File photo of M-5 rocket launch. Photo: ISAS

A compact Japanese space probe embarked on an ambitious mission today bound for a series of close encounters with an almost equally small asteroid to gather samples for return to Earth.

Liftoff of the M-5 rocket was within a precise launch window from the Kagoshima Space Center at 0429 GMT (12:29 a.m. EDT). The MUSES-C payload was placed into a transfer orbit within minutes of launch.

It marked the first flight of the M-5 since a launch over three years ago failed to successfully loft an international observatory to orbit due to a nozzle failure on the first stage.

The 1,166-pound MUSES-C spacecraft's trajectory is expected to culminate with arrival in orbit around asteroid 1998 SF36, an object roughly 2,300 feet by 1,000 feet in dimensions.

After its arrival in June 2005, the satellite will orbit some 12 miles above the surface of the space rock for several months conducting scientific investigations before using its propulsion system to dip down in at least three "touch-and-go" maneuvers that aim to gather up to one gram of material from a variety of sites on the asteroid.

These sample collections consist of a tiny metal projectile fired toward the surface at very close range, which will cause an impact crater and debris from the asteroid to be trapped within a funnel that then will feed the material into the chamber within the capsule that will return to Earth.

An illustration of MUSES-C mission. Credit: ISAS

MUSES-C is expected to be en route back to Earth by the end of 2005 after a five-month stay at 1998 SF36. Shortly before arrival, a 44-pound re-entry section will jettison from the main spacecraft body and will undergo a high-speed entry into the atmosphere before making a parachuted touchdown in Australia in June 2007.

During the cruise phase of the mission, MUSES-C will be driven by a cutting edge ion propulsion thruster that saves propellant.

The spacecraft also features a high technology autonomous control system that will govern much of the final approach during the sample collection runs because of the long communications lag between 1998 SF36 and Earth.

An artist's concept of MUSES-C. Credit: ISAS

MUSES-C has gone through a number of setbacks since the project's start, including launch vehicle failures and delays, the cancellation of a NASA rover to be dropped on the target asteroid and a change in destination.

The mission undertaken by Japan's Institute of Space and Astronautical Science, if successful, will be the first to return material back to Earth from an asteroid. NASA's Stardust satellite will soon be gathering cometary dust that will come back to Earth, while the Genesis mission is collecting solar wind samples.

Scientists say even just one gram of returned material could hold key clues about the early solar system because asteroids hold some of the best preserved and oldest matter in the solar system.

Carried aboard MUSES-C are also the names of 877,490 people etched within a target marker that will be released on the surface of 1998 SF36 during each of the sample collection passes.