COROT mission l Orbit parameters Two orbit models

COROT mission l Orbit parameters ð 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) ð 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 COROT Science Week, Paris, 13 -16 May 2002 1

COROT mission l Orbit parameters ð 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 Xs+ Sun direction Thruster along Xs Eclipse COROT Science Week, Paris, 13 -16 May 2002 2

COROT mission l Orientation of the satellite - flight domain Sun COROT Science Week, Paris, 13 -16 May 2002 3

COROT mission l The sky observed by COROT Science Week, Paris, 13 -16 May 2002 4

COROT mission Xs+ l Satellite design / axes Zs+ Ys+ Equipment bay Upper compartment with sensitive equipment Fine thermal regulation subsystem COROT Science Week, Paris, 13 -16 May 2002 5

COROT mission l Platform design ð “PROTEUS Evolution” family § series of 5 platforms § upgraded electrical and AOCS chains ð 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 incidence no need to rotate on the boresight axis after 5 months ð New Magneto Torquer Bars § higher capacity (180 A m 2) better convergence of the Safe Hold Mode § equipment driven by a proportional control law no more pointing disturbances due to MTB activations ð Other features : new star trackers (SODERN), 2 -antenna GPS COROT Science Week, Paris, 13 -16 May 2002 6

COROT mission l New mission schedule ð Thermal constraints shrunk to payload constraints § the Ys+ satellite wall (focal unit radiator) must be in the shade as much as possible ð No more 180° rotation on Xs between CP and EP ð No more EP 2 critical thermal configuration for payload design ð Several possibilities for the scheduling § Exploratory Programs can be carried out either at the beginning or at the end of a 6 -month period § an alternate schedule CP 1, EP 1, CP 2, EP 2 is operationally recommended ð Focal unit radiator temperature worst cases in 1 b and 2 b § 1 b and 2 b zones crossed by the Line of Equinoxes § temperature depending on direction of observation and roll angle COROT Science Week, Paris, 13 -16 May 2002 7

COROT mission l 180° rotation on Zs Previous schedule Spring “Peace and Love” Line of Equinoxes Line of nodes Zs- Summer Xs+ Solar declination up to +23° Zs. Ys+ Satellite axes in a fixed orbital reference frame ROF Xs+ Earth orbit Central Program 1 Central Program 2 Center (18 h 50) Anticenter (6 h 50) S ZOF YJ 2000 XOF Winter Exploratory Programs 1 & 2 Xs+ Equatorial plane Ys+ Zs- Solar declination down to – 23° Xs+ 180° rotation on Xs Autumn 12. 5° 180° rotation on Zs COROT Science Week, Paris, 13 -16 May 2002 8

COROT mission l 180° rotation on Zs Updated schedule Spring “Apple pie” Line of Equinoxes Zs- Line of nodes 1 a Satellite axes in a fixed orbital reference frame ROF 2 b Zs. Earth orbit Summer Solar declination up to +23° Xs+ Ys+ Xs+ Central Program 1 Central Program 2 Center (18 h 50) Anticenter (6 h 50) S ZOF YJ 2000 XOF Exploratory Programs 1 & 2 Equatorial plane 1 b Winter Solar declination down to – 23° 2 a Autumn 12. 5° 180° rotation on Zs COROT Science Week, Paris, 13 -16 May 2002 9

COROT mission l Performance management ð 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 periodic perturbations (hidden lines) in EP runs i 2 Ai / ( bphot (T)) 1 / Qi < 100 Hz ð 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 thermal regulation (level, variability) function of the roll angle criticity of the straylight intensity if any COROT Science Week, Paris, 13 -16 May 2002 10

COROT mission l Focal unit configuration Ys+ CCD A 1 Right Left Zs+ 0 E 1 CCD E 1 0 A 1 CCD A 2 CCD E 2 Right Left Right 0 A 2 2. 70° 0 E 2 XV Buffer dump direction YV Frame transfer direction 3. 05° COROT Science Week, Paris, 13 -16 May 2002 11

COROT mission l Spacecraft roll domain angle for optimum power budget : = arctan (-tan sin ) = 5. 25° winter CP and EP n° 2 Ys+ Zs+ Objective : ± 20° S COROT Science Week, Paris, 13 -16 May 2002 E 12

COROT mission l angle for optimum power budget : = arctan (-tan sin ) = 5. 25° Spacecraft roll domain summer CP and EP n° 1 Objective : ± 20° E S Zs+ Ys+ COROT Science Week, Paris, 13 -16 May 2002 13

COROT mission l Spacecraft roll domain ð The ± 20° requirement may prove to be difficult to meet ð The following points must be checked § power budget (solar flux incidence) CNES Li-Ion battery likely to improve the power budget § masking of the star trackers’ field of view by the Earth ASPI Accommodation 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 ð Set of conclusions available in September COROT Science Week, Paris, 13 -16 May 2002 14

System progress report l Technical status ð 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 ð System engineering activity currently focused on § § command an control interfaces on-board software light curve corrections and data processing ground segment architecture ð Ground Segment & System Review in November 2002 ð Contract with the launcher to be signed this year COROT Science Week, Paris, 13 -16 May 2002 15

AOCS performances l Pointing and AOCS ð 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] m. Hz ð Instrument used for angle error measurements § random and periodic sensor errors divided by 10 § thermo-elastic variations between star tracker and payload frames removed 1999 preliminary budget § Small gaps of perturbations (< 3 % of the time) should remain during : eclipse entries/exits, MTB activations and solar panels rotations COROT Science Week, Paris, 13 -16 May 2002 16

AOCS performances l Pointing and AOCS Target quaternion Sensors PROTEUS Estimator Controller Actuators Gyroscopes Kalman Wheels Star Tracker Filter MTB AOCS loop modified COROT payload A 2 E 2 Chain 2 E 1 Chain 1 A 1 ( , , )1 or 2 COROT Science Week, Paris, 13 -16 May 2002 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 17

AOCS performances l Requirements at spacecraft level The PSF movement on the CCD surface is split up into 3 spacecraft rotations ð Random requirements (1 ) § 0. 3 arcsec on Ys, Zs § 24 arcsec on Xs (inertia Iyy, Izz >> Ixx) Ys ð Periodic requirements (0 -peak amplitude) § 0. 1 arcsec on Ys, Zs § 4. 4 arcsec on Xs l Xs Requirements at instrument level Zs Based on temporary worst case estimates ð Random requirements (1 ) § 0. 09 arcsec on Ys, Zs § 15 arcsec on Xs lever effect : 1, 000 pixels pixel size : 2. 32 arcsec ð Thermo-elastic periodic requirements (0 -peak amplitude) § 0. 06 arcsec on Ys, Zs § 9 arcsec on Xs COROT Science Week, Paris, 13 -16 May 2002 18

AOCS performances l Spacecraft dynamic simulations (1) ð work undertaken by CNES and ASPI § CNES as prime § ASPI as industrial architect ð objectives § characterization of each perturbation (environment, hardware) § consolidation of the requirement set § reference data for further system analyses ð 6 -month activity run in 3 steps § preliminary analysis § simulation software upgrade § simulation campaign ð results available since December 2002 COROT Science Week, Paris, 13 -16 May 2002 19

AOCS performances l Spacecraft dynamic simulations (2) ð 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 ð PASIFAE simulation software upgrade § dynamic filter implementation § MTB proportional control law ð Simulations § assessment of each external/internal perturbation torque § global simulations for system analysis COROT Science Week, Paris, 13 -16 May 2002 20

AOCS performances Kinematic filter COROT Science Week, Paris, 13 -16 May 2002 Dynamic filter 21

AOCS performances COROT Science Week, Paris, 13 -16 May 2002 22

AOCS performances Scientific bandwidth 0. 005 Hz COROT Science Week, Paris, 13 -16 May 2002 0. 05 Hz 23

AOCS performances l Random noise budget Simulation-based ð The requirements are met in any case ð Typical 2 D value of 0. 3 arcsec COROT Science Week, Paris, 13 -16 May 2002 24

AOCS performances l Periodic noise budget Scientific bandwidth ð The instrument harmonic errors are not rejected § 9 arcsec on Xs at 0 § 0. 06 arcsec on Ys, Zs at 0 ð Many perturbation lines on Ys and Zs due to external environment § gravity gradient at 2 0 § Earth magnetic field even harmonics at 2 0, 4 0, 6 0 ð Most of 2 D pointing noise requirements are met ð Frequency band polluted < 100 Hz COROT Science Week, Paris, 13 -16 May 2002 25

AOCS performances l Conclusion ð The simulations give hope for a random noise of 0. 3 arcsec (1 ) ð The duty cycle is improved (+ 2. 7 %) by the removal of the MTB periodic perturbations ð Despite several lines due to gravity gradient and magnetic torque in [0. 1 ; 1] m. Hz, the spectrum pollution is less than 100 Hz ð 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 COROT Science Week, Paris, 13 -16 May 2002 26

AOCS performances l Other works in progress ð 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 ð 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 ð Multi-mode AOCS simulator implementation § Safe Hold Mode simulations (Monte Carlo) § validation of the Mission mode performances COROT Science Week, Paris, 13 -16 May 2002 CNES 27