Flexibility issues in discrete on-off actuated spacecraft: Numerical and experimental tests

Spacecraft are often characterized by the presence of large appendages with very low natural frequencies. Control strategies of such systems must necessarily take the rigid-flexible dynamics interaction into account. In particular, an unstable behavior can occur when important characteristics of a real control system, such as the time delay affecting the navigation and control loop, are considered. In fact, it is possible to show that the stability delay margins can become insufficient, and the maneuver, that can be aimed to change the platform attitude or just to damp the elastic oscillations, fails. In the present work, this problem is solved by compensating the time delay by means of a modelbased prediction algorithm. A free floating platform is used to test the navigation, control and delay compensation algorithms, confirming the soundness and the robustness of the approach.