1 COROT Science Week, Paris, May 2002 COROT mission Orbit parameters ðTwo 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) ðThe altitude will be chosen as a compromise solution §instrument/satellite performances (straylight, pointing) §duty cycle (radiation fluxes) §satellite-to-ground TC/TM link capacity

2 COROT Science Week, Paris, May 2002 COROT mission Orbit parameters ðThe 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

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

4 COROT Science Week, Paris, May 2002 COROT mission The sky observed by COROT

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

6 COROT Science Week, Paris, May 2002 COROT mission Platform design ð“PROTEUS Evolution” family §series of 5 platforms §upgraded electrical and AOCS chains ðLi-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 ðNew 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 ðOther features : new star trackers (SODERN), 2-antenna GPS

7 COROT Science Week, Paris, May 2002 COROT mission New mission schedule ðThermal constraints shrunk to payload constraints §the Ys+ satellite wall (focal unit radiator) must be in the shade as much as possible ðNo more 180° rotation on Xs between CP and EP ðNo more EP2 critical thermal configuration for payload design ðSeveral 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 CP1, EP1, CP2, EP2 is operationally recommended ðFocal 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

8 COROT Science Week, Paris, May 2002 COROT mission Previous schedule “Peace and Love” Line of nodes Summer Winter Autumn Solar declination up to +23° Ys+ Solar declination down to –23° Central Program 2 Exploratory Programs 1 & 2 180° rotation on Zs 180° rotation on Xs 180° rotation on Zs Satellite axes in a fixed orbital reference frame R OF X J2000 Y J2000 X OF Z OF 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)

9 COROT Science Week, Paris, May 2002 COROT mission Updated schedule “Apple pie” Line of nodes Summer Winter Autumn Solar declination up to +23° Solar declination down to –23° Central Program 2 Exploratory Programs 1 & 2 180° rotation on Zs Satellite axes in a fixed orbital reference frame R OF X J2000 Y J2000 X OF Z OF Equatorial plane 12.5° Earth orbit Central Program 1 Line of Equinoxes Spring S Xs+ Zs- Ys+ Zs- Xs+ Ys+ 1b 1a2b 2a Center (18h50)Anticenter (6h50)

10 COROT Science Week, Paris, May 2002 COROT mission Performance management ðPerformance 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 b phot = f(1/  T obs ) in Fourier space  spectrum analysis less sensitive to periodic perturbations (hidden lines) in EP runs  i 2 Ai / (  b phot (T)) 1 / Qi < 100  Hz ðTo 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

11 COROT Science Week, Paris, May 2002 COROT mission Focal unit configuration 0 E2 CCD A1CCD E1 CCD E2 CCD A2 XVXV YVYV Left Right Buffer dump direction Frame transfer direction 0 E1 0 A1 0 A2 3.05° 2.70° Ys+ Zs+

12 COROT Science Week, Paris, May 2002 COROT 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°

13 COROT Science Week, Paris, 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 mission

14 COROT Science Week, Paris, May 2002 COROT mission Spacecraft roll domain ðThe ± 20° requirement may prove to be difficult to meet ðThe 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 EarthASPI Accommodation of the SED-16 star trackers to be worked on §payload thermal constraintsCNES, Soditech +20° or -20° reachable for a given observing run TBC ðSet of conclusions available in September

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

16 COROT Science Week, Paris, May 2002 AOCS performances Pointing and AOCS ðStringent 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 ðInstrument 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 1999 preliminary budget

17 COROT Science Week, Paris, May 2002 AOCS 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 ControllerActuators Wheels MTB Target quaternion Sensors Chain 2 Chain 1 A1 A2 E1 E2 PROTEUS  1 or 2

18 COROT Science Week, Paris, May 2002 Requirements at spacecraft level The PSF movement on the CCD surface is split up into 3 spacecraft rotations ðRandom requirements (1  ) (inertia Iyy, Izz >> Ixx) §0.3 arcsec on Ys, Zs §24 arcsec on Xs ðPeriodic requirements (0-peak amplitude) §0.1 arcsec on Ys, Zs §4.4 arcsec on Xs Requirements at instrument level Based on temporary worst case estimates ðRandom requirements (1  ) lever effect : 1,000 pixels §0.09 arcsec on Ys, Zs pixel size : 2.32 arcsec §15 arcsec on Xs ðThermo-elastic periodic requirements (0-peak amplitude) §0.06 arcsec on Ys, Zs §9 arcsec on Xs AOCS performances Zs Xs Ys

19 COROT Science Week, Paris, May 2002 AOCS performances Spacecraft dynamic simulations (1) ðwork undertaken by CNES and ASPI §CNES as prime §ASPI as industrial architect ðobjectives §characterization of each perturbation (environment, hardware) §consolidation of the requirement set §reference data for further system analyses ð6-month activity run in 3 steps §preliminary analysis §simulation software upgrade §simulation campaign ðresults available since December 2002

20 COROT Science Week, Paris, May 2002 AOCS performances Spacecraft dynamic simulations (2) ðpreliminary 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 ðPASIFAE simulation software upgrade §dynamic filter implementation §MTB proportional control law ðSimulations §assessment of each external/internal perturbation torque §global simulations for system analysis

21 COROT Science Week, Paris, May 2002 AOCS performances Dynamic filterKinematic filter

22 COROT Science Week, Paris, May 2002 AOCS performances

23 COROT Science Week, Paris, May 2002 AOCS performances 0.05 Hz0.005 Hz Scientific bandwidth

24 COROT Science Week, Paris, May 2002 AOCS performances Random noise budget Simulation-based ðThe requirements are met in any case ðTypical 2D value of 0.3 arcsec

25 COROT Science Week, Paris, May 2002 AOCS performances Scientific bandwidth Periodic noise budget ðThe instrument harmonic errors are not rejected §9 arcsec on Xs at  0 §0.06 arcsec on Ys, Zs at  0 ðMany 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 ðMost of 2D pointing noise requirements are met ðFrequency band polluted < 100  Hz

26 COROT Science Week, Paris, May 2002 AOCS performances Conclusion ðThe simulations give hope for a random noise of 0.3 arcsec (1  ) ðThe duty cycle is improved (+ 2.7 %) by the removal of the MTB periodic perturbations ðDespite several lines due to gravity gradient and magnetic torque in [0.1 ; 1] mHz, the spectrum pollution is less than 100  Hz ðThe 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

27 COROT Science Week, Paris, May 2002 AOCS performances Other works in progress ðOptical 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 ðMission 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 ðMulti-mode AOCS simulator implementationCNES §Safe Hold Mode simulations (Monte Carlo) §validation of the Mission mode performances