Multibody Approach to Controlled Removal of Large Space Debris with Flexible Appendages

Abstract

The space environment is ever-changing with space structures getting larger and the orbits getting increasingly crowded with time. This creates a need for removal of large defunct satellites to avoid the disastrous Kessler syndrome, which poses a major threat to the future of space exploration. This research examines the dynamics and control involved in the active removal of a large space debris - Envisat. European Space Agency's e.deorbit mission aims to de-orbit Envisat using a chaser satellite, which synchronises, docks, detumbles and deorbits it. The presence of large flexible appendages makes the configuration prone to elastic perturbations leading to complex dynamics that cannot be represented using rigid body dynamics. Therefore, a unique multibody approach based on the absolute interface coordinates in the floating frame formulation is used to model the Flexible Multibody Dynamics. The novel method proves to provide a good balance between computation time and efficiency for the control application. The controllability characteristics of two phases of the e.deorbit mission are analysed using a linear PD controller and an Incremental Nonlinear Dynamic Inversion controller. For the first phase, both controllers successfully synchronise the chaser with the target debris tumbling at the rate of 3.5 deg/s about all axes. However, during the detumbling phase, the large appendage (14.2 m) in the stacked configuration introduces complex dynamics, which could not be stabilised completely by applied controllers. Nonetheless, interesting relationships could be established between the dynamics and control of the system, which will facilitate robust control design in future work.