AOCS performances

1
AOCS 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 (lt 3 of the time)
  should remain during eclipse entries/exits, MTB
  activations and solar panels rotations

1999 preliminary budget
2
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

Target quaternion
PROTEUS
Sensors
Estimator Kalman Filter
Controller
Actuators Wheels MTB
Gyroscopes
Star Tracker
COROT payload
Chain 1
(?, ?, ?)1 or 2
A1
E1
Chain 2
A2
E2
3
AOCS performances

• Requirements at spacecraft levelThe PSF movement
  on the CCD surface is split up into 3 spacecraft
  rotations
• Random requirements (1 ?) (inertia Iyy,
  Izz gtgt 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

4
AOCS 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

5
AOCS 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-offcontroller noise
  outside the scientific bandwidth
• worst case identification for subsequent
  simulationssolar 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

6
AOCS performances
Dynamic filter
Kinematic filter
7
AOCS performances
8
AOCS performances
Scientific bandwidth
0.05 Hz
0.005 Hz
9
AOCS performances

• Random noise budgetSimulation-based
• The requirements are met in any case
• Typical 2D value of 0.3 arcsec

10
AOCS 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 2?0
• Earth magnetic fieldeven harmonics at 2?0, 4?0,
  6?0
• Most of 2D pointing noise requirements are met
• Frequency band pollutedlt 100 ?Hz

11
AOCS 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
  estimateif 6 ? mv ? 8 and 500 pixels between
  stars at least

12
AOCS 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