[meteorite-list] Hayabusa Heads Back to Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 5 Feb 2009 12:59:58 -0800 (PST)
Message-ID: <200902052059.MAA15372_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n0902/05hayabusa/

Asteroid sampler spacecraft heads back to planet Earth
BY STEPHEN CLARK
SPACEFLIGHT NOW
February 5, 2009

Japan's Hayabusa probe, potentially loaded with the first rock samples
from an asteroid, fired up one of its ion engines Wednesday to begin the
second phase of the explorer's return voyage to Earth.

Hayabusa ignited a single ion engine at 0235 GMT Wednesday to begin
pulsing for up to 8,000 hours to finish guiding the spacecraft toward
Earth, according to the Japan Aerospace Exploration Agency, or JAXA.

The spacecraft's ion propulsion system has already completed than 31,000
hours of operations since its launch in 2003.

The probe carries four ion engines, but engineers believe some of the
devices are not capable of long-duration firings. Officials designed a
taxing return trajectory using a single engine to reduce the odds of a
major failure.

Despite the hard work of several dozen engineers, Hayabusa still faces
more hurdles before making its scheduled parachuted landing in Australia
in June 2010.

"We are not so optimistic, but not so pessimistic," said Makoto
Yoshikawa, Hayabusa project scientist.

Officials said the ion engine must accelerate Hayabusa by nearly 900 mph
by March 2010, when engineers will turn off the machine to begin the
probe's final approach to Earth.

"If the current status of Hayabusa (remains) until the final stage, we
are sure that it will come back to the Earth," Yoshikawa said.

The spacecraft still has enough xenon gas to power the ion engine and
control its orientation in space, according to JAXA.

"We are continuing to pay careful attention to our onboard equipment and
are doing our utmost to operate the Hayabusa with the greatest care,"
officials said in a statement.

The craft's ion engines use microwave discharge to ionize xenon gas and
accelerate the plasma to high speeds. The highly-efficient engines
produce little thrust, but the devices can operate for months to propel
the spacecraft across the solar system using small amounts of fuel.

Hayabusa completed the first round of return trip ion engine operations
in October 2007 after a burn lasting about four months.

The mission's ground team refined operations plans since 2007 to
increase the odds of Hayabusa's successful return, according to Yoshikawa.

Scientists also devised methods to find Hayabusa's entry capsule after
landing and created plans to transport the sample canister from
Australia to a specially-outfitted science lab in Japan, Yoshikawa said.

The science team is currently testing the mission's curation facility
and discussing how to analyze asteroid samples returned by Hayabusa.

But officials still are not sure if the 950-pound probe is actually
carrying the priceless samples.

Hayabusa spent three months near asteroid Itokawa in late 2005, studying
the space rock and attempting a series of close approaches to collect
bits of rock and dirt.

A pellet was supposed to be fired into the surface of Itokawa to force
the rocks through a funnel to guide the precious samples into a
container for the voyage back to Earth.

Those plans did not materialize in November 2005 and Hayabusa spent up
to 30 minutes on the asteroid's surface during a failed retrieval
attempt. Officials later reviewed telemetry data from a subsequent
attempt and determined the pellet likely did not fire because the system
was disarmed.

Scientists hope some particles were funneled into the collection
chamber, even if the pellet did not fire as planned.

Engineers were forced to postpone the start of Hayabusa's return trip by
a year after the mission was struck by a fuel leak and communications
problems.

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.
Received on Thu 05 Feb 2009 03:59:58 PM PST