[meteorite-list] Thruster Glitch Puts Hayabusa in Safe Mode

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Nov 29 13:15:03 2005
Message-ID: <200511291813.jATIDWR24960_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn8385-thruster-glitch-puts-asteroid-probe-in-safe-mode.html

Thruster glitch puts asteroid probe in 'safe mode'
Maggie McKee
New Scientist
29 November 2005

The successful landing of the Hayabusa spacecraft on asteroid Itokawa on
Saturday was almost immediately followed by another glitch for the
troubled mission - a fuel thruster glitch that forced it to go into
"standby" mode.

Mission controllers are working to restore the spacecraft back to normal
so it can return to Earth in 2007 with its cargo of the first-ever
samples from an asteroid.

The probe touched the asteroid for just one second at 0707 Japanese time
on Saturday (2207 GMT Friday). On touchdown, it fired two pellets into
the space rock to drive up material for collection in a cone-shaped horn.

But about four hours later, mission officials noticed the spacecraft was
pointed in an unexpected direction - apparently because of a problem
with one or two of its 12 fuel thrusters. These are used to manoeuvre
the spacecraft around the asteroid but have also been responsible for
controlling Hayabusa's orientation since two of the craft's three
stabilising reaction wheels failed in July and October 2005, respectively.
          
Dark clouds

The thruster problem had first been noticed during the craft's descent
towards Itokawa, prompting ground controllers to switch to a backup
system. When the craft was changed back to the main thruster system and
the problem returned, it felt like "dark clouds were creeping over the
control room", says Yasunori Matogawa, associate executive director of
the Japan Aerospace Exploration Agency (JAXA).

Officials were relieved when the spacecraft then put itself into "safe"
mode, shutting down all unnecessary systems to protect it from damage.
JAXA controllers are now working to bring it out of this mode by testing
how it responds to various commands.

"The big question is can they bring the spacecraft back to normality,
identify which of the thrusters have a problem and perhaps shut them
down," says mission team member Don Yeomans of NASA's Jet Propulsion
Laboratory in Pasadena, California, US. He is confident they will: "I
don't think it's a big problem."
          
Double bounce

The difficulty may have been caused during the craft's first landing on
Itokawa on 20 November, when Hayabusa bounced twice, then sat on the
asteroid's surface for 30 minutes. "It may have landed on a thruster and
caused some damage in the process," Yeomans told New Scientist.

The spacecraft stayed on the asteroid's surface during that touchdown
because it received opposing commands from onboard sensors. One detected
a potentially damaging boulder on the asteroid's surface and commanded
the spacecraft to rise away from the asteroid, while another found that
the spacecraft was not in the correct orientation for an emergency
ascent. This confusion also meant that no pellets were fired into the
asteroid.

Although all appeared to go well with Saturday's touchdown, JAXA
controllers have yet to receive the telemetry signals that will confirm
for sure whether the pellets were fired and whether the spacecraft was
oriented so that it could collect the resulting debris. That data will
come in the next few days, but scientists will only be certain they have
samples when they open the capsules on Earth.

If everything did go to plan on Saturday, mission controllers will
cancel a possible second sampling attempt being considered for 1
December. "They have one more pellet, so they could come down once
again," says Yeomans. "But if the pellets did fire on Saturday - and I
think they did - I would be surprised if they tried another descent.
It's too risky."

The spacecraft must leave Itokawa by mid-December to take advantage of
gravitational assists from other bodies in the solar system to return to
Earth using as little power as possible. It will use an ion engine to
propel itself during the 18-month trip and should drop a capsule
containing the asteroid samples to the Australian desert in June 2007.
Received on Tue 29 Nov 2005 01:13:31 PM PST