Hayabusa's Way Back to Earth by Microwave Discharge Ion Engines

The cathode-less electron cyclotron resonance ion engines, μ10, propelled the Hayabusa asteroid explorer, launched in May 2003, which is focused on demonstrating the technology needed for a sample return from an asteroid, using electric propulsion, optical navigation, material sampling in a zero gravity field, and direct re-entry from a heliocentric orbit. It rendezvoused with the asteroid Itokawa after a two year deep space flight with a delta-V of 1.4 km/s, 22 kg of xenon propellant consumption and 25800 hours of total accumulated operational time of all the four ion engines added up. Though it succeeded in landing on the asteroid on November 2005, the spacecraft was seriously damaged. This delayed the Earth return in 2010 from the original plan in 2007. Reconstruction on the operational scheme using remaining functions and newly uploaded control logic made Hayabusa leave for Earth in April 2007. After a coasting period of 2008, the ion propulsion was reignited in February 2009. Although most of the neutralizers were degraded and unable to be used by fall of 2009, a combination of an ion source and its neighboring neutralizer has been successfully operated for the last 3230 hours including a series of final trajectory correction maneuvers. Before reentry, the total accumulated operational time reached 39637 hours consuming a total of 47 kg Xenon propellant. Total duration of powered spaceflight is 25590 hours which provided a delta-V of 2.2 km/s and a total impulse of 1 MN·s, approximately. Finally, the spacecraft returned to Earth. Its reentry capsule, which may contain samples from asteroid Itokawa, was retrieved from the Australian outback according to plan .