[meteorite-list] Japan's Hayabusa Swings By Earth on Way to Asteroid Itokawa

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue May 18 16:38:29 2004
Message-ID: <200405182038.NAA00918_at_zagami.jpl.nasa.gov>

http://planetary.org/news/2004/hayabusa_earth-swingby_preview.html
 
Japan's Hayabusa [MUSES-C] Swings By Earth on Way to Asteroid Itokawa
By A.J.S. Rayl
The Planetary Society
18 May 2004

The Japan Aerospace Exploration Agency's Hayabusa is on course to make its
swing-by Earth tomorrow, May 19, on its 1 billion kilometer mission to land
on the asteroid Itokawa and return home with a sample of its surface.

Formerly known as MUSES-C, Hayabusa is scheduled to arrive at Itokawa in
June 2005. After its initial rendezvous, the spacecraft will spend five
months near the asteroid named after the late rocketeer Hideo Itokawa,
father of Japan's space program. The spacecraft will not go into orbit
around the asteroid, but will remain in a station keeping, heliocentric
orbit close by.

During that time, Hayabusa will conduct detailed observations of Itokawa
with various instruments onboard and capture more precise images of the
surface using its high-performance camera. The mission team will then select
target areas and dispatch a robot to touch down on the near Earth asteroid's
surface to collect one gram's worth of dust samples from three sites on the
big rock, which it will return in June 2007.

"This is an audacious and exciting mission, to bring back a sample of
near-Earth object is significant scientifically, and as an engineering
achievement," noted Planetary Society Executive Director Louis Friedman.
"Such objects have profoundly influenced the evolution of Earth."

Hayabusa's journey, from beginning to end, will take about four and a half
years, and is estimated to cost the equivalent of $170 million.

In addition to its somewhat daunting scientific objective, the mission also
has some prime space engineering and technology directives -- to test a few
new technologies developed in Japan for this and future sample return
missions:

 o The high performance electric propulsion system - comprised of four
microwave-discharge-type ion engines, known in America as ion drives;

 o An autonomous navigation system;

 o An asteroid-landing robot that can touch down, seize samples, and hop off;
and

 o A spacecraft/re-entry capsule system for returning the samples to Earth.

Hayabusa is powered by a system of four ion engines designed to be activated
throughout the flight to and from the asteroid. During the swing-by
tomorrow, the spacecraft's accumulated velocity vector by its ion-engine
acceleration will be diverted in the direction of Itokawa and the spacecraft
will be accelerated continuously then on, heading on a straight shot course
to the asteroid. This week's event will mark the first time any spacecraft
has performed a swing-by maneuver using an ion engine as the main thruster.

"Use of these technologies is very important -- both for solar system
exploration generally, and for Japan as a major player in space," Friedman
said. "No one country can do eveything, and this is the great advantage of
international cooperation -- to share the work and the rewards of
exploration."

Last week, controllers at the Deep Space Control Center of the Institute of
Space and Astronautical Science (ISAS) division of JAXA, successfully made
some final adjustments to Hayabusa in preparation for its swing-by maneuver.
Now, word from Japan is that the spacecraft is operating nominally or, in
other words is 'steady as she goes,' to coin a phrase from Star Trek.

----------------------------------------------------------------------------
In Japanese, Hayabusa means peregrine falcon. This bird of prey is known for
its ability to swoop down and snatch its prey in its talons -- exactly what
the Japanese are looking to Hayabusa the spacecraft to do -- swoop down and
snatch samples of the asteroid's surface.
----------------------------------------------------------------------------

Like most space missions, Hayabusa has had its share of tense moments. It
was originally slated to investigate asteroid 1989 ML, but the project's
original launch date in July 2002 on an M-5 three-stage solid-fuel rocket
was delayed when a similar M-5 rocket failed to deliver Japan's Astro Ex-ray
observatory into orbit. That delay meant that 1989 ML would be beyond the
mission's grasp by the time the spacecraft could launch again. So, a new
target -- asteroid 1998 SF36 -- was selected, and shortly thereafter the
International Astronomical Union (IAU) bestowed it with its permanent name
-- Itokawa.

The asteroid explorer was finally ferried aloft by Japan's M-V-5 rocket from
the Uchinoura Launch Center at Kagoshima on Kyushu Island last year, on May
9, in what controllers described as a picture perfect launch, into "blue
skies." When the spacecraft's radio signal was received at Kagoshima station
after the Earth had rotated beneath it, and telemetry data at the Goldstone
Tracking Station showed that the rocket had pretty accurately put it into
the planned orbit, Japan christened MUSES-C with its new name, Hayabusa, and
sent it on its way.

----------------------------------------------------------------------------

MUSES stands for 'Mu Space Engineering Spacecraft' -- a space engineering
spacecraft launched by a Mu rocket -- and 'C' means, in essence, 'the
third.'

MUSES-A, the first of the series, was called HITEN and was launched by the
M-3SII launch vehicle in 1990, targeting technologies such as a swing-by
using the Moon's gravity.

MUSES-B, the second of the series, was called HALCA and was launched by the
M-V launch vehicle in 1997. It currently plays an active part in JAXA
missions as a VLBI (very-long baseline interferometry) satellite in the
radio wave region.

----------------------------------------------------------------------------

By July last year, the Hayabusa team had completed engine tests and
adjustments were completed, and the spacecraft transitioned into its
cruising mode of continuous acceleration. It has, for the most part, been
cruising steadily through space since then with its four ion-drive electric
propulsion engines propelling it at a slow and steady 12 meters per second.

Compared to the conventional chemical propulsion engines, electric
propulsion engines are extremely efficient. On the other hand, their thrust
levels are quite low; therefore, they must operate continuously for a longer
period of time to perform the same level of orbital maneuvers as that of the
chemical propulsion engines. Hence, ion drives propel spacecraft in a slow
and steady manner -- the tortoise-to-the-hare fable is often noted as
analogy.

Many space exploration scientists and engineers view the high efficiency of
ion drives to be an essential technology for deep space cruising on future
planetary missions.

Hayabusa's engines ionize the propellant, Xenon, by microwave, then
accelerate the ions in a strong electric field and expel them at high speed.
That provides the reactionary energy that propels the spacecraft. Although
NASA's Deep Space 1 holds the distinction of being the first spacecraft to
use ion drive, Hayabusa is the first Japanese craft to employ the
technology, and the first to use microwaves to ionize xenon fuel.

Developed by the electric propulsion engineering section at the ISAS
division of JAXA, Hyabusa's engines promise long life and high reliability.
Since they do not use the discharge electrodes for plasma generation,
deterioration is not an issue. The operation record of 8,000 hours per unit
in space achieved last year is a world-class accomplishment.

For Hayabusa it was smooth sailing until last November when the spacecraft
encountered the biggest solar flare in history. The little 1100-pound [500
kilogram] spacecraft, however, came through unscathed, and once it swings by
Earth tomorrow, it will be on a trajectory that will take it straight to
Itokawa.

By the time Hayabusa reaches the vicinity of the asteroid next summer, it
will take radio waves 10 minutes to traverse the distance from the
spacecraft back to Earth, so the designers have equipped the spacecraft with
a highly autonomous navigation system that will enable it to decide each
move on its own. It will do that by measuring the distance to and the shapes
of the asteroid surface using an Optical Navigation Camera and Light
Detection and Ranging instrument.

Although just getting to Itokawa will be a significant achievement,
Hayabusa's journey really just begins with its arrival. Landing on top of
the asteroid is going to be tricky. Current estimates measure Itokawa's size
at 490 by 180 meters -- that's just 1600 feet by 590 feet. And that's why
Hayabusa will spend five months intensely studying this rock with a host of
instruments including, infrared and X-ray spectrometers, in addition to its
cameras and light detection and ranging instrument.

----------------------------------------------------------------------------

Asteroids: Big Rocks. Big Deal

  Frequently referred to as 'celestial fossils,' asteroids are important to
 study, because they contain pristine records of the early days of the solar
  system. While planets and moons undergo significant thermal alterations,
scientists believe that asteroids are pretty much the same as they were when
they, and the solar system, were formed. The small samples to be gathered by
 Hayabusa promise great scientific reward by enabling scientists to uncover
  more clues about the raw materials that made up the early planets and the
 asteroids, as well as gain a better understanding of the state of the solar
                nebula around the time of the planets' birth.

  It is also important to know as much as possible about asteroids that one
    day might head toward Earth. Any asteroid orbiting within 7.5 million
 kilometers of Earth's orbit is considered potentially hazardous because the
gravity of the Sun and other planets could alter its course and send it on a
 trajectory toward Earth. Itokawa's orbit around the Sun brings it to within
 1.8 million kilometers of Earth's orbit, which places it in the category of
                            near Earth asteroids.

----------------------------------------------------------------------------

After the mission team makes a final decision on where to gather its
samples, Hayabusa will begin its descent to Itokawa, measuring the relative
position and attitude to the surface with its Optical Navigation Camera and
Light Detection and Ranging instrument, autonomously adjusting the
propulsion engine as it transmits an image of the whole process to Earth. At
about 100 meters altitude, the spacecraft will release Target Markers onto
the asteroid.

Although Hayabusa's Mission Control cannot maneuver the spacecraft in real
time, it can send an order to stop the descent when assessing a danger, but
that is about all it can do. Most of the essential decisions have to be made
by the spacecraft itself.

Prior to the final touch down, the spacecraft shuts down the propulsion
engine and enters into a free fall descent. This is to prevent the jets from
contaminating the asteroid surface by coming too close to it.

The next task -- collecting a sample - may be an even greater challenge. The
surface gravity of the asteroid is really small and is less than 1/100,000
of that of the Earth. Anything -- a drill or any other digging tool - that
is not secured by a strong anchor into the surface may just be pushed away
before the drill actually bores a hole.

Since we do not know what the asteroid is really made of, there is no way of
knowing how hard the surface will be or how difficult this collection of
surface dust will be. The Japanese are employing a simple, direct strategy
-- to "break the surface" by using a tiny pyrotechnic device to fire
'sampler horns' into the three targeted sites on the asteroid.

Once the collections of surface dust are completed, the spacecraft will
start the engine, lift off, and resume its hovering position at 100 meters
altitude as it waits for the next order from Mission Control.

In the final phase of the mission, Hayabusa will send a small reentry
capsule with the asteroid sample into the Earth's atmosphere at a velocity
more than 7,500 miles per second [12 kilometers per second]. The maximum
heating rate of the capsule in the reentry is several tens times higher than
that of the Space Shuttle and several times higher than the Apollo recovery
module. The heat shield material, therefore, is state of the art. After
being fully decelerated by the atmosphere, the capsule is designed to deploy
a parachute for soft-landing. On landing, the capsule will send out a beacon
signal until it is retrieved in 2007.
Received on Tue 18 May 2004 04:38:14 PM PDT