A number of well-funded and well-connected entrepreneurs are kicking off Planetary Resources, a company devoted to harvesting materials from near-Earth asteroids.

Now before you go scoffing (or wondering how to “greatly enable” things) – this is by no means a crazy idea. Many of the technologies one might want to prospect asteroids are not difficult to conceive of today. Commercial launch services seem to be on the brink of an explosion. And, yes, there certainly are resources on asteroids! I’m eager to welcome to the space community a group that is willing to embrace greater risk in order to reap greater rewards.

I’d like to point out just a few of the challenges Planetary Resources will face, and why asteroids might be an interesting target for resource exploitation.

First of all, asteroids boast uniquely available resources, if only we can get to them. Some classes of asteroids are wholly or partially composed of metals – or even other useful substances, such as water or carbon compounds. It might be easier to access those resources on an asteroid, if it has a “rubble pile” structure, than it would be if we have to drill down into the surface of a planet or moon. We are also not likely to have to drill or dig as far. Once we get our precious asteroid resources in hand, it’s also much easier to move them to another space destination than it would be from the surface of a moon or planet: we just have to give the blocks of metal a shove to push them out of the asteroid’s wimpy gravity well!

Second, having resources available to us in space would be a tremendous boon. The biggest obstacle to the commercial, industrial, scientific, academic, Starfleet, or any other kind of development in space is straightforward to identify: launch costs. What if we could take that all or part of the way out of the equation? What if, instead of building spacecraft on Earth and launching them into space, we instead build them right where we need them, and shuttle asteroids or special components up as necessary?

The challenge preventing us from jumping right on a von Neumann-style space exploration architecture is that we will have to develop this remote-controlled manufacturing base. Figuring out how to steer robots in space is not an unsolved problem, but figuring out how to control a robotic mining and fabrication facility is something else. I don’t think it’s intractable – but there are going to be a lot of difficulties with reliability and robustness. I don’t think Planetary Resources has self-replicating machines on its immediate business plan, but it is going to face some similar obstacles: how does the robot (or human miner, even) dig into the asteroid in microgravity? How does the miner get ore to the surface? What other processing has to happen?

Then, once the resources are in hand, what will Planetary Resources do with them? It is very tempting to make statements about the value of those materials to the global market…but, remember, it’s always harder to send a spacecraft to a destination and back than it is to send it one-way. If we want to return asteroid mine products to Earth, we will have to boost them with delta-vee of the same order as that we used to send the miners on their way – which means we need to send return vehicles with the miners. Perhaps the mining can solve its own problem by providing fuel for its return rocket, but still, the cost and complexity of the mission will mount up. On top of that, once the resources get to Earth, we will have to decelerate, capture, and eventually do-orbit them. All that takes energy: de-orbiting, in particular, is tricky because we often rely on ablation to carry away the energy from an object moving at 7 km/s…and we don’t want to burn up the resources we just spent all that time and effort extracting. For that reason, I think it may make more sense to keep those resources in space and find ways to use them there.

From Planetary Resources’ descriptions of fuel depots and expanding the exploration of space, that may be what they intend.