Status of the Hayabusa
April 4th, 2007 JST
Japan Aerospace Exploration Agency
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 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.
April 6, 2007