Why we won’t be ‘saved’ by space mining

Before you get all excited about the prospect of investing in a space-mining operation that could deliver “near-infinite” amounts of scarce (here on Earth, anyway) metals and minerals, let us say one word: energy.

Yes, Planetary Resources‘ just-announced “bold” — or “audacious” or “visionary” — plan to mine near-Earth asteroids for precious resources could, in theory, make economic sense at some point. As an article in Wired notes, “Mining the top few feet of a single modestly sized, half-mile-diameter asteroid could yield around 130 tons of platinum, worth roughly $6 billion.” So even if all the upfront research and development costs, say, $10 billion, two simple (as if) back-and-forth trips to an asteroid would be more than worth the investment, yes?

Unfortunately, this is the same logic often applied to another precious, Earth-bound resource: oil. Many economists (and others) argue that we’ll never run out of oil because, once the cheap stuff is gone, the hard-to-get, expensive stuff in deep water, under the Arctic, etc., will automatically be worth going after. Except that, as we discovered in 2008, $140-plus oil tends to kind of help crash the economy.

Sure, platinum isn’t as vital to the daily functioning of our global society as oil is. So maybe the cost of asteroid-mined platinum won’t be as big an economic worry as is the cost of drilling for oil under the North Pole. Instead of economics, then, let’s look at the energy equations of space mining.

Fortunately, University of California-San Diego physicist Tom Murphy has saved us the trouble by already doing so, and he did it well before Planetary Resources’ “audacious” announcement.

In a 2011 post titled “Stranded Resources” at his blog “Do the Math,” Murphy looks at the energy requirements for bringing a small — one cubic kilometer — nickel-metal asteroid back to Earth orbit for mining:

“To get this asteroid moving at 5 km/s with conventional rocket fuel (or any ‘fuel’ that involves spitting the mass elements/ions out at high speed) would require a mass of fuel approximately twice that of the asteroid. As an example, using methane and oxygen, (4 kg of O2 for every 1 kg of CH4), we would require two years’ of global natural gas production to be delivered to the asteroid (now multiply this by a large factor for the fuel to actually deliver it from Earth’s potential well). The point is that we would be crazy to elect to push the asteroid our way with conventional rockets.”

A solar sail might work, he continues, but it would need to be a big one — the size of Egypt — to capture the needed energy from solar wind pressure. Furthermore, he calculates, using that solar sail would take 350 years to bring the asteroid to a speed of 5 kilometers per second.

There’s another trap as well: the cost — and energy — that would need to go into building an infrastructure to support this kind of large-scale, space-mining venture. Murphy addresses this in another post titled “The Energy Trap,” where he talks about the energy investment needed to build a non-fossil fuel energy system:

“The construction of that shiny new infrastructure requires not just money, but … energy. And that’s the very commodity in short supply.

Finally, there’s one more thought from Murphy that applies to the Planetary Resources idea, and this comes from a post titled “Why Not Space?”:

“We have not yet known a modern existence without an ever greater scale of fossil fuels, and it is their availability that has catalyzed our progress. This century, we will enter a new phase, untested by humanity. Dismissing the challenge this presents by looking beyond to a future in space is one of the best ways to ensure that such a future never comes to pass.”


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