HITTING THE MARTIAN HIGHWAY

By Jeffrey Kluger

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.

The going will be slow. Commands from Cooper's computer will take 11 minutes to travel from Pasadena to Mars; it will take another 11 minutes for the rover to acknowledge that it has received the instruction. To prevent Sojourner from blundering into a chasm or over a cliff, engineers designed it to move no faster than 1.3 ft. per minute. Onboard gyroscopes and lasers will help it feel for dangers the camera might have missed. If Sojourner spots an obstacle, it will try to avoid it or simply stop. "We'll give it a point to go to and an amount of time to get there," says Cooper. "If it doesn't, we'll find out what the problem was."

Painstaking as the rover's exploration of Ares Vallis will be, it should be worth the effort. The water that flooded the valley billions of years ago came from all over the planet, carrying all manner of rocks with it. Sojourner will pick through this geological boneyard, photographing the remains and using X-ray spectrometers to study their composition.

The rover will not operate for long--no more than a month--before Mars' punishingly cold climate (-15[degrees]F by day but plunging as low as -125[degrees]F at night) kills it. The Pathfinder lander, also able to take readings, could function for up to a year. No matter when the machines wink out, however, Mars is unlikely to remain unattended. On Sept. 12, Global Surveyor, another robot probe, will arrive at the planet, settle into a 250-mile-high orbit and begin two years of mapping the surface. A second lander-and-orbiter pair is set to be dispatched Marsward in 1998, with more to follow roughly every other year until 2004. Finally, in 2005, the program will culminate in a first-ever round trip: a probe that lands on Mars and flies back home, carrying a bit of local soil with it.

That, at least, is the way NASA planners hope things will go; so far it looks as if they'll get their wish. The ships that will be used for these ambitious missions are remarkably cheap ones, hammered together from available, off-the-shelf parts. While this makes for less elegant vehicles, it also makes for less pricey ones. They cost no more than $250 million, in contrast to the $1.48 billion it costs to build luxury liners like the still-to-be-launched Cassini Saturn probe. Cheap ships means more of them, and for space planners that is a good thing.

"If you only fly two missions a decade and you lose one of those two spacecraft," says NASA Administrator Daniel Goldin, "you're set back for a decade. By breaking the mission into smaller parts and spreading it out, you have a continual return of science."

Congress likes this kind of budgetary horse sense, and though Washington hasn't guaranteed NASA funds for even a stripped-down Mars program, the enthusiasm for Pathfinder on Capitol Hill bodes well. "An entire generation has grown up in the two decades since we last viewed the soil of Mars close up," says Congressman James Sensenbrenner, chairman of the House Committee on Science. "I can't wait for our kids to see those pictures." Whatever may happen to future missions, this week the kids should start to see plenty.

--Reported by Dan Cray/Pasadena and Joanna Downer/Washington

With reporting by DAN CRAY/PASADENA AND JOANNA DOWNER/WASHINGTON