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1COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Orbit parameters Two orbit models are used at system level
inertial polar circular orbit right ascension of the ascending node : = 12.5° ( ± 180 ) altitude 826 km ( a = 7204 km ) altitude 900 km ( a = 7278 km ) preferred for phase properties (orbit cycle of 7 / 14 days)
The altitude will be chosen as a compromise solution instrument/satellite performances (straylight, pointing) duty cycle (radiation fluxes) satellite-to-ground TC/TM link capacity
2COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Orbit parameters The orbit will not be kept phased after commissioning
risk of sun glare in case of semi-major axis correction maneuver semi-major axis drift over 5 years : - 7 km (atmospheric drag) orbit period stability over 6 months : better than 1 s
Eclipse
Xs+
Thruster along Xs
Sun direction
3COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Orientation of the satellite - flight domain
South
North
Orbit plane
Perpendicular to the orbit plane
boresightRoll angle
Sun
4COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
The sky observed by COROT
0°
30°
60°
90°
120°
150°
180°
210°
240°
270°
300°
330°
0h2h4h6h8h10h12h14h16h18h20h22h
SummerZone of observationcentered at 18h50
WinterZone of observationcentered at 6h50
Galaxy
5COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Satellite design / axes
Zs+
Xs+
Ys+
Equipment bayUpper compartment with sensitive equipmentFine thermal regulation subsystem
6COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Platform design “PROTEUS Evolution” family
series of 5 platforms upgraded electrical and AOCS chains
Li-Ion battery higher capacity (80 A h)
no more problem of power supply in Safe Hold Mode lower thermal dissipation
the battery sidewall can withstand any solar incidenceno need to rotate on the boresight axis after 5 months
New Magneto Torquer Bars higher capacity (180 A m2)
better convergence of the Safe Hold Mode equipment driven by a proportional control law
no more pointing disturbances due to MTB activations
Other features : new star trackers (SODERN), 2-antenna GPS
7COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
New mission schedule Thermal constraints shrunk to payload constraints
the Ys+ satellite wall (focal unit radiator) must be in the shadeas much as possible
No more 180° rotation on Xs between CP and EP No more EP2 critical thermal configuration for payload design Several possibilities for the scheduling
Exploratory Programs can be carried out either at the beginningor at the end of a 6-month period
an alternate schedule CP1, EP1, CP2, EP2 is operationally recommended
Focal unit radiator temperature worst cases in 1b and 2b 1b and 2b zones crossed by the Line of Equinoxes temperature depending on direction of observation and roll angle
8COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Previous schedule“Peace and Love”
Line of nodes
Summer
Winter
Autumn
Solar declinationup to +23°
Ys+
Solar declinationdown to –23°
Central Program 2
Exploratory Programs 1 & 2
180° rotation on Zs
180° rotation on Xs
180° rotation on Xs
180° rotation on Zs
Satellite axesin a fixed orbital reference frame ROF
XJ2000
YJ2000
XOF
ZOF
Equatorial plane
12.5°
Earth orbit
Central Program 1
Line of Equinoxes
Spring
S
Xs+
Zs-
Xs+
Zs-
Ys+
Xs+
Zs-
Ys+
Zs-
Xs+ Ys+
Anticenter (6h50)Center (18h50)
9COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Updated schedule“Apple pie”
Line of nodes
Summer
Winter
Autumn
Solar declinationup to +23°
Solar declinationdown to –23°
Central Program 2
Exploratory Programs 1 & 2
180° rotation on Zs
180° rotation on Zs
Satellite axesin a fixed orbital reference frame ROF
XJ2000
YJ2000
XOF
ZOF
Equatorial plane
12.5°
Earth orbit
Central Program 1
Line of Equinoxes
Spring
S
Xs+
Zs-
Ys+
Zs-
Xs+ Ys+
1b
1a 2b
2a
Center (18h50) Anticenter (6h50)
10COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Performance management Performance management consists in choosing the most favorable edge for
each observing run a slight drop in periodic performances (compatible with the requirements) can be tolerated
for the EP observing runs white noise bphot = f(1/ Tobs) in Fourier space
spectrum analysis less sensitive to periodicperturbations (hidden lines) in EP runs
i 2 Ai / ( bphot (T)) 1 / Qi < 100 Hz
To define a scenario, the users shall have a series of criteria direction of observation roll angle to optimize the projection of the targets onto the CCD criticity of the thermal regulation (level, variability) function of the roll angle criticity of the straylight intensity if any
11COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Focal unit configuration
0E2
CCD A1 CCD E1
CCD E2CCD A2 XV
YV
Left
Left
Left
Left
Right
Right
Right
Right
Buffer dump direction
Frame transfer direction
0E1
0A1
0A2
3.05°
2.70°
Ys+
Zs+
12COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Spacecraft roll domainwinter
Ys+
Zs+
S E
CP and EP n°2
Objective : ± 20°
angle for optimum power budget : = arctan (-tan sin) = 5.25°
13COROT Science Week, Paris, 13-16 May 2002
Spacecraft roll domain summer
Ys+
Zs+
CP and EP n°1
E S
Objective : ± 20°
angle for optimum power budget : = arctan (-tan sin) = 5.25°
COROT missionCOROT mission
14COROT Science Week, Paris, 13-16 May 2002
COROT missionCOROT mission
Spacecraft roll domain The ± 20° requirement may prove to be difficult to meet The following points must be checked
power budget (solar flux incidence) CNESLi-Ion battery likely to improve the power budget
masking of the star trackers’ field of view by the Earth ASPIAccommodation of the SED-16 star trackers to be worked on
payload thermal constraints CNES, Soditech+20° or -20° reachable for a given observing run TBC
Set of conclusions available in September
15COROT Science Week, Paris, 13-16 May 2002
System progress reportSystem progress report
Technical status Major instrument sub-system PDR held in the coming months
mechanical, thermal and optical architecture in progress much work on straylight rejection and thermal regulation performances
System engineering activity currently focused on command an control interfaces on-board software light curve corrections and data processing ground segment architecture
Ground Segment & System Review in November 2002
Contract with the launcherto be signed this year
16COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
Pointing and AOCS Stringent pointing stability requirements
coupled attitude/photometry noise if the image spot moves random : 0.5 arcsec (1 sigma) periodic : 0.2 arcsec (amplitude) for 2-ppm spectral lines in [0.1 ; 1] mHz
Instrument used for angle error measurements random and periodic sensor errors divided by 10 thermo-elastic variations between star tracker and payload frames removed
Small gaps of perturbations (< 3 % of the time) should remain during : eclipse entries/exits, MTB activations and solar panels rotations
Amplitude ( line of sight)Perturbation f
PROTEUS COROTThermo-elastic f0 1" 0"Sensor errors f0 6" 0,03"Gravity Gradient 2f0 0,08"Sensor random noise 1" < 0.08"Eclipses (transitory) 5"MTB commands 18" (could be reduced) 1999 preliminary budget
17COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
Pointing and AOCS
AOCS loop modified
ecartometric data generated by each seismology channel (frequency 1 Hz)
2 stars used by the ecartometric algorithm (least square method)
breathing corrected by real time focal length estimate
COROT payload
Gyroscopes
Star Tracker
Estimator
Kalman
Filter
Controller Actuators
Wheels
MTB
Target quaternion
Sensors
Chain 2
Chain 1
A1
A2
E1
E2
PROTEUS
1 or
2
18COROT Science Week, Paris, 13-16 May 2002
Requirements at spacecraft levelThe PSF movement on the CCD surface is split up into 3 spacecraft rotations Random requirements (1 ) (inertia Iyy, Izz >> Ixx)
0.3 arcsec on Ys, Zs 24 arcsec on Xs
Periodic requirements (0-peak amplitude) 0.1 arcsec on Ys, Zs 4.4 arcsec on Xs
Requirements at instrument levelBased on temporary worst case estimates Random requirements (1 ) lever effect : 1,000 pixels
0.09 arcsec on Ys, Zs pixel size : 2.32 arcsec
15 arcsec on Xs
Thermo-elastic periodic requirements (0-peak amplitude) 0.06 arcsec on Ys, Zs 9 arcsec on Xs
AOCS performancesAOCS performances
Zs
Xs
Ys
19COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
Spacecraft dynamic simulations (1) work undertaken by CNES and ASPI
CNES as prime ASPI as industrial architect
objectives characterization of each perturbation (environment, hardware) consolidation of the requirement set reference data for further system analyses
6-month activity run in 3 steps preliminary analysis simulation software upgrade simulation campaign
results available since December 2002
20COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
Spacecraft dynamic simulations (2) preliminary analysis
kinematic filter replaced by a dynamic Kalman filter(state vector including position, speed, drift, perturbation torque)gyrometer noise divided by 3, robust for inertial pointing
choice of the reaction wheel set configuration choice of a 0.05 Hz bandwidth after noise/stability trade-off
controller noise outside the scientific bandwidth worst case identification for subsequent simulations
solar wings at 90° and Sun in the orbit plane
PASIFAE simulation software upgrade dynamic filter implementation MTB proportional control law
Simulations assessment of each external/internal perturbation torque global simulations for system analysis
21COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
Dynamic filterKinematic filter
22COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
23COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
0.05 Hz0.005 Hz
Scientific bandwidth
24COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
Random noise budgetSimulation-based
The requirements are met in any case Typical 2D value of 0.3 arcsec
Random (1 sigma)Items X Y Z
Environment Perturbations 0,38 0,115 0,102+ MTB commandsRWS command quantif ication noise 0,056 0,134 0,081Gyro Unit noise 0,466 0,019 0,018Payload noise 1,907 0,112 0,094
Typical noise = quadratic sum 2 0,21 0,162
Simulation Worst Case 3,056 0,261 0,217
Requirements 24 0,3 0,3
25COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
Scientific bandwidth Periodic noise budget The instrument harmonic
errors are not rejected 9 arcsec on Xs at 0
0.06 arcsec on Ys, Zs at 0
Many perturbation lines on Ys and Zs due to external environment gravity gradient at 20
Earth magnetic fieldeven harmonics at 20, 40, 60
Most of 2D pointing noise requirements are met
Frequency band polluted< 100 Hz
26COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
Conclusion The simulations give hope for a random noise of 0.3 arcsec (1) The duty cycle is improved (+ 2.7 %) by the removal of the MTB
periodic perturbations Despite several lines due to gravity gradient and magnetic torque
in [0.1 ; 1] mHz, the spectrum pollution is less than 100 Hz The periodic requirements should be met after sensibility study
and consolidation of the payload thermo-optical performances angle error measurement simulations in progress improvement expected from real time focal length estimate
if 6 mv 8 and 500 pixels between stars at least
Payload Requirements EstimatesRandom Ys, Zs 0.09 arcsec 0.01 arcsecRandom Xs 15 arcsec 4 arcsecPeriodic Ys, Zs 0.06 arcsec 0.01 arcsecPeriodic Xs 9 arcsec 1 arcsec
27COROT Science Week, Paris, 13-16 May 2002
AOCS performancesAOCS performances
Other works in progress Optical distortion variability under assessment CNES/LAM
for seismology channel : to consolidate the angle error budget for exoplanet channel : to check the amplitude of the border/chromatic noise (in the
field of view) set of optical performances under verification point by point
Mission mode architecture study CNES/ASPI inventory of AOCS loop modifications Command & Control Transition from the PROTEUS standard mode DHU performances and channel switching feasability FDIR
Multi-mode AOCS simulator implementation CNES Safe Hold Mode simulations (Monte Carlo) validation of the Mission mode performances