#asteroid retrieval

How to actually grab an asteroid is a tricky problem, complicated by the fact that asteroids spin. There’s a bunch of engineering issues with the task, but honestly it really does come down to just finding some way to envelop the asteroid or get a grip on it. Personally I like the pac-man version in the upper right of the image at the start of this post, not for any practical reasons, just because I like the way it looks.

The trouble is that there’s a pretty good chance that the asteroid you’re looking for isn’t the size you think it is. It’s entirely possible that we could send out our pac-man only to find out that its pellet is bigger than its mouth is.

For most asteroids, our only real information about their size comes from how bright they are when we spot them in a telescope. Since an asteroid can reflect anything from 3 to 60 percent of the light hitting it, how bright it is doesn’t tell us as much as we’d like about how big it is.

We’ll assume that one way or another, any asteroid that gets picked for retrieval will be one that we actually have a good size estimate for, and a way of grabbing hold of.

All good?

Almost. We still need to figure out how to bring it home. Asteroids can be heavy.

I’ve talked about propulsion systems before, and I hope I’ve made it clear that I don’t think there’s a magic one-size fits all solution to spacecraft propulsion. Different needs call for different solutions. For the foreseable future, a manned mission needs to get where it’s going fast. With people as the cargo, fuel efficiency is nowhere near as important as being able to accelerate hard and get your crew somewhere where they aren’t being bombarded with unmitigated cosmic radiation as fast as possible. For bringing back an asteroid, you’re in almost the exact opposite situation. Your cargo is a rock that’s been in space for billions of years, just about the only concern you have is having a fuel efficiency high enough to let you bring back a really big rock. For NASA’s look at near-earth asteroid retrieval, this means solar electric propulsion - ion engines powered by solar panels.

For this kind of mission, the advantage of using ion engines instead of chemical propulsion is overwhelming.

(same paper)

All of this is to say that yes, we probably can go out and grab an asteroid, even a several thousand ton asteroid, and bring it back.

Doing so would open up lots of scientific opportunities for us, it might give us some conveniently accessible resources for future space activities, and it should give us valuable experience moving stuff around in space on the off chance we find ourselves needing to deal with an asteroid that’s going to come to Earth all by itself.

So do I think we should do it?

Yes, depending on who ‘we’ are, when we’re planning on doing it, and what we plan on doing with it once we’ve got it in some parking orbit or other.

I think that there’s enough private interest in asteroid mining that there’s not much need for NASA to do this one themselves.

I think there’s no point in planning an asteroid retrieval until we’ve picked an asteroid to retrieve, and that should wait until we’ve done a more thorough job of surveying the available candidate asteroids to find out critical information like how big they are.

And honestly, I don’t see a point to bringing the entire asteroid back unless we’re going to use it. If it’s just grabbing samples, a probe can go and come back without dragging the entire rock. If it’s so astronauts can experience dealing with an asteroid… well can’t that wait until we have something productive for them to do with it?