Command shaping for a flexible satellite platform controlled by advanced fly-wheels systems
- Paper number
IAC-05-C1.P.05
- Author
Dr. Dario Izzo, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Mr. Lorenzo Pettazzi, ZARM - University of Bremen, Germany
- Year
2005
- Abstract
Coping with flexibility is an important issue in space applications as it allows to design lighter structures and therefore to save important amounts of mass. A number of works have been published in the past showing how a careful design of the attitude control system may drastically improve the system response reducing the residual vibrations. In this paper we consider the coupling between the flexibility of a spacecraft equipped with Variable Speed Control Moment Gyros and its attitude control system in the framework of command shaping techniques. We write down the complete equations of motion in an explicit form (and with a unitary mass matrix) considering a flexible platform and N wheels gimballed to it. The equations are written by standard multibody dynamics techniques. The wheels are generic Variable Speed Control Moment Gyroscopes (two degrees of freedom) and their control system is designed upon a Lyapunov based feedback relying on a rigid body model. Whenever the structure is not stiff enough, flexibility degrades the performances of the controller that fails to track the desired attitude history due to the induced vibrations. We therefore study the possibility of altering the tracking signal fed to the controller trying to get rid of the relevant frequencies notch filtering them or convolving the original signal with an ad hoc impulse sequence (input shaping) in order to reduce the vibrations. Both attitude acquisition manoeuvres and attitude tracking manoeuvres are discussed and results are given in terms of the control system performances (VSCMG gimbal angles and wheels speed are also discussed together with singularity avoidance issues). It is interesting to note how in some tracking manoeuvres the error introduced by changing the original tracking signal is smaller than the benefit acquired by reducing vibrations. This leads to an overall improvement of the control system performances also in the case of tracking manoeuvres and to the possibility of somehow coping with the structural vibrations during them.
- Abstract document
- Manuscript document
IAC-05-C1.P.05.pdf (🔒 authorized access only).
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