goce technical presentation
DESCRIPTION
Mission Design. GOCE Technical Presentation. Geoid. Gravity Anomalies. System Concept. Presentation Outline. Mission Rationale Science & Application Mission Design Performance Conclusions. - System Concept - Instruments - Attitude and Drag Control - Conventional Mission Elements - PowerPoint PPT PresentationTRANSCRIPT
T 1The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEGOCE Technical PresentationMission Design
Geoid
Gravity Anomalies
T 2The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCE
•Mission Rationale
•Science & Application
•Mission Design
•Performance
•Conclusions
- System Concept
- Instruments
- Attitude and Drag Control
- Conventional Mission Elements
- Programmatics
System Concept
Presentation Outline
T 3The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEFrom Scientific to Satellite Requirements
• The scientific requirements are 1 mgal (gravity) and 1 cm (geoid) at 100 km resolution
• To carry a gradiometer and a GPS/GLONASS receiver
• Using the mission simulation tools, these scientific requirements, have been transformed in mission and satellite requirements:
– gravity gradient (mE),
– satellite position (cm),
– orbit altitude
– and mission duration
System Concept
T 4The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEDerived Satellite Requirements
• Orbit altitude: 250 km
• Orbit inclination: 96.5º (Sun-synchronous)
• Orbit local time of ascending node: 6:00
• Mission duration: 20 months
• Gradiometric performance target: 4 mE/Hz
• SST-hl performance target: 2 cm
System Concept
T 5The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCESatellite Configuration
• Symmetric
• Slender (0.8 m2)
• Large Solar Array
• Without mechanisms
• 770 kg
• 1100 W
• 4 m longVelocity
ZenitSun
Mission Design
T 6The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEMission Timeline
2 5 0 k m
2 4 0 k m
T 0 T 0 + 3 m o n th s T 0 + 9 m o n th s T 0 + 1 4 m o n th s T 0 + 2 0 m o n th s
2 6 0 k m
2 7 0 k m
O rb itA ltitud e
E clipseD ura tio n
5 m in .
1 0 m in .
1 5 m in .
4 3 d 3 5 d3 5 d 1 3 5 d
S pacecraftC o m m issio n ing
G rad io m eterC alib ra tio n
1 .5 1 .5 6 m on th s 4 .5 m o n th s .5 6 m on th s
G rad io m eterS e t-up andC alib ra tio n
M easu rem en tIn te rrup tio n
F irs t M easu rem en tP hase
S eco nd M easurem en tP hase
3 0 m in .
2 5 m in .
2 0 m in .
System Concept
T 7The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEObservables Frequency Ranges
• The gravity and the perturbing forces change in space and time
• The satellite observe them as time series
• Signal and noise are studied in the frequency domain
Fx (along velocity)
Fy (transversal)
77 km770 km7700 km
System Concept
Hz
Acc
eler
atio
n PS
D (m
/(s2s
qrtH
z))
Dra
g fo
rce
(mN
)
s
T 8The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEInstruments Synergy
• The gradiometer has good performance at high frequency and the SST-hl receiver at low frequency
• Overlapping frequency is 0.005 Hz
• The gradiometer provides the external accelerations to the SST-hl receiver that provides long term stability to the gradiometer
System Concept
Resolution (km)
Frequency (Hz)
Gradiometer range (0.005-0.1 Hz)
SST-hl receiver range
200200010000
300
66.6
0.110.0380.00380.00038
T 9The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCESatellite Error Budgets
Total error on gravity gradient terms Vxx, Vyy and Vzz = 4 mE/ Hz
Instrument errors3 mE/Hz-1/2
Ins-sat couplingerrors
1 mE/Hz-1/2
Satellite errors2 mE/Hz-1/2
Post-flight errors1 mE/Hz-1/2
Resolution 3 Linearaccelerations 0.88
Selfgravity 0.2 Centrifugal forcesrecovery 1
Quantization 0.5 Angularaccelerations 0.45
Pointing 2
Stability 0.2 CoM offset 0.11 Position, time 0.2
Self gravityvariation 0.11
System Concept
SST-hl total error: 2 cm (1 cm, receiver, 1 cm GPS ephemeris, 1 cm satellite accelerations)
Gradient error:
T 10The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThe Gradiometer
• It provides the high resolution terms of the gravity field
• Three pairs of accelerometers perpendicular to each other. Baseline 0.5 m
– The difference of read-out of a pair of accelerometers provides one component of the gravity gradient
– The addition of the read-out provides the external linear acceleration
– Angular accelerations are also obtained
• Measurement bandwidth (mbw): 0.005-0.1 Hz
• Resources: 125 kg, 75 w, 1 Kbps, 0.8 0.8 1.2 m
Instruments
T 11The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThe Gradiometer: Accelerometer Principle
C1
C2
S
S
Instruments
T 12The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThe Gradiometer Accelerometer Design and Status
• Benefits from many years of development
• Pt-Rh proof mass (441 cm, 320 g) grounded by a gold wire.
• Control electrodes in gold coated ULE glass.
• External body in Invar.
• Benefits from many years of development
• GOCE drag control allows better accuracy
Proof Mass
Electrodes
Exploded View
IntegratedView
Instruments
T 13The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThe Gradiometer: Instrument Resolution
• 3 mE/Hz specified
• The predicted performance curve has been derived from a combination of analysis and test
• Predicted results in line with requirements
Specified noise value
Predicted noise values
Instruments
T 14The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThe Gradiometer: Instrument Satellite Coupling Errors
• External linear and angular accelerations couple with instrument missalignments to produce errors
• 1 mE/Hz allocated to this error source.
• The resulting gradiometer alignment accuracy is 10-5 rad. It has been verified by test.
d
d
c c
Instruments
T 15The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThe Gradiometer: Pendulum Test Bench
• A servo controlled pendulum test bench has been developed for the testing of the gradiometer
• Tilting angles can be controlled down to 10-10 rad
• By tilting the platform, alignments and scale factors can be measured to 10 -5 rad
Instruments
T 16The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThe Gradiometer: Configuration (Exploded View)
External thermal protection
Internal thermal protection
Gradiometer core
Thermally regulated platform
Structural support
Structural support Platform
Mechanical decouplingdevice
Mechanical decouplingdevice
Instruments
T 17The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThe Gradiometer: Configuration (Integrated View)Instruments
T 18The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThe Gradiometer: Thermal Stability
• Lack of dimensional stability will produce errors
• 0.2 mE/Hz allocated
• Two thermal domains configuration
• Ultra stable Carbon&Carbon structure
• The performances (0.8 mK over 200 s and 9 µK over 10 s) fulfill these requirements
TMDD
Inner thermaldomain (passive)
Outerthermaldomainpassiveandactiveto 20 °
Coax cables
Spacecraft gradiometer enclosure
MLI
MLI Heaters
Heaters
Gradiometer
Regulated platform
Instruments
T 19The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCECalibration Principle
d
d
c c
d d
• The satellite will be shaken in orbit with specified forces and torques by the micro-thrusters and the accelerometers alignment errors will be measured
• This will also be done on ground using the pendulum bench as shaker
Instruments
T 20The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCESST-hl GPS/GLONASS Receiver
• It provides the low resolution part of the gravity field
• 12 channel dual-frequency GPS and GLONASS receiver
• Less than 1 cm of measurement noise. Two off-the shelf receivers fulfilling GOCE needs will be available in Europe soon: GRAS and Lagrange
• Reference interface data are:
– Planar hemispherical zenith looking antenna
– System is: 10 kg, 40 w, 2 Kbps. Electronic box is 250 164 203 mm, Antenna is 300 300 50 mm,
Instruments
T 21The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCESystem Requirements
• Linear acceleration: 10-6 m/s2 (total), 2.5·10-8 m/s2Hz (mbw)
• Angular acceleration: 10-6 rad/s2 (total), 2.5·10-8 rad/s2 Hz (mbw)
• Pointing: 0.35 mrad (total), 8.6 ·10-6 rad/ Hz (mbw)
• The analysis including close-loop simulation, has demonstrated that the requirements are fulfilled
• Low flying altitude drives: redundant system for the ‘nominal’ modes plus fully independent emergency mode sensors and actuators
Attitude and Drag Control
T 22The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEArchitecture
Attitude and Drag Control
and drag
Normal modeSafe mode
T 23The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEPerformance
• Pointing requirement: 8.6·10-6 rad/Hz fulfilled (2 mEHz)
• Drag control requirements: 2.5·10-8 m/s2Hz fulfilled (0.9 mEHz)
Drag requirement
Pointing requirement
Velocity requirement
Acceleration requirement
Attitude and Drag Control
m/s2Hz unit/Hz
10-7
10-8
Frequency (Hz) Frequency (Hz)
10-3 10-1
10-8
10-3 10-1
10-5
10-7
10-9
T 24The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEIon-Thrusters Principles and Requirements
• It is used to compensate the atmospheric drag
• Xe gas is first ionised, then accelerated by high voltage and expelled. This produces thrust
• The main requirements are:
– Normal thrust range: 1-12 mN. Orbit change thrust: 20 mN
– Minimum thrust step: 18 N
– Thrust modulation speed: 10 mN in 1000 s and 25N in 0.1 s
– Bandwidth 10 Hz
• Two thrusters (full redundancy) located at the bottom of the satellite
Attitude and Drag Control
T 25The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEIon-Thrusters Development Status
• Most requirements have been verified by analysis or by test
• The verification of the long term thrust direction stability is pending25 N step
in 1 ms
Ion-thruster test set-up
Thruster step test result
Attitude and Drag Control
T 26The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEThermal and Structural Elements
Structure allows easy assembly and disassembly
Conventional thermal control
Upper equipment
bay
Lower equipment
bay
Instrument bay
Equipment radiator
Instrument radiators
Equipment radiator
Conventional Mission Elements
T 27The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEAvionics
Ion Propulsion
SA
24-36 V power bus
Power controlelectronics
Gradiometer
Radiation Monitor
Attitude and Drag ControlCommunications
Thermal Control
Data bus
1 Mbps
S band
Solar Array 265 1100 W
SST receiver
Data Handling
Battery 265 Wh
Data bus MIL-1553
Conventional Mission Elements
4 Kbps
1 Gbit memory
T 28The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCESatellite Mass and Power Budget
Mass (kg) Power (W)
Gradiometer 125 75
SST-hl receiver 15 40
Avionics 44 95
Electrical Power 126
Attitude and drag control 20 60
Micro thrusters 35
Ion-thrusters 44 475
Structure and thermal control 230 45
Total dry 639
Total with fuel 799 755
Conventional Mission Elements
T 29The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEGOCE Operations
• 5 Kbps, no real time data, instruments always on
• Once a month recalibration
• Change of altitude several times during the mission
• Robust strategy to avoid mission loss in case of failure of the drag or attitude control
– Sophisticated attitude and drag control modes
– Autonomous and resilient satellite
• S band 1 Mbps down-link rate
• Two passes per day are enough for data downlink
Conventional Mission Elements
T 30The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEGround Segment Architecture
• IGS data for POD
• Geoid and gravity fields are produced during the mission and consolidated once the mission is finished
• Real time checking of the data quality is done using the trace-less property
.
TT&C
Command and Data Acquisition Elements
Mission and Sat.Control Element
Processing and Archiving Element
UsersScienctific Proccesing
External entities
International GPSGeodynamics
ServiceTT&C
Data Acquisition
Level 0 Proc.
Proccesing
Level 1 a Proc.
Level 1 b Proc.
Data Distribution
Data/ProductsArchive
Level 1b data
Level 2data
Level 2data
Users services
Qua
lity
Con
trol
SatelliteControl
MissionControl and
Planning
ESA Net &others (LEOP)
Conventional Mission Elements
T 31The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEDevelopment and Mission Risk
• The gradiometer benefits from the accelerometers development
• The SST-hl receiver is available
• The already performed pre-development on the ion-thrusters provide a very high degree of confidence on the approach
• The proportional micro-thrusters have not yet gone through all its key development stages but the last developments are encouraging
• Launch window is one month. If it is not met it would imply one year launch delay.
• Low flying altitude is necessary. Specific features have been implemented to minimize this risk: redundancy, safe mode, aerodynamic stability, autonomy. Up to 20 days without ion-thrusters can be recovered
Programmatics
T 32The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCESatellite at ESTEC in 2004Programmatics
T 33The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEGOCE TestingProgrammatics
T 34The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCE
Schedule
2000 2001 2002 2003 2004Phase A
Phases C/D
Phase BESA
GOCE UserMilestones
AO’s
National Entities ESAG ?
Airborne Gravity Survey
2005
ESTECWorkshop
ISSI EGS
EGG-C: Level 1 - Level 2 Data Processing Architecture
Gravity User Workshops
ESRINWorkshop
2006
Cal/Val AO Data AO
HPF/CMF&RPF Development
Validation Campaign?
AO Workshop
Phase E
Launch
IAG/IAPSO
Data Processing
T 35The Four Candidate Earth Explorer Core Missions Consultative Workshop12-14 October 1999, Granada, Spain, Revised 2006-01-05 by CCT
GOCEDevelopment and Mission Risk
• The gradiometer benefits from the accelerometers development
• The SST-hl receiver is available
• The already performed pre-development on the ion-thrusters provide a very high degree of confidence on the approach
• The proportional micro-thrusters have not yet gone through all its key development stages but the last developments are encouraging
• Launch window is one month. If it is not met it would imply one year launch delay.
• Low flying altitude is necessary. Specific features have been implemented to minimize this risk: redundancy, safe mode, aerodynamic stability, autonomy. Up to 20 days without ion-thrusters can be recovered
Programmatics