Validating a formation flying control system design: the grace project experience

摘要

The Gravity Recovery and Climate Experiment (GRACE) mission will produce a new model of the Arth's gravity field with unprecedented accuracy every 15-30 days for a period of 5 years. The GRACE mission involves flying two satellites in a tandem formation spaced 100 to 500 km apart. The mission uses two co-orbiting satellites which are themselves the instrument. Variations in the Arth's gravity field are manifested in differential orbit perturbations on the two co-orbiting satellites. Inter-satellite range varitions are measured using a high frequency inter-satellites. Inter-satellite range variations are measured using a high frequency inter-satellites. Inter-satellite range varitions are measured using a high frequency inter-satellite cross-link with micron-level precision. Precision 3 axes accelerometer measurements are processed to remove non-gravitational contributions to the range change. The GRACE Attitude and Orbit Control System uses star tracker attitude measurements and GPS based orbit determination to precisely point the two spacecraft at each other using cold gas thrusters and magnetic torque rods. The program is cosponsored by NASA and the German Space Agency, DLR, and is being developed by an itnernational U.S.-German design team. It is scheduled for launch in mid 2001.