The Magnetic Attitude Control of ABRIXAS

ABRIXAS is a small astronomical satellite planned by the Astrophysical Institute Potsdam (AIP) and the German Space Agency DARA. Its main scientific objective is to survey the total hemisphere; the satellite rotates once per orbit along the sun line, and after half a year the survey mission will be fulfilled. The attitude control system is one of the most critical subsystems with respect to cost and mission success, and an independent study was done. With a momentum biased system, three magnetic torquers and a sun sensor the mission requirement of 10 arc-minutes accuracy can be achieved, if the torquer current is controlled by an analogous driver unit. Using the BREM-SAT simulation software (which has been verified by flight results), the "onboard" software module had been developed and tested thoroughly. For the momentum wheel discharge new procedures had to be developed which work even at equatorial orbits. As a result of this study, hardware cost reduction and early software implementation and testing had become possible.