science case mission analysis system engineering outreach€¦ · inca. final presentation, august...

1Final Presentation, August 2nd 2012

Alpbach Summer School 2012

iTOURInvestigative Tour Of URanus

TEAM ORANGE


Outline

• Science case

• Mission analysis

• System engineering

• Outreach


Mission Statement

The iTOUR mission will study the Uranus system to give crucial

answers about its current state and evolution, paying particular

regard to the unusual inclination and characteristics of the

magnetosphere by flying a slave satellite in addition to the main

orbiter.


What do we know about Uranus?

Facts from Voyager 2 fly-by in 1986:

– 14.5 times as big as Earth

– Rotational period 17 hrs, 14 mins

– Each pole has 42 years sunlight, 42 years darkness

– 27 known satellites, 5 larger moons

– 11 rings

– High winds in upper atmosphere

© NASA


Composition of Uranus

• Coldest planetary

atmosphere

• Density of 1.27 g/cm3

• Various ices (water,

ammonia)

• Rocky core, icy mantle

and an outer gaseous

helium / hydrogen

envelope.


Striking aspects of Uranus’ atmosphere

• The unexpected high

velocities winds in the upper

atmosphere.

• The latitudinal wind profile

that presents a prograde

wind jet at equator and

retrograde wind jets at mid

latitudes (~ 50°).


Magnetosphere of Uranus

• Axial tilt of 97.77o

• Magnetic field 59o from

axis of rotation

• Magnetic field does not

originate from geometric

centre

• Sun will be on opposite

side to this diagram for

our selected arrival date© Atmosphere of Uranus


Uranus’ Magnetosphere


Aurora of Uranus

• Around both magnetic poles

• Strong aurorae radio emissions at frequency (1–1,000

kHz)


Uranus’ five largest moons

• Four show signs of

internal geological

processes on their

surfaces

• Miranda shows

evidence of a surface

impact

• Titania & Oberon may

harbour liquid water

undergroundEncylcopedia of Science website


ESA’s cosmic vision 2015 - 2025

• How does the solar system work?

• What are the conditions for life and planetary formation?

• What are the fundamental laws of the universe?

• How did the universe begin and what is it made of?

• NASA’s decadal survey specifically recommended a mission

to Uranus


Science Objectives

• Characterise Uranus’ interior

• Characterise Uranus’ atmosphere

• Characterise & investigate

Uranus' magnetosphere

• Study Uranus' satellite

and ring system

© NASA


Interior?

Rotation rate?

Bulk composition & internal

mass distribution

Gravity field &

aggregation?

Radio emissions to provide a

proxy measure of the rotation,

gravity and two point

observations of magnetic field

High resolution imaging,

multispectral

spectrometry and gravity

field close to the planet

Visible

Infra-red

Spectrometer

Radio Science

Instrument

Radio Plasma

Wave Instrument

Magnetometer

Characterise Uranus‘ interior

Magnetic field?

Two point

observations of

magnetic field close

to the planet


Structure & composition Dynamics Thermal

What are the condensables? Winds? Heating effect of Aurora?

Imaging

sample of

atmosphere

IR, NIR, UV

Vertical

structure of

horizontaly

propagating

waves, top

velocity winds,

IR and NIR

Charcterize

dynamics,

IR and NIR

Composition,

IR and NIR for

traces in the

troposphere

Pressure

Profile,

Radio

occultation

(X-Band)

Velocity,

vertical

temperature

profiles,

submm

Doppler

Browaden-

ing

Vertical

temperature

profile,

submm,

Aurora

imaging UV

and NIR

Ultra

stable

Oscillator

Visible

Infra-red

Spectrometer

Submm

Wave

Instrument

Camera Ultraviolet

spectrometer

Clouds?

Characterise Uranus‘ atmosphere


Different altitude approaches for

Sounding Uranus’ atmosphere

Upper atmosphere - µbar pressure level – UV from Rayleigh

scattering + aurora features: Ultraviolet spectrometer

Visible – Reflected solar radiation at cloud tops:

Camera Visible

Thermal IR + Spectral: Visible and IR

spectrometer

Sub mm – Collision induced transition

absorption of H2 gas and aerosol particles: Sub

millimeter spectrometer

Radio – deep atmosphere and ice layer

sounding: Ultra Stable Oscilator


StructureInteraction with

solar windDynamics

Boundaries? Plasma

population?

Aurora?

Measure inner

magnetosphere ions

& electrons

distribution function

and magnetic field

at < 20Ru

Measure outer

magnetosphere ions &

electrons distribution

function and possible

two point observations

of magnetic field at

about 20Ru.

Radio

emission

Imaging of

aurora and

solar wind

monitoring in

UV

Radiation belts,

ionosphere and

near tail?

Plasma

Package

Ultraviolet

Spectromet

er

Radio

Plasma

Wave

Instrument

Visible

Infra-red

Spectrometer

Plasma

circulation &

current system?

Simultaneous remote and in situ

observations of magnetosphere

& solar wind monitoring: ions &

electrons distribution function at

two points observation of

magnetic field at < 20Ru, and

UV Imaging aurora & ENA

imaging

Magnetometer

Characterise & investigate Uranus' magnetosphere

Interaction

with moons

& rings?

Measuring

neutral particles

near the rings &

moon

interaction

ENA

imager


Structure &

composition

Dynamics &

interactions

Geology, age and

surface processes

Shape, size of

known and new

discoveries?

Surface

properties?

Shape &

size?

Interior?

High spatial surface

imaging <5m for

Miranda and

Titania to identify

crater rates &

cracks

Gravity and

magnetic field

anomalies,

Miranda and

Titania

High spectral

resolution

imaging of

Miranda, VIS

(<200m), IR

(spectral ?)

Specific structures, high

spatial resolution at the

beginning of the

mission & several

images at the end of the

mission; 50ms-200s

exposures

Global mapping

<1km, NAC + UV +IR

at the beginning of

the mission &

several images at

the end of the

mission

Camera

Radio

Science

Instrument

Visible

Infra-red

SpectrometerUltraviolet

Spectrometer

Tectonics &

subsurface

activities?

Surface

imaging for all

satelites, low

spatial

resolution

<1km

Structure &

composition

Temporal

variation?

Plastma

Package

Magneto

meter

Study Uranus' satellites and ring system


Requirements – Highlights (1)

• Imaging of Uranus for atmospheric dynamics

– High spectral resolution � High data volume (4 Mbits/line)

– Large spatial coverage with spatial resolution < 100��

– Good illumination-viewing conditions � ~3.5��

• Atmospheric and � profile soundings

– Few numbers (10 − 20) of Sun Occultation measures

• Atmospheric chemical composition sounding

– Day & night-side sounding distributed around Uranus surface

– Acquisition time: 1�� per measurement



• Magnetic field and Charged Particles

– High variability of magnetosphere � Measures every orbit

– Close to recombination points

– Continuous measurement of magnetic field with Magnetometers

• Imaging of the aurora

– Night-side observation + Near cusp region (~4 hours observation time)

– Total Data Volume (UVIS+RPWI): 120 Mbits

• Uranus Gravity field

– RSI operations close to pericentre � No Remote Sensing on the night-

side due to HGA operation constraints



• Moon Imaging and Gravity field

– High-spatial res. multispectral/PAN imaging (<10m)

– High-spectral res. with moderate spatial res. (<100m)

• Rings characteristics and dynamics

– 10 PAN images with resolution <500 m + 1 Multiband (6 bands) � 200

Mbits

– Good illumination conditions


Why two spacecraft ?

● Several designs not realistic (balloon, cubesats etc)

● Feasible designs: Orbiter & Probe vs Two orbiters

● The two orbiters design is the best compromise to fit the

science case and the engineering requirements.

Design For Against

Orbiter & Probe- In situ measurements of the surface

(noble gazes)

- The magnetic field become

secondary

Two Orbiters

- Two simultaneous measurement

points

- Main orbiter: 3 axes stabilized for

remote sensing measurements

- Slave orbiter: spinning for

magnetospheric study.

- In situ measurements of the

surface impossible

- Data rate of the spinner

may be low


Instrument specifications

VIRHIS (Visible and InfraRed Hyperspectral Imaging)

FOV [°]:

Spectral Range [nm]:

Filters:

Image Format:

Pixel Size [μm]:

Exposure Time [ms]:

Spatial Scale TELE:

Spatial Scale WIDE:

Operating Temperature [°C]:

Mass [kg]:

Peak Power [W]:

Data Volume [MB/s]:

Heritage:

3.4

400 – 5200

2

480 x 480

27

0 – 60 000

62 m/pixel @ 500 km

125 m/pixel @ 500 km

< - 143

17

20

5

JUICE

UVIS (UltraViolet Imaging Spectrometer)

FOV [°]:


Spatial scale:

Exposure Time [ms]:

Pixel Size [μm]:


Mass [kg]:

Peak Power [W]:

Data Volume [KB/s]:

Heritage:

0.1 x 2

50 – 320

512 x 512

1000

80

0 – 30

6.5

24

34

JUICE

Main Spacecraft

UltraViolet Imaging Spectrometer



SWI (Submm Instrument)

FOV [°]:

Spectral Range [μm]:

Filters:

Exposure Times [s]:


Mass [kg]:

Average Power [W]:

Data Volume [GB/year]:

Heritage:

0,15 – 0,065

550 – 230

CTS

1 – 300

- 20 to +20

9.7

48.5

5

JUICE

LORRI (Narrow Angle Camera)

FOV [°]:


Filters:

Image Format:

Pixel Size [μm]:

Pixel Binning:

Mass [kg]:

Electrical Power [W]:

Heater Power [W]:

Data Volume [MB/s]:

Heritage:

0,29

350 – 850

None (Filter wheel used from

Mars Pathfinder)

1024 x 1024

13

4 x 4

8.6

5

10

12

New Horizons

RSI (Radio Science Instrument)


Mass [kg]:

Power [W]:

Data Volume [MB/s]:

Heritage:

-25 till 60

4.5

26

5

JUICE

RPWI (Radio Plasma & Wave Instrument)


Mass [kg]:

Power [W]:

Range [RWI}:

Range [Search Coil Mag]

Heritage:

-20 to +50

6.8

7.0

10 kHz – 45 MHz

0.1 Hz – 600 kHz

CASSINI



Plasma Package:

ELS (Electron

Spectrometer)

HPS (Hot Plasma

Spectrometer)

DPU (Digital

Processing Unit

Scanner

Heritage:

0.7kg

1 – 20,000 eV

0.8kg

1 – 30,000 eV

2.0kg

1.5kg

JUICE

INCA ENA Imager

Operating [keV]:

Mass [kg]:

Power [W]:

Data Volume [KB/s]:

Heritage:

3 - 300

16

14

7

CASSINI

INCA


Instruments specifications

Search Coil Magnetometer (SCM)

Operating Frequency [Hz]:

Mass [kg]:

Power [W]:

Heritage:

0.1 – 8,000

2.0

0.090

THEMIS

FGM (Flux Gate Magnetometer)

Range:

Resolution: (lowest-

highest range)

Mass [kg]:

Peak Power [W]:

Data Volume [B/s]:

Heritage:

±128nT to ±32764nT

15pT - 4nT

3.1

3.6

1211

DOUBLESTAR

Search Coil Magnetometer

Flux Gate Magnetometer


Model Payload - orbiter

Instrument Mass [kg] Margin

Total

mass [kg] Heritage

Main Spacecraft

VIRHIS (Visible and InfraRed Hyperspectral Imaging

Spectrometer) 17 20% 20.4 JUICE

UVIS (UltraViolet Imaging Spectrometer) 6.5 20% 7.8 JUICE

RSI (Radio Science Instrument) 4.5 10% 4.95 JUICE

SWI (Submm Instrument) 9.7 30% 12.61 JUICE

NAC (Narrow Angle Camera) 8.6 20% 10.32 LORRI

- Filter wheel for NAC 0.5 20% 0.6 Mars Pathfinder

Radio & Plasma Wave instrument (inc Search Coil Magnetometer) 6.8 5% 7.14 CASSINI

FGM (Flux Gate Magnetometer) 3.1 5% 3.255 DOUBLESTAR

MENA (Medium Energy Neutral Atom imager) 16 5% 16.8 CASSINI

Plasma package:

ELS - 1 (Electron Spectrometer) 0.7 30% 0.91 JUICE

HPS - 1 (Hot Plasma Spectrometer) 0.8 30% 1.04 JUICE

Scanner 1.5 30% 1.95 JUICE

DPU (Digital Processing Unit) 2 30% 2.6 JUICE



D-DPU (Digital Processing Unit) 1.5 30% 1.95 JUICE

Total: 94.3


Model Payload – Slave satellite

Slave Satellite Mass [kg] Margin

Total

mass [kg] Heritage


SCM (Search Coil Magnetometer) 2 20% 2.4 THEMIS

Plasma package (Juice)



DPU (Digital Processing Unit) 2 30% 2.6 JUICE

Total: 10.2

Total payload for orbiter & slave satellite: 104.5


Model Payload – Power consumption

Instrument

Peak Power

[W] Margin Peak Power [W] Heritage

Main Spacecraft

VIRHIS (Visible and InfraRed Hyperspectral Imaging Spectrometer) 20 20% 24 JUICE

UVIS (UltraViolet Imaging Spectrometer) 24 20% 28.8 JUICE

RSI (Radio Science Instrument) 26 10% 28.6 JUICE

SWI (Submm Instrument) 46.8 30% 60.84 JUICE

NAC (Narrow Angle Camera) 15 20% 18 LORRI

- Filter wheel for NAC n/a Mars Pathfinder

Radio & Plasma Wave instrument (inc Search Coil Magnetometer) 7 5% 7.35 CASSINI


MENA (Medium Energy Neutral Atom imager) 14 5% 14.7 CASSINI

Plasma package (Juice) 18.6 20% 22.29 JUICE

Slave satellite

Magnetometer package


SCM (Search Coil Magnetometer) 0.09 20% 0.108 THEMIS

Plasma package


HPS - 1 (Hot Plasma Spectrometer) JUICE

DPU (Digital Processing Unit) JUICE


Observation scheduling: Constraints

• Limit data volume 2 Gbits/orbit (average)

• Simultaneous payload operation limited by available ASRG

power (110Wmaster, 25W slave)

• Best solar viewing angles achieved when the orbiter is ~ 3.5

R� from the planet

• Magnetosphere measures to be taken in-situ within the

magnetopause (< 20R�)

• Mission operations for 5 years


Observation scheduling: Proposal

Operation schedule and observation modes for best scientific

return, fulfilling downlink, power and time constraints:

1) First scientific phase: 2 years in the baseline orbit for

reconnaissance of the Uranus system

2) Second scientific phase: Uranus satellites & magnetic field

exploration


Observation scenario: Proposal

Proposed observation modes :

• Uranus System Survey (USS) mode: Reconnaissance of the

Uranus system by imaging the planet, rings and

measurements of the magnetic field and magnetosphere

• Atmosphere & Interior (A&I) mode: Thorough analysis of

Uranus atmosphere composition and dynamics together with

gravity field & magnetic field measurements

• Magnetosphere Research (MR) mode: Exhaustive study of

Uranus magnetic field and magnetosphere

• Moon Flyby (MF) mode: Detailed observation and analysis of

each Moon, focusing on surface and inner composition


Observation Scenario



USS mode: Uranus System Survey

Operations Data

Volume

[Mbits]

Peak

Power [W]

1) 120 VIRHIS samples on the day-side with along-track

scanning and 30 soundings with SWI

2) NAC imaging of the rings from 4 ��3) Continuous acquisition by Plasma Package (both

satellites) when s/c @4-20 ��4) 20 VIRHIS samples with Sun-occultation technique

5) UVIS & RPWI measuring the aurora region and 30

soundings of atmosphere with SWI

VIRHIS: 600

SWI: 960

NAC: 200

Plasma

Package: 20

UVIS: 100

RPWI: 20

70

Total Data

Volume:

1.9 Gbits



A&I mode: Atmosphere & Interior

Operations Total Data

Volume

[Gbits]

Peak

Power [W]

1) 240 VIRHIS samples on the day-side with along-track

scanning and 80 soundings with SWI

2) UVIS & RPWI measuring the aurora region together

with magnetosphere study (Plasma Package)

3) 40 frames high spatial res. frames with PAN (NAC) at

same area previously scanned with VIRHIS

4) 10 Sun-occultation technique measures using the HGA

(Ultra-Stable Oscillator)

VIRHIS: 1040

SWI: 1280

NAC: 500

Plasma

Package: 15

UVIS: 100

RSI: n/a

100

Total Data

Volume:

3 Gbits



Operations Total Data

Volume

[Gbits]

Peak

Power [W]

• High resolution measures (Plasma Package) for 2 days

between 4-20 ��• Medium resolution measures (Plasma Package)for 2

days near perapsis

• Low resolution measures (Plasma Package) outside

the bow-shock & MENA imaging

• Imaging (UVIS & RPWI) of the aurora regions for a

total time of 4 hours

0.8 50

MR mode: Magnetosphere Research mode


Mission Profile

• Two spacecraft

– Master

– Slave

• Transit to Uranus: 18.5 years

• Science operations: 5 years

– Uranus Science Phase: ~2 years (1.5 x 70 Ru, polar orbit)

– Moons Science Phase: ~3 years (similar orbit, increasingly larger apocenter)


Interplanetary Trajectory

Interplanetary Trajectory Data

Launch Date Sep 11, 2026

Arrival Date Mar 20, 2045

Gravity Assists VEEJ

AR 5 ECA Launch Capacity 4300 kg (5160 kg)

Mass at Launch needed 4100 kg

Comments:

• Jupiter rad. Belts

• Could use VVEE


Choice of Science Orbits

Orbit Scientific Requirements

• Master

– Small periapsis

– Elliptical orbit

– High inclination

– Sun illumination

• Slave

– Elliptical orbit

– Cross the dayside

magnetopause

– Visit the magneto tail

Orbit Engineering Constraints

– Small periapsis for gravity

assist during Uranus orbit

insertion

– Small angle between

incoming orbit vector and

Uranus orbit apoapsis vector

– Slave cannot perform ∆V

(no propulsion)

Design orbits to satisfy

Requirements and Constraints!


Considered Orbits

# Advantages Disadvantages

1

- Magneto tail

- Close to Uranus

in the day side

- Night side all the

time

- No time for remote

measurements

(at dayside)

2

- Bow shock

- Time for remote

measurements

- Long enough in

the magnetosphere

- We can’t study the

magneto tail

- Part of the time

outside the

magnetosphere

3

- Bow shock

- Time for remote

measurements

- Spends too much

time outside of the

Magnetosphere

- We can’t study the

magneto tail

Id Magnet. Remote Total

1 10 50 60

2 90 70 160

3 70 80 150

90 deg. Incl.


Chosen Baseline Orbit

Intermediate Orbit:

• Good illumination conditions for remote sensing

• Crosses bowshock at dayside & close to reconnection points

• Spends enough time in the magnetosphere


Uranus Science Phase

• Starts after Uranus orbit insertion

• Both Master satellite and Slave satellite are inserted at the same orbit

• Separation after insertion

• Science operations at baseline orbit for both satellites: 1 – 2 yr

• Once the science requirements are sufficiently fulfilled, go to Moons

Science Phase

Master

Slave

Comments

1.5 x 70 RU orbit feasible


Moons Science Phase

• Follows Uranus Science Phase

• Slave stays on baseline orbit

• Master allocated 650 m/s total

∆V for moon tour

• Raise orbit of Master to cross

moon orbit (e.g. Miranda)

• Resonant Master – moon orbits

to perform flybys

• Move on to outer moon once

done

• Repeat!


∆V Budget

Maneuver ∆V (km/s)

Interpl. navigation 0.125

Uranus OI 0.92

Miranda orbit 0.08

Ariel orbit 0.12

Umbriel orbit 0.1

Titania orbit 0.18

Oberon orbit 0.15

Moon tour navigation 0.17

TOTAL + MARGIN 1.93


The Spacecraft Design

Cassini

BepiColombo© ESA

© NASA


Overview

• Study Flow

• Science Driven Mission Architecture Selection

• System design trades and choices

• Programmatic issues and constraints


SYSTEM DESIGN

BASELINE

Study Flow/Systems Engineering

Science

Requirements

Options for the

Architecture

First Estimation

for Trajectories

Trade-Off and

Selection

Concept

ExplorationTrade-Off

Systems Design

Top-down

Bottom-up

Systems

Integration


Possible Architectures

• Orbiter only

– „Standard“ configuration, low complexity

– Science: no simultaneous measurements

• Two orbiters, smaller

– Less common design, but with heritage: BepiColombo

– Science: magnetospheric package and observations at multiple locations possible simultaneously

• Orbiter and „slave satellites“

– No heritage

– Science return insignificant because of limited lifetime

• Orbiter probe

– Heritage: Cassini, Galileo

– Probe is not required for defined science requirements


Architecture trade-off

• Todo: Add table

• Outcome of trade-off: 1 main orbiter, 1 slave spinner

– Science driven result, needed for observations

– Feasible engineering wise


Top Down Estimation

y = 6.952x + 212.1

R² = 0.800

0

500

1000

1500

2000

2500

3000

0 50 100 150 200 250 300 350 400

To

tal

Dry

Ma

ss [

kg

]

Payload Mass [kg]

Mission Heritage

Mission Heritage

Linear (Mission Heritage)


Configuration

• BepiColombo heritage, fits in AR 5

• Antenna side mounted for science operations


Communication with Earth

Design

• Required data downlink/orbit: 2 Gbit

• High Gain (with radio science package) and Low Gain Antenna

• Cassini like system 3.6 m HGA incl. LGA (100 kg)

– Size limited by launcher fairing

• Data rate from Uranus to Earth 3200 bps (X-band)

Ground Segment

• ESA ESTRACK 35 m Deep Space Antennae

– Cerebros (Spain), New Norcia (Australia)

• ESOC Mission Operations Centre

• NASA DSN compatible

• ESA ESAC data centre,

science operation planning

© ESA


Communication Master / Slave

- Low Gain Helical Antenna (Huygens heritage)

- Transmitting in orbit plane to HGA (main)

- Max. distance is 2 Mkm, data rate is 12 kbps

- 4 h of transmission per orbit

- 2 Redundant systems

- Mass of antenna 0,5 kg

- Amplifiers and subsystems (40 W / 5 kg)

Fig.: S-Band QFH Antenna

© SSTL

Requirements from instrument on-time:

minimum is 80 Mbit per orbit

Uranus

2 million km


Propulsion System

• Master satellite

– NH4/MMH bipropellant system

– 500N/>321s EAM of EADS Astrium

– 1/1 tanks for Lox/Fuel, 2 He tanks

~ 0.6 m spherical radius, ~ 60 kg

– Total mass: 187 kg

• Slave satellite

– No main propulsion unit

– AMPAC DSD-12 NH4 monopropellant

RCS system

– Used for spin-up, adjustments


Thermal Control System

Temperature range for instruments/electronics 273 - 293 K

Instrumentation with low temperature:

1. NAC 217K (passive cooling)

2. UVIS 173 K (passive cooling)

3. VIRHIS 73 K (active cooling)

Power input• RTG: 480 W (3x160W) for Master

(363 W after 23 years)

• RTG: 160 W for Slave satellite (121 W after 23 years)

• Power at Venus flyby (just bus):• 150 W for Master satellite

• 70 W for Slave satellite

• Power at Uranus with margin (bus and instrumentation):

• 247 W for Master satellite

• 92.4 W for Slave satellite

Heat shields


Thermal Control System

Cold case (Normal operation at Uranus):

- High emittance (ε): Master 0,74, Slave 0,9

- Solar Radiation: 3,4 W/m2

- Heat is generated by subsystem and instruments: Master 247 W/m2, Slave 92,4 W/m2

- Radiator: Master 0,84 m2, Slave A = 0,3 m2

Hot case (Flyby at Venus):

- Low absorptance (α): Master 0,07 Slave 0,12

- Solar Radiation: 2657 W/m2

- Heat is generated by subsystem: Master 150 W/m2, Slave 69,6 W/m2

- Master is shielded by the HGA, Slave is shielded by dedicated shield

- Radiator can never be directed towards the sun

- Multiple layers of isolation


Power System

• TODO (Fabian)


Driven by 0.8 arc/sec (1 sigma) pointing accuracy and 0.01˚/h pointing stability.

Master Satellite

(AOCS DV = 1700 m/s)

• 3-axis stabilised

• 3 EADS HYDRA star trackers

• 2 Honeywell MIMUs

• 4 RSI 25 Nms reaction wheels

• 24 EADS 5N hydrazine reaction

control thrusters

Slave Satellite

(AOCS DV = 700 m/s)

• Spin stabilised

• 2 EADS HYDRA star trackers

• 2 Honeywell MIMUs

• Dutch Space nutation damper

• 12 EADS 5N hydrazine reaction

control thrusters

© Rockwell Cullins© EADS Astrium

AOCS


Load Bearing Hexagonal/Octagonal Structure

• Hexagonal inner structure:

– Improved resistance to propulsion

system loads

– Ease of propellant tank mounting

• Octagonal outer structure:

– Improved resistance to launch stress

– Ease of instrumentation, antenna

and RCS mounting

– Weight saving truss structure


Power consumption

Base load Watt

AOCS 40

OBDH 8

Thermal Control 15

Communication (receiving) 50

Power 12

Base load at any time 125

Base load with 20% margin 150

Payload Operation Mode I 80

Communication X-band Operation Mode 90

Orbiter Slave

Base load Watt

AOCS 16

OBDH 8

Thermal Control 5

Communication (receiving) 17

Power 12Base load at any time 58

Base load with 20% margin 70

Payload Operation Mode I 60

Communication X-band Operation Mode 35

Degradation/Year %/Year Years Total Watt after 23 Y

Orbiter 1,20% 23 363,62

Slave 1,20% 23 121,21

Power sourcesOrbiter: 3 x ASRG with total power of 480 W

Slave satellite: 1 x ASRG with total power of 160 W


Separation Mechanism (Huygens Probe Heritage)

• The separation mechanism for the Cassini/Huygens mission was developed by RUAG Space

• Separation via Pyro-nuts and bolt-cutters

• Ejection by means of compressed springs

• Spin-up of Slave satellite via helical tracks and rollers

• Umbilical connectors separation system

• Small volume and low mass (23 kg)

© Dr. Udo R. Herlack et al.


Antenna Articulation Mechanism

Mission Requirements

• Allows for simultaneous optical,

particle and gravitational field

measurements

• High shock and vibration resistance –

Ariane 5 launch platform

• Low temperature performance: 50K

min and 343K max (reflective coating

on antenna) i.e. design for lower limit

• High pointing accuracy: ≈ 0.1°

• If mechanism failure occurs moment

arm programmed to return to

optimal static configuration


Challenging Lifetime

Cassini

• Planned lifetime 20 years

• Launch date: 1997

• Saturn’s radiation level is

worse than Uranus

iTOUR

• 23 years duration (expected)

• 18,5 years journey

• ~5 years mission (expected)

• Launch date: 2026 (expected)

• Cold environment

• Technology improvements may

be expected

Life time infered in comparison with Cassini:

Conclusion: 23 year life-time is possible


Mass Budget

Sub-systemMass without

margin (kg)

Total mass

(kg)

AOCS 60,2 66,2

Power 110,0 121,0

Comm 170,0 187,0

Propulsion 294,8 324,3

OBDH 65,0 71,5

Thermal 60,0 66,0

Structure 200,0 220,0

Payload 94,3 113,2

Boom 3,0 3,3

Sub-system total 1057 1171

System margin 20 %

Dry mass Orbiter 1407

Slave Satellite Wet 409

Total Dry mass 1407

Propellant 2285 2285

Launch mass 4100

Orbiter Slave

Sub-systemMass without

margin (kg)Total mass (kg)

AOCS 36,7 40,4

Power 38,0 41,8

Comms 30,0 33,0

Propulsion 14,7 16,2

OBDH 23,0 25,3

Thermal 15,0 16,5

Structure 65,0 71,5

Payload 11,0 13,2

Boom 6,0 6,6

Sub-system total 240 265

System margin 20 %

Dry mass 317

Propellant 82,9 91

Wet mass 409


Risk Management

Mission profil

What Likelihood Impact Mitigation activities

1 Failure @ Orbit insertion C 5

simulations, inhibit safe mode,

residual risk remains

2 Collision with unknown object C 5 early investigation of equatorial disk

3 Large gradiant hot/cold case B 5 design issue

4 RTG risk on launch B 5

5 RTG risk on earth fly-by B 5

6 Failure of Ejecting Slace Satillite C 4 redundant ejection mech.; qualification

7 Failure of Boom deployment B 4

8 Failure of HG Antenna deplyoment C 4 extensive qualifications

9 Low dose rate failure C 4

10 Reaction wheel failure C 2

InstrumentsWhat Likelihood Impact

1 Failure of LORRI B 4

2 Failure of VIRHIS B 4

Comination of Severity and Likelihood

E Low Medium High Very High Very High

D Low Low Medium High Very High

C Very Low Low Low Medium High

B Very Low Very Low Low Low Medium

A Very Low Very Low Very Low Very Low Low

1 2 3 4 5


Mission end of life

• Uranian system planetary protection: Class II

• Brief Planetary Protection Plan required

• At end of life: shut down systems, leave vehicles in orbit

– Reinvestigate if compromising discovery is made

• Mission extension may be investigated in 2050, RTGs will still

deliver sufficient power for reduced operations

© NASA


Vehicle Disposal

• Uranian system planetary protection: Class II

• Primary option:

– Controlled collision into Titania (last moon visited) in 2050

– Allows for remote science from Earth (orbit)

– Slave’s orbit remains unchanged

• Secondary option:

– Extend operations

• Choice can be deferred

© NASA


Mission Phases

Phase 0

• 2012 - 2013

Phase A/B1

• 2013 - 2015

Phase B2/C/D

• 2015 - 2024

Margin

• 2024 - 2026

Interplanetary Flight

• 2026 - 2045

Science Operations

• 2045 - 2050

End of life

Extension?

• 2050 - ??


Mission Critical Items

Issues

• Thermal environments Venus/Uranus

• Low solar flux dictates use of RTGs

• Distance from sun requires big antenna

• RTG availability

To be investigated in further detail

• Interface Master/Slave

– in stacked configuration, on orbit

• Impact of RTG radiation on instrumentation

• Low data rate, European foldable antennae?

• Reduce radiation at Jupiter flyby by trajectory optimisation

• Optimise mission analysis, especially tour of moons

• RTG in Arianespace launcher, launch approval


Cost Estimation Assumptions

Model based on expert analysis, rough order of magnitude output:

Estimation Paramater Input

Launcher Ariane 5 ECA

Number of Spacecraft 2

Cruise Duration 18 years

Operational Phase 5 years

Number of Ground Stations 1 x 8 hrs, 35 m DSA

Master Dry Mass/Payload Mass 1280 kg/ 100 kg

Slave Dry Mass/Payload Mass 308 kg/ 20 kg

Master/ Slave Propellant Mass 2000 kg/ 91 kg

Master/ Slave Total Power 430 W, 3 RTGs/160 W, 1 RTG

Specific Needs 4 Gravity Assists, Intercomms.


Total Lifecycle Cost Estimate

Contributor Cost/M€

Ariane 5 with RTG mods. 175

Master: Platform 1150

Master: Payload 100

Slave: Platform 200

Slave: Payload 20

Total 1750

• Typical L- class mission: M€1000 (including payload)

• Payload usually covered by member states

• Thanks to Denis Moura!


Descoping Options/Cost Reduction

• Downgrading the launcher to Soyuz only possible if 50 % of

payloads are dropped

• Slave satellite

– Saves 500 kg, M€ 220

– Should be last resort, slave satellite is needed for magnetospheric

science

• Try implementing high level of operations autonomy to

reduce costs


Firsts achieved by iTOUR/Outreach

1. First orbiter of an ice giant

2. First detailed study of the Uranus system

3. First detailed investigation of Uranus’ atmosphere

4. First detailed study of Uranus´ magnetic field

5. First outer planet mission with two orbiters

• Exploration of an underexplored system

– We expect Cassini- like public outreach

• University and school involvement


Announcement Of Opportunity!

• 700 kg Launch capacity remaining

• International project involvement by adding a probe?


investigative Tour Of URanus - iTOUR

Thanks to all tutors and lecturers for your help.

We are looking forward to your questions!


Appendix


Ground Segment Infrastructure

iTOUR Operations


Radiation

Electrons (dominating) & protons up to 4 MeV

Uranus Pathfinder (1UR / 16y):

Using SPENVIS (SHIELDDOSE-2) estimate a total

mission radiation dose of 20 kRad (18 krad from

cruise) behind 4 mm of aluminium.

iTOUR has its closest approach at 2UR but has

18.5 y until Uranus TID > 20 krad

Fly-by at Jupiter within 15 RJ / 42 h

�� Single Event Effects

© B

. H

. M

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Studied configurations

Cassini heritage BepiColombo heritage

Fixed antenna

SlaveInstruments

Instruments

Slave

Movable antenna


Studied configurations

Config Hexagonal -simple manufacuring

-easy accommodation

of the instruments

HGA top - stable

- high

reliability(previous

mission)

- shielding the main

structure

- low risk , less

mechanism

- resistance to launch

stresses

- easy stacking in the

fairing volume

Sub-sat side - Requires heat shield

(Huygens Probe)

- unbalanced after

discarding

Constraints/To do Main engine must be

gimbaled

(stability complexity

and implies

mechanism for engine

maneuvers )

The orbiter and sub-

sat release

mechanism

Tube inner structure

for distribution of

stresses

Config Hexagonal - simple manufacuring

- easy accommodation of the

instruments

HGA side - easier pointing for

communication with ground

station

- less propellant required

- no complex stability

problems with the sub-sat on

top

- difficult to fit in fairing

- detailed analysis of stresses

during launch (future work)

- required reinforcement of

the primary structure

- risks of mechanisms failure

of the retractable arm

- balanced with instruments

Sub-sat top - better stacking sequence for

stress behaviour

- shielding by pointing the

HGA

To do cylinder and arm attachement

the shielding of the sub-sat by

the HGA is always possible (?)

Cassini heritage BepiColombo heritage


Thermal Design• Selection of material for radiator in the worst case with consider absorptance (low (α) for Venus)

and emmitance( high (ε) for Uranus) where the second value is more important, because distance

from Sun increase during travel

• Uranus environment was first consider during selection, where area for radiator include

temperature of inside of satellite, power of system and environment of Venus during flyby.

• Radiator can never be face direct to Sun.

• Warming system in orbit of Uranus with switch on/off instrument and subsystem.

• 23 Kapton layers of isolation

• OSR for Master satellite and white paint silicate for slave satellite

Planet Satellite

Solar

radiationAlbedo

Albedo

radiation

Planetary

radiationPower of system Absorptance Emittance Temperature Area

- - - K

Uranus

Master

3.4 0.2820(~) 0(~)

247 0.07 0.74 293 0.84

Slave 92.4 0.12 0.9 293 0.30

Venus

Master

2657 0.820(~) 0(~)

150 0.07 0.74 303 0.84

Slave 70 0.12 0.9 281 0.30


Possible Add-on Science

Jupiter flyby

• The interaction between the Jovian magnetospheric plasma with Europa’s

torus can be investigated through the detection of energetic neutral atoms

(measurements during the Jupiter approach (Krimigis et al., 2004) with the

ENA imager instrument).

• During the close flyby to Jupiter VIRHIS and SWI can be used to measure

the composition and density of some molecular species (already tuned in

the SWI instrument for Venus).

• Additionally, the VIRHIS instrument is also able to perform cloud tracking

at high spatial resolution.


AOCS Delta V budget

• 100 % margin on AOCS DV budget

• Assumptions: Master satellite

– Every orbit one 10 m/s manoeuvre

– 5 x 50 m/s for safe mode recovery

• Assumptions: Slave satellite

– Every two orbits one 10 m/s manoeuvre

– 1 x 50 m/s for safe mode recovery


Material for Radiator OSR for Master Satellite White Paint Silicate for Slave Satellite

Planet Satellite

Solar

radiationAlbedo

Albedo

radiation

Planetary

radiation

Power of

systemAbsorptance Emittance Temperature

Area of

radiator

- - - K

Uranus

Master

3.4 0.2820(~) 0(~)

247 0.07 0.74 293 0.84

Slave 92.4 0.12 0.9 293 0.30

Venus

Master

2657 0.820(~) 0(~)

150 0.07 0.74 305 0.84

Slave 70 0.12 0.9 281 0.30


AOCS Block Diagram

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