1 COROT Science Week, Berlin, December 2003 COROT Week 5 Corotweeks' progress reports Operational orbit & its environment (I) Mission constraints Reference orbit parameters Housekeeping & maneuvers Environment & troublemakers Duty cycle Proposal for an orbit drift (II) Illustrated example Displays on Corotsky

2 COROT Science Week, Berlin, December 2003 Proposal for an orbit plane drift Orbit plane drift Objective to observe the seismology main targets (CP) and the associated exoplanet fields in a configuration close to the eye center (low level of straylight) at the end of the mission : to observe other targets in a wider zone of observation Principle if not strictly polar (i=90°+  i), the orbit plane drifts at d  /dt a maneuver to change inclination can start or stop the drift system constraint : drift toward Line of Equinoxes with d  / dt < 0 scale :  V = 13 m/s   i = -0.1 deg  d  /dt = -4 deg/year Proposal  initial value : 14.5 ° i maneuver to create a drift of -4 deg/an after 1 year cost : 26 m/s (to start and stop the drift)

3 COROT Science Week, Berlin, December 2003 Proposal for an orbit plane drift Position of the seismology core program main targets  (ANTICENTRE)  (CENTRE) Declination  = 12.5 deg E S S E

4 COROT Science Week, Berlin, December 2003 Proposal for an orbit plane drift  (ANTICENTRE)  (CENTRE) Declination Movement of the observation cone along the Equator  = 14.5 deg  = 6.5 deg

5 COROT Science Week, Berlin, December 2003 Proposal for an orbit plane drift Example of a scenario (2-year drift at a speed of -4 deg/year) ANTICENTRECENTRE Time (year)  (deg) deg/an Distance (r.a) between target and eye center

6 COROT Science Week, Berlin, December 2003 Proposal for an orbit plane drift Effects on displays (Corotsky) Eye shape the position of the target stars is given as a setpoint and the satellite slowly rotates to compensate the apparent movement of the sky at every moment of an observation phase, the line of sight must remain inside the observation cone (straylight constraint) the authorized observation zone is reduced to the intersection of two circles (useful zone : autocorrelation function)  (t-t 0 )

7 COROT Science Week, Berlin, December 2003 Proposal for an orbit plane drift Effects on displays (Corotsky) Zero for spacecraft roll domain the roll angle for optimum power budget  = arctan (-tan  sin  ) will change scale : if  varies between 15° and 0°,  varies between 6° and 0° not significant over 6 months, but must be taken into account over the mission ± 20° Example for Anticenter

8 COROT Science Week, Berlin, December 2003 Proposal for an orbit plane drift The drift strategy must be confirmed now  need of satellite and payload requirements for thermal study (movement of the Sun in the spacecraft reference frame)   V budget before launcher preliminary mission analysis  ground interfaces for space mechanics  system tools for Corotsky (scheduling of runs) Perimeter of decisions to be taken by the Sc. Committee  change of  initial value 14.5°  agreement on direction and maximum speed of drift - 4 deg/year  but the scenario of observation itself (list of targets, scheduling) doesn’t need a quick decision Proposal Line of sight in range 17h20 ; 19h40 5h20 ; 7h40

9 COROT Science Week, Berlin, December 2003 Proposal for an orbit plane drift Domain covered over 3 years o o o o o Example : GALACTIC CENTER