Robby, a $1 million robot rover vehicle designed to explore Mars, successfully picked its way along a rocky dry river bed without human help, NASA said. ``This is the first time that an autonomous vehicle has ever navigated rugged terrain using video cameras,'' said Roger Bedard, planetary rover program manager at the space agency's Jet Propulsion Laboratory. ``Robby himself wouldn't go to Mars. He's a test vehicle.'' NASA called the Sept. 13 test ``a significant milestone'' in developing a planet-roving, computer-guided vehicle that would explore Mars to find suitable landing sites for a manned mission to the red planet. It will be about 1995 before engineers fully develop rover technology, and about 2000 before one can be built to go to Mars, Bedard said Wednesday. During the test, Robby took four hours, 20 minutes to crawl along a 109-yard course in the rugged Arroyo Seco, a dry river bed in a canyon next to the laboratory. NASA wants a real Mars rover to travel about 13 miles daily. Bedard said engineers told Robby where it was and where it was supposed to go, but the six-wheeled vehicle used its twin television cameras and computer to navigate a safe course around boulders and other obstacles. Other tests were conducted last week. Robby is about 15 feet long, 6 feet wide and 6 feet tall. It was named after Robby the Robot in ``Forbidden Planet,'' a 1956 science fiction film. The robot's television cameras give it stereoscopic vision, allowing it a three-dimensional look at objects about 6{ feet in front of it. Robby moves about 6{ feet at a time, then stops to survey another 6{-foot stretch of terrain before proceeding. Robby runs on a battery recharged by an onboard gasoline generator. A Mars rover would be powered by the radioactive decay of plutonium, Bedard said. The only unmanned rovers to explore another planet were two Soviet Lunakod vehicles that explored the moon in the early 1970s, Bedard said. NASA astronauts used a manned vehicle on the moon. The National Aeronautics and Space Administration doesn't yet have specific plans to put rovers on Mars, Bedard said. The Soviets are considering using rovers and terrain-hopping balloons during a 1994 mission to Mars. During the past week, 30-foot-tall balloons that would repeatedly rise and settle on Mars' surface were tested in California's desert by engineers from France, the Soviet Union and the Planetary Society, a group that advocates space exploration. Balloons have the advantage of not needing to navigate rough terrain, rising during the heat of day and settling to the Martian surface at night to take measurements. Bedard said rovers can be directed to explore areas of scientific interest, rather than taking a route that depends on prevailing winds.