Abstract

To reacquire the attitude of a satellite wholly or partially stabilized on three axes a test is executed to determine if a terrestrial sensor is sensing the Earth (test 1) and if a star sensor is sensing a star whose magnitude is at least approximately equal to that of a given reference star (test 2).* Phase a. If the results of tests 1 and 2 are positive, the Earth and the star are captured and the consistency of roll information supplied by the Earth and star sensors is checked: if the information is not consistent phase (b) is carried out.* Phase b: If the results of test 1 only is positive, the Earth is captured and the satellite is caused to rotate in yaw until the result of test 2 is positive. The reference star is captured and the phase (a) consistency test is carried out.* Phases c and d: If the result of test 1 is negative, the pitch speed is reversed for at most a given time. If the result of test 1 becomes positive, test 2 is carried out. If the result of test 2 has remained negative, phase (b) is carried out. Otherwise the consistency test is carried out. Failing any result, Sun acquisition mode is selected.