[meteorite-list] Japan's Asteroid Explorer Begins Voyage Back to Earth (Hayabusa)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 26 Apr 2007 09:02:30 -0700 (PDT)
Message-ID: <200704261602.l3QG2Ud19744_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n0704/25hayabusa/

Japan's asteroid explorer begins voyage back to Earth
BY STEPHEN CLARK
SPACEFLIGHT NOW
April 25, 2007

A small Japanese asteroid probe riddled by a streak of bad luck began
its slow limp home Wednesday, but officials still face a myriad of
challenges to bring the craft back in 2010.

Controllers sent commands for the Hayabusa probe to start one of its
four ion engines Wednesday, officially beginning its three-year journey
to Earth.

The milestone came after months of tests to determine whether the
900-pound spacecraft was healthy enough to attempt the voyage. Hayabusa
is running on a damaged battery and just one of its four ion engines is
currently deemed ready for long-term operations, according to the
Japanese Aerospace Exploration Agency, or JAXA.

Hayabusa also lost two of its three fast-spinning reaction wheels
responsible for attitude control. After the failures, the craft was
forced to exhaust all of its chemical propellant reserves.

Engineers devised a new attitude control scheme using excess xenon fuel
used by Hayabusa's electric propulsion system. Officials estimate
Hayabusa's tanks still hold more than 66 pounds of xenon, while only
about 44 pounds are needed for the Earth-bound leg of its mission.

JAXA officials remain cautious about the chances of Hayabusa
successfully reaching Earth.

"This is not an optimistic operation, but a very tough operation," said
Junichiro Kawaguchi, Hayabusa project manager, in a February interview.
"The spacecraft is not in a very healthy state."

The probe is still located in the vicinity of asteroid Itokawa, a small
potato-shaped space rock that was the subject of three months of
scientific scrutiny by Hayabusa in 2005. Ground teams believe the
spacecraft is currently about 50 million miles from Earth.

Hayabusa will have to complete two more orbits around the Sun before
reaching Earth in June 2010, when it is expected to separate its return
capsule for a parachuted landing in southern Australia.

The reentry vehicle was designed to house small chunks of Itokawa
retrieved as Hayabusa swooped down to the surface of the asteroid. A
small pellet was to fire into the asteroid to force dust and rocks into
the sample chamber, but reviews of data streaming back from the
spacecraft later caused engineers to question whether the system worked
as planned.

Officials will likely not know for sure if the capsule contains any
samples until it lands.

The start of the return trip was postponed by a year after a fuel leak
in December 2005 threw Hayabusa off course and cut off communications
with the probe for six weeks.

On Tuesday, JAXA released a heap of catalogued raw science data from
Hayabusa's mission. The data included more than 1,600 optical images,
about 135,000 pieces of spectral data in the near-infrared and X-ray
bands, and 1.7 million data points from a laser rangefinder.

Scientists also assembled a three-dimensional shape video of Itokawa,
which is believed to have been formed by the collection of several
smaller bodies linked together by loose material and weak gravity. See
the movie clip here
<http://hayabusa.sci.isas.jaxa.jp/data/shape/movies/itokawa_g070104.mov>.
Received on Thu 26 Apr 2007 12:02:30 PM PDT