Attitude and Orbit Control Subsystem for ERS-1 and Its Subsystem Test

Abstract

This paper presents the design and EM Subsystem test of Attitude and Orbit Control Subsystem (AOCS) for Earth Resources Satellite-1 (ERS-1). Fine attitude control is required in the mission operation phase of the satellite. In this phase the AOCS adopts 3-axis strapdown attitude determination and zero momentum system using 4 skewed reaction wheels. The control law is calculated by On-Board Computer in Attitude and Orbit Control Electronics (AOCE). In the subsystem test, Dynamic Closed Loop Test (DCLT) has been performed by using all real hardware components. Earth sensor and sun sensors were attached on the servo-tables in DCLT, and two different test methods were adopted for Inertial Reference Unit (IRU). One of them was conventional method in which IRU was attached on servo-table, and the other one was the torquing-loop method which used bias current in the IRU gyro rebalance loop. The results of DCLT are as follows:-Torquing-loop method is very useful for ERS-1 AOCS.-AOCS EM has acceptable performances that attitude error is 0.11 deg max. and stability is 0.0014 deg/sec max.