A Case for Asteroid Missions

Asteroid bases in our future?
Asteroid bases in our future?

We’ve discussed President Obama’s plans for NASA in my research group. Things look good for us: as a team working on spacecraft technology research, looking for things that will make construction, maneuvering, and other activities in space easier, cheaper, and better, we are very happy to see the technology research arm of NASA finally getting the funding it deserves. (It’s amazingly ironic that “space age” technology means thirty-year-old tech.) However, one grad student in my group questioned the value of targeting asteroids, specifically, for exploration. Is it worth it to send people to asteroids? Do we gain anything by doing so?

I think we do, and I’m going to explain why here. But first, I want to make clear two things I am not going to do. I am not going to make a scientific case for going to asteroids. The reason why I’m not going to use science to justify asteroid missions is that we can gain scientific knowledge wherever we go. We can learn new things anywhere. I’m not going to try to prioritize that knowledge, because in the end, it’s all valuable and it’s likely that there will be breakthrough theories germinated from any field of endeavor. In addition, I am not going to make a case against returning to the Moon or going directly to the Martian surface. I am not going to list reasons opposing either of those destinations simply because I don’t think there are any. Rather, I am going to focus on the reasons why I think asteroids are exciting destinations.

Reason one: Operations on and around asteroids are extremely challenging.

On the one hand, anything in space is challenging. But asteroids may be especially tricky, mostly because we don’t yet understand what being around an asteroid would be like. We have only a few close-up pictures of asteroid surfaces, and have only touched the surface of asteroids with two robot spacecraft that I can think of. As far as we can tell, their surfaces are covered with fine regolith, perhaps like the Moon, but their odd shapes give them very strange (micro)gravity fields. Imagine you’re standing on the “side” of a tiny, potato-shaped world like Ida. Which way is down? Harder question than you might think!

243 Ida and Dactyl
243 Ida and Dactyl

NASA can simulate operations on planets and moons by visiting “analog” sites on Earth, trying out procedures in mock space suits and pretend capsules. NASA also has a wealth of free-fall experience from its operations in low Earth orbit with the Space Shuttle and Space Station. But no space agency has any experience with or ways to simulate environments like asteroids. So, not only are asteroids tricky places to be, but the only way to learn about being around asteroids is to go to an asteroid. We’ve never done or thought about this stuff before, at least not in detail. I think that’s exciting!

In particular, I think the challenge of operations around asteroids demands that we send people there. There has been a lot of talk about how the new NASA plans will leave our astronauts without jobs and focus entirely on robotic missions. Whether you think that is a good thing or not, I think it is untrue. While robotic precursor explorers will give us some inkling about what to expect, figuring out how to actually do things on asteroids (science, construction, etc) may be better achieved through an in-situ human learning process. The closest analog we have to asteroid operations is work around the outside of ISS, which we do not yet trust to robots and have tremendous experience with. Astronauts around asteroids could rapidly tell NASA Mission Operations analysts what the major differences are between an ISS spacewalk and asteroid spacewalk. At the same time, a human’s ability to learn on-site, manipulate four limbs in a coordinated manner, and perceive situations clearly and directly would be desirable qualities.

Why do we care about learning how to operate crewed missions around asteroids? Well, Reason Two is that these asteroid operations skills are transferable.

Buzz Aldrin likes to talk about Phobos. Well, if we want to go to Mars, then the first question we must answer is exactly what sort of mission profile we want to use. Options include a Moon-landing-like sortie mission, in which we put boots on the planet, bounce around picking up rocks for a couple weeks, plant a flag, and then take off for home. We could also send a mission that lasts a year or two and involves building a temporary (or permanent) base, establishing laboratories, and zipping around in rovers; this probably involves multiple launches to and from the Red Planet. Or we could go for the interesting option of picking 50 or so people and sending them to Mars, in one launch, with everything they need to be self-sufficient. The point of all this is that, depending on the mission, it might be valuable to use Phobos as a way station. And if we want to be around Phobos, we have to learn how to be around Phobos. More than that, we have to learn how to be around Phobos and be very, very far from and out of reach from Earth.

Moreover, microgravity operations around small bodies are exactly the kinds of operations that would be relevant in the asteroid belt. Or around the Jupiter Trojans. Or in Jupiter’s moon system. Or Saturn’s moon system. Or near comets. Or by near-Earth asteroids. You get the picture: small-body operations will be important for the manned exploration of the Solar System beyond the Moon and Mars, and the more capabilities we develop, the easier it will be to get to and function in exotic places.

Next, reason three: not only is there science to be done, but around asteroids, we could learn techniques that may be necessary for Earth defense.

Yeah, I’m talking about defending the planet from rogue asteroids. We certainly won’t be doing this by launching a team of misfit miners and Bruce Willis. Now, the asteroid deflection techniques we develop may or may not involve manned missions, but when we’re talking about the survival of a city – or the entire human race as we know it – why remove any tool from our kit?

The fourth reason is one that ought to appeal to space technologists out there: asteroids could provide resources for construction which are much easier to get into orbit than the resources on Earth.

Asteroids are made of useful things. Nickel-iron asteroids are composed of metals, both common and rare. Carbonaceous asteroids contain other materials. Some even have organic compounds. There is even recent evidence that many asteroids have water! These potential resources may be easy to get to, if the asteroids are rubble-piles, or the useful materials are in the asteroid regolith, or if the asteroid is entirely made of metals that can be melted or dissolved for processing.

Budding space industrialists may be disappointed, but mining asteroids for rare metals to sell on Earth isn’t likely to be economically viable. (It’s too hard to safely get those metals from the asteroids down to Earth’s surface – for instance, we would have to spend more money to launch a Space Shuttle than we would get for the mass of materials that Shuttle could bring down from orbit – a launch costs roughly $450 million, and at current prices, the Shuttle could bring down $15 million in pure silver if filled to the brim. We’d have to find asteroids made of pure gold and platinum and cram the Shuttle to make that come out positive.) However, what could be viable is mining and processing the resources on asteroids into spacecraft bodies, components, consumables, and fuels, which could be jettisoned from their parent asteroids with very little effort. This is simply because asteroids have very small escape velocities compared to planets and moons. If we could get ISRU going, it could be the great moneysaver of the space industry!

ISRU, or in-situ resource utilization, is already a hot topic of research; applications include processing lunar regolith into bricks or reacting chemicals with Martian soil to produce rocket fuels. This would be the next level of complexity: imagine landing a facility on an asteroid that grapples to the rock, bores its way down, processes the metals in the asteroid, and extrudes spacecraft pieces that are ready to assemble. Or perhaps a spacecraft that can land on an asteroid and scoop up material to refill its fuel and consumables. These abilities would let humans build whole new classes of spacecraft, capable of going further than any before. And, given the complexity of building the International Space Station, many of these activities will probably require the involvement of astronauts.

The last reason I can think of – at least, right now – why asteroids make very cool targets is that the asteroids themselves could be used as spacecraft.

The science-fiction way to do this is to find an asteroid and hollow it out with tunnels, crew compartments, fuel tanks, or big, cylindrical chambers. The excess rock and metal from the digging can be fed to mass drivers (or combined with antimatter) to propel the asteroid.

As big a fan as I would be of asteroid colonies or arkships to the outer Solar System and beyond, that’s a pretty farfetched idea at this point. However, an interesting possibility if we want to get to far-flung destinations is to locate an asteroid in an orbit that starts somewhere easy to get to and goes somewhere we want to go, and then hitch a ride. There’s an interesting class of resonant orbits called “cyclers,” which have the property that they rendezvous with two bodies of interest at least once per synodic period. For example, the so-called Aldrin cycler is an orbit trajectory that matches up with the Earth and Mars, with a travel time of 146 days between planets. All we’d have to do is get there and grab on!

We’re not likely to find an asteroid that is naturally on such an orbit, but we may locate asteroids that are on other potentially useful orbits. If we learn enough about asteroid deflection from our planetary defense studies, we might even be able to nudge asteroids onto such orbits, on purpose!

The Moon is a cool place to go. Mars is a cool place to go. Jupiter is a cool place to go. But, you know what? Asteroids are cool places to go, too. We will learn and benefit from any exploration destination. Small bodies, which come in all sorts of shapes, sizes, and compositions, may be very, very different from planets and moons. If we can learn how to use them as platforms for exploration, then perhaps we can jump off them to explore all the far reaches of the Solar System.

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