Asteroid mining may not be commercially viable after all, a Harvard astrophysicist has said.
The claim by Martin Elvis of the Harvard-Smithsonian Centre for Astrophysics was made in a paper published in the journal Planetary and Space Science, posted online at Arxiv.org. He sought to quantify how many ore-bearing near-Earth objects (NEOs) there are, with ore classed as a commercially viable material, in particular those from the platinum group metals (PGMs) and water. His research was based on the premise that there's no point launching missions that will demand huge expenditure, unless we know with some degree of certainty that we are likely to strike gold -- or platinum, in this case.
Quite troubling for the likes of Planetary Resources and Deep Space Industries (DSI), two companies in the midst of planning for launches of cubesats to carry out asteroid recon missions, Elvis' estimates put the number of PGM-carrying asteroids at just ten, or one percent of known NEOs, and water at around 9,000 -- though he says these will probably be small and therefore tricky to find. Water-bearing asteroids bigger than 100m in diameter, he puts at 18.
The equations his finds are based on take into account delta-v, the velocity rate needed to reach the asteroid and return. This in itself has to be commercially viable, taking into account distance from Earth and additional velocity needed for the return trip.
"The return delta-v is more important than the outbound delta-v because a much larger mass of ore needs to be returned than the mass of the mining equipment sent out," writes Elvis. "Small changes in delta-v make for large differences in the mass that can reach an NEO.
"Choosing an NEO with delta-v = 4.5 km s-1 can double, or even quadruple, the payload delivered to the NEO compared with the median. This value includes only a small fraction of all known NEOs."
The problem, according to Elvis, is there are few NEOs in the delta-v range he has calculated that are larger than 100m in diameter -- that small size reduces the chances they will be carrying precious minerals to one in 2,000.
"As 100m diameter NEOs are needed to have a value [worth mining] and the population of NEOs larger than 100 m diameter is around 20,000, the total population of PGM ore-bearing NEOs is roughly 10," the paper concludes.
The precious minerals he focussed on included platinum, rhodium, osmium, iridium, palladium and rhenium, all elements that are rare in the Earth's crust because they dissolve in molten iron so are generally trapped in the Earth's core. These, he says, provide the "most promising enterprise for asteroid hunters, because of their high value on Earth" and will be found on M-type asteroids which are known to deliver PGM-rich nickel-iron meteorites to Earth. Water was also focused on because it's been predicted it will be the first product that is mined: "it would be used in space either for life support or, separated into hydrogen and oxygen for rocket fuel."
Speaking to the BBC, Planetary Resources cofounder Eric Anderson poked a few holes in the predictions though, arguing that the NEOs most likely to contain PGMs are C-type, not M-type as Elvis says, and that Planetary Resources will include asteroids that need a delta-v of 7km/s. "I think the study is probably off by a factor of 100, conservatively, and I think it's off by a factor of 1,000 optimistically," Anderson concluded in the interview.
Elvis does, however, continually point out in his research paper that the estimates are conservative, and that far more work needs to be done to improve upon these predictions. In fact, the paper is more of a call to action that a warning from a naysayer.
"The apparently limited supply of potentially profitable NEOs argues strongly for an accelerated rate both for discovery and especially for characterisation, which is lagging badly behind discovery," writes Elvis. "At the expected discovery rate of about 2,000 NEOs/year from 2015 onwards… it will take a decade or so to essentially complete the discovery surveys.
"Significant research is needed in all areas: on meteorite composition, on telescopic discovery and characterisation, and on both of these together for the small asteroids about to impact the Earth, on local assay probes, and on in-space engineering challenges, both at the ISS and with a returned small asteroid."
It might be, Elvis suggests, that before the actual business of mining explodes, a secondary business based on discovery and identification of ore-bearing asteroids might emerge. It "could itself become commercially valuable intellectual property," writes Elvis.
In all fairness, asteroid mining companies are already focussing on the research and discovery side of things. DSI is set to launch a fleet of Firefly spacecraft in 2015, followed by Dragonfly spacecraft in 2016, all for reconnaissance and about a decade prior to actual mining launches.
0 comments:
Post a Comment