[meteorite-list] Hayabusa Yields Insight For Planetary Defense

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Dec 14 15:57:35 2005
Message-ID: <200512142056.jBEKu1V17628_at_zagami.jpl.nasa.gov>

http://www.space.com/businesstechnology/051214_after_hayabusa.html

Asteroid Probe Yields Insight For Planetary Defense
By Leonard David
space.com
14 December 2005

BOULDER, Colorado - Following roughly two months of notable operations
at asteroid Itokawa, Japan's Hayabusa probe is damaged goods. Hindered
by thruster and gyroscope breakdowns, the spacecraft is under makeshift
attitude control with engineers hoping to finesse the craft onto a
homeward-bound trajectory back to Earth.

On Wednesday, the Japan Aerospace Exploration Agency (JAXA), announced
that the troubled spacecraft would not begin its return flight back to
Earth for at least another three years, owing to critical system
failures including a fuel leak. Hayabusa was to begin its trek home in
mid-December, when Earth and the asteroid it now orbits are at a
relatively close distance. The probe was to drop a capsule in the
Australian outback in June 2007.

Whatever its destiny, Hayabusa, has generated priceless data for future
treks to similar objects - by robots and humans. The intrepid robot is a
heads up, not only for how best to utilize asteroid resources, but also
to spoil a space rock's aim if found to be on a direct-hit heading for
Earth.

Multi-tasked robot

Now some 180 million miles (290 million kilometers) distant from Earth,
Hayabusa is over 340 miles (550 kilometers) away from Itokowa, chugging
through space at a modest three miles (5 kilometers) per hour. A turning
on of the craft's propulsive ion engine this week is planned.

Hayabusa is a project of Japan's Institute of Space and Astronautical
Science (ISAS), a research arm of JAXA.

The multi-tasked robot not only deployed hardware atop the space rock.
It made repeat touchdowns on the asteroid too. But whether it succeeded
in bagging specimens of Itokawa'a goal of the complex mission - remain
unclear.

During operations at Itokawa, the probe released an ultra-small
MIcro/Nano Experimental Robot Vehicle for Asteroid - MINERVA for short.
But it was released too high above the asteroid with the camera-carrying
device never reaching Itokawa's rock-strewn surface.

Important rehearsals

When it arrived at its target in September, Hayabusa began a close-up
imagery sweep of the potato-shaped Itokawa, roughly measuring 1,800 feet
(549 meters) long by 590 feet (180 meters) wide.

"The rocky and rough surface of the asteroid was surprising," explained
Donald Yeomans, Supervisor of the Solar System Dynamics Group at the Jet
Propulsion Laboratory in Pasadena, California. "The 16-minute light
travel time [between Earth and the spacecraft] makes real-time
communications very difficult."

The Hayabusa team did manage a near perfect touch-and-go operation on
November 15, Yeomans pointed out, but the subsequent communications with
the spacecraft was well below the nominal rate of data stream.

Yeomans said that touching down on the surface of asteroid Itokawa was a
tough assignment. "The Hayabusa Operations Team changed strategies and
plans as they learned more about the navigation of a spacecraft near a
nearly mass-less body," he said.

Hayabusa operations spotlighted that rehearsals were very important for
touchdown on the small asteroid, Yeomans said.

A true pathfinder

"My personal opinion is that results from the Hayabusa mission can be
used to engineer more robust strategies for future asteroid rendezvous
missions," said Daniel Scheeres, Associate Professor of Aerospace
Engineering at the University of Michigan in Ann Arbor.

Scheeres said that the Japanese probe is a true "pathfinder" and an
important technical demonstration mission.

"The results from the current mission will be essential for developing a
better understanding of the actual asteroid environment, and for making
large advances in asteroid science," Scheeres told SPACE.com.

"Clearly, the lessons learned from this mission will fundamentally
influence all future asteroid rendezvous missions," Scheeres said.

Anticipate and impede

Over the years, various schemes have been proposed to deflect an
asteroid found to be scary to Earth.

Blasting an asteroid with focused sunlight, strapping rocket motors to
one, detonation with with a nuclear bomb or just smacking it via a
kinetic impactor similar to that used during NASA's Deep Impact mission
in July - all these and other techniques have advocates and detractors.

What's needed, however, is better understanding of asteroid structures
before a deflection is undertaken.

The Hayabusa mission has been closely monitored by officials within the
B612 Foundation, an organization with the goal of significantly altering
the orbit of an asteroid, in a controlled manner, by 2015.

The group's name stems from the asteroid home of the Little Prince in
Antoine de Saint-Exupery's child's story: The Little Prince. The
foundation advocates honing the capability and technological wherewithal
to anticipate and impede Earth-impacting asteroids.

Of late, the group has been on the campaign trail to call attention to
asteroid Apophis. The object makes an exceptionally close flyby of Earth
on April 13, 2029. More importantly, this passer-by might have its
trajectory altered during the swing-by, possibly putting it on a
devastating direction toward Earth seven years later.

The B612 group has advocated placing an active radio transponder on the
object. Doing so at a fairly early date would yield the requisite
orbital accuracy of the asteroid as it careens through space.

Cosmic choreography

It is no wonder that B612 Foundation chairman, Russell Schweickart, a
former Apollo astronaut, has been keenly observing Japan's Hayabusa
mission, the loss of the MINERVA, as well as the touch-and-go cosmic
choreography done by the probe.

"Things don't 'fall' normally around small cosmic bodies," Schweickart
told SPACE.com from his office in Tiburon, California. "The local
gravity is so low that any lateral velocity has an exaggerated effect.
The behavior of objects around asteroids is counter-intuitive, if not
absolutely chaotic," he explained.

"Because of this low gravity, we B612'ers talk about 'docking with' a
near Earth object and not 'landing on' one," Schweickart added.

In fact, NASA astronaut Edward Lu - on the B612 Foundation's board of
directors, recently co-authored a plan with fellow astronaut Stanley
Love for a "no touch" asteroid tractor.

The idea is to use gravitational forces of a spacecraft to
ever-so-slightly pull an asteroid into a non-threatening orbit if the
object was indeed found to be on a collision course with Earth.

Schweickart said that he's eager to learn more about what Hayabusa was
able to glean about its asteroid target, from finding out the mass of
the space rock and its spin rate, as well as the orientation of the spin
axis of Itokawa.

"These are the sorts of parameters that we would have to determine prior
to docking in preparation for an 'asteroid tugboat' type operation."
Schweickart added. "Of course, for the stand-off gravity tractor, these
things are not necessary bits of knowledge...only interesting."

Proof-of-concept

In some ways, deciphering genuine difficulties encountered by the
Hayabusa mission itself from glitches in spacecraft hardware has been
tough to do.

Still, it is apparent that Hayabusa has offered both important science
data regarding asteroids, as well as information on how to operate
spacecraft around and on the mini-worlds, said Clark Chapman, a
planetary scientist here at the Southwest Research Institute's
Department of Space Studies. He is also on the B612 Foundation's Board
of Directors.

As an asteroid specialist, Chapman noted that he was thrilled by the
images produced by Hayabusa, but very disappointed about the loss of
MINERVA.

"Remember this is a proof-of-concept engineering mission, not a science
mission," Chapman explained. "We really do have to learn how to operate
in the vicinity of an asteroid if we are ever going to use them for
space resources or if we are going to have a reliable capability to
deflect a dangerous one," he told SPACE.com.
Received on Wed 14 Dec 2005 03:56:00 PM PST