THE SPOT 5 AOCS IN ORBIT PERFORMANCES

摘要

SPOT 5 is the latest in a series of CNES satellites designed to fulfill an Earth observation and imaging mission. SPOT 5 is positioned on a Sun-synchronous orbit. It carries an optical observation payload featuring an image resolution one order of magnitude better than its predecessors Spot 3 and Spot 4. SPOT 5 has been successfully launched on an Ariane 4 on May 4th, 2002. The first part of this paper summarizes the major characteristics of the SPOT5 Attitude and Orbit Control System (AOCS). The second part of the paper presents the actual behaviour of the AOCS during the Launch and Early Operation Phases. The behaviour of the AOCS will be illustrated from actual flight telemetry data. In particular, the operation sequence of the commissioning phase will be presented. It includes : 1. the smooth behaviour of the Rate Reduction Mode, for an in orbit injection very close to the expected optimum values, 2. the Earth acquisition, performed in about 2 minutes, 3. the Solar Array deployment phase, with the nominally expected resulting attitude perturbations, 4. the next re-acquisition phase to converge into the operational mode, 5. the attitude update using the Star Sensor units. The last part of the paper presents the results of the commissioning analyses performed to estimate and to compensate the initial biases observed between the Earth Sensors measurements, the Star sensor, the gyros, and the payload images. Beside the improvement and simplification of the payload operations, the identification and compensation of the biases are needed for the nominal AOCS operations. The sensitive on-board autonomous Failure Detection, Isolation and Reconfiguration would otherwise trigger if an unexpected bias or an unwanted estimation drift error remained during the operational phase. The commissioning phase is now over. After correction of biases, the pointing and estimation performances are satisfactory.