As already reported, the spacecraft Hayabusa had been out of communication due to
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
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.
● Since Jan of 2006, when Radio Communication was Restored.
・Spacecraft operation intensively performed Attitude Control and Spin Orientation
・Baking, Test-drive of ion engines, Orbit Determination, Re-charging broken Li-ion battery
and so on were performed successfully.
・Successful closure, latching & sealing of the capsule lid were done on Jan 17th and 18th,
The spacecraft now undergoes the new attitude control strategy test on orbit, preparing
for the actual cruise back to Earth at the beginning to middle of April by driving ion engines
●Major Operation History in 2006 to 2007
4B Attitude Control via Xe-jet. Baking of Reaction Control System.
4E Test Drive of IES-B, D. They were confirmed operable.
5E Radiation Pressure Attitude Control started.
７E Charging Li-Ion Battery.
9E Aphelion (1.7AU) 7 cells were charged safely.
10 One Heater line was lost. Potential Fuel Freeze.
11 Distance to Earth shorter than 1AU.
12 Orbit Determination
12/16 RCS Thrusters Baking.
12/22 Attitude Reorientation via Xe-thrusters.
12/23 At the Opposition Geometry.
1/10 Orbit Determination
1/13-14 Heating Actuators for Capsule & Transfer Mechanism
1/17-18 Sample Transferred. Closing the capsule lid and Latch & Seal.
1/22- Uploading new attitude control laws and preparation for Cruise.
●Discharge-to-Charge History in Hayabusa Li-Ion Battery
Four cells among the 11 lithium-ion battery cells were not functional caused by the short-
circuit occurred in the out-of-communication period in Dec, 2005, while the solar power
was not available owing to the tumbling motion and the battery was over discharged. The
seven healthy battery cells had been slowly recharged at a minimum current, until the
recharging operation was successfully completed in Sept, 2006.
●Hayabusa Sample Collection Device
●What the ‘Lid-Closure’ Operation was?
●Lid-Closure Operation Result
The sample-catcher was actually transferred into the capsule and latched and sealed
successfully on Jan 17th?to 18th, 2007.
When the cool Sampler-Catcher (6deg C) was transferred into the warm Capsule (8deg C),
the Capsule temperature exhibited decreasing tendency. It well agreed with the ground test
performed before launch and can be regarded as an indirect proof of successful insertion.
●Return Trajectory to Earth in 2010
・New trajectory (red line) leaving Itokawa vicinity in spring of 2007, returning to the Earth in
June of 2010 is shown here.
・The Xenon gas consumption meets the current amount that remains. Xe left amounts more
than 30kg. Cruise flight requires less than 20kg.? Adequate Xe gas amount for the rest of flight.
●Trajectories of Hayabusa & Itokawa
Light blue circle shows Itokawa and Blue circle shows Hayabusa positions in June of 2010,
when the spacecraft returns to the Earth.