THE LAST TIME WE SAW MARS

By LEON JAROFF

How cheap is NASA's new "better, faster, cheaper" design philosophy? Compare this week's Pathfinder mission with the two Viking missions 21 years ago. Conceived in the heady era of big-budget NASA programs, the Vikings cost nearly $3 billion (measured in 1997 dollars) and were as ambitious and customized as Pathfinder is spare and off the shelf. NASA's old principle of superredundancy is reflected in the fact that there was not one but two Viking spacecraft, the second an exact replica of the first.

Pathfinder owes much to the trail-blazing Vikings, which snapped the high-resolution pictures that enabled Pathfinder scientists to choose an appropriate landing site. The Vikings also pioneered the heat-shield and parachute technology that contributed to Pathfinder's safe and remarkably precise descent.

Project Viking's major goal was to search for signs of life on Mars. Each of the twin spacecraft consisted of an orbiter and a lander. Slipping into Mars' orbit in June 1976, Viking 1 spent a month shooting detailed pictures of the surface, photos that enabled J.P.L. controllers to choose a safe spot for Viking 1's lander to touch down. On July 20, lander 1 separated from its orbiting mother ship. Using retrorockets, deploying a parachute and finally firing three descent engines, it bumped gently onto a rock-covered slope on the planet's southern hemisphere. Forty-five days later, the Viking 2 lander plopped down on more rugged terrain far to the north.

Each of the landers carried a $50 million biology lab with some 40,000 components--pumps, chambers, filters and electronic parts--all packed into a 1-cu.-ft. box. On orders from Earth, Viking 1 stretched out a spindly mechanical arm, reached down, scooped up a heaping tablespoon of reddish Martian soil and, in effect, swallowed it.

Inside the lander, computer-driven devices measured the soil samples and fed them into the miniature biology lab, where they were analyzed for signs of growth, metabolism and respiration, processes that would signal the presence of living microorganisms. In one of the tests, a soil sample dampened with "chicken soup"--a nutrient broth--gave off a burst of oxygen. In another, unexpectedly large amounts of carbon dioxide and carbon monoxide were released. While both results produced flurries of excitement at J.P.L., scientists eventually--though reluctantly--concluded that the gases resulted not from life processes, but from some exotic Martian chemistry. Their conclusion was bolstered when neither lander detected any organic compounds that would have signaled the presence of microorganisms, dead or alive.

By 1982, when the last Viking craft fell silent, the orbiters had returned 52,000 photographs, including the first close-up pictures of the Martian moon Phobos, mapped 97% of the planet's surface, and determined that its northern polar cap consisted largely of frozen water. The landers took an additional 4,500 photos, recorded a major Martian earthquake (6.5 on the Richter scale), and discovered nitrogen in the largely carbon-dioxide atmosphere. They also sent daily weather data, which led Viking meteorologist Seymour Hess, in 1976, to issue the first weather report from Mars: "Light winds at 15 m.p.h., shifting as any sensible wind is supposed to do. Temperatures Tuesday ranging from a low of -122[degrees]F to an early afternoon high of -22[degrees]F and pressure of 7.70 millibars." There was no precipitation report; it had not rained on Mars for eons.

--By Leon Jaroff