June 24, 2014


Observation strategy

CoRoT is placed by a Soyuz launcher in a polar inertial circular orbit (90-degree inclination) at an altitude of 896 km. Not to be perturbed by the Earth straylight (scattered by the limb), the viewing zone is in the equatorial direction.

Twice a year, when the Sun gets closer to the orbit plane and is about to blind the telescope, the spacecraft performs a reversal attitude maneuver, dividing the year into two 6-month periods of observation (by convention, summer and winter).

  CoRoT boresight

During the observing runs (alternately 20 and 150 days), the spacecraft is 3-axis stabilized with asterocentric pointing. The jitter of stars on the detector is then less than 0.5 arcsec (0.2 pixel). The seismology channel provides the platform with the angular data feeding the attitude control system. The target line of sight and the programming of the payload are elaborated by the Mission Center, whereas the Control Center performs the pointing maneuver and sets the ACS to fine pointing mode.

The right ascension of the orbit plane (12.5°) has been chosen after a ground preparatory observation campaign: CoRoT will look in the sky at 6:50 in winter and 18:50 in summer. Thanks to the baffle efficiency, it is possible to get closer to the Earth limb direction and thus orientate the satellite inside a cone with a 10-degree radius. When projected onto the sky, this cone draws the 2 eyes of CoRoT, where will be selected the stellar fields to be observed.

A slight orbit drift (by a housekeeping maneuver of inclination change) will make it possible to broaden the viewing zone and to put the stellar fields observed closer to the eye center, where the level of straylight is the lowest. The instrument performance is thus optimized.

Seen from the satellite, the movement of the Sun is a rotation of 1° every day. To guarantee a correct level of battery charge, the solar wings are rotated every 14 days.

To know more about the CoRoT mission notably about: