Hayabusa mission status, 04/07/2007 (Forwarded)

Japan Aerospace Exploration Agency
Tokyo, Japan

April 4th, 2007

Status of the Hayabusa

As already reported, the spacecraft Hayabusa had been out of communication
due to the leakage of the RCS (Reaction Control System) propellant for 7
weeks since Dec 9th, 2005, until the communication was resumed in Jan,
2006. The operations carried out since then included the baking of the
spacecraft, slow recharging of the lithium-ion battery, the closure of the
capsule lid, the attitude control and spin management tests with the new
attitude control strategy via Xe cold-gas thrusters taking the advantage
of the solar radiation pressure torque, and the test operations of the ion
engines;

A new trouble in an electric heater circuitry at the RCS occurred in Nov,
2006. It was conceived related and due to the RCS propellant leakage
incident in 2005. Since the potential RCS propellant was anticipated
frozen, the baking operation was again performed to vaporize the
potentially-frozen material in order to avoid abrupt vaporization that
might cause the attitude tumbled. Small perturbation disturbance in the
spin motion was detected actually during this baking operation, but it was
within an admissible range and not critical. The project team identified
the baking and out-gassing operation was successfully performed.

Four cells among the 11 lithium-ion battery cells were not functional
caused by the short-circuit phenomenon occurred during the
out-of-communication period in Dec, 2005, while no solar power was
available owing to the tumbled spacecraft motion. The battery power was
indispensable for inserting the sample-catcher into the recovery capsule,
and also for the lid-closure operation that includes the latching and
sealing of the lid. The seven healthy battery cells, thus, had been slowly
recharged at a minimum current, until the recharging operation was
successfully completed in Sept, 2006. Simultaneously in parallel to this
operation, the ground simulation tests using a similarly and
artificially-built short-circuited cell to the onboard battery cells were
carried out in order to evaluate the operational safety associated with
the sample-catcher insertion operation. After the safety was securely
confirmed, the sample-catcher was actually transferred into the recovery
capsule, and latched and sealed successfully on Jan 17th to 18th, 2007.

The spacecraft has been undergoing the new attitude control scheme on
orbit since Feb, 2007. The new scheme takes it into account that two of
the three reaction wheels are lost and not available and the chemical
thrusters propellant is completely lost. The attitude control and spin
management maneuver are performed via Xe cold-gas thrusters and the solar
radiation pressure was made good use of to make the ion engines thrust
vector aligned to the intended acceleration direction. Under the new
attitude control scheme, the ion engines have been successfully ignited
and operated in the preparation tests so far done toward the return
cruise.

The spacecraft plans to start the actual return cruise in the beginning to
the middle of April, 2007. Though the operation of the Hayabusa is still a
challenge with full of difficulty, the project will make its best effort
taking an aim at returning it to the earth in June, 2010.

* The amount of Xe gas left on the spacecraft is more than 30kg while the
cruise flight requires less than 20kg. Thus Xe gas is adequate for the
rest of flight even taking the attitude control into account.

[NOTE: Images supporting this release are available at
http://www.isas.ac.jp/e/snews/2007/0406.shtml ]