[meteorite-list] Hayabusa Update - April 4, 2007

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 12 Apr 2007 08:33:17 -0700 (PDT)
Message-ID: <200704121533.l3CFXIr09035_at_zagami.jpl.nasa.gov>

http://www.isas.ac.jp/e/snews/2007/0406.shtml

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 ]
Received on Thu 12 Apr 2007 11:33:17 AM PDT