The rehearsal landing followed an earlier attempt that was aborted due to mechanical trouble, but the space agency said it is still targeting actual landings on the potato-shaped asteroid Itokawa on Nov. 19 and Nov. 25.

The Hayabusa probe successfully released the Minerva surface-exploring robot on Saturday, but Minerva appeared to start drifting away from the asteroid's surface, according to a release from JAXA, Japan's space agency. Minerva was expected to land and hop around on the asteroid's surface collecting data with three small color cameras.

"Unfortunately, it appears Minerva did not recognize the surface,'' JAXA said.

Minerva was still in radio contact with Hayabusa late Saturday, and mission controllers were trying to find out more about its condition and location, JAXA said. Officials, however, expected the transmissions to give out soon, Kyodo News agency reported.

"It is very disappointing that it did not work out nicely,'' JAXA official Junichiro Kawaguchi was quoted as saying by Kyodo. "We found out various things about the asteroid, so we will study the data and hope it will lead to the successful landing of Hayabusa.''

Another procedure Saturday to collect surface data with laser altimeter was largely successful, the agency said.

JAXA hopes Hayabusa, launched in May 2003, will be the world's first two-way trip to an asteroid. A NASA probe collected data for two weeks from the Manhattan-sized asteroid Eros in 2001, but did not return with samples.

Hayabusa has until early December before it must leave orbit and begin its 290 million kilometer (180 million mile) journey back to Earth. It is expected to return to Earth and land in the Australian Outback in June 2007.

The asteroid is named after Hideo Itokawa, the father of rocket science in Japan, and is orbiting the sun between Earth and Mars. It is 690 meters (2,300 feet) long and 300 meters (1,000 feet) wide and has a gravitational pull only one-one-hundred-thousandth of Earth's, characteristics that make landing a probe there difficult.

JAXA scrubbed a rehearsal landing earlier this month, when Hayabusa had trouble finding a landing spot. The probe had an earlier glitch with one of its three gyroscopes.

Japan was the fourth country to launch a satellite, in 1972, and announced earlier this year a major project to send its first astronauts into space and set up a base on the moon by 2025.

Examining asteroid samples is expected to help unlock the secrets of how celestial bodies formed because their surfaces are believed to have remained relatively unchanged over the eons, unlike those of larger bodies such the planets or moons, JAXA said.