Planetary Scientists Propose Swarms of Penetrator Probes

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NEW YORK — Touching down on an alien surface typically requires a delicate landing approach that evokes the graceful spacecraft ballet of “2001: A Space Odyssey,” or at least some cushioning airbags. But several proposed future missions could take a more crude approach by firing swarms of cheap, bullet-shaped penetrator probes at planets.

Such an approach could be used to carry out both large and small planetary missions, even if some probes fail to survive impact upon slamming into their targets. The concept’s ability to accept risk sets it apart from past and present space missions that only have one chance to get it right, lest they waste hundreds of millions of taxpayer dollars.

“A penetrator shouldn’t be treated as a hammer for every mission,” said Stefan Slagowski, a systems engineer at the Cambridge, Mass.-based Draper Laboratory. But he added that it could enable “planetary science missions on multiple scales and at low cost.”

Swarms of cheap probes could also enable big science by deploying sensor networks across the surface of planets. Such missions might gauge the seismic activity on Mars or help study the lunar underground on grand scales that single-lander missions can not begin to approach.

The huge challenge comes from surviving impact decelerations ranging from 500 times the force of gravity, or 500 g, up to 10,000 g, depending on the hardness and type of landing surface. Survivability must also balance against keeping costs down so that the loss of some probes becomes acceptable.

“Unknown surface conditions mean that risk mitigation requires deploying enough penetrators with the acceptance that a certain percentage may be lost,” Slagowski told a crowd at the International Academy of Astronautics’ ninth Low-Cost Planetary Missions Conference, held in Laurel, Md., the week of June 20. “But the cost needs to be acceptable.”

One such past mission, the Mars Polar Lander, carried two Deep Space penetrator probes designed to bury themselves in the martian surface. But both probes failed to report back upon entering the martian atmosphere, and the Mars Polar Lander itself was lost after a likely high-impact landing itself in December 1999.

Another penetrator probe mission, Japan’s canceled Lunar-A, would have aimed to study the Moon’s seismic activity and interior heat flow.

That has not discouraged Slagowski and colleagues at the Draper Laboratory from studying the science and economic case for one day deploying penetrators. They hope to eventually test the concept with technology demonstrations.

Some future mission concepts may yet deploy the penetrator probes. The proposed Polar Night orbiter could deploy three penetrators at the lunar poles. And a U.K. Penetrator consortium has pushed for penetrators that might bring networked sensor science to Earth’s moon and Jupiter’s icy moons.