PARIS -- Japan's Hayabusa asteroid sample-return spacecraft has lost the use of a second reaction wheel, forcing increased reliance on its chemical-propellant thrusters for attitude control and raising questions about whether it can make its planned asteroid touchdown in November, Japan's Institute of Space and Astronautical Science (ISAS) announced Oct. 4.

Hayabusa, known as MUSES-C before its May 2003 launch, remains in a stable position 6.8 kilometers from its target, the Itokawa asteroid, now 305.9 million kilometers from Earth. Using two reaction control systems with the remaining reaction wheel, the probe is scheduled to continue scouting possible landing sites on Itokawa in the coming weeks.

ISAS said part of the mission -- to take high-resolution pictures of the asteroid -- almost is completed. The mission also has validated the performance of the on-board optical navigation camera, according to ISAS.

Hayabusa ground controllers must now alter their mission profile to conserve fuel burned by the unanticipated use of the reaction control system. The first reaction wheel failed in July. The most recent failure occurred late Oct. 2 Japan Standard Time.

If the original mission scenario is maintained, Hayabusa in November will perform what ISAS calls "touch and go" maneuvers -- briefly landing on the asteroid, scooping up small samples and then taking off -- before beginning its return voyage to Earth, with the samples, in December. Its arrival is scheduled for June 2007.