Design and development of the first Quasi-Zenith Satellite attitude and orbit control system

The quasi-zenith satellite (QZS-1) is the first Japanese first navigation satellite to demonstrate the technology for providing GPS interoperable and augmentation services around Japan and Oceania. The attitude and orbit control system (AOCS) of the QZS-1 has several features that improve the mission availability. The use of a star tracker in a GEO altitude orbit and yaw steering function for high inclination are important features. In addition, robust software can maintain nominal operation, even in cases where one failure would occur in attitude sensors, actuators, or the main computer. Furthermore, the intervals of reaction wheel momentum unloading and orbital maneuvers are maximized by optimizing the system design and considering disturbances, such as solar radiation pressure, orbital perturbations, and thrust variations. As described herein, we present an overview and the design results of the QZS-1 attitude and orbit control system.