Quantum Rocketry

Europa, the second Galilean moon of Jupiter, has been my favorite planetary body for a long time. The reason I like Europa so much is that it’s a world whose orbital dynamics with Jupiter, its orbital resonances with the other Galilean moons, and its own rigid-body dynamics have a strong hand in creating its surface features – and giving it the potential to harbor life. It’s one of perhaps two or three extraterrestrial places in the Solar System where we might hope to find life. Europa is also easier to get to than Enceladus or Titan. As such, I think it ought to be one of the highest-priority exploration targets for robotic space probes. (Human exploration would be nice, too, but if you think radiation exposure on the way to Mars is hard, you don’t even want to consider putting people in the Jovian system!)

Thanks to magnetometer measurements and images from the Galileo mission, it’s pretty much established at this point that Europa has an icy outer shell over a global liquid ocean, with a rocky core on the inside.^* The only question is how thick that ice shell is – I’ve read estimates ranging from 10 meters to 100 kilometers, with a pretty high confidence of ones to tens of kilometers. The ice shell gives rise to a number of interesting surface features. A particularly cool sort of feature, found with global extent across Europa, is the double ridge.

A prominent double-ridge feature on Europa, most likely a crack in the icy shell

Planetary scientists have a number of models for how these double ridges form, and they generally seem to agree that the ridges mark the locations of cracks in the ice crust. One especially well-established model suggests that these cracks occur when Jupiter raises tides in Europa’s ocean – just like how the Moon raises tides in terrestrial oceans, but much stronger, because Jupiter is frakking huge compared to Earth’s moon. Europa’s ice crust bulges out over the ocean’s tidal swell and then cracks under the incredible stress. (I like to take a moment to think about the mindbogglingness of that statement: the whole moon’s surface cracks. I’ve stood on a frozen pond when a crack pings through the foot or so of ice on top of the water – Just imagine standing on Europa when this happens!) Once a crack forms, the tides don’t go away. As Europa rotates, about once every three and a half Earth days, the tides periodically lever these cracks apart and squeeze them back together again. In this model, every time the cracks gape open the subsurface ocean gets exposed to space. The surface water boils and rapidly crusts over with ice, and when the cracks get smushed closed, all this ice gets crushed up and forced to the top and bottom of the crack, forming the ridges. The ridges appear in pairs because the crack opens up again after that. These double-ridge features are mounds of crushed ice flanking passages into Europa’s ocean!^†

Dr. Richard Greenberg is a planetary scientist who thinks that these cracks in the ice shell might be potential sites for life to take hold. Unlike the rest of the subsurface ocean, they get exposed to sunlight, which means that photosynthesis could take place. The periodic in-and-out forcing of the crack would also drive strong currents, which is another energy source Europan life could use. (Those aren’t the only energy sources: other possibilities include thermal gradients in the water, volcanic vents on the ocean floor, or even induction as Europa travels through the Jovian magnetic field.) Of course, that life would also have to adapt to the crack opening and closing once every 3 1/2 Earth days!^‡

Europa's possible ice-fissure biosphere (from New Scientist; click for full article)

We do at least know, from the Galileo mission, that these cracks often have accompanying veneers of organic (e.g. carbon-based) molecules and salts splashed onto the ice surface. This is why the cracks appear as brown stripes in large-scale context images. The crack/veneer combination suggests that there are organic molecules and salts in the Europan ocean, and that those compounds get pumped to the surface through these cracks.

So, let’s take stock: Europa is the only extraterrestrial world with a global liquid water ocean, there is a definite possibility for life in that ocean, and these double-ridged cracks are a possible gateway into the alien biosphere.

Well, then, let’s go diving! Read on for my concept system architecture for an ambitious Europan ocean-exploring mission, which I call the Ice Fracture Explorer.

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…full of unsolved yet soluble mysteries!

Mysterious craters on Mars

I’m shamelessly bouncing all you readers over to the Bad Astronomy blog for this post, which is a great outline of the detective process that is planetary geology. It’s also a great illustration of how much context matters and how leaping to conclusions is…bad. AND it’s a good demonstration that, when there are several hypotheses in consideration, elements of each could be synthesized into the proper conclusion.

All things for us to keep in mind, in science and in everyday life!

(Also, way cool pictures that are reminders of TOTALLY AWESOME events in the past!)

When I wrote my original article on the physics of space battles, and the accompanying short story, I made the creative decision to speculate on how space battle technologies and tactics would play out if we built from the present day – or, at least, the very near future. The obvious thing to look at next is what a more distant future might hold – so, I’ll embrace my status as That Space Battle Physics Guy!

A possible near-future space fighter radiating excess heat between battles

I think that extrapolating or projecting space battle technologies forward in time is a difficult thing to do, even for the cleverest science fiction geeks. I say this for two reasons: first, aside from some general trends, it’s hard to predict exactly where technology will go in the next ten or twenty or fifty years; second, nobody gets to play this game against a live opponent – and that’s really how combat tactics and technology develop. Still, given the trends, it’s fun to speculate! Physics won’t change radically for quite some time, so we have some direction in which to proceed.

I’m going to proceed from the assumption that “spacecraft” are different from launch and reentry vehicles. Let’s take some possible combat spacecraft systems, think about the related problems that spacecraft engineers try to solve, and see what might (!) happen if the aliens wait till we have some operational space colonies before they invade…

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I think that President Obama’s vision for NASA holds a great deal of promise. However, I seem to be in the minority – with people from Senators with NASA-associated districts to Stephen Colbert to Jesus Diaz on Gizmodo talking about the “end” of the human space program. I often wonder why they don’t see what I see. Obama has both increased the NASA budget and explicitly stated that he wants more astronauts flying in the coming decade than ever before, so he clearly is not trying to “cancel the human spaceflight program.” Given that, it seems straightforward to me that the NASA centers will still need to train astronauts, build vehicles, and conduct mission operations; NASA vehicles will still push the boundaries of capability, and NASA astronauts will explore the Solar System beyond Earth space. The only difference is just that astronauts won’t get to those new vehicles atop Ares launchers, but rather perched on something like the Falcon 9 – which is much, much closer to operation – and our targets are more ambitious. So why the enormous gap in opinion among space exploration proponents? And what might NASA administrator Charlie Bolden do to consolidate support?

I think the problem is that, without a NASA launch vehicle, critics have a hard time envisioning how the new generation of NASA astronauts will get around and what they will do. There won’t be any dramatic Space Shuttle or Saturn V launches – instead, the astronauts will be…”taxiing.” And they will taxi up to…what, exactly?

President Obama wants humans to leave the Earth-Moon system by 2025, get to Mars orbit by 2030, and develop the capability to live and work in space indefinitely. Here’s where Administrator Bolden could step in. NASA systems engineers and artists could crank away and produce concept studies to suggest a new fleet of NASA crewed vehicles. By starting right in on the design of new vehicle concepts, and setting explicit deadlines for their launch and operation, the new NASA vision could become more clear and exciting. The public will start to see what I see – a NASA program that develops dedicated space exploration vehicles, which carry astronauts for months at a time on journeys to deep space, asteroids, and other planets. Clearly, that is no end of the human spaceflight program. It’s the next step.

Below the break, I’ll outline such a possible concept vehicle fleet.

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Launch of STS-132

Space Shuttle Atlantis touched down at 8:48.11 Eastern time at Kennedy Space Center. This makes Atlantis our first Space Shuttle to retire. (I think that also makes it the second reusable space vehicle to retire, after SpaceShipOne decommissioned in 2004.)

This is a sad day in space exploration…but it is long overdue. In what other modern industry or field of endeavor other than space exploration do we continue to use 30-year-old vehicles and devices, and in what other field do we consider those vehicles to be “cutting-edge?” This is the beginning of a period of transition, and I can’t wait to see us get started on what’s next. That day, also, is long overdue.

Congratulations to Atlantis and its many crews on the successful completion of all its missions.

First: Go Atlantis!!!

Now, on to the purported topic of this post: The SpaceX Falcon 9 is slated to launch in less than a week!

Beautiful photo of Falcon 9 on the pad (SpaceX)

Ever since the FY11 NASA budget came out, I’ve been anxious to see the success of the Falcon 9, SpaceX’s heavy-lift vehicle, and the Dragon capsule. A good Falcon launch and successful Dragon flight demo would be like jumping NASA’s Constellation program straight to an Ares I/Orion system prototype. This is the rocket and capsule that the new budget banks on for ISS resupply and astronaut transport. Of course, SpaceX had already won the ISS resupply contract before the new NASA budget came out, so this really isn’t that big a change from the status-quo solution to the space access gap – except that a successful man-rated Dragon would close that gap entirely!

For the bajillionth time, Mike Griffin’s Constellation Program was on track to do what we did 40 years ago, with what we used 30 years ago, 20 years from now. I know the program says “by 2020,” but it ain’t gonna happen, even with billions of extra dollars.

The new budget focuses NASA on in-space vehicles. Vehicles for carrying people throughout the Solar System. Vehicles for building colonies in space. Vehicles for taking people to planets. Vehicles for exploring planets. The kinds of vehicles that cannot be built on Earth and launched, whole, on a Saturn or Ares rocket. The kinds of vehicles that nobody but NASA would try to build. The kinds of vehicles that would move the human spaceflight program forward!

But, in exchange, NASA is not going to develop boosters. The space agency is going to send its astronauts – still NASA astronauts, dammit! – up to LEO on board  vehicles bought from commercial providers. The outcry against this concept is based primarily on the objection that the commercial space access providers are “unproven.”

Well, phenomenal success of the Delta and Atlas lines aside, this is the proving ground. There’s a lot riding on the Falcon 9 flight test; the space community consensus could go dramatically one way or the other depending on the outcome. If SpaceX makes it, we can almost consider NASA fast-forwarded to what Constellation would have done in 2015, or later. (And we’ll be much closer to buying tickets to space!) They just have to buy their launchers from SpaceX, instead of….contracting to ATK to build them.

Good luck to the SpaceX launch crews! Hope the launch is spectacular!

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

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.

STS-131 / Exp 23 group photo

The Space Shuttle mission which just undocked from the International Space Station, STS-131, has beamed down from orbit some great photos of astronauts in space. This is a wonderful chance for us stuck planetside to remind ourselves that we have people living and working in spaceships!

The Discovery crew in the Cupola

And, of course, this mission is historic for having the largest number of women simultaneously in space – four out of the thirteen total crew. Considering small-number statistics, that is pretty close to a fifty-fifty split! Here is the orbiting Bay Stater, Stephanie Wilson:

MS Wilson in the Kibo laboratory

And here’s JAXA’s Naoko Yamazaki in the Destiny laboratory at a robotics console made of lots of ThinkPads taped to the ISS wall,

MS Yamazaki in Destiny

although I think this is my favorite picture of Yamazaki!

In the Cupola!

That’s where JAXA astronaut Soich Noguchi has been taking and Twittering down amazing Earth-observation and Space Station photos. (That is the single best application of Twitter I have ever seen, and is not likely to be surpassed, ever.)

Finally, I will leave you with astronaut family dinner!

I love astronauts (PS - obey the speed limit: 28,000 kph!)

While President Obama’s speech this afternoon wasn’t a slam-bang Kennedyesque dream vision, I thought he expressed some good ideas. Of course, there aren’t too many substantial differences between the plan we heard and the plan Charlie Bolden presented in February; the President’s remarks today sounded much more defensive than visionary. Given the amount of criticism his NASA ideas have received, I don’t really blame him…but still.

The most frustrating thing to me about the new NASA plan is how distorted it has become in the media. The first thing Obama said this afternoon was that he is increasing NASA’s budget by $6,000,000,000 – at a time when he has frozen discretionary spending and we are looking for ways to deal with crisis after crisis. There were even headlines two days ago to that effect. Ohmigosh, the budget is going up! Well, yeah. It went up in February. It’s a wonder that the story in the media since then has been uniformly about NASA budget cuts; that attitude has permeated commentary even from sources inside NASA. It’s amazing how an idea like that can spread, even in the face of direct evidence of exactly the opposite.

Most of President Obama’s remarks today were familiar to me. Billions of dollars for robotic precursor missions, game-changing technology research, technology demonstration missions, and new human spaceflight capabilities. Buying launches from American companies rather than having NASA contract out for launchers to call its own, to close the LEO access gap. Extending the Space Station. All this we’ve seen before, and I still think all this sounds good.

We heard about two new development programs this afternoon: an ISS crew-escape vehicle based on the Orion capsule, which will evolve into our deep-space crew vehicle designs, and an accelerated heavy-lift program with the goal of having ready-to-build designs by 2015.

The Orion-derived crew lifeboat I think is stupid. To me, this looks like either pandering to the people at Marshall Space Flight Center who were annoyed that they didn’t have a capsule to build, pandering to the people who think tat a Dragon capsule wouldn’t meet NASA safety requirements, or pandering to the pining-for-the-Cold-War neocons who have been crying about how our ISS astronauts will be “held hostage” without US access to space. Having an ISS lifeboat may sound like a great idea, but the station already has a few reliable Soyuz vehicles for exactly that purpose. An Orion lifeboat is a waste of money and effort. The one good thing about this program is that it is supposed to feed into our designs for true space vehicles – but I would have preferred it if the President had just told the Orion teams to concentrate on that purpose.

The accelerated heavy-lift program is more exciting. I’d love to see NASA developing the capacity to fling wonderful new hardware to high Earth orbit and beyond, and I understand that it is valuable to keep the engineering expertise to develop such a vehicle within the NASA organization.  I’m very happy to see a date of 2015 attached to the designs for that system – and remember that Ares I was projected to be ready no earlier than 2018, and Ares V around 2030 – so the new heavy lift program is a much more ambitious one than either of these!

In addition to these new programs, President Obama finally announced a series of targets and dates. Criticisms of the new NASA vision have come from all across the board and contained all sorts of specific elements – but the one shared element, heard from ’round the space community, were: where is NASA going? and when is it supposed to get there?

Well, today we heard the following:

• Ready-to-build heavy lift designs complete by 2015.
• Human crews fly beyond the Earth-Moon system before 2025.
• Human crews land on an asteroid sometime between 2025 and the mid-2030′s.
• Human crews orbit Mars by the mid-2030′s.

Human landings on Mars are supposed to follow “shortly thereafter.” I’m thrilled to see these dates; they are nicely within my lifetime and identify specific targets. Perhaps they could have been presented with a bit more polish and panache, but I’m happy to have them!

(Side note: The Augustine Commission found that, with $3 billion/year extra funding, the Constellation Program would miss its 2020 deadline and get us to the Moon around 2030. So….eat it, Mike Griffin.)

Finally, I want to comment that it occurs to me that a lot of people in the space community have been contrasting Obama’s new plan to Kennedy’s speeches in the early ’60s. Obama’s speech today couldn’t have illustrated the differences between the two Presidents’ characters better – Kennedy seemed to run on pure emotional vigor in his space speeches, while Obama was his usual cool, collected, rational self. I like what he’s planning, but it wasn’t exactly couched in stirring rhetoric. However, I don’t think that speaks poorly of Obama’s commitment to space exploration. I think the difference between Obama and Kennedy is simply one of pragmatism. When I look at the goals he laid out, and compare them to Norm Augustine’s comments at the opening of the space summit (made as I began this post!), they make a lot of sense in that light. What Augustine said is that NASA’s goal, in the eyes of his commission, the NASA administrator, and the President, is to land people on Mars – but the trouble is that we just don’t have the technological capability yet to do that. Obama’s vision for NASA starts with developing that capability.

Put another way, imagine Kennedy had Obama’s character. His stated goal, expressed in that famous speech to a joint session of Congress shortly after Alan Shepard’s first flight, would not have been to land a man on the Moon and return him safely to the Earth. It would have been to develop and demonstrate technologies like orbital rendezvous, multi-person spacecraft, computer control of spacecraft, heavy lift, and planetary landing stages. Essentially, it’s as if Kennedy’s goal had been to complete the Gemini program. But the deadline for completing that goal would have been shorter than a decade, and the story wouldn’t end there. The groundwork would be in place for whoever was President at the time of Gemini’s completion to say, “okay, we’ve got that under our belt…now let’s get to the Moon!”

In short, Obama could have said something like, “Let’s land on Mars by 2040!” But instead, he gave us more incremental, shorter-term goals with a much higher chance of success. And he laid the groundwork for a future President to say, “okay, we can keep people alive in space for years and get to Mars orbit…let’s put boots on the ground!”

I recently spent over a week in full research-promotion mode, and I’m finding it tough to switch back into research-doing mode. Coincidentally, I don’t think I’ve actually written a blog about my graduate research yet, though I’ve put descriptions of it on both my personal web site and Cornell group web site. So, I’m going to try and get it all out of my system…

Suppose you ask: Hey, Joe! What’s your research about?

Well, it’s about building Transformers in space out of Legos connected by tractor beams. Seriously. Okay, fine, they’re not “tractor beams,” more like…”tractor fields.” But other than that, not a bad description. Here’s an old-ish video version:

First: Why?!

There are a lot of possible reasons why we ought to be thinking about building large-scale structures in space. Imagine assembling a huge space telescope out of hundreds of mirror segments, giving the telescope an effective light-gathering area of hundreds of meters and letting us peer into the dimmest corners of the Universe – from the most distant objects to extrasolar planets. Or, if we’re interested in space-based solar power (putting solar power collectors in space, where they could gather sunlight 24 hours a day without atmospheric filtering, and then beaming that power down to Earth) we would want to make the biggest collector area we can. Proponents of geoengineering approaches to climate change mitigation have been seriously considering constructing a giant sunshade to reduce solar incidence on the Earth, a short-term solution that could stave off environmental impacts while we work up longer-term fixes. And finally, if we want to maintain a long-term human presence in space – from Mars explorers to microgravity research and manufacturing technicians to paying space tourists – we will need vehicles and stations with enough room to accommodate many people, hold life support and other supplies, and provide equipment to stave off the detrimental effects of microgravity on human physiology.

All of these possible applications – any one of which would have tremendous implications for our lives on Earth – demand that we build a large structure in orbit out of smaller components. The reason for this is simple: launch vehicles can only carry so much mass and volume into orbit. Those limits are on the “stowed” size of spacecraft, so we do have the option to build craft that deploy, or unfold, out of their tightly-packed, mostly cylindrical launch configuration and into some more spindly and useful shape. For example, most Earth-orbiting satellites get their power from large solar panel “wings” that would not fit into a launch vehicle fairing unless rolled up in some clever way. There’s a lot of research these days on inflatable spacecraft, that could expand to many times their stowed size and get structural support from their internal pressure, but even those balloon-like craft cannot get indefinitely bigger than their launch envelope. Deployments and inflatables only make the volume or length of the spacecraft larger – so, for the same mass, you end up with spindlier structures, which might be fine for some applications but not others. So, in order to get the really big spacecraft, we must assemble smaller pieces to make the final system. Think of the International Space Station assembly process.  Read the rest of this entry »