ESA GNC Conference Papers Repository

Airbus CMG - an enabler for high pointing accuracy missions
D.L. Lasnet, P.h.F. Faucheux
Presented at:
Salzburg 2017
Full paper:

After 16 Airbus Defence and Space CMG 15-45 in orbit, cumulating over 50 years of operations, and more than 20 CMG to come, agility performances and reliability are no longer to be demonstrated. In a similar way, in orbit performances of the Pléiades and Spot6/7 satellites have been the subject of several past publications and clearly demonstrated the high level of maturity reached by the Airbus Defence and Space agile AOCS concepts. The overall mission success drivers around the spacecraft pointing accuracy are a complex combination of multiple participations, however, CMG design choices and intrinsic performances are one of the major enablers for such a result. It is thus worth elaborating on the relation between the overall system performance and the local CMG features that proved efficient in contributing to the system performance. Indeed, although CMGs are clearly not the only contribution to AOCS pointing performances, an appropriate CMG design is definitely the best way to reach success, with a lower overall system design complexity. Knowledge of the CMG status (gimbal position, generated momentum for instance) is a key for an adequate handling of the internal angular momentum, be it for offloading or guidance algorithms. On this level, encoder accuracy (resolution and precision) is obviously at stake, but mechanical design is also granting access to accurate information on the CMG behavior. Realization is the second key. With adequate CMG component design, the correct execution of the AOCS commanded momentum and torque is driving the pointing accuracy for both stability and absolute realization. Here again the encoder performances are a major point. But more difficult to master are the motor performances and overall mechanical behavior - be it friction or any other internal disturbance - that the control loop will have to reject. Airbus Defence and Space CMG design permits a high flexibility for the accommodation inside the spacecraft. The choice of independent mechanisms that could be located without constraints between each of them and of a deported electronic box allows adapting to lot of types of satellite architectures. Tilted bracket assembled under the mechanism simplifies integration of the CMG on the platform with simple mechanical interfaces. The resulting overall CMG design, closely related to AOCS architecture, is eventually a matter of balance between high end components and realistic requirements on sub-assemblies, while unavoidable imperfections are compensated by the equipment control loops. This approach allows offering in the end an optimized, performing and reliable CMG based AOCS.