Since January 10 this year (2018), the third phase of the ion engine operation has been underway. This was completed this week on June 3, ending the use of the ion engines for the outward approach towards asteroid Ryugu.
During the operation on June 3, Hayabusa2’s velocity was confirmed via Doppler data (the shift in radio wave frequency corresponding to the speed of the spacecraft along the line-of-sight from Earth) and the decision was made to stop ion engine operation at 14:59 JST at machine time (the time recorded by Hayabusa2’s on-board clock). The telemetry data from the spacecraft received at 15:16 confirmed that ion engine operation has ended normally.
In this third phase of ion operation, the continuous operation time was about 2,426 hours, producing a velocity increase of 393 m/s (hourly speed of 1,400 km/hr).
From here on, accurate orbital determination of both the spacecraft and the asteroid will be made via radio and optical navigation as Hayabusa2 approaches Ryugu. We will return to report on the results of the ion engine operation and up-coming optical navigation soon.