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

The space environment is ever-changing with the space structures getting larger and the orbits getting increasingly crowded with time. This creates a need for removal of large de-funct satellites to avoid the disastrous Kessler syndrome, which poses a major threat to the future of space exploration. This paper 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 make the configuration prone to elastic perturbations leading to complex dynamics that cannot be represented using rigid body dy-namics. 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 new 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 ^◦ /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 by applied controllers.