[meteorite-list] Hayabusa Does Have Enough Power to Fly Home

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Jun 5 17:53:47 2006
Message-ID: <200606051605.JAA12085_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn9269-hayabusa-does-have-enough-power-to-fly-home.html

Hayabusa does have enough power to fly home
Maggie McKee
New Scientist
05 June 2006

Japan's problem-plagued Hayabusa spacecraft has enough power to make it
back to Earth, tests on two of its four ion engines have revealed.

If the craft does return as planned in 2010, researchers would finally
find out whether it collected the first-ever samples from an asteroid
during its two landings on the tiny space rock Itokawa.

Hayabusa was meant to collect the samples by firing pellets into the
surface of the 535-metre-long rock and scooping up the resulting debris.
But data from two landings in November 2005 suggest the pellets never
fired because the craft's onboard computer sent conflicting signals to
its collection instruments. Still, mission officials hoped to bring the
spacecraft back to Earth in case some asteroid dust had slipped into its
collection chamber by chance.

But hope for the spacecraft's return faded after a fuel thruster leak in
late November sent it spinning out of control. When some contact with
the craft was restored at the end of January, mission controllers
realised all of the fuel in the 12 chemical thrusters had seeped away.

The chemical thrusters were already compensating for the loss of two of
three stabilising reaction wheels a few months earlier, so after the
leak the craft had to rely solely on its four ion engines, both to
control its orientation and provide the thrust to make the journey back
to Earth. The engines ionise xenon gas and then use electric fields to
accelerate the ions, providing a steady - though weak - thrust.

In good shape

But mission managers were worried that the fuel leak and resulting spin
had damaged the engines. Now they have tested two of them and found they
are "in very good shape", says mission manager Jun'ichiro Kawaguchi.

A third engine will be tested in January 2007 when the spacecraft's
orbit takes it closer to the Sun, making it less prone to damage from
the cold of space. The fourth engine will be reserved as a spare and
will therefore not be tested.

Normally, three of the engines are used together while the fourth is
kept as a backup. But Kawaguchi says: "The return cruise is possible
even with two engines." And he says there should be enough fuel for the
journey.

In fact, the spacecraft's spin rate was recently lowered to one rotation
every five minutes in order to conserve the xenon gas, which - in
neutral atomic form - is being vented to control the spacecraft's
orientation.

Kawaguchi says mission controllers are having no problems communicating
with or operating the spacecraft. However, they are not in the clear as
yet: "The spacecraft was seriously injured and operating it and making
it resume cruise are still very hard things."

Mission planners hope to begin the return trip in March 2007, when the
distance between Earth and the asteroid is once again at its minimum.
After a three-year journey, the spacecraft would drop a capsule in the
Australian outback in June 2010.
Received on Mon 05 Jun 2006 12:05:25 PM PDT