(Image: NASA/Paul E. Alers/(CC BY-NC 2.0))

What do those in the know make of the bold plans dreamed up by wannabe asteroid miners Eric Anderson and Chris Lewicki of Planetary Resources? Few outfits are more familiar with asteroids than the Minor Planet Center at Harvard University. Paul Marks asked its director Tim Spahr if he thinks the operation will succeed

Read more: “Meet the asteroid miners“

What was your reaction when you first heard about Planetary Resources‘ plan to mine the asteroids?

My interest was initially piqued by the fact that they also want to study space objects with their small space telescopes. That’s my background: the discovery of these bodies and their orbits. I view mining asteroids as quite difficult. A lot of the technology required to do that has not yet been demonstrated. Of course, that’s what somebody would have told you about brain surgery or heart surgery before it was actually done. So while this hasn’t been demonstrated yet, the only way to do so is to throw a whole lot of money at the problem and to undertake a lot of experiments on Earth and in space.


Well, with their Google billionaire backers I guess they have the money?

Potentially. You never know exactly how such things will go. People who thought they had a lot of money from donors in 2008 when the markets collapsed found they did not have so much after all.

Planetary Resources mention the concept of moving an asteroid nearer to Earth to make mining it more economically feasible? Is that possible?

It would take an awful lot of energy. And that’s one calculation that’s rather easy to do. We know the speed of every object that we observe because that’s part of the calculation of the orbit. And you know what energy you need to supply to alter that speed. And so you can sit down, with your pen and paper, or your computer, and compute the integral and see what it is. But it’s certainly a long way from my comfort zone, figuring out how much propellant is required to do that. I suspect that’s a lot of energy.

Why does it take so much energy to change the orbit of an asteroid?

Because the sun is in charge of the dynamics of the solar system. It is the sun you are messing with at that point. If you wanted to park an object in orbit around the Earth that’s going to take quite a bit of energy, because you’ll have to alter the velocity of the object so that it is no longer orbiting the sun.

If you do coax an asteroid back towards the Earth and you mine it, reducing its mass, could that change its orbit, too?

Well, that’s your standard recoil problem. If you’re standing in your slippers in the middle of an ice hockey rink and you shoot your shotgun, you’re going to move. That is simple momentum transfer. You’ve flung a piece of yourself away, in this case, the bullet at high velocity, and so the recoil pushes you a little bit. Those are minor issues though. Again, you compute what sort of thing you’re doing, how much mass you’re moving away when you take off with what you’ve mined. I suspect that would not be much of a problem. They would know what they’re moving and what the reaction would be. My intuition is this would be a very small factor.

Should we worry that bringing asteroids closer to Earth and making some kind of trajectory error might damage constellations of key satellites, like the GPS network, or worse, hit the Earth?

Honestly, I view a lot of this kind of talk as sort of alarmist. We have a giant belt of spacecraft up there right now. None have ever been hit by anything despite the fact that we have marble-sized junk flying at the Earth all the time. The International Space Station has never been decompressed and the danger is not from something we’re going to bring into the area; the real danger is the fact that there is little stuff the size of baseballs and footballs flying in the Earth’s vicinity literally every day. The US air force keeps track of everything down to small sizes in the vicinity of the Earth anyway, so they know where everything is.

Planetary Resources’ co-founder Eric Anderson makes the point that we already have the 417,289 kilogram ISS up there and it could cause great damage on Earth if it accidentally re-entered and yet no-one considers that a risk.

Yes. Whoever will be doing the orbital mechanics for the asteroid project would be well aware of what sort of uncertainties there are. And again, I tend to remind most people that hitting the Earth is a damn hard thing to do.

Do you think they’ll mostly go to an asteroid, sit on it and mine it, rather than move it anywhere?

I suspect that would be the first thing to do. And that presents a number of extremely difficult challenges. Think of Newton’s law of equal and opposite reactions: there’s no gravity on the asteroid. How do you actually dig a shovel in? It’s not like you’re going to put a front-end loader or a John Deere tractor up there and start scraping the surface, because the instant you do that, the opposite reaction is going to fling you right off of that. You’re going to have to find a way to bolt your mining material down.

And your robots and your people of course…

Yes, in an environment where the average, small near-Earth asteroid rotates in several minutes, not hours, but minutes

So putting a spacecraft into orbit next to it will be tough?

That will be hard. I’m quite sceptical. I think that they face a lot of challenges and this will certainly be a multi-decade, multibillion dollar endeavour just to get it off the ground. They’re not going to just spend 500 million bucks, fly up there, mine the asteroid and make $1 trillion. That will not happen.