PERFORMANCE OF THE NEAR GC SYSTEM DURING CRUISE, EROS ORBIT, AND CONTROLLED DESCENT

摘要

The Near Earth Asteroid Rendezvous (NEAR) spacecraft performed a one-year orbital phase about asteroid 433 Eros until end of mission on 12-Feb-2001. This mission phase consisted of daily science data collection events interspersed with 25 Orbit Correction Maneuvers (OCMs) to meet orbit geometry requirements, and 15 individual Momentum Correction Maneuvers (MCMs) to dump spacecraft system momentum when needed. The mission culminated with a five hour controlled descent and soft landing on the surface, where the spacecraft continued to operate until powered off two weeks after the end of mission target date. These events all required precise spacecraft pointing and optional thrusting control. The G&C system was critical for these events and the process for modeling and developing the attitude and thrusting plans is described. Designed vs achieved OCM statistics are given. Of particular interest was the controlled descent that consisted of five pointing and thrusting events as well as image collection. This event was monitored in real-time by plotting laser ranger data against a predicted range curve and using it as a metric to assess trajectory performance as the descent unfolded. Because the spacecraft unexpectedly survived the landing, telemetry data pertaining to the final resting attitude was collected.