[meteorite-list] Troubled Asteroid Mission Stumbles on Road Home (Hayabusa)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 9 Nov 2009 16:54:57 -0800 (PST)
Message-ID: <200911100054.nAA0swnw009762_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n0911/09hayabusa/

Troubled asteroid mission stumbles on road home
BY STEPHEN CLARK
SPACEFLIGHT NOW
November 9, 2009

Hopes are fading for the return of the Hayabusa space probe after
another of its ion thrusters failed last week, leaving just one
already-damaged engine to guide the hard-luck spacecraft back to Earth,
potentially with the first precious samples of an asteroid.

Hayabusa's four experimental microwave discharge ion engines consume
xenon gas and expel the ionized propellant at high speeds to produce
thrust. Two of the thrusters already failed before another engine shut
down last Wednesday, according to the Japan Aerospace Exploration Agency.

Thruster D's failure was caused by a voltage spike due to problems with
a neutralization vessel. A similar anomaly triggered the failure of
another engine in 2007.

The fourth ion propulsion unit, called Thruster C, was already shut down
after signs that it also might succumb to high voltage damage. Engineers
are now testing that engine to determine if it is capable of
long-duration firings.

Ion engines are more efficient than conventional chemical thrusters
because they use less fuel and can operate continuously for thousands of
hours.

Hayabusa's thrusters have accumulated almost 40,000 hours of burn time
since the probe launched in May 2003.

The engine that failed last week had been firing since February to bend
the 950-pound probe's trajectory, allowing it to reach Earth by June
2010 and release a small re-entry capsule possibly carrying samples from
asteroid Itokawa.

In February, JAXA officials said Hayabusa needed to accelerate by about
900 mph to reach Earth. Thruster D was slated to continue operating
until March, when Hayabusa would begin coasting toward its parachuted
return over the desert of Australia.

Officials now say they are evaluating the asteroid mission's return
course after last week's glitch.

Hayabusa spent three months exploring Itokawa in late 2005. The probe
took 1,600 pictures and collected about 120,000 pieces of near-infrared
spectral data and 15,000 data points with its X-ray spectrometer to
investigate the small potato-shaped asteroid's surface composition.

The spacecraft approached Itokawa several times, attempting to fire a
pellet into the asteroid's surface and retrieve rock samples through a
funnel leading to a collection chamber.

During a failed sampling attempt in November 2005, Hayabusa made an
unplanned landing and spent up to a half-hour on Itokawa, becoming the
first spacecraft to take off from an asteroid.

Although telemetry showed Hayabusa likely did not fire its projectile
while on the surface, scientists were hopeful bits of dust or pebbles
found their way through the funnel and into the sample retrieval system.

Hayabusa was later stymied by a fuel leak and ground controllers
temporarily lost communications with the spacecraft, which is about the
size of an average refrigerator.

Controllers labored to overcome the issues, which were compounded by the
loss of two orientation-controlling reaction wheels and power cells in
an electrical battery.

The craft's departure from Itokawa was delayed a year because of the
problems, postponing its return to Earth from 2007 until 2010.
Received on Mon 09 Nov 2009 07:54:57 PM PST