[meteorite-list] Ambitious Mission Hopes to Return Bits of Asteroid (Hayabusa)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Aug 23 11:48:22 2005
Message-ID: <200508231546.j7NFksY28987_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n0508/22hayabusa/

Ambitious mission hopes to return bits of asteroid
BY STEPHEN CLARK
SPACEFLIGHT NOW
August 22, 2005

Slowly pulling alongside a space rock the size of several typical city
blocks, a Japanese probe is preparing to begin scooping the first dusty
samples of material from the surface of an asteroid this fall for an
eventual return to Earth.

Japan's Hayabusa spacecraft is halfway through a four-year $100 million
mission to chase down a small celestial target, retrieve pieces of its
rocky crust, and return them safely to Earth in a capsule designed to
survive the intense heat as it enters the atmosphere and parachutes to a
safe landing.

Formerly known as MUSES-C, the Hayabusa craft was launched in May 2003
aboard a solid-fueled M-5 rocket to embark on its journey to visit
asteroid 1998 SF36. The asteroid, named Itokawa, is in an orbit that
brings it close to Earth and is classified as a near-Earth asteroid,
meaning its closest approach to the Sun is inside a point 1.3 times
further than Earth's orbit.

En route to Itokawa, Hayabusa completed one orbit of the Sun and
conducted a high-speed flyby of Earth in May 2004, using Earth's gravity
to "slingshot" the 1,000-pound probe on an arcing trajectory outward
from the Sun to intercept its small target this year.

Hayabusa is busy this month calibrating instruments and cameras in
advance of its crucial arrival in the vicinity of Itokawa in the middle
of September. Its star tracker sighted the asteroid in late July and
took a series of 24 images through August 12 to refine the craft's
course to the object. Higher resolution imagery will be gathered in the
next few weeks using the optical navigation camera. As of August 15, the
asteroid had reached magnitude four when viewed from Hayabusa.

One of the probe's three reaction wheels responsible for controlling the
orientation of the spacecraft failed on July 31 when friction levels
went out of limits. Software governing modes of operation for the
reaction wheels can support the use of only two of the assemblies, and
officials are confident the fix will work. The wheels were built by the
Ithaco company based in upstate New York.

Operated by the Japanese Aerospace Exploration Agency's space science
division, Hayabusa has been propelled chiefly by three ion drive engines
relying on xenon gas and electricity to tweak its path toward Itokawa.
The high-efficiency propulsion system generates very low levels of
thrust, and therefore it must fire nearly continuously for thousands of
hours to produce optimal results.

A hands-free navigation system is also aboard Hayabusa, demonstrating
key technologies that allow the probe to precisely approach Itokawa
without intervention or commands from ground teams. During the
high-stakes approach, the hybrid system will combine optical and laser
data from on-board assets with radio data obtained from ground
telescopes on Earth.

With the craft now within 6,000 miles of its destination and closing at
82 feet per second, the most critical phase of the mission will soon
begin. By Thursday, range will be less than 4,800 miles and the closing
rate will be near 50 feet per second.

Once it reaches a point around 2,200 miles from the asteroid near the
first of September, the ion engines will be turned off to leave Hayabusa
coasting toward its target at about 33 feet per second. That closing
rate will then be slowed by smaller thrusters using chemical propellants.

Although exact dates remain elusive, Hayabusa should come to a relative
stop in what officials call the "gate position" a little over 12 miles
from Itokawa in mid-September. There it will begin to study the asteroid
as it completes one rotation every 12 hours.

Hayabusa will not enter orbit, but instead it will remain in a fixed
position after the tedious rendezvous sequence. The spacecraft could
push onward to the "home position" within five miles of the asteroid's
surface before October if all goes as planned.

The arrival at Itokawa was delayed two months from earlier this summer
after a violent solar flare in 2003 caused damage to the craft's solar
array panels that produce electricity, which is needed to power the
probe's ion propulsion system needed during the approach.

Itokawa is roughly potato-shaped and its dimensions measure about 2,000
feet by 942 feet by 866 feet. It is a member of the Apollo class of
near-Earth asteroids that pose potential impact threats to our planet
because they often cross paths with Earth during their trip around the
Sun. The asteroid travels in an elliptical solar orbit stretching from a
furthest point of over 157 million miles to a closest approach to the
Sun of around 88 million miles.

The asteroid was discovered in September 1998 by a telescope operated by
a joint team of U.S. Air Force and MIT scientists under the Lincoln
Near-Earth Asteroid Research, or LINEAR, program.

>From its static positions five and 12 miles out, the probe will
exhaustively survey the asteroid using its science payload comprised of
a high resolution imager, near-infrared and X-ray spectrometers, and
light detection and ranging equipment to map the surface in resolution
as high as three feet as Itokawa rotates below.

"Taking advantage of asteroid rotation, remote sensing is possible,"
said Jun Kawaguchi, Hayabusa's project manager.

Studies from several ground-based telescopes during Itokawa's last close
pass by Earth in 2001 revealed the object is brighter and more
reflective than would be expected with most asteroids of its type and size.

An extrapolation of these results was used to determine hypothesized
surface characteristics, which indicates a strong likelihood that
Hayabusa will find a relatively smooth but rocky surface. However, other
data suggests a complicated surface with rough terrain and larger
boulders widely strewn due to collisions with other space materials.
Officials say the surface is "enigmatic" and awaits the arrival of
Hayabusa, according to a report presented at 2004's Lunar and Planetary
Science Conference.

Scientists hope to gain an even better understanding of the physical
properties and chemical make-up of the asteroid using Hayabusa's
instruments to locate potential locations for sample retrieval,
scheduled to get underway in November.

When landing sites are chosen, the Hayabusa spacecraft can make up to
three passes to attempt to capture a total of one gram of surface
samples, or about two one-thousandths of a pound.

The approaches will heavily lean on the autonomous navigation system
aboard the probe, which must operate correctly with little input from
engineers 200 million miles away on Earth and cope with the extremely
weak gravity field of Itokawa. A target marker will be released on the
surface as the spacecraft closes in.

During each opportunity, a 16-inch funnel will first make contact with
the asteroid, followed by the firing of a small metal projectile into
the surface at well over 600 feet per second. Rocks and dust kicked up
by the impact will be gathered by the funnel and fed into the sample
collection capsule to be returned to Earth.

"It breaks the surface and ejecta climbing up through a funnel-like
device are collected by a sample catcher," Jun Kawaguchi explained.

On the first pass, it is planned for Hayabusa to deploy a tiny rover
called MINERVA to move across the asteroid for up to two days by leaping
from place to place in Itokawa's near-microgravity environment. The
1.3-pound rover will take stereo images using three cameras, and six
thermometers will gather temperature measurements.

A larger rover -- provided by NASA -- was originally part of Hayabusa's
payload, but the project was cancelled due to funding issues.

Due to positioning of Itokawa and Earth in their solar orbits, Hayabusa
must depart the asteroid by December to make its trip home. The delay in
the craft's arrival shortened the length of time available for
operations at Itokawa, but officials are hopeful all goals of the
mission will be achieved in the three-month stay.

Hayabusa will fire its ion drive propulsion system once more during the
cruise back to Earth, culminating with the return capsule's fiery
re-entry to the planet in June 2007 after separating from the
mothership. Streaking into the atmosphere at almost eight miles per
second, the canister will be slowed by friction before making a
parachuted touchdown in the Australian outback.

Scientists will then access the capsule to recover the first materials
ever returned from an asteroid, or from the surface of any body other
than the Moon. The samples will be analyzed for the precise chemical
components of Itokawa to help scientists better string together the
evolution of the early solar system, of which asteroids are believed to
be ancient relics.

The data will also help bridge a connection between the asteroid and
certain types of meteorites that have fallen to Earth. Other scientists
will be anxious to see the results to determine what minerals and
elements on Itokawa would be commercially viable to mine if such
ventures become reality in the coming decades.
Received on Tue 23 Aug 2005 11:46:53 AM PDT