[meteorite-list] Daring Asteroid Probe on Course to Reach Earth in June (Hayabusa)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 11 Jan 2010 10:07:42 -0800 (PST)
Message-ID: <201001111807.o0BI7gHY023397_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n1001/11hayabusa/

Daring asteroid probe on course to reach Earth in June
BY STEPHEN CLARK
SPACEFLIGHT NOW
January 11, 2010

Japan's gritty Hayabusa probe isn't the first mission to be called the
little spacecraft that could, but the small robot is on the verge of
concluding a remarkable journey through the cosmos.

Running three years late after a harrowing fuel leak and cascading
system failures, Hayabusa is on the home stretch of a remarkable
seven-year journey through the solar system.

Hayabusa was primarily conceived as a demonstration mission to test
satellite technologies, including an innovative and highly-efficient ion
propulsion system that consumes xenon gas. The mission's secondary, but
more visible, objective was to fly to an asteroid and scoop samples off
its rocky surface for return to Earth.

Japanese space officials are expected to announce this week that the
probe's return to Earth is becoming more likely. Hayabusa's ion engines
will put the craft on a path by about Wednesday to be captured by
Earth's gravitational pull sometime in June, according to mission
officials.

"We think, as a technology demonstrator, Hayabusa has a big mission of
accomplishing a round trip to asteroid," said Junichiro Kawaguchi,
Hayabusa's project manager. "And from that point of view, we are about
to complete the mission."

Kawaguchi is referring to the Hill sphere, the region of space where
Earth's gravity is the dominant force affecting nearby objects. Earth's
Hill sphere extends about 1.5 million kilometers, or 932,000 miles, in
all directions from the planet.

Entering the Hill sphere does not mean Hayabusa is on course to
intercept Earth.

Hayabusa's sole operating ion engine will continue thrusting until March
to guide the spacecraft on a razor-thin trajectory to release a hardened
capsule for re-entry over Australia. The rest of the refrigerator-sized
probe will burn up in Earth's atmosphere.

Officials won't reveal a specific date for the arrival, saying they wish
to prepare for the recovery away from the glare of publicity. Japan has
a mixed history with robotic deep space missions, including the failed
Nozomi mission to Mars and the ambitious and successful Kaguya probe
that studied the moon.

The Nozomi mission was afflicted with problems similar to Hayabusa, and
Japan maintained the probe could reach Mars until the spacecraft missed
the Red Planet and flew into solar orbit in 2003.

The Hayabusa spacecraft is now limping through space, propelled by a
makeshift ion engine using components from two powerplants previously
declared failed. Ground teams rigged the new thrusting technique after
Hayabusa's last fully operational engine stopped working in November.

Hayabusa is also down to one reaction wheel to maintain the probe's
orientation in space. The craft's other two reaction wheels failed
within two years of launch.

"We have devised a (plan) to lower the rotation speed and also relaxed
torque level for Hayabusa," Kawaguchi said. "However, it is kind of a
miracle that the wheel is still alive and available."

Engineers are also worried that residual propellant from a 2005 fuel
leak could still coat the spacecraft's outer skin. When Hayabusa travels
closer to the sun as it approaches Earth, the fuel could heat up and
evaporate, causing an "eruption" that may send the spacecraft in an
out-of-control tumble, according to Kawaguchi.

Assuming Hayabusa survives those toils, the spacecraft's return capsule
must survive a fiery-hot re-entry into the atmosphere with a heat shield
two years beyond its design life.

That's because a series of problems after Hayabusa's 2005 reconnaissance
of asteroid Itokawa forced managers to postpone the probe's return from
2007 until 2010.

If Hayabusa successfully returns to Earth, Japanese engineers will have
accomplished a feat unmatched by the world's other space agencies -- the
return of a spacecraft from the surface of an asteroid.

Such an achievement wasn't by design.

Hayabusa inadvertently spent about 30 minutes on the surface of Itokawa
in November 2005 during a botched attempt to gather samples from its
gravelly surface.

The sample collection system was designed to fire a projectile into the
asteroid's surface, breaking loose bits of rock and funneling the
material into a chamber.

According to an analysis of telemetry recorded from the spacecraft,
Hayabusa never fired a pellet during two sample collection attempts,
deflating the hopes ot scientists.

Itokawa is a potato-shaped asteroid with a very low density. Scientists
describe such objects as rubble piles.

Kawaguchi said there is a low chance fine grains from Itokawa were
transported into the collection chamber as Hayabusa bounced on the
asteroid's surface. But there would be "no surprise" if the container is
empty, Kawaguchi said.

Despite long odds, Hayabusa has overcome every obstacle thrown in its
path since its launch in May 2003. Only five months stand between
Hayabusa and history, but the mission's toughest challenges may still be
ahead.

Kawaguchi gives a 60 percent chance of Hayabusa completing its journey
and returning its re-entry capsule to the ground, with or without a
cache of precious samples.
Received on Mon 11 Jan 2010 01:07:42 PM PST