Study of formation flying for the XEUS mission and the ISAS Design of the Detector Spacecraft

Strategy of formation flying for the X-ray Evolving Universe Spectroscopy mission (XUES) is discussed. in which an X-ray telescope of 10 in diameter and 50 in focal length will be constructed in orbit by formation flying the X-ray mirror and the focal plane X-ray detectors on two separate spacecrafts. We first studied the thrust, force required to keep the detector spacecraft (DSC) in the non-Keplerian orbit. We find the, direction of the thrust vector rotates twice per a single spacecraft orbital evolution along a circle parallel to the orbital plane. The absolute value of thrust needs to be varied by a factor of two or less. The maximum thrust force required is 0.47 N assuming a 600 km altitude and a 4000 kg DSC mass. The present baseline design requires no moving mechanism. instead requires a large amount of propellant because of relatively, low thruster efficiency. The spacecraft is estimated to weigh about 6000 kg. We studied an alternative design in which the thruster efficiency is optimized and showed that the spacecraft mass can be reduced to 4000 kg. This. however. requires a rotation mechanism and additional constraints on the spacecraft operation.