[meteorite-list] Hayabusa Has Steering Trouble

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Oct 7 12:26:37 2005
Message-ID: <200510071625.j97GPKX18269_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn8112-japans-asteroid-probe-has-steering-trouble.html

Japan's asteroid probe has steering trouble
Kelly Young
New Scientist
07 October 2005

Japan's asteroid-probing spacecraft has a steering problem that could
become an obstacle to the completion of its scientific mission.

The second of three reaction wheels on the Hayabusa spacecraft failed on
3 October. The reaction wheels keep the spacecraft's instruments pointed
at the asteroid Itokawa and its solar arrays pointed at the Sun. The
first wheel failed on 31 July 2005.

With the second failure, the spacecraft has had to use precious
hydrazine fuel to keep it from gradually descending toward the asteroid
and to keep it from drifting in the wrong direction. Japanese flight
controllers are currently studying the problem and determining how long
the spacecraft's fuel will last.

Launched on 9 May 2003, Hayabusa aims to be the first craft to bring
pieces of an asteroid back to Earth. Currently at the asteroid, Hayabusa
will descend toward the surface and touch down twice in November. Each
time, a fabric cone will touch the surface, triggering the firing of a
pellet into the asteroid at 300 metres per second. After each shot, the
probe will take off and attempt to catch dust ejected by the impact.
          
Shortened stay

The problem is that hydrazine fuel is needed to push off the asteroid
each time, and one rehearsal manoeuvre is also planned for November.
Hayabusa will spend mid October scouting out touchdown sites.

"They wouldn't eliminate the touchdown manoeuvres unless it was
absolutely impossible to carry them out," Don Yeomans, the mission's US
project scientist at NASA's Jet Propulsion Laboratory in Pasadena,
California, told New Scientist.

Instead, they could shorten the amount of time that Hayabusa spends at
the asteroid, thus reducing the amount of fuel that will be used to keep
the probe properly oriented. Hayabusa is scheduled to begin its journey
back to Earth in December 2005 and should arrive in June 2007.

The craft has almost finished mapping the surface of the asteroid. It
found rubble on its surface, but no visible craters, although the chunks
of rubble are consistent with material thrown out of a crater during an
impact. And the size of the rocks and blocks suggest they were thrown
out of a large crater, Yeomans says.

It is possible that something, such as seismic shaking, may be filling
in the craters. "There have to be craters there, somewhere," Yeomans
says, "they're just not obvious."
Received on Fri 07 Oct 2005 12:25:19 PM PDT