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Pathfinder Mission: Low Cost, High Risk

Mars-Bound Craft Carries a Light Load and Has No Backup Systems, but Holds Great Promise

December 05, 1996|K.C. COLE | TIMES SCIENCE WRITER

When NASA's Pathfinder arrives at Mars on July 4 next year, it will be the first visitor to the red planet's surface in more than 20 years. But aside from Tuesday night's successful launch at Cape Canaveral, the mission has little in common with its predecessors.

The days of elaborate, expensive missions are long gone, replaced by a "faster, better, cheaper" approach that's both potentially promising and highly risky.

The 1976 Viking missions to Mars lugged enormous cargoes of instruments, fuels and backup systems. In contrast, Pathfinder carries the equivalent of a space age overnight bag: a 3-foot-tall package of essentials designed to sustain it for 30 days on the surface.

To keep costs down, it has no redundancy--backup systems that allow it to recover from mistakes. If something goes wrong, it can't be fixed. "It's very risky, and a little scary," said project manager Anthony Spear of the Jet Propulsion Laboratory in Pasadena, which built and manages the spacecraft.

Viking took the scenic route to Mars, sliding into orbit, then gently settled down on slender legs with the delicacy of a ballerina.

Pathfinder is taking what NASA calls a "ballistic" entry--which means essentially that it's getting thrown at Mars like a fastball, traveling more than 7 miles per second. Only a flimsy parachute and small rockets will help slow it down. Seconds before it crash-lands, an enormous shell of air bags will inflate and surround the lander like a cluster of party balloons. Then it will bounce around like a bungee jumper for several minutes until it settles down.

When Viking got to Mars, it sat in one place and conducted experiments on the barren soil--a site chosen for its flatness (and ease of landing) rather than geological interest. "Viking landed in the equivalent of the Sahara," said NASA chief Daniel Goldin.

When Pathfinder settles down, it will open like an egg to reveal a 22-pound robot named Sojourner that will roam the surface, putting its stethoscope-like detectors on whatever interesting rocks it happens to find. Goldin calls it a "22-pound geologist."

The robotic researcher should have rich pickings, NASA scientists say, because its destination was at one time flooded with more water than our Great Lakes--and water is required for life. (Coincidentally, the rocks at this site are the same age, researchers think, as the meteor from Mars that contained what might be evidence of ancient microscopic life.)

Moreover, a wide array of different kinds of rocks were probably swept in with the flood. "The place is a grab bag," Spear said.

Sojourner can roam an area the size of a football field, and while controllers at JPL will tell it where to go, it can make up its own computerized mind about the best route to get there. "It extends our ability to reach out and touch those rocks that are the library books on the history of Mars," Spear said.

Pathfinder's primary mission is to test a new way of getting instruments to Mars that can land just about anywhere--including rocky, hostile terrain inaccessible to Viking-like landers, and the most promising niches for life.

"Those are the exciting places," Spear said.

Named for the African American Sojourner Truth, who traveled the country during the mid-19th century to argue for equal rights, this Sojourner robot is also something of a pioneer. Folded in a fetal position inside the Pathfinder for its seven-month, 310-million mile journey to Mars, the robot only stands to its full height of 1 foot after its arrival.

With six fat wheels that can each move independently, it is limber enough to crawl up a person's leg. It can dig holes with its wheels to get an idea of the soil beneath the surface, and study its own tracks for clues to the properties of the Martian crust.

The small robot carries an instrument that shoots helium nuclei at outcrops of rock, then detects whatever radiation or particles bounce back. By analyzing the backscatter, the detector can identify minute traces of any element, except for hydrogen. Although Sojourner itself cannot identify complex molecules, and therefore evidence of life, the mission will pave the way for future craft that will be able to detect organic substances.

The instrument aboard Sojourner, called an Alpha Proton X-ray Spectrometer, sits on the end of a flexible arm that can reach out and touch rock surfaces at many angles.

Sojourner will wander about on solar power, and return at the end of each day to Pathfinder, where it will hibernate through the cold Martian night until the sun warms it back to life the next day. "It's kind of reptilian," said flight system manager Brian Muirhead at JPL.

While the rover looks at rocks, Pathfinder's stereo cameras will take panoramic views of Mars in several wavelengths (or colors) and beam back nightly reports on temperature, winds and atmospheric pressure.

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