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Scientists Are Aiming for Smashing Success in Mars Landing --Literally

SCIENCE FILE

JPL team developed tiny probes housed in rugged cases to withstand free-fall from Polar Lander at 400 mph. If devices survive the impact, experts say, it could herald cheaper techniques for planetary exploration.

December 02, 1999|ROBERT LEE HOTZ | TIMES SCIENCE WRITER

Sarah Gavit and Suzanne Smrekar plan to do the one thing on Mars tomorrow that a generation of planetary explorers have done their utmost to avoid: smash their two space probes into the planet's surface at 400 mph.

For the past 11 months, the tiny craft have been riding aboard the Mars Polar Lander, which is positioning itself around Mars for a landing attempt Friday. Five minutes before it enters Mars' upper atmosphere, the lander will jettison the two probes.

There will be no aerobrakes, no retrorockets, no parachutes or air bags to cushion their abrupt fall from space.

In any other planetary mission, it would be a heartbreaking failure when each probe's acorn-shaped, silicon carbide aeroshell shatters on impact near the Martian south pole on Friday and the bullet-like cluster of instruments inside plows into the dirt.

But to Gavit and Smrekar, the engineer and the scientist, respectively, who are in charge of the Jet Propulsion Laboratory's $30-million Deep Space 2 project, it could be a moment of elation.

The mission's major goal will be achieved if the probes simply survive the brutal landing.

If successful, the experimental techniques developed to protect the electronic innards of the two probes from the crush of an uncontrolled crash landing could herald a fundamental change in the technology of planetary exploration, space experts said.

These two probes are designed to search for underground traces of water vapor, but researchers envision a day when scores of such hardy sensors could be thrown like seeds across the solar system to monitor the weather, seismology, electromagnetic flux or seasonal changes of other worlds.

Linked in networks, these sturdy microprobes would be cheaper, because they would not require complex and fragile landing systems. And, because many could be launched at the same time, they could be deployed over a much wider range than a conventional lander.

Orbiting swarms of tiny communications satellites could one day link these networks of surface microprobes in an interplanetary Internet to transfer unprecedented amounts of data about alien worlds to scientists on Earth.

Plans for a solar-system-wide web already are being drawn up at JPL, with schemes in the works for separate Internets for the moon, Mars and other planets connected by a new generation of hardier computer transmission protocols and more robust routers.

For now, however, the challenge is to survive that crash landing.

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"We were given the challenge of designing a system that was small and lightweight enough that [eventually] you could put 10 or 15 [probes] on one mother ship . . . but could also survive the high-energy impact," said project manager Gavit.

"It provides a whole new way of accessing a planet," she said. "It is an idea whose time has come. Until recently the technology just wasn't there."

Unlike any spacecraft before them, the probes must endure impact forces up to 60,000 times the force of Earth's gravity as they hit the surface.

By comparison, the Mars Pathfinder, which was cushioned by a girdle of air bags, was subjected to about 17 times the force of gravity during its landing. And the Mars Polar Lander, which will investigate climate and soil conditions, is designed to settle gently to the surface, balanced on the fire of 12 rocket thrusters.

The probes' miniaturized electronics must also function on the Martian surface at temperatures as cold as minus 184 degrees Fahrenheit, something conventional circuits cannot do.

To develop a design that could survive this kind of impact, the engineers of the Deep Space probes started by hurling their handiwork repeatedly from a Cessna aircraft cruising at 10,000 feet over the Mojave Desert to see how well they survived the bounce on the hard-packed desert floor.

The survivors of those aerial trials were then fired from a powerful compressed-air cannon at the Sandia National Laboratory into tubs of simulated Martian soil. The winning design, selected from 10 alternatives, emerged after 70 test firings.

The end result was a pair of compact, cantaloupe-sized probes of tungsten, steel and magnesium, packed with bonded, shockproof microchips. There are no screws to unthread, no conventional wires to short-circuit, or joints to seize up, and few welds to crack.

The assemblage of lithium batteries, accelerometers, diode laser, micro-radio and tiny tungsten drill is so compact it had to be put together under a microscope.

In all, each probe cost about as much as an episode of the weekly television series "ER" to develop, launch and operate, Gavit said--about $13 million. One day, the engineering techniques may be used to harden more homely terrestrial devices ranging from cell phones to television remote control units and laptop computers.

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