HITTING THE MARTIAN HIGHWAY

Later this week, Brian Cooper will at last get the chance to drive the company car. Ordinarily this wouldn't be a cause for worry, but Cooper has reason to be nervous. Hundreds of his co-workers and more than a thousand reporters will be looking over his shoulder--to say nothing of the 25 million people who are expected to tune in live on the World Wide Web.

What fascinates this global audience is not so much the nature of the vehicle; at just 1 ft. tall and 2 ft. long, the boxy, six-wheeled, 22-lb. car is nobody's idea of a roadster. But while Cooper will be at the controls at NASA's Jet Propulsion Laboratory in Pasadena, Calif., the car will be 119 million miles away, touring the arid Ares Vallis floodplain on Mars.

The drive through the Martian countryside should begin this Friday, July 4. At about 10 a.m. Pacific time, after a seven-month journey, NASA's Pathfinder spacecraft will deposit the robot car--dubbed Sojourner--on the Martian surface, marking the first time an American spacecraft has kicked up the Martian soil since the Viking landings in 1976. More important, it will be the first time that NASA has been able to move an unmanned vehicle from place to place on a foreign world. "I truly believe," says project scientist Matthew Golombek, "that Pathfinder will change our view of Mars."

Before the little rover can traverse the Martian surface, of course, it must reach the Martian surface, and that won't be easy. The 1,300-lb. spacecraft will slam into the planet's atmosphere at 16,300 m.p.h., ultimately causing it to experience deceleration forces of 20 Gs. The vehicle's cork-and-silicon aeroshell should absorb most of this body blow. Both a parachute and a retrorocket will slow its plunge, and an array of airbags will inflate to cushion the shock of landing. And finally, the spacecraft will simply drop to the surface, striking the ground like a beach ball and rolling to a stop in the ancient floodplain.

If Pathfinder survives its inelegant touchdown unscathed, NASA scientists will waste no time getting to work. After the spacecraft gets its bearings, they'll send it a signal causing it to open up, revealing the papoose-like Sojourner rover inside. A camera on the lander will snap a picture of both the car and the landscape, and by 6 p.m. on the West Coast, NASA hopes to release the image both to the press and on the Web mpfwww.jpl.nasa.gov/) After that, it will at last be time for Brian Cooper to take the wheel.

The Sojourner control console at J.P.L. is equipped with a 24-in. video monitor, a 3-D mouse and a set of stereoscopic goggles. Before the rover leaves the lander, its camera will scan the terrain and transmit what it sees to J.P.L., where software will combine the images into a three-dimensional vista. Donning the goggles, Cooper and other scientists will then scout the virtual riverbed. When they find a likely place for Sojourner to visit, they'll start up the car and, using the mouse, tell it where to go.