POSTIMPACT DYNAMICS OF 2 MULTIBODY SYSTEMS ATTEMPTING DOCKING BERTHING/

Berthing/docking of two spacecraft systems will become quite routine i n future operations. The shuttle will dock with the space station duri ng the latter's construction and operation. Malfunctioning satellites will be serviced by the shuttle or other free flyers. Ideally the rend ezvous between the two spacecraft systems should be smooth, but in pra ctice, there is always a velocity differential leading to an impact. U ndesirable attitude drift, and structural motion if there are flexible components, will follow this impact. This paper studies the dynamics of two multi-body systems attempting a manipulator assisted docking/be rthing considering various impact scenarios. The equations of motion f or the two multi-body systems before and after docking/berthing attemp t are obtained using the Lagrangian formulation for individual bodies and then eliminating the constraint forces and moments with the help o f the natural orthogonal complement of the velocity constraint matrix. An impact model is developed which can handle impact from fully plast ic to fully elastic. Two parameters characterizing the impact-the ener gy loss parameter and the friction parameter-are introduced. Simulatio n of the post-impact dynamics shows that the values of these parameter s have significant influence on the dynamics. Whether the end-effector is free or locked also influences the dynamics. Response using a cont rol scheme to eliminate the undesirable motion in the fully plastic ca se (i.e. for successful berthing) is presented. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.