[meteorite-list] Hayabusa's Contributions Toward Understanding the Earth's Neighborhood

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Aug 16 11:04:06 2005
Message-ID: <200508161503.j7GF36c01444_at_zagami.jpl.nasa.gov>

http://neo.jpl.nasa.gov/missions/hayabusa.html

Hayabusa's Contributions Toward Understanding the Earth's Neighborhood
Don Yeomans
Near Earth Object Program
August 11, 2005

Beginning in early September 2005, the Japanese Hayabusa spacecraft will
rendezvous with near-Earth asteroid (25143) Itokawa. Itokawa, a 600 meter
sized, potato-shaped asteroid, is named after Hideo Itokawa, a Japanese
rocket pioneer. Although the primary objectives of the Hayabusa mission
are to test new technologies, the mission will also provide a wealth of
scientific returns. For the three month period from September through
November 2005, the science instruments on board the Hayabusa spacecraft
will undertake an intensive study of near-Earth asteroid Itokawa. After
closely observing the asteroid for several weeks, a few pellets will be
fired from the spacecraft at close range into the asteroid's surface and
about a gram of the pellet's impact ejecta will be collected into a
sample capsule. This capsule will then be brought back to Earth and
parachuted into the Australia outback in June 2007 so that some of the
asteroid's surface minerals can be studied in Earth-based laboratories.
This will be the first asteroid sample return mission.

After the successful launch of the spacecraft on May 9, 2003 from the
Japanese Kagoshima Launch site, the mission name was changed from
MUSES-C to Hayabusa. Hayabusa, which is Japanese for "falcon," will act
much like its namesake, descending to the asteroid's surface, capturing
its prey and returning it to Earth. While the scientific knowledge of
near-Earth asteroids will be significantly advanced by the Hayabusa
mission, the primary goals are to test four advanced technology systems:
the electric propulsion (ion drive) engines; an autonomous navigation
system; the sample collection system; and the sample capsule that
re-enters the Earth's atmosphere.

A year after launch, on May 19, 2004, the spacecraft returned to Earth
and made a close approach (altitude = 3725 km), thereby gaining the
extra velocity it needed to reach the near-Earth asteroid Itokawa.
During the Earth swing-by, the spacecraft also took images of the Earth
and moon to test and calibrate the on board camera called AMICA
(Asteroid Multi-band Imaging Camera). These Earth and lunar images can
be viewed at: http://www.isas.ac.jp/e/snews/2004/0519.shtml . Because
the efficiency of the solar panels were slightly degraded as a result of
a solar flare in late 2003, the ion engines no longer receive quite as
much electricity as they should so the spacecraft's arrival at the
asteroid was delayed from mid-summer until September of 2005.

Upon arriving at the asteroid, the Hayabusa spacecraft will spend about
three months hovering above the asteroid with its high gain antenna
pointed toward Earth and its science instruments pointed toward the
asteroid's surface. Using the spacecraft camera, the entire surface of
the asteroid will be mapped so that its size, shape and volume can be
determined. The Hayabusa spacecraft carries infrared and X-ray
spectrometers that will identify the asteroid's most common minerals and
chemical constituents. In mid-September, the spacecraft will evolve down
to its so-called "gate position," 20 kilometers above the asteroid's
surface, where it will begin the global mapping of the surface features
and determine its surface composition. Toward the end of September, the
spacecraft will move to its "home position," which is only seven
kilometers above the surface. At this home position, a more detailed
surface map will be generated and the surface composition differences
will be examined as the asteroid rotates underneath the hovering
spacecraft.

In the second half of November, the spacecraft will collect up to three
surface samples as its sample horn captures small pieces of the asteroid
ejected when tantalum pellets are fired into its surface at 300 meters
per second. With these surface samples tucked safely into the
spacecraft's sample capsule, the spacecraft will return to Earth,
arriving in June 2007, and the sample capsule will parachute to the
ground in Australia. The samples will be analyzed in various
laboratories to study their detailed chemical composition and determine
which meteorite examples in Earth-based collections provide the best
match for Itokawa's particular composition. Once this question is
answered, then future Earth based observations can be used to identify
the likely minerals in other asteroids that share the same spectral
characteristics as Itokawa.

During the first descent to fire a pellet into the surface, a small
coffee-can-sized surface hopper, called MINERVA, will be dropped slowly
onto the asteroid's surface. For one to two days it will slowly leap
about the asteroid taking surface temperature measurements and
high-resolution images with each of its three miniature cameras.

Hayabusa's observations will address each of three major issues
concerning asteroids:

1.) their role as the building blocks of the solar system, 2.) their
potential for impacting Earth and 3.) their future use as raw materials
for building space structures.

   1. The scientific interest in asteroids is due largely to their
      status as the remnant debris from the inner solar system formation
      process that occurred some 4.6 billion years ago. Since the
      chemical compositions of asteroids have remained relatively
      unchanged since their formation, knowledge of their elemental
      makeup would provide an understanding of the chemical mix from
      which the inner planets, including Earth, formed.

   2. From time to time, near-Earth asteroids collide with Earth. Should
      one of them be found upon an Earth threatening trajectory,
      scientists would need to understand its composition and structure
      before a successful strategy could be undertaken to deflect the
      object away from Earth.

   3. Some of the near-Earth asteroids that are potentially the most
      hazardous because they can closely approach the Earth are also the
      objects that could be most easily reached and exploited for raw
      materials. The minerals, metals and water ices on near-Earth
      asteroids and comets could be used to manufacture the space
      structures and rocket fuel that will be required to explore and
      colonize our solar system in the 21st century. We need to examine
      the chemical composition of some of these objects to understand
      which among them are richest in mineral wealth and other raw
      materials.

The Hayabusa asteroid sample return mission is the next giant step
forward in understanding the role of near-Earth asteroids in the origin
of the solar system, their potential threat to Earth and the future use
of their raw materials to expand the human presence beyond Earth.

Additional information:

Hayabusa Project (JAXA main site)
http://www.isas.ac.jp/e/enterp/missions/hayabusa/index.shtml

SPACE NEWS (JAXA) -- Hayabusa acquired images of the earth and the moon.
http://www.isas.jaxa.jp/e/snews/2004/0519.shtml

Planetary Society:
http://planetary.org/news/2004/hayabusa_earth-swingby_preview.html

Hayabusa Science Objectives

AMICA - Asteroid Multiband Imaging Camera

    * Map surface morphology including surface features to one 1-m
      resolution
    * Determine spin state, colors, size, shape, volume, and rotation
      characteristics
    * Search for possible asteroid satellites and dust rings
    * Establish a global map of surface features and colors
    * Reveal history of impacts from other asteroid and comet fragments
    * Determine optical parameters of regolith particles using
      polarization degree vs. phase curve at large phase angles
    * Map mineralogical composition of asteroid and identify rock types
      present
    * Determine most likely meteorite analog for composition of asteroid

Near-IR Spectrometer
    * Map mineralogical composition of asteroid and provide main
      evidence for rock types present on surface at scales as small as 20 m
    * Characterize surface heterogeneity
    * Together with elemental composition measurements provided by (XRS)
      and color imagery from camera, IR spectrometer will provide link
      between this asteroid and a meteorite type

X-Ray Spectrometer (XRS)
    * Map the major elemental composition of the surface as the asteroid
      rotates under the spacecraft
    * Determine the major elemental composition at localized areas
      during asteroid approach phases
    * Measure surface composition accurately enough to establish
      relationship between asteroids and meteorites and identify type of
      meteorite to which asteroid is linked
    * Provide elemental abundance maps to investigate inhomogeneity of
      regolith

Sample Return Analysis
    * Samples returned to Earth will provide a detailed and definitive
      elemental composition analysis of the asteroid's surface materials
      and hence forge an unambiguous link between the asteroid's
      composition and a meteorite type

LIDAR

    * Provide accurate shape and mass determinations for asteroid
    * Map asteroid's surface with a maximum resolution of about 1-meter
Received on Tue 16 Aug 2005 11:03:05 AM PDT