km

I=30deg, H=600/600 km

Europa Mission

Assumes 4 pi steradian exposure

Use “Dose-Depth Curves” to define top level dose requirements

“Total Dose” includes contributions from

» Trapped protons

» Trapped electrons

» Solar protons

Minimum design margin of “x2” added to account for uncertainty in environment models and variation of device response within flight lots

Dose-Depth CurvesDose Variation with Orbit

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Galactic Cosmic Ray Ions All Elements in Periodic Table Energies in GeV Found Everywhere in Interplanetary Space Omnidirectional Mostly Fully Ionized Cyclic Variation in Fluence Levels

» Lowest Levels = Solar Maximum Peak» Highest Levels = Lowest Point in Solar Minimum

Single Event Effects Hazard Model: CREME96

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GCRs: Solar Modulation

Years

CN

O (

#/c

m2/s

ter/

s/M

eV

/n)

CNO - 24 Hour Averaged Mean Exposure Flux

GCRs: Shielded Fluences - FeInterplanetary, CREME 96, Solar Minimum

Energy (MeV/n)

Part

icle

s (#

/cm

2/d

ay/M

eV

/n)

GCRs: Integral LET Spectra

LET F

luence

(#

/cm

2/d

ay)

LET (MeV-cm2/mg)

CREME 96, Solar Minimum, 100 mils (2.54 mm) Al

Galactic Cosmic Rays

» Long term cyclic variation» Peak at solar minimum» Shielding ineffective for high energy

ions» Attenuation by magnetosphere

effective for low inclination, low altitude orbits

Solar events

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Solar Particle Events Increased Levels of Protons & Heavier Ions Energies

» Protons - 100s of MeV» Heavier Ions - 100s of GeV

Abundances Dependent on Radial Distance from Sun Partially Ionized - Greater Ability to Penetrate

Magnetosphere Number & Intensity of Events Increases Dramatically

During Solar Maximum Problem for Total Ionizing Dose, Displacement Damage,

& Single Event Effects Models

» Dose & Displacement Damage - SOLPRO, JPL, ESP» Single Event Effects - CREME96 (Protons & Heavier Ions)

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Sunspot Cycle with Solar Proton Events

Pro

tons

(#/c

m2)

Year

Proton Event Fluences

Solar Protons: Orbits

Proton Levels Predicted by CREME 96

Energy (MeV)

Pro

tons

(#/c

m2/s

/MeV

)

Solar Proton Events

» Solar proton events correlate with the sunspot cycle

» Only low inclination, low altitude orbits are protected from solar proton events

» A problem for degradation & single event effects

» ESP model by NRL/NASA

0 50 100 150 200 250 300

Energy (>MeV)

107

108

109

1010

1011

1012

Sol

ar P

roto

n F

luen

ce (

#/cm

2 )

7 Years6 Years5 Years4 Years3 Years2 Years1 Year

95% Confidence Level

ESP Model of Solar Proton Cumulative Fluences

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Effect of Shielding on Heavy IonsGalactic Cosmic Ray & Solar Heavy Ion

Spectra

Flu

ence

(#

/cm

2/s

)

LET (MeV-cm2/mg)

Solar Heavy IonsIntegral LET Spectra , 100 mils AL

LET (MeV-cm2/mg)

LET F

luence

(#

/cm

2/s

ec)

» Frequency & intensity increase during solar active phase of the solar cycle

» Attenuation by magnetosphere effective for low inclination, low altitude orbits

» Solar heavy ion levels are orders of magnitude higher than galactic cosmic ray levels

» Shielding more effective than for galactic cosmic ray heavy ions

0.1 1.0 10.0 100.0 1000.0 10000.0 100000.010-16

10-15

10-14

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

Solar PeaksSolar Worst DaySolar Worst WeekGCR Solar MinGCR Solar Max

Differences in Energy SpectraGalactic Cosmic Ray & Solar Heavy Ion Spectra

Flu

ence

(#

/cm

2/s

)

Energy (MeV)

Carbon, 100 mil ShieldInterplametary

All Elements, 100 mil ShieldInterplametary

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Summary Requirements for the definition of the radiation

environment for a programmatic methodology were defined.

The variations in the radiation environment which must be considered in the definition were described.

Appropriate models for defining the radiation environment were presented.

References:» “Emerging Radiation Hardness Assurance (RHA) Issues: A NASA Approach for

Spaceflight Programs,” K. A. LaBel, J. L. Barth, R. A. Reed, and A. H. Johnston, IEEE Trans. on N.S., December 1998.

» “Applying Computer Simulation Tools to Radiation Effects Problems, Part I: Modeling Space Radiation Environments,” J. L. Barth, Published in 1997 IEEE NSREC Short Course Notes, July 1997.