Along for the ride: microprobes

Each probe will penetrate up to 3 feet into the martian soil (Click image for annotated graphic)

On a broader scope, the probes will provide an initial test for a new NASA approach to determining the character of bodies in space: placing multiple probes in locations all around a planet, or moon, rather than depending solely on data from a single landing site.

In this case, it will involve three craft, the main Mars Polar Lander and the two hitchhiking probes. The probes will separate from the main craft and crash to the surface about 60 miles from the main landing site.

It will mark the first time more than two vehicles have landed on extraterrestrial terrain at the same time. The concept, says project scientist Suzanne Smrekar, amounts to no less than "a new way of exploring planets."

Smrekar points out that the experiment is extremely high risk but underscores what she feels is the project's biggest accomplishment.

"We were able to develop all sorts of cutting edge technology, and we can do it again," she says. "It is a secondary mission, and there are so many tiny things that could go wrong. But we have learned how to do this."

Deep Space 2 is the second mission under NASA's New Millennium program, which is designed to test new, high-risk technology for future space flight without putting a high-end major scientific mission on the line. NASA has placed the cost of Deep Space 2 at $29.2 million, of which $28 million was devoted to pre-flight development.

By contrast, the costs for the Mars Polar Lander and Climate Orbiter total $235.9 million, $193 million of which went toward development.

The Polar Lander itself will settle on the barren steppe near Mars' south pole to make more far-reaching scientific robotic explorations into the planet's atmosphere and soil and to search for traces of water.

Five minutes before the lander enters Mars' upper atmosphere, the encased microprobes will separate and dive towards the surface, striking about 50 to 85 seconds before the lander touches down 100 kilometers (60 miles) away.

The business part of each probe, which the aeroshells are designed to protect, is no larger than a grapefruit. Tom Rivellini, lead mechanical engineer on the Deep Space 2 project, relates the size of the miniature laboratory -- which will bury itself two to three feet into the Martian surface -- to that of a coffee shop salt shaker, about 3 inches long and 1.5 inches around.

Each miniscule chamber holds a laboratory's worth of paraphernalia: a tiny computer and signal processor, power conversion electronics, a tiny motor and drill to collect a 1/250th of an ounce of soil, a oven the size of a pencil eraser to heat and test the sample, a water vapor analysis chamber and a laser-sensor apparatus.

Even the umbilical wire that will tether the submerged probe to the aftbody on the surface was especially developed and extensively tested for the first-of-its kind project.

Central to the experiment, says Rivellini, will be the ability of each little package and its complex micro equipment to withstand up to 60,000 Gs of gravitational pull and remain fully intact -- a test that he says could have vast implications for future exploration.

Furthermore, the forbody buried in the martian soil must withstand temperatures as low as minus 120 C (minus 184 F), while the aftbody on the surface must withstand an environment as low as minus 80 C (minus 112 F).

The most important aspect of the project, Rivellini says, "is the ability, in a high-risk project, to take this miniature electronics-mechanical system and force it all into one super-small package. It's individual technology pushed to extremes." The computer itself, he says, would fit on the face of a domino.

Smrekar dubs the total package "the laptop of space vehicles."

The protective shells that will house this laptop are made of tested and retested opaque silicon carbide. They are designed to shatter on impact, but in a manner where the tiny and delicate electronics and equipment inside remain unscathed and maintain the force to enter the soil.

To test this, scores of prototypes were dropped from aircraft and shot into the Earth by giant cannons.

The aftbody of the probe package will remain on the soil to transmit data via the Mars Global Surveyor spacecraft, which has been orbiting Mars since September 1997.

With luck, NASA scientists say, at least one of the two bullet-like probes will make it into the ground without hitting a rock, another reason for sending two.

"It at least doubles our chances of not hitting something solid," Rivellini said.