GPS structural modifications for on-orbit servicing

Abstract

BACKGROUND On-orbit servicing of space systems may provide a means to implement new capabilities and to increase useful life. While me cost effectiveness of servicing architectures has been the subject of several studies, the impact of servicing on spacecraft design has not been fully addressed. The Aerospace Corporation, in cooperation with the Air Force Institute of Technology, recently conducted a preliminary assessment of structural modifications necessary to enable servicing of GPS spacecraft. Two scenarios were considered: addition of new components on-orbit, and replacement of existing components. Design modifications compatible with remote servicer concepts ranging from microsatellites to multi-arm robotic servicers were identified. The additional structural mass for servicing features was estimated using a combination of sizing algorithms and extrapolation from existing hardware. Then, an estimate of the system mass impact was determined by including modifications to power and processing requirements. Depending on the level of serviceability, the spacecraft on-orbit mass increases from 100 to 700 lb. While the mass impact may be manageable, the implementation of such concepts will depend on the resolution of several technical challenges including: design of thermal and electrical disconnects, maintenance of EMC integrity, avoidance of antenna and solar array blockage during servicing, attitude control of a coupled system, and on-orbit verification of new components.