When we finally make the jump to fully colonizing the Solar System, we’re going to want to use asteroids as stepping stones. We can use them as way stations, research facilities, even as spacecraft to further explore the Solar System. Today we’ll talk about the science and science fiction of hollowing out asteroids.
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Female Speaker: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit www.astronomy.swin.edu.au for more information.
Fraser Cain: Astronomy Cast episode 381, Hollowing Asteroids. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos. We help you understand not only what we know, but how we know what we know. My name is Fraser Cain. I’m the publishers of Universe Today. And with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville and the director of CosmoQuest. Hey Pamela, how you doing?
Pamela Gay: I’m doing well. How are you doing, Fraser?
Fraser Cain: Good. So once again, it’s – the summer season is upon us. And that means that your neighborhood is being threatened with all kinds of inclement weather. So if we hear –
Pamela Gay: We may have a little bit of thunder during this podcast.
Fraser Cain: Yeah, we had some thunder happen in the preshow as we were getting prepped. I heard some thunder in the background of your recording. So leave it in, Preston, if you hear this. Leave it all in.
Pamela Gay: I’m not sure –
Fraser Cain: Yeah, don’t worry with the –
Pamela Gay: – how you remove thunder.
Fraser Cain: Don’t remove the thunder. Yeah, exactly.
Pamela Gay: Although it looks like the storm is turning just slightly north of us, so we may get lucky.
Fraser Cain: So you’ve got some – a bit of an announcement to talk about some of our Astro Gear.
Pamela Gay: Yes. So it is an amazingly exciting summer. We have – everyone is totally aware. Pluto, Pluto, Pluto. Everyone is talking Pluto. And we have a shirt over at www.astrogear.spreadshirt.com that says, “Explore Planet Pluto Classic.” It’s a total parody of the Coke Classic logo, fully legal under parody law.
And there’s also Ceres. People keep forgetting it’s the other former planet. So in the name of parodying, we parodied the “Pork, the Other White Meat” logo and made a “Ceres, the Other Former Planet.” So you can show if you’re team Pluto or team Ceres by getting yourself your own former planet t-shirts.
Fraser Cain: Awesome. Do that. Okay, great. Well, let’s get on with the show.
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Fraser Cain: When we finally make the jump to fully colonizing the solar system, we’re gonna wanna use asteroids as steppingstones. We can use them as way stations, research facilities, and even as spacecraft to further explore the solar system. So today, we’re gonna talk about the science and science fiction of hollowing out asteroids. Now, Pamela, this is clearly one of your pet favorite ideas. You bring it up often.
Pamela Gay: Yes.
Fraser Cain: And it’s great. And it’s funny; in preparing for the show and looking back, this has been a big idea that’s been shared for a lot of researchers, a lot of NASA people, for decades.
Pamela Gay: Yeah. And it’s one of those things that the science fiction and the science have just sort of always hung out there saying the exact same things of, “Hey, we can do this! We should do this! This is really cool! Look at how awesome it is!” And yet we never quite get to doing it. So this is where we named this in science and science fiction because it is near future fiction that people are working to make real right now.
Fraser Cain: Yeah, absolutely. So then let’s kinda go back a bit and just sort of talk about why – like, I guess what is the idea here? So you take an asteroid; what do you want to do to the poor asteroid?
Pamela Gay: Well, the asteroid doesn’t care, luckily. The idea is that, well, nowadays, you can grab yourself one of these nice carbonaceous, silica-rich asteroids that has an orbit that is very, very similar to the Earth’s orbit. So it doesn’t take a lot of energy to bring it to earth if that’s what you wanna do, or to get to it, which you’re gonna have to do either way.
And once you’re there, you can use the material that the asteroid is made of with a 3D printer to turn the asteroid into whatever you want. You can simply bore into it and hollow yourself out a hobbit hole in the side of an asteroid, attach engines, get the thing spinning. You have a spacecraft that had built-in radiation protection because all of that nice dirt wall, it’s there to protect you.
Now, admittedly, these carbonaceous chondrites, these silica-rich asteroids, they’re gonna be kinda fragile, maybe. We don’t really know. Some of them are actually just rubble piles. But a little less than 10 percent of the asteroids are actually metal-rich, made of iron and nickel and platinum and all of these other metals that you can just flat-out mine and turn into a spaceship. So there’s a lot of potential things that you can do.
Fraser Cain: All right. So let’s talk about, like, what it would take to actually get a mission to an asteroid and begin to do some of these things because I think – I’m a classic oversimplifyer. I know that. I know that’s one of the things that I do. But we saw with the Rosetta mission, with Philae trying to land and bounce on the surf – and how it bounced on the surface of 67P, that it’s actually a really difficult environment to try and work in. So what are kind of the challenges to actually interacting with an asteroid like this?
Pamela Gay: Well, the No. 1 challenge is how do you catch the sucker? You have an object that’s moving at a bazillion kilometers per second basically, as it happily treks around the sun. So you have to get out of the Earth’s gravitational well and find an asteroid with an orbit that it’s easy to sync up with.
Now, once you can find that asteroid, it actually takes what’s called a lower Delta-v – a lower change in momentum brought about by change in your velocity – to get to an asteroid than it does to get to the moon because the moon is orbiting the earth, and it’s just hard to match that.
Fraser Cain: Yeah, people don’t realize that.
Pamela Gay: No, it’s a pain in the butt.
Fraser Cain: Yeah, the moon is actually difficult to get to, when in fact there are asteroid where the Delta-v to get to those asteroids is really slight compared to going to Mars or going to the moon.
Pamela Gay: Yeah. So you start out by finding the asteroid that has a near Earth orbit. There’s a bunch of these out there, and they have neat names. One of my favorite random moments in geekdom was talking to Richard Hatch and explaining to him that a lot of the asteroids that strike the earth’s atmosphere, including the Chelly events asteroid, are Apollo class asteroids that have semi-major axises – this is the half-size of their long axis – that is a little bigger than the Earth’s orbital axes and cross the Earth’s orbit twice as they go around the sun.
So these are asteroids that we have the potential to overlap with, which would be really bad. But they’re also fairly easy to get up and close and personal with, which is really good if you’re trying to catch one. So catching one of these Apollo asteroids.
There’s also Amor asteroids, which have orbits a little bit bigger than ours. And all of these different things, we just need to go out and find them, which is its own challenge. But this is why we’re building the Large Synoptic Survey Telescope. This is why we have the Catalina Sky Survey. Finding asteroids is something we know how to do.
Fraser Cain: Right. And there are ones –
Pamela Gay: So Step 1, find it.
Fraser Cain: – I think – was it asteroid Tutatas? There’s a bunch that have been identified many times that they, as you said, they have an orbit that kind of interacts with the Earth’s orbit. And in some cases, they’re pulled a little. As they approach us on their orbit, they’re pulled a little forward. And then other times we catch up to them. And we sort of have this interplay with these various asteroids, and it just makes them super easy to get to.
So okay, great. We’ve identified a few hundred candidate asteroids that might work well for us to try and get to. So what’s next?
Pamela Gay: So next you figure out, am I going to bring it back? Am I going to bring it home with me? “Mom, the asteroid came home with me.”
Fraser Cain: Yeah. Yeah. “You’re gonna have to feed it. You’re gonna have to take care of this thing.”
Pamela Gay: Exactly. Then if you’re not gonna do that, how are you going to mine it in situ? So if you’re gonna try and bring it back with you, you have some options. You can paint it to change how it interacts with solar radiation so that it’s either pushed more or less than it’s currently pushed. You can blow things up near it so the shockwave affects the orbit. You can stick something really massive nearby so that it gets dragged gravitationally into a slightly new orbit because you’re assuming that whatever it is that you put in front of it has rockets to steer. Or you can just attach engines to it right off the bat.
Fraser Cain: You could shoot it with lasers to try and –
Pamela Gay: You could shoot it with lasers.
Fraser Cain: – vaporize material. You could put some kind of mass driver cannon on it and shoot those – chunk of the asteroid off into space to affect its speed. So there’s a lot of – or – and if you’re really clever, you can use various flybys of smaller asteroids that you’ve been able to engineer and try to sort of do some gravitational slingshots with it. So many options.
Pamela Gay: Right. So figure out how you’re gonna move it. And then what do you want to do with it? And the thing that I love the idea of the most is turning these things into actual spacecraft, where you first utilized the material that’s inside of them, hollowing them out. If you’ve ever read Ender’s Game, so I always imagine the way the insects, the buggers, hollowed out asteroids ant-style.
Except now do it with the same kind of massive machinery like is putting in the new tube in London or has built channels between England and France and between different parts of Japan. Find one of these massive tunnelers – but built-in in space – and tunnel yourself out an asteroid. And use the leftover material to build the structures you need on the surface, to build additional spacecraft, to 3D print. I mean, there’s so many different things you can use that rock for, given modern technology.
Fraser Cain: Yeah, I mean, the difficulty as we saw, as I mentioned with Rosetta, is just interacting with – such a low-gravity world has a whole series of complications.
Pamela Gay: Now, luckily, asteroids do have a significantly higher density than comets. So if you find an asteroid the same size as comet C-G/67P, because of that difference between water and rock, you are going to have a little bit higher gravity. But that is going to be a problem.
Now, we have managed to land things on asteroids before. We’ve settled spacecraft onto their surfaces after exploring. We’re sending OSIRIS-REx out to do a sample. But it does require very carefully matching the spin rate, very carefully not bouncing, as was realized by Philae.
Now, the difference likely between the types of asteroids that we’ve landed on in the past and Chury-Geri is while I’m sure there are rubber duck shaped asteroids out there, you can purposefully choose to try and land on something that is more potato shaped. Rosetta didn’t know it was headed towards this extremely complex topography that was spinning around a really weird rotational axis, trying to land on something that has a wonky spin or really weird shape, and almost no gravity. That’s three different marks against you. If you can at least get normal rotation access, potato, it makes life a lot easier.
Fraser Cain: Yeah, absolutely. Okay, so you’ve figured out how to either move the asteroid or you’re gonna go to it. And we’ve talked a bit about the kinds of technology that we would use to maybe hollow it out, use some kind of drill. Maybe we’re gonna use kind of more traditional explosives, the way we mine here on Earth, to try and smash pieces out. So how would you then turn that into a place that people could maybe live?
Pamela Gay: There’s several different models that are out there. One of my favorites that has cropped up in several different books – it was in Seveneves, although it wasn’t asteroids; it was chunks of moon with Seveneves. It’s in Kim Stanley – Seveneves is by Neal Stephenson. It’s is 2312 by Kim Stanley Robinson.
The idea is you completely hollow out the object and set it spinning to create artificial gravity, and then use this to create a pocket environment. And the amazing idea put forward in 2312 is imagine as we’re trying to protect the various ecological systems here on the Earth as climate change is, well, moving where the ecological systems are comfortable. The thermal gradient of the oceans is changing; our deserts are shifting. This is having – this is causing things like polar bears and penguins to really struggle.
Now, imagine that you could recreate each of these different ecological systems inside one of these asteroids, to not just create a Noah’s ark of seeds and genetics, but a Noah’s ark where we’re actually sending the animals – not two by two, but probably genetically diverse multiples of at least eight or ten at a time – and, well, setting them loose in these different ecological niche asteroids.
Fraser Cain: And so that – this idea that you spin them – you haul them out, you spin them, you get artificial gravity on the, I guess on the edge, on the inside rim of the whole asteroid. How big of an asteroid do you need that you could actually set it spinning and use that gravity?
Pamela Gay: Well, it’s a matter of how fast do you wanna set it spinning? One of the problems with a normal donut spacecraft that we think about is you build multiple stories. And it’s a thin ring, so you want to set up those multiples stories. And if it has too small a radius, you very quickly have radical gravitational changes over very short distances. If you had something that was just 100 meters or so but single-storied on the inside, you’d be fine.
Fraser Cain: Right, 100 – it’s the single story.
Pamela Gay: It’s the single story that makes the difference. Yeah.
Fraser Cain: Right. And I’ve read some descriptions of this, right? That as you try to climb up a ladder in one of these spinning things, your gravity would change rung by rung as you went up the ladder. You’d start at, say, one Earth gravity. And as you got to the top of the ladder, you’d be at zero gravity again. It’d be pretty weird to kind of move between those situations.
Pamela Gay: And this is another one of those things that comes up over and over in fiction books because if you sit down and you do quick calculations, it very quickly becomes apparent that yeah, the rung by rung is all it takes to suddenly find yourself in zero gravity instead of full gravity.
One of the ideas that comes up in a variety of different fictions is you end up actually, unfortunately, having a caste system, where it’s the wealthy who live at 1g. It’s the wealthy who get all of the physical and psychological benefits of having sufficient gravity to make things easy to deal with. And as you become more and more impoverished, you end up getting essentially thrown away to the lower gravity areas where you physically suffer.
This is one of those problems if you think about doing a mined out, termite style, anthill style asteroid, setting that kind of asteroid instead of one that’s fully hollowed. Rotating means that you still have the center of the asteroid that has no gravity and is just spinning. And that’s not useful for anybody.
Fraser Cain: So what would you do with the material that you pull out of the asteroid?
Pamela Gay: It depends on what it is that you’re pulling out. If you’re dealing with a metallic asteroid, well, that’s clearly the type of material that you use to build additional spacecraft, additional machinery, to build your rocket engines, to build your control systems, the things that you’d mount on the outside of your asteroid that turn it into that fully steerable spacecraft.
On the other hand, if you’re dealing with more of a silica asteroid, ideas of using it for 3D printing have been put forward. Or the idea of you just basically pitch it out the side has been put forward.
Then there’s also the question of water. People worry about, do I need to harvest water from perhaps Jupiter’s moons and bring that water back to the planet Earth or to the asteroids that you’re harvesting? But what we’re learning today is some of these asteroids are actually the sources of, well, probably the water here on Earth. And so we probably need to be mining asteroids for water.
So in a perfect world, you find that thus-far not documented asteroid that is a healthy mix of silica and metals and water, where you 3D print whatever you need from the silica, you mine out the metals and use it to build your engine parts, and you have the water you need to start building that environment. That’s the one problem with the hollow asteroid idea is you still have to get the gasses to fill the asteroid from somewhere.
Fraser Cain: Right. And so you could image that maybe they might be ice mining as they try to move through the – it’s not just gonna be rock. It might be rock mixed with ice, since you can imagine these kind of tunnels of rock and ice as they move through the asteroid.
So what are the advantages of, I guess, of having this kind of a place? I mean, you talked about let’s keep it as a lifeboat to help preserve some of our genetic material so that if something ever happens to Earth, we’ve got another place where this stuff exists. But I guess, what is really the advantage of just having manufacturing facilities and stuff in orbit already? I mean, there’s tons of benefits to that, right?
Pamela Gay: One of the big benefits is you’re out of Earth’s gravity. Once you’re out of Earth’s gravity, it becomes much less energy intense to figure out, okay, how do I take off for Jupiter? How do I head into the inner solar system? And if you can build all of your high mass, difficult to move objects in space already, you don’t have to lift them out of Earth’s gravity well. There’s a huge savings in fuel.
So you start from the, hey, I’m saving energy by doing this in space. And this follows up with the, you’re not depleting the Earth of resources. And in fact, you’re revealing resources that you can potentially bring back to Earth. This is, again, something that comes up in numerous sci-fi stories, the idea that – and it’s also part of what Planetary Resources is looking to do. We have only limited resources on the planet Earth. At a certain point, we are going to run out of certain rare metals. We’re going to run out of Helium-3. As we run out of these things, outer space is pretty much the only place we have to go to, well, refuel ourselves.
Fraser Cain: Right. So it’s almost like the value of that material in space is so high that as you hollow out the asteroid, you can sell the stuff that you’re pulling out. The water/ice will be super useful for rocket fuel, for breathing, for making food. The silica, you can use that for building materials. The metals, you can use those for, as you said, rocket parts, or you can sell them to Earth. And you can send back huge chunks of palladium and platinum and have those safely come back into orbit – come back, reenter the Earth’s atmosphere, and make them available to people on Earth. And that could fund the whole process. So yeah, there’s definitely some money to be made to pay for the exploration.
One thing I’d like to talk about then is sort of the big sci-fi dream is that you could use this as a spacecraft, both to explore the solar system, but maybe even to go to other stars.
Pamela Gay: And one of my favorite books – and it is one that will utterly wreck you. Like, I was on the London Underground sniffling and blinking back tears. It will wreck – you have happy, fluffy, goodness and light, young adult fiction waiting to read afterwards.
Mary Norris Russell’s book, The Sparrow, starts from the idea that we detect signals, music, from an alien – we assume – alien civilization. And while most of the people of Earth are debating, “What do we do?” and the governments are trying to figure out if they have money to do anything, this is in a future where we are mining asteroids. And the Catholic church has enough money to – while no one else is looking – dispatch a asteroid turned into a spacecraft on a relativistic journey toward this alien civilization with 1g acceleration the entire way, where you’re accelerating up to the halfway point and decelerating down from there.
And this is kind of that core idea of in the future when we want to get from one place to another, accelerate the entire time, have the gravity that you want. And asteroids are just there waiting to be used, waiting to be mined. And we don’t have to solve the radiation protection problem with them. That’s the thing I really appreciate about them.
Fraser Cain: And the micrometeorite impact problem, which …
Pamela Gay: Yeah, they’re used to that.
Fraser Cain: Yeah, but it’s huge. I mean, you look at the solar array on the International Space Station, and there are holes from either space debris or micrometeorites that are pelting this. And so any one of those could just smash a hole right through your spacecraft in an instant moving at 27,000 kilometers per hour. I mean, you would just be destroyed. So having 100 meters of rock around you would be really helpful for those kinds of impacts.
Pamela Gay: Well, you’re probably not gonna have a thickness of 100 meters around you, but having sufficient thickness of rock around you. Think adobe walls –
Fraser Cain: Yeah, [inaudible][00:25:21].
Pamela Gay: – but reinforced. Yeah, and the book series that I was forgetting the name of is James S. A. Corey’s Leviathan Wakes series. Throughout this series, which is classic space opera with a twist of zombie for flavor, it has throughout it that humanity has expanded past its ability to remain confined to the planet Earth. There’s just too many humans.
And so we spread out across the solar system, including hollowing out Ganymede, Vesta, these other worlds throughout our solar system. And there’s the amazing notion that you’re walking along the halls on Ganymede, and you can’t touch the walls because you’ll freeze your skin. And that’s just a really neat thing to think about, that we do need to worry about those things as we start hollowing these rocks.
Fraser Cain: So I mean, this is just mad science fiction. And it makes me – and science –
Pamela Gay: And science.
Fraser Cain: – but it makes my mad speculation just look like stone cold reality. So what work is being done right now to sort of move us in this direction? You mentioned briefly, what, Planetary Resources?
Pamela Gay: Planetary Resources, I think, are really the leaders in putting their money where their mouth is. They have kick started early test technology. They have a multi-year plan. They have the company. This is something they are working to do, and they’re working to discover and map out the asteroids. They’re really the people to watch.
But they’re not the only people in the process of doing this. There’s an international organization, Project Hyperion, that is done by a group called Icarus. Different nations are looking at this. I’ve heard graduate students present the maths in hopes of someday living in reality.
Fraser Cain: Yeah, and NASA is actually right now figuring out a mission to go to an asteroid, pick up a big boulder, and bring that back and put into orbit around the moon, and start to manipulate these space rocks, which is sort of a really big first step for us to be able to go down the road of being able to reach out to them, land on them, mine them, live on them, be a true space-faring civilization.
Pamela Gay: And this is clearly one of those places where, yeah, everyone wants to go back to the moon, and I think the commercial folks are gonna be the ones to do that for us. Lots of people wanna go to Mars. I think it’s gonna be Elon Musk that does it for us.
The asteroids are these kind of not-so-photogenic potato and avocado and dog bone shaped objects that lurk out, well, just about everywhere. And they don’t get the hype they deserve as really being the place with the resources that we’re gonna need going into the future. And yeah, it’s awesome to see that as much as people try and redirect all the resources back to moon or Mars, the asteroids and their low Delta-v requirements continue to be one the places we’re looking to go.
Fraser Cain: Yeah. Great. Well, this was a nice palette cleanser from all of the science/physics experiments series that we had done. So we’ve got a few more of these as we reach our summer hiatus. So. Well, thanks, Pamela.
Pamela Gay: Thank you.
Fraser Cain: Thanks for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay.
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