Project scientist Donald Yeomans said the mission is really a test for further exploration of asteroids and comets.

"This is a high-risk mission," he said. "Its not really science driven."

Yeomans said this is the first of a type of craft to conduct an accurate census of what composes asteroids. Future explorers, colonists and miners will need to know if water or minerals are available.

The unglamorous sounding MUSES-CN stands for Mu Space Engineering Spacecraft, with "C" meaning third in the series and "N" for NASAs participation. The Japanese Institute of Space and Astronautical Science and NASAs Jet Propulsion Laboratory in Pasadena, California work together on the project.

Jones explains that the U.S. space agencys involvement began after the Japanese agency wanted to strike a deal.

"They needed some things and said theyd give us a kilogram payload," Jones said.

The Japanese agency needed tracking support from the Deep Space Network, use of Ames Research Center at Moffett Field, California, and a sparsely populated area in the United States for the sample return capsule to land.

In return, the Japanese probably thought NASA would fly some simple scientific experiments or "the usual stuff" as Jones puts it.

Instead Jones and colleague Brian Wilcox thought of the nanorover.

About 20 scientists and engineers, including some who worked on Sojourner, are developing the rover to carry a high-resolution video camera and near infrared and alpha X-ray spectrometers. To conserve weight, the rover has no batteries, but relies on solar cells for power.

The rover has four wheels and a rocker suspension similar to Sojourner. This allows it to traverse small obstacles and to point its forward-facing optics at the asteroids surface.

Jones said one rover to fly and a back up should be ready by September 2000. He estimates the cost of the rovers to be about $20 million with an additional $10 million for support such as DSN, Ames Research Center and recovery of the sample capsule.

While developing such a small craft presented technical challenges, the team also had to build and program the rover to survive the strange and harsh environment of the asteroids surface.

Nereus has a diameter of about one mile, with a horizon line at about 30 feet. The gravity is about 100,000 times less than Earths.

If the rover moves too quickly or uses its strut suspension system to hop, it could launch itself into orbit before the end of its one-month mission.

"I like to tell people it cant go faster than a speeding bullet, but it can leap tall buildings in a single bound," Yeomans jokes.

The rover will move at fractions of an inch per second. Yeomans described the low gravity surface as akin to driving a car on ice.

Due to the low gravity, the rover will almost float to the asteroid after release and is programmed to right itself if it lands upside down.

The rovers main task is to move around the surface taking high-resolution images in the visible and non-visible spectrum and transmit them back to Earth relayed through the probe.

Just before touchdown of the Japanese probe, it will fire a pellet into the asteroid and collect the debris thrown off. The rover will then investigate the crater with its camera.

The rover will stay on the asteroid, but Jones said plans are being developed to build even smaller and better-equipped rovers.

Eventually, rovers may be five to 10 time smaller than the MUSES-CN.

This rover will probably have one last test after it completes its mission though.

"Well do some jumps after weve finished everything else," Jones said.