Hayabusa asteroid explorer had been executing the powered flight toward Earth using a single
reaction wheel and the microwave
discharge ion engines since April this year.
The achievement of the
first leg of orbit maneuver around the perihelion led Hayabusa into
turning off them and shifting the spin mode from three-axis attitude
stabilization on October
24, 2007 according to the plan. The ion
engines generated 1,700 m/s delta-V with 31,000
hours in total
accumulated operational time up to now and still keep good thrust
and enough propellant. Hayabusa will fly in ballistic
manner with the spin axis tracking toward
Sun by the solar pressure
torque without any propellant consumption. And it will resume the
orbit maneuver in the second leg from February 2009 aiming for Earth
return on June 2010.
The remaining delta-V toward Earth is only 400m/s.