They propose adding a more advanced version of the probe to MUSES-C, a Japanese mission to return an asteroid sample to Earth in June 2006.

Wheeled robots work well on moons and planets, but the very low gravity of asteroids and comets poses problems. The traction needed for horizontal motion comes from the vehicle's weight pressing down on the surface, but on an asteroid only 2 kilometres across the force of gravity is about 100 000 times weaker than on Earth. That leaves so little traction that the robot's wheels will slip unless they move very slowly.

Researchers at the Jet Propulsion Laboratory in Pasadena, California, have already developed a wheeled rover for MUSES-C, to be launched in July 2002. Planetary scientist Don Yeomans says the 1-kilogram rover will crawl at one or two millimetres per second across the surface of asteroid 1989 ML.

The wheels are mounted on pivoting struts, which can be pulled together to push the little craft upwards and make it hop, but JPL won't try that until the main part of the mission is complete. "You can hop tens of metres or even a hundred metres at a clip," Yeomans says.

The Japanese hopping robot has a significantly different design, as Takushi Kubota of the Institute of Space and Astronautical Science in Kanagawa made clear in Baltimore last week at the fourth International Conference on Low-cost Planetary Missions.

It is a cylinder measuring 10 by 12 centimetres, and weighing 550 grams. Switching on an electric motor makes a disc within the robot rotate. Its body reacts by turning in the opposite direction, flinging it up into the air like a spring-loaded toy.

Stopping the motor changes the robot's spin, helping to control its motion. And spinning a second disc inside the sealed robot can steer it in a different direction. Kubota's group calculates that the hopper could leap 9 metres in a jump that would take 15 minutes and bring it in for a soft landing.

His group would like to test their robot on MUSES-C. But Yeomans thinks that's unlikely to be possible because the JPL rover carries more instruments and the spacecraft is already overweight.

This article appeared in the May 13 issue of New Scientist New Scientist. Copyright 1999 - All rights reserved. The material on this page is provided by New Scientist and may not be published, broadcast, rewritten or redistributed without written authorization from New Scientist.

ROBOSPACE
Rovers Get Muscles For Asteroid Mission
JPL - February 24, 1999 - Artificial muscles that should give space robots animal-like flexibility and manipulation ability will get their first test on a small NASA rover destined to explore an asteroid.