Development of integrated orbit and attitude hardware-in-the-loop simulator system for satellite formation flying

The development of an integrated orbit and attitude hardware-in-the-loop simulator (HILS) system for autonomous satellite formation flying is presented here. The integrated simulator system consists of an orbit HILS based on a GPS simulator and an attitude HILS based on a 3-DOF table-top air-bearing system and performs four processes (orbit determination, orbit control, attitude determination, and attitude control) which interact with each other in the same manner as actual flight processes do. Orbit determination is conducted by a relative navigation algorithm using double-difference GPS measurements and an extended Kalman filter (EKF). Orbit control uses a sub-optimal state-dependent Riccati equation (SDRE) technique. Attitude is determined from an AHRS sensor, and a PD feedback controller is used to control the attitude HILS via three momentum wheel assemblies. An integrated HIL simulation is performed for a formation reconfiguration scenario in which a deputy satellite moves from planar motion with a 500m baseline to coplanar motion with a 1,000 m baseline. By performing the four processes adequately, a 3D RMS position accuracy of 5.428 mm is achieved for relative navigation, and the deputy satellite successfully arrives at the target reconfiguration position with an accuracy of 2.598 m. Consequently, the performance of the integrated HILS and the feasibility of the applied determination/control algorithms are demonstrated by the integrated HIL simulation. The integrated simulator system developed here thus provides a ground-based testbed for realistic orbit/attitude coupled simulations of satellite formation flying missions. It can also be used as a basis for the future development of a hardware testbed for satellite formation flying technologies.