Mining Asteroids
An artist's conception of an astronaut preparing an asteroid for retrieval to Earth. Astronomers estimate that selecting one with potentially valuable minerals or water will take perhaps a dozen preliminary probes, depending on how many pre-launch characterization observations can be done.
Last month NASA held a forum to explore the possibility of a human mission to an asteroid, motivated in part by its longer-term goal: the human exploration of Mars. An asteroid mission, besides providing new science on the origins of the asteroids and the solar system, would also result in more practical results, from advanced rocket propulsion systems to enhanced detection techniques, and including the potential mining of precious metals. The first step in such a mission is likely to be the robotic recovery of a nearby asteroid, a near-Earth object (NEO). The current Asteroid Recovery Mission concept proposes to capture robotically a smallish NEO (between five and ten meters in diameter) and tow it into an orbit around the Earth where a crew of astronauts would rendezvous with it and retrieve samples.
CfA astronomers Martin Elvis and Thomas Esty explore the economic realities of mining an asteroid in their new paper in Acta Astronautica, "How Many Assay Probes to Find One Orebearing Asteroid?" There are estimated from statistical analyses to be about ten million NEOs larger than about twenty meters to choose from. The selection problem is driven mainly by a lack of information about the location, size, and composition of each one. The astronomers therefore use a probabilistic approach in their analysis. (Other CfA astronomers have meanwhile been actively characterizing NEO sizes and properties using infrared measurements from the Spitzer Space Telescope.) In Elvis' earlier work, he concluded that about one-in-a-thousand accessible asteroids has a concentration of water high enough for practical recovery, and about one-in-two-thousand has a high enough concentration of platinum group metals. If NASA were to send out probes to complete in situ measurements of candidate asteroids prior to a recovery, the team concludes that for a 90% chance of success in finding a mineable asteroid, between ten to twenty probes would be needed.
If additional remote observations could be performed first, to further characterize the population, and if these observations used sensitive space-based telescopes with current capabilities, the scientists calculate that the search could be narrowed and the probe fleet reduced to fewer than half-dozen missions, at considerable cost savings. The paper concludes that the recovery of economically worthwhile ore-bearing asteroids is indeed possible, but that improved prior characterization would greatly enhance the effectiveness of the program.
"How Many Assay Probes of Find One Ore-Bearing Asteroid?," Martin Elvis and Thomas Esty, Acta Astronautica, 96, 227, 2014.