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
COROT Science Week, Berlin, 10-12 December 2003
1
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
•
•
•
•
3
2
if not strictly polar (i=90°+i), the orbit plane drifts at d/dt
d / dt  J2ae
2
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

i
a7 / 2
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)
COROT Science Week, Berlin, 10-12 December 2003
2
Proposal for an orbit plane drift
Position of the seismology core program main targets
a (CENTRE)
292.5
282.5
272.5
262.5
 = 12.5 deg
10
171834
175726
E S
S E
Declination
5
43587
181555
49933
0
177552
46558
171234
43318
49434 45067
-5
-10
a (ANTICENTRE)
112.5
102.5
COROT Science Week, Berlin, 10-12 December 2003
92.5
82.5
3
Proposal for an orbit plane drift
Movement of the observation cone along the Equator
a (CENTRE)
292.5
282.5
272.5
 = 14.5 deg
262.5
 = 6.5 deg
10
171834
175726
Declination
5
43587
181555
49933
0
177552
46558
171234
43318
49434 45067
-5
-10
a (ANTICENTRE)
112.5
102.5
COROT Science Week, Berlin, 10-12 December 2003
92.5
82.5
4
Proposal for an orbit plane drift
Example of a scenario (2-year drift at a speed of -4 deg/year)
Time
(year)
0

(deg)
ANTICENTRE
CENTRE
43318 43587 45067 46558 49434 49933 171234 171834 175726 177552 181555
93,89
14.5
94,32
96,32
98,54
102,1
102,7
278,4
6,1
1
5,3
6,1
14.5
284,2
286,3
290,3
0,3
5,3
-1,8
0,3
-5,8
-1,8
-5,8
10,6 10,2 8,2
6,0
2,4
1,8
8,6
8,2
6,2
4,0
0,4
-0,2
4,1
3,3
2,1
2
6,6
6,2
4,6
4,2
4,2
2,0
2,2
6.5
-0,7
-1,9
2,6
2,2
2,6
0,2
2,2
0,2
2,2
2,6
0,2
2,2
0,2
-5,7
-2,7
-2,7
-1,9
2,6
-3,8
-3,7
-7,8
-5,8
-9,8
-9,8
-11,8
-13,8
-9,8
-13,8
-13,8
-9,8
-13,8
-13,8
-7,8
-7,7
Distance (r.a)
between target
and
eye center
-2,0
-5,6
-6,2
-2,0
-5,6
-6,2
-1,9
4
-1,7
1,3
-1,6
-2,2
0,0
-3,6
-4,2
0,1
3
279,2
10,6 10,2 8,2
6,0
2,4
1,8
10,6 10,2
8,2
6,0
2,4
1,8
-7,7
-2,7
-9,8
-7,7
-2,0
-5,6
-6,2
-2,0
-5,6
-6,2
-1,9
6.5
COROT Science Week, Berlin, 10-12 December 2003
-2,7
-1,9
-7,7
-2,7
-9,8
-7,7
5
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-t0)
COROT Science Week, Berlin, 10-12 December 2003
6
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
Example for Anticenter
± 20°
COROT Science Week, Berlin, 10-12 December 2003
± 20°
7
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
Proposal
14.5°
 agreement on direction and maximum speed of drift
Proposal
Line of sight in range
17h20 ; 19h40
5h20 ; 7h40
- 4 deg/year
 but the scenario of observation itself (list of targets, scheduling) doesn’t need
a quick decision
COROT Science Week, Berlin, 10-12 December 2003
8
Proposal for an orbit plane drift
Example : GALACTIC CENTER
Domain covered over 3 years
o 171834
o 175726
o 171234
o 181555
o 177552
COROT Science Week, Berlin, 10-12 December 2003
9