Two-Way Asteroid Trip Takes Off
Summary (May 11, 2003): The Japanese spaceprobe called Muses-C launched Friday, to begin its four and a half year roundtrip to return samples of an asteroid back to Earth. The mission highlights the highly-efficient ion engine, along with a unique bullet and sample-horn method of returning extraterrestrial rocks and dust. If all goes well, the asteroid samples and probe will land in the Australian Outback around June 2007.

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Two-Way Asteroid Trip Takes Off

A Japanese rocket lifted off Friday on the world's first mission to collect samples from the surface of an asteroid, part of a four-year journey covering nearly 400 million miles.

Video: NEAR Shoemaker flyover of Eros. Credit: Johns Hopkins Univ. APL

Taking off from Kagoshima in southern Japan on its 22 month outbound trip, the Muses-C space probe is scheduled to visit the 1998 SF36 asteroid, 186 million miles from Earth, and bring back a single gram of rock in four years' time.

'Asteroids are known as the fossils of the solar system,' said mission leader Junichiro Kawaguchi of Japan's Institute of Space and Astronautical Science. This body designated 1998SF36, like other small objects in the solar system, is believed to act as a record of aspects of the state of the early solar system and this exciting mission will return fragments of the asteroid's surface to the Earth for detailed analysis. The MUSES-C spacecraft will approach and stay near the asteroid for about five months

'By examining them, you can find out what substances made up the solar system, including Earth, in the distant past.'The asteroid belt is a doughnut-shaped area that measures some 175 million miles wide and 50 million miles thick. The material in the belt travels at speeds up to 45,000 mph and ranges in size from dust particles to rock chunks as big as Alaska. [Pioneer 10 was the first spacecraft to pass through the asteroid belt, considered a spectacular achievement, and then headed on toward Jupiter.]

The rocks inside a crater on the Asteroid Eros. Numerous small impacts on the asteroid show brown boulders visible interior to the less exposed (white) lip of the crater. False-color for emphasis. Credit: NEAR Project, JHU APL, NASA

If successful, the "Muses-C" will be the first probe to make a two-way trip to an asteroid. A NASA probe collected data for two weeks from the surface of the Manhattan-sized asteroid Eros in 2001, but it was not designed to return with samples.

The unmanned Muses-C was launched Friday atop a $60 million M-5 rocket from the Kagoshima Space Center on the island of Kyushu in southern Japan.

Iwao Hashizume, an Institute of Space and Astronautical Science spokesman, said the Muses-C had reached its orbit heading away from Earth at 6.9 miles per second. Its solar energy panels had unfolded and its sample-collecting arm had responded to tests, Hashizume said. Total mission time is about 4.5 years.

Propelling MUSES-C during its four-year space journey are ion engines, also a key technology for the spacecraft. Instead of liquefied fuel, the engines use xenon gas and ionize its atoms. Thrust is generated by expelling these ions at high speed with the help of a strong electric field. It will be the first attempt in the world to use ion engines as the main propellant, although a number of test probes including the Deep Space probe have pioneered the small, but steady, microwave push given by charging particles. The propellant Xenon is first ionized by the microwave, followed by acceleration with high voltage to generate the thrust. Ion engines, as well as many other types of electric propulsion, have a very high efficiency when compared to chemical propulsion methods.

Shaped like a rugby ball some 500 meters (yards) long, the target asteroid is twice as far away as the sun, but still one of the nearest to Earth.It is one of numerous asteroids between Mars and Jupiter and is on an elliptical orbit that comes close to Earth and Mars.

Muses-C is set to land on the asteroid's surface and fire a small projectile into the crust, scooping up the resulting rock fragments. Even a tiny amount will be sufficient for research purposes, Kawaguchi said. The procedure requires the spacecraft to land a "sampler horn" on the asteroid surface. A metal bullet weighing 5 to 10 grams will be fired from inside the horn into the surface at a speed of about 300 meters per second.

The bullet will smash into the surface, sending fragments flying about. They will be captured by the horn and funneled into a sample container. Just after samling, the spacecraft will lift off immediately. The time for each of the contacts with the asteroid surface is planned to be on the order of 1 second.

Because of the asteroid's small mass and gravity, any gentle push off would send the space probe back off the surface. Such low escape velocities (30 cm/s) mean that you don't so much land on the asteroid surface as "dock" with it - and any sort of digging tool will need a strong anchor otherwise you may end up just pushing the spacecraft away without the spade actually going into the material. So mission planners will fire a small bullet and vacuum up any fragments into a horn-shaped collector.

On return to Earth's atmosphere around June 2007, the sample container is designed to break away from the probe and parachute back to land in the Australian desert, or Outback. After being fully decelerated by atmospheric drag, the capsule deploys a parachute for soft-landing. The capsule with the asteroid sample is retrieved by localizing its position from ground stations that track a beacon signal from the capsule.

Scientists say they hope examinations of particles from the asteroid's surface will provide clues on how the planetoid was created.

'Bringing back a sample is an extremely difficult proposition,' Kawaguchi said, when asked about the mission's chances of success. If successful, it will be the first sample collected from an asteroid, and the first of a celestial body following the moon stone sampling by the U.S. Apollo missions from 1969 to 1972.

What's Next

Artist's concept of Muses-C spacecraft, flying down toward the asteroid. Credit: ISAS

In the next 5 or so years, there will be no fewer than five encounters of spacecraft with comets and asteroids. All the following missions are fully funded, though only not all have already been launched (the others will follow in 2003 to 2004):

2001 Sept. 22	Comet	Borrelly	Deep Space One	(simple flyby)
2003 Nov. 12	Comet	Encke	CONTOUR	(simple flyby)
2004 Jan. 1	Comet	Wild 2	Stardust	(coma sample return)
2005 July 3	Comet	Tempel 1	Deep Impact	(big mass impact)
2005 Sept.	Asteroid	1998 SF36	Muses-C	(sample return)

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Related Web Pages

Great Impact Debate I: Benefits of Hard Bodies
Great Impact Debate II: Much Ado About Nothing?
Impact Hazards Website
NASA/JPL Near Earth Object Program
Mini Solar System
Cosmic Dust (Univ. Wash, St. Louis)
Stardust (JPL)
University of Washington (Seattle)
Don Brownlee (U of Wash)



Note: Asteroids, Comets and Meteors: [2003-05-11]

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Sunday, May 11, 2003