July 30, 2007 4:00 AM PDT

How to land a spacecraft on an asteroid

NASA is exploring the possibility of sending astronauts to an asteroid, with hopes of making deep-space exploration more feasible.

The DigitalSpace Commons, a Santa Cruz, Calif.-based company that develops an open-source 3D rendering system, has come up with the design for a new NASA spacecraft and a mission that could eventually allow humans to land on and explore an asteroid, or so-called near-Earth objects (NEO). The privately held company plans to unveil the design publicly Monday.

The project dovetails with NASA's Constellation Program, a plan to send astronauts back to the moon by 2020. Along with the lunar mission, the space agency is investigating the possibility of using its future crew navigation vehicle for missions to an asteroid, which could help scientists better understand the minor planets or assist in eventually getting humans to Mars. Over the last six months, NASA studied how it might modify its own lunar vehicle for trips to NEOs and found that it was feasible, according to David Morrison, a senior scientist in NASA's Astrobiology Institute.

"The concept of human flights to near-Earth objects is exciting for science, and it's a logical, technological stepping stone to Mars because it's intermediate in flight length," said Morrison. "It's not literally on the way, but it's on the way for developing the technology for deep space."

Images: A vision for an asteroid mission

Last summer, DigitalSpace said NASA asked it to develop a simulation for such a mission that would draw on the Constellation Program's spacecraft architecture. DigitalSpace's simulations attempt to deal with the unique nature of landing on an NEO.

For starters, gravity is almost nonexistent on an asteroid, which can be as small as only a few hundred feet across or as big as tens of miles in diameter. And because asteroids have rocky, sometimes crumbly surfaces, DigitalSpace's proposed spacecraft includes a system that would anchor it like a boat in a harbor. The design includes a ring of airbags with sensors to detect the stability of the ground. Once a landing is deemed secure, barbed tethers would deploy to latch the craft onto the surface of the NEO. Like car airbags, the ship's airbags would compress against an asteroid's surface.

"On an asteroid, it's a different environment that requires a whole new way to land a spacecraft," said Bruce Damer, president and CEO of DigitalSpace. "It's like insects being blown around by the wind; they have all this technology to hold onto your arm."

A large part of the interest in asteroids is self-preservation, given that they have hit Earth in centuries past, causing mass destruction. In 1908, for example, a meteor struck the deep woods in Siberia, unleashing the energy equivalent of a 10- to 15-megaton atomic bomb. As a result, scientists want to study the composition and behavior of asteroids and better predict their trajectories. Morrison said scientists have only discovered a small fraction of the millions of asteroids that could be potential hits.

In addition, asteroids are composed of materials that could be useful for replenishing supplies on lengthy missions into space far in the future.

"In the long term, we don't know enough about asteroids and how much it would take to use them for resources," said Morrison.

He said the problem with traveling to an asteroid is finding one with an orbit that's similar to Earth's, so that astronauts could get there and back in a short period of time, less than roughly three months. NASA needs to conduct surveys to find a suitable asteroid for travel, he said, but DigitalSpace projects that such a flight with NEO targets could be feasible by 2017.

NASA's feasibility study looked at altering its lunar crew-exploration vehicle for an NEO mission in such a way that it would hold fewer astronauts (to make room for sufficient supplies) and include a different configuration of launch rockets, according to Morrison.

DigitalSpace then came up with a detailed configuration that could deal with the unique conditions of an asteroid, giving a better picture of how it might be done.

"We wanted to show the world how you might do a human mission to an asteroid," said Damer.

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