The mid-size solid-fuel M-5 rocket, carrying an unmanned MUSES-C probe, lifted off from the Kagoshima Space Centre in the southern Japanese town of Uchinoura at 1:29 pm (0429 GMT) as scheduled.

"What we can say at the moment is everything is okay so far," an official said, adding the formal declaration on whether the launch was a success would come late Friday.

But Yasunori Matogawa, head of the space centre, told reporters at the launch site "the launch was a 100 percent success," according to Jiji Press news agency.

The M-5, the fifth such rocket to be launched, deployed the probe into its targeted "transfer orbit", setting it off on a huge loop outside Earth's orbit around the sun and towards asteroid 1998SF36.

If successful, the mission will be the first time any samples from space have been brought back since the US Apollo project gathered Moon rocks three decades ago.

The project, to achieve the world's first two-way trip to an asteroid, has been developed by the science and education ministry's Institute of Space and Astronautical Science (ISAS).

"This is a very ambitious probe which has gained international attention, and I earnestly hope this will be a success," Atsuko Toyama, minister for education, culture, sports, science and technology told a news conference before the launch.

The MUSES-C is due to reach the asteroid, 300 million kilometresmillion miles) away from Earth, in two years' time, according to a description of the mission on ISAS' website.

1998SF36 is now between Mars and Jupiter and on an Earth-approaching orbit, having been pulled out of the Kuiper asteroid belt by the gravitational force of Jupiter. It is estimated to measure 500 metres (1,650 feet) in diameter.

The MUSES-C will spend some five months near the asteroid, making observations of its surface and gathering samples.

It is programmed to make three one-second touch-and-go contacts with the asteroid, during which it will fire small projectiles into its surface to smash part of it and catch the resulting particles in a cone-shaped funnel as they rise up in the low-gravity environment.

Before touch-down, the probe will drop a ball-shaped light-emitting target marker onto the asteroid's surface. The names of 880,000 people from across the world who responded to a campaign offering to leave their names in space are printed on the inside of the marker ball.

The probe is expected to return to Earth orbit in the summer of 2007, when it will release a re-entry capsule containing the samples. The capsule is to make a parachute-assisted landing in the Australian outback.

Although they are likely to weigh only one gram (0.035 ounce) or so, the samples are expected to help scientists study how the solar system was created.

Friday's launch is a chance for ISAS to erase the humiliating failure of the last M-5 exploration in February 2000.

Japan lost a 100-million-dollar satellite after the fourth M-5 rocket went awry, triggering a drastic review of its disaster-prone space programme.

Japan started its space development programme in 1969, the year US astronauts landed on the Moon.

The National Space Development Agency launched one of its H-2A rockets carrying Japan's first spy satellites in March. The rocket is hoped to allow Japan eventually to gain a slice of the commercial satellite launch market.

SPACE.WIRE