Postcapture Dynamics of a Spacecraft-Manipulator-Payload System

Abstract

Space manipulators will play an increasingly signie cant role in future space operations. They will handle payloadsofvarying geometricorphysicalpropertiesdependingontheirmissions.Intheidealcase,themanipulator should approach the payload in such a manner that, at the time of capture, the relative velocity between the endeffector and the payload grapple point is zero. Then the capture will be without impact and a smooth one. In practice, however, this is not likely, and there will be a nonzero relative velocity between the end effector and the payload grapple point, leading to an impact. In this paper we study the dynamics of the manipulator, the mother spacecraft, and the payload after such a capture with an impact. The dynamic models of the spacecraftmanipulator system before capture and spacecraft-manipulator-payload system after capture are obtained using the Lagrangian formulation. An impact model is developed to calculate the changes in the generalized velocities caused by the impact. These are then used as initial conditions for simulation of the postimpact dynamics of the combinedspacecraft-manipulator-payloadsystem.Bothrigidande exiblepayloadsareconsidered.Thesimulations show that the dynamics response can besignie cantly differentdepending on whether the capture issmooth or with an impact and whether the payload is e exible or rigid. If the dynamics are uncontrolled, the response can be undesirably large; a control scheme based on feedback linearization is proposed to avoid this.