Basic Aspects in Designing Space Grasper Missions

Automation of in-orbit activities represents a goal of great interest for the aerospace research, due to high risk and cost related to tasks performed by astronauts. Following this approach manned mission could be replaced by servicing orbiters, conceived as graspers with arm-like appendages, whose job is to "capture" the to-be-repaired spacecraft and therefore perform the required fixes. These topics match with current interest for manipulators operating in the space environment, with a clear trend towards systems smaller than the big arms developed in the past for the Shuttle. In the frame of present paper several aspects of a grapser mission concept have been identified and investigated: i) trajectory optimisation from the parking to the servicing orbit for the space grasper; ii) rendez-vous phase navigation and guidance, in order to smoothly dock the end of the grasper link to the satellite; iii) optimal path planning of the links in order to perform a grasping manoeuvre; iv) effects of oscillations due to the flexibility during the guided manoeuvre; v) guidance, navigation and control. Carried out numerical simulations take into account all previous items. Moreover the first findings of a research program recently started at the Università degli Studi di Roma "La Sapienza" are considered while implementing the model.