Hayabusa Rounds Earth

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

At 6:23 am (Greenwich time) on May 19, the Japanese Hayabusa spacecraft successfully made a close Earth approach (altitude = 3725 km), thereby gaining the velocity it needs to reach the near-Earth asteroid Itokawa, named for the father of Japanese rocketry.

If successful, the Hayabusa will be the first probe to make a two-way trip to an asteroid. A NASA probe (NEAR) 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.

Originally called the MUSES-C spacecraft when launched May 2003, the Hayabusa is now headed for its target, as the world’s first mission to collect samples from the surface of an asteroid and part of a four-year journey covering nearly 400 million miles. After its arrival in June 2005, the spacecraft will gather up to one gram of material from a variety of sites on the asteroid.

During this Earth swingby, the Hayabusa spacecraft took images of the Earth and moon [banner image] to test and calibrate the on board camera called AMICA (Asteroid Multi-band Imaging Camera).

Upon its arrival at the asteroid in the summer of 2005, the Hayabusa spacecraft will hover near the asteroid’s surface for about four months. Its instruments will study the surface in detail, determine the asteroid’s mass and bulk density and determine which minerals are present.

Large, smooth basin. At bottom lie scattered boulders that appear like pebbles by comparison to the crater.
The rocks inside a crater on the Asteroid Eros, as imaged before impact with the NEAR spacecraft. 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

A small coffee-can-sized surface hopper, called MINERVA, will leap about the asteroid taking surface temperature measurements and high-resolution images with each of its three miniature cameras.

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. 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 sampling, 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.

"Asteroids are known as the fossils of the solar system," said mission leader Junichiro Kawaguchi of Japan’s Institute of Space and Astronautical Science.

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. This body designated Itokawa, like other small objects in the solar system, is believed to offer a record of the early solar system.

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. 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 devised the collection method of firing the small bullet while vacuuming up any fragments into the horn-shaped collector.

With these surface samples tucked safely into the spacecraft’s sample capsule, the spacecraft will return to Earth, arriving on June 10, 2007, and the sample capsule will parachute to the ground in the Australian 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.

Earth as seen on May 18 during Hayabusa flyby. Banner shows mosaic of images taken from Hayabusa of the Earth and moon (not to perspective size).
Credit: JAXA

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.

"By examining them, you can find out what substances made up the solar system, including Earth, in the distant past," said Kawaguchi.

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 at the time, and then headed on toward Jupiter.]

"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 sampling by the U.S. Apollo missions from 1969 to 1972.

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.

Related Web Pages

Hayabusa Project (JAXA main site)
Hayabusa acquired images of the earth and the moon.
Planetary Society: Swingby
Great Impact: Part I
Great Impact: Part II
Great Impact: Part III
Impact Hazards Website
NASA/JPL Near Earth Object Program