Japan Aerospace Exploration Agency (JAXA) promoted Hayabusa asteroid sample return mission, which was launched in 2003 and returned to Earth in 2010. The retrieved capsule contained many particles originating from the S-type asteroid Itokawa. Based on the Hayabusa's achievements, Hayabusa-2 succeeded to rendezvous with the C-type asteroid Ryugu in 2018. It has accomplished all of the proximity operations such as remote sensing, robot separations, crater formation, landings, and so on, and will come back to Earth in 2020. JAXA is now putting our space assets, from Mercury to Jupiter, which will make the JAXA Deep Space Fleet to elucidate 4.6-billion-year history of the Solar System.
The Hayabusa spacecraft rendezvoused with the asteroid Itokawa in 2005 after the powered flight in the deep space by
the μ10 cathode-less electron cyclotron resonance ion engines. Though the spacecraft was seriously damaged after the
successful soft-landing and lift-off, the xenon cold gas jets from the ion engines rescued it. New attitude stabilization
method using a single reaction wheel, the ion beam jets, and the photon pressure was established and enabled the
homeward journey from April 2007 aiming the Earth return on 2010. The total accumulated operational time of the ion
engines reaches 31,400 hours at the end of 2007. One of four thrusters achieved 13,400-hour space operation.
Strategy of formation flying for the X-ray Evolving Universe
Spectroscopy mission (XUES) is discussed, in which an X-ray telescope
of 10 m diameter and 50 m 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.
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