Attitude Control of the AsteroidFinder/SSB
The German Aerospace Center (DLR) aims to develop and operate a standard satellite bus (SSB). It will be suitable for multi-type missions and applications. It will enable independent and fast access to space for DLR’s research institutes. It will also establish necessary capabilities and facilities for satellite development within DLR. DLR’s Institute of Space Systems is supervising the program while the department of Guidance, Navigation and Control Systems is responsible for the Attitude Control System (ACS) of the SSB
The SSB program is based on the Bi-Spectral-Infra-Red-Detection (BIRD) and the Technologie-Erprobungs-Träger (TET) satellite busses, which were built with contributions from DLR. It uses the experience and expertise gained during these two programs. The SSB will extend the capabilities of these two programs to achieve a more sophisticated system which can be adapted to a broader range of mission requirements.
BIRD, TET and SSB are all compact satellites with an overall mass of approximately 100 kg to 150 kg. The dimensions of each satellite allow a piggy-back launch.
The primary payload of the SSB is the AsteroidFinder. AsteroidFinder is an optical telescope that will search for asteroids. The focus is placed on identifying and discovering asteroids with an orbit that is inside the Earth’s orbit around the Sun. Such Asteroids and Inner Earth Objects (IEOs) could be a potential risk for the Earth. Today there are only a few IEOs discovered.
The optical payload is placing challenging requirements towards the Attitude Control System. Especially the stability during the observation time is a driving requirement. These requirements have to be addressed during every design phase. Due to restrictions of the available hardware it is challenging to meet the required performance with a compact satellite like SSB.
To be able to control the SSB it uses reaction wheels for the precise control. In addition to this magnetic torques are used to desaturate the reaction wheels. Beside the attitude control the attitude determination is important. This is realized with sun sensors, magnetometers, star cameras, gyroscopes and a GPS-Receiver.
The main focus for the attitude control system is to identify and design algorithms that are suitable for the AsteroidFinder mission. These algorithms have to be precise and autonomous enough to allow a successful mission. Especially the attitude determination algorithm has to be good enough to determine the attitude and the angular rates of the satellite in a sufficient way. Therefore the payload (a telescope) itself is included as an additional attitude sensor.
Another point are the internal and external disturbances which have to be addressed. Here are the internal disturbances which are introduced by the reaction wheels a relevant disturbance source.
The design of an Attitude Control System which addresses all of these aspects is necessary for a successful AsteroidFinder/SSB mission.