Why NASA Should Nab an Asteroid

NASA and its partners snatch a small asteroid from deep space, bag it for delivery, and tow it into a safe orbit around our moon. There the captured asteroid creates an easy stepping-stone for astronaut explorers who want to explore an ancient rock from the dawn of the solar system, and creates a target for miners who might extract valuable water and metals. If successful, the grab demonstrates that humans could divert a dangerous space rock if necessary.

Science fiction or a glimpse into our space future? Right now, a team of space scientists and engineers put together by the Keck Institute for Space Studies in Pasadena, Calif., is urging NASA to pursue this futuristic mission to help America's space agency achieve its mission of operating beyond low Earth orbit and the International Space Station. I was an astronautics and asteroid consultant to the team, which spent six months analyzing techniques for pulling off the asteroid grab. Our conclusion: NASA could execute this affordable mission within 10 years.

Team co-leader John Brophy, from NASA's Jet Propulsion Lab and Caltech, discussed the plan at AIAA's Global Space Exploration Conference in Washington last month. He said the team was surprised to find that the Asteroid Capture and Return (ACR) mission could be done using existing or near-term technology, and at a cost comparable to that of a Mars rover mission, roughly $2.6 billion over the next decade. And the 500 tons of crumbly, claylike asteroid material might eventually produce 100 tons of water, worth $2 billion at today's launch prices.

Brophy and his co-leaders, Louis Friedman of the Planetary Society and Fred Culick of Caltech, say the "Goldilocks" size for a target asteroid would be about 7 meters across?about the size of a garage (though a space rock of this size would have a mass of 500 tons). Asteroids this size are big enough that astronomers could spot a potential target using Earth-based telescopes, yet small enough that an efficient low-thrust electric propulsion system could nudge it toward the Earth?moon system. The current generation of asteroid-search telescopes should find about five attractive small-asteroid targets every year, and that's a drop in the bucket compared with the few hundred million or so that exist.

The asteroid-capture spacecraft, about the size of a typical communications satellite, would carry a pair of 40-kw solar arrays to power five Hall thrusters. Propelled by these ion engines, the craft would take about four years to reach the target asteroid. Rendezvous would occur millions of miles from Earth. Once alongside the space boulder, the robot craft would match its spin. It would then deploy an inflatable fabric bag to engulf the asteroid, stop its spin, then begin the two-to-four-year return trip, ending in a safe, high orbit around the moon. There it would be easily accessible to robot and astronaut prospectors but safely isolated from any chance of collision with Earth. (The object would be too small to penetrate our atmosphere anyway.)

The ACR mission would go after a water-rich C-type, or carbon-rich, asteroid. These bodies contain up to 20 percent water and up to 6 percent organic material that's similar to black, asphalt-like tar sands. The water and light elements in these bodies would be valuable as propellants, drinking water, breathing oxygen, and industrial chemicals for an off-planet economy. Plus, the residue left behind from further extraction of nickel and iron would be rich in prized cobalt and platinum-group elements. Altogether, a 7-meter C-type asteroid with a mass of 500 tons could produce up to 200 tons of water, 90 tons of metal (83 tons of iron, 6 tons of nickel, and 1 ton of cobalt), plus 200 tons of silicate rock valuable for their semiconductor elements and radiation shielding. Brophy says that an existing Atlas V booster is powerful enough to place the 18-ton robot craft into low Earth orbit to start its solar-powered journey. If it snared and returned 500 tons of asteroid material, the mass multiplication factor (or payback ratio) would be at least 28:1.

If a robot mission like this succeeded, it would put an intriguing, ancient, resource-rich body within reach of astronaut-carrying craft like Orion and its huge Space Launch System booster NASA is now tasked with building. Such a mission would be a major step forward in our ability to operate and move big scientific payloads (or astronaut craft) using solar?electric propulsion, a forerunner for piloted deep-space asteroid missions that NASA plans for the mid-2020s.

The ACR mission hits hot buttons in all three categories of deep-space objectives: scientific exploration, planetary defense, and space resources. In the final chapter of the ACR mission, NASA could boost commercial space partnerships by turning the object over to private mining firms for dissection and conversion to marketable products like rocket fuel. Snaring an asteroid would be a terrific way to jump-start the entire field of asteroid mining. If capturing an asteroid were incorporated into its deep-space plans, NASA could bring home the space bacon before 2025.

Tom Jones is a veteran NASA astronaut, planetary scientist, and author of Sky Walking: An Astronaut's Memoir.

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