A FORMATION FLYING CONTROL ALGORITHM FOR THE CANX-4&5 LOW EARTH ORBIT NANOSATELLITE MISSION

摘要

The latest Canadian Advanced Nanospace experiment (CanX-4&5) is a dual-satellite formation flying demonstration mission. The mission objective is to prove that satellite formation flying can be accomplished with sub-meter tracking error accuracy for low ΔV requirements. The formation flying maneuvers for this mission require the development of control algorithms for autonomous formation maintenance and reconfiguration in the presence of orbital perturbations. In this paper, the development of suitable relative reference trajectories is discussed, and a linear quadratic regulator state-feedback solution for the control problem is described. A discrete thrusting scheme, using pulse width modulation, is applied to account for the fixed impulse limitation of the real spacecraft. A navigation algorithm uses Global Positioning System (GPS) carrier phase and Doppler data to obtain relative position and velocity measurements to within 2-5 cm and 1-3 cm/s, respectively. Using an extended Kalman filter, the estimated state of the spacecraft is formed by combining noisy GPS measurements with a simulated state. Four formations will be flown on the CanX-4&5 mission: two along-track orbit formations with spacecraft separation distances of 1000 and 500 m, and two projected circular orbit formations with separation distances of 100 and 50 m. The transition between each formation is achieved via a series of impulsive maneuvers performed by the deputy satellite. Current simulations of the overall mission-50 orbits in each formation-demonstrate submeter tracking errors during formation maintenance and a total required ΔV of 6.93 m/s.