The primary aim of this work is to construct the high precision formation flight control law applicable to the Formation Flight All-Sky Telescope mission, FFAST. FFAST is the X-ray telescope mission consisting of two formation flying small satellites. The focusing distance is 20 m, which is difficult for one satellite to realize, however precisely controlled formation flight enables to construct the long focus X-ray telescope system. The relative distance between the two satellites is required to be maintained within 20 m ± 5 cm. To estimate the feasibility of the high precision formation flying control law under "real-world" dynamics, perturbed forces caused by the Earth's gravitational potential, the air drag, the solar radiation pressure and the disturbing forces by the other celestial bodies are considered in this paper.
