Quantum Rocketry

A number of well-funded and well-connected entrepreneurs are kicking off Planetary Resources, a company devoted to harvesting materials from near-Earth asteroids.

Now before you go scoffing (or wondering how to “greatly enable” things) – this is by no means a crazy idea. Many of the technologies one might want to prospect asteroids are not difficult to conceive of today. Commercial launch services seem to be on the brink of an explosion. And, yes, there certainly are resources on asteroids! I’m eager to welcome to the space community a group that is willing to embrace greater risk in order to reap greater rewards.

I’d like to point out just a few of the challenges Planetary Resources will face, and why asteroids might be an interesting target for resource exploitation.

First of all, asteroids boast uniquely available resources, if only we can get to them. Some classes of asteroids are wholly or partially composed of metals – or even other useful substances, such as water or carbon compounds. It might be easier to access those resources on an asteroid, if it has a “rubble pile” structure, than it would be if we have to drill down into the surface of a planet or moon. We are also not likely to have to drill or dig as far. Once we get our precious asteroid resources in hand, it’s also much easier to move them to another space destination than it would be from the surface of a moon or planet: we just have to give the blocks of metal a shove to push them out of the asteroid’s wimpy gravity well!

Second, having resources available to us in space would be a tremendous boon. The biggest obstacle to the commercial, industrial, scientific, academic, Starfleet, or any other kind of development in space is straightforward to identify: launch costs. What if we could take that all or part of the way out of the equation? What if, instead of building spacecraft on Earth and launching them into space, we instead build them right where we need them, and shuttle asteroids or special components up as necessary?

The challenge preventing us from jumping right on a von Neumann-style space exploration architecture is that we will have to develop this remote-controlled manufacturing base. Figuring out how to steer robots in space is not an unsolved problem, but figuring out how to control a robotic mining and fabrication facility is something else. I don’t think it’s intractable – but there are going to be a lot of difficulties with reliability and robustness. I don’t think Planetary Resources has self-replicating machines on its immediate business plan, but it is going to face some similar obstacles: how does the robot (or human miner, even) dig into the asteroid in microgravity? How does the miner get ore to the surface? What other processing has to happen?

Then, once the resources are in hand, what will Planetary Resources do with them? It is very tempting to make statements about the value of those materials to the global market…but, remember, it’s always harder to send a spacecraft to a destination and back than it is to send it one-way. If we want to return asteroid mine products to Earth, we will have to boost them with delta-vee of the same order as that we used to send the miners on their way – which means we need to send return vehicles with the miners. Perhaps the mining can solve its own problem by providing fuel for its return rocket, but still, the cost and complexity of the mission will mount up. On top of that, once the resources get to Earth, we will have to decelerate, capture, and eventually do-orbit them. All that takes energy: de-orbiting, in particular, is tricky because we often rely on ablation to carry away the energy from an object moving at 7 km/s…and we don’t want to burn up the resources we just spent all that time and effort extracting. For that reason, I think it may make more sense to keep those resources in space and find ways to use them there.

From Planetary Resources’ descriptions of fuel depots and expanding the exploration of space, that may be what they intend.

If you follow space news, you’ve likely seen one of the articles on this event. Woah!

I’ve like to contribute just a couple things to the wild speculation at this point. The MIT Technology Review article concludes that asteroid mining is the only possible thing of interest in space – but really, that is just one writer’s blog. I want to point outthat there are other possibilities:

• Space-based solar power systems: either a constellation of satellites or a system of stations on the lunar surface that collect solar energy and beam it back to Earth, with the potential to provide inexpensive (after the initial investment!), reliable electricity to anywhere on the globe. Phil Plait at Bad Astronomy correctly identified this as a possibility. Tom Jones’ involvement makes me think this possibility less likely, though.
  
  
  
  
  

• Lunar mining: not only are there potential resources on asteroids,  but there are some on our nearest planetary neighbor! While the Moon had higher gravity than an asteroid – requiring a little more than a token kick to lift return vehicles – its proximity makes it a more reachable target.
  
  
  
  
  

• Water mining: outer solar system moons are often covered with water ice laced with minerals or organic compounds. A robot could land on the surface, cut out blocks of ice, and thenshove them Earthward.  I’m not sure there is an economic case for this activity, but I wouldn’t rule it out as a bad idea for all time.
  
  
  
  
  

My bet is that they are going for asteroids or the Moon, but I think space power systems are a potential line of business for Planetary Resources. Maybe they plan on becoming a general space-based utility company! 

Wired’s “Danger Room” has an article which presents a good overview of the military’s (and NASA’s) move from expensive mega-scale spacecraft to smaller missions. It presents some interesting perspectives on the forces driving these trends in the space industry, and explores a few of the reasons why things are the way they are – and way they might be evolving in the future.

I’m a big fan of the idea that our space programs should embrace smaller missions: spacecraft that are less expensive and have a faster development cycle can explore higher-risk, higher-reward technologies and mission architectures than can monolithic “heritage” programs. I want to see technology demonstrators in space, and I want to see the fruits of those programs feeding into a robust research and development effort that pushes our space program where it has truly never gone before: robots to sail Titanian seas or burrow into Europan ice, observatories to unveil Earthlike planets in other star systems, and ships carrying humans to our neighbor worlds.

This coming week is National Engineers’ Week, a combined celebration of engineers’ technical accomplishments and outreach event designed to promote STEM field awareness. A couple of my co-workers and I visited a local high school to talk to some of the students about what we do as aerospace engineers. (I used my favorite, and not entirely inaccurate, job description phrase: I steer spaceships.)

As a guidance and control engineer, a lot of what I do requires a solid grasp of the motion of a spacecraft; the orientation of various sensors, thrusters, solar arrays, and transmitters; and the geometry of the spacecraft, the Earth, the Sun, and other things in the space environment. Some of the control algorithms I work with, for example, might be designed to point the solar panels at the Sun while a camera or transmitter stares at a spot on the Earth – all while the satellite zips along its orbit at several tens of thousands of miles an hour. Visualizing all this stuff going on can be tricky. We have some 3D graphical tools (a few written by me, as I was trying to puzzle all this stuff out). We do a lot of vector math and look at plots of vector components in various reference frames. But, often enough, we just can’t beat a good, solid, hand-held model of the spacecraft to swoosh around and help us try to picture what’s happening on the real thing.

As a result, just about everybody in my group has a little cube made out of paper, or cardboard, or foam board, that is labelled with relevant features of the satellite. I have this:

I used the free Design by Me software from Lego to design myself a model of our spacecraft, and then order all the parts I would need. (I was sure to get myself lots of extra doodads to be antennae, reflectors, sensors, thrusters, and other such stuff!) What you see in the picture above is a generic configuration of the spacecraft, representative of the class of satellites that I work on, rather than a specific spacecraft. Of course, at work I have lots of extra flat plates which I have labelled with various details!

While it’s certainly not to scale or completely accurate, it’s about the right shape and size and – important for visualization – I can move the solar panels around. It’s pretty easy to think to myself, “okay, the Earth is down there and the Sun is over there, so my satellite is doing this…” Legos give the model just the right amount of heft. And they are just plain fun!

This model is not just helpful at work, but it’s also a tremendous attention-getter. I find it valuable to make my work more concrete. So I certainly made sure to bring it with me on that school visit.

Well, since I just had some discussion about orbits and other fundamental physical concepts in science fiction, here’s a short scene I’ve been sitting on. It’s set in the Cathedral Galaxy, and I’m not quite sure what I want to do with it yet.

~

The Kite stretches his solar wings wide, spanning over five hundred meters. He fans out his array of electromagnetic membranes, thermal structures, transceiver antennae, and weapon emitters, flourishing. The Kite’s voice booms out over the electromagnetic spectrum, mingling with the others in the Coliseum, as they announce themselves to the assembled spectators:

“In salute, we die and live by the will of the Imperium!”

The Kite pulls one solar wing out from the light flux to tack. He wheels around, scanning and assessing his competitors. He catalogues their capabilities but pays special attention to their faces – distended from all the grafts and alterations, stone-gray and glassy-eyed from the environmental treatments, yet still faces. The younger competitors growl and sneer at him, while the more experienced repay his cool appraisal in kind. Today, The Tiger and The Worm worry him.

Silence falls across the EM bands, leaving The Kite with only the intermittent discharges from the Coliseum walls. His stomach (though no longer really a stomach) lurches in anticipation. A moment drags on in the flickering silvery shell of the Coliseum, buried in the sparse mist of an orange nebula. This could be the day, thinks The Kite, when I die. Again.

The call:“Begin!”

The Kite pulses an electromagnetic field, launching himself away from the spherical inner surface of the Coliseum. The others do the same. Read the rest of this entry »

Yesterday I was invited to give a presentation to the Global Physics Department, and online group of college and high school physics educators moderated by Prof. Andy Rundquist from Hamline University. The group gathers to hear virtual speakers on math, physics, science, and education on a weekly basis. Andy found my blog (hi!) and asked me to work up a presentation on science and its presence (or absence) in science fiction. You can see the recording here. (There are lots of other interesting presentations on the site, too.)

I spent a while thinking about the approach I wanted to take with this presentation. Of course, the easiest thing to do would have been to pick some choice examples from science fiction and pick them apart, criticizing the presence of sound in space or starships that move like boats and airplanes. I did a little of that, but I also wanted to bring up some other approaches that might encourage students to explore the intersections of science and science fiction, including looking at some of the things that science fiction gets mostly “right,” examining what it would take to give us science-fiction gadgetry using current knowledge, and trying to extrapolate realistic scenarios using scratch paper and our imaginations.

All in all, I think it was a fun evening – but I barely scratched the surface! My only “disappointment” was that it would have been fantastic to really open things up for discussion at the end. But with a topic so rich, it’s hard not to run into the time limit!

NASAspaceflight posted an article about the human spaceflight “exploration roadmap” using the Senate Space Launch System rocket. It makes me feel a bit better about the SLS situation.

I’m glad to see that the roadmap revolves around interplanetary vehicles assembled in space, and I’m glad to see that there’s some careful thought here about how to move the human presence throughout the Solar System in a more sustainable way than flags-and-footprints missions. Still, I’m not convinced that the SLS is an efficient or effective way to do that compared with, say, a cluster of Falcon launches. Remember: the SLS is not going to be up to its peak design payload capacity until 2020 2030, and it will likely fly once a year, which doesn’t bode well for the parts of this roadmap that call for a “fleet of SLS” launches.

The best apart about this article is that it demonstrates that NASA is still thinking about how it can achieve human spaceflight capabilities – regardless of what a petulant Congress insists on.

NASA just closed their latest application drive for astronaut candidates. A staggering 6372 people applied - the second-largest candidate group in NASA’s entire history! (Personally, I’m rooting for this one.) What gives? Do people love science and technology a lot more all of a sudden? Is it American pride? Is it Newt’s promise to build a Moon base for less than $2 billion?^*

It is clear to anyone who follows space activities that the end of the Space Shuttle program was not anything close to the end of NASA itself. The astronaut program is no exception: every few months, a Russian Soyuz blasts off carrying three human beings up to the Space Station or back down to Earth. The completion of the Shuttle program also meant the completion of Space Station construction, allowing the ISS to become an orbital scientific workstation in earnest.

Perhaps it’s the profusion of photoblogging, twittering, and facebooking astronauts driving the upsurge. When we have astronauts writing stuff like this, while in orbit, allowing people to get their own glimpse of life in space, it’s a small wonder that people still want to be astronauts!

^* In case you’re curious, $1.9 billion would be 10% of NASA’s budget (devoted to prizes, of course). For comparison, the entire Apollo program cost approximately $25 billion. In 1973 dollars.

This week has been great for exoplanet news!

Artist's concept of exoplanet systems. Credit: ESO/M. Kornmesser

Ever since the launch of the Kepler space telescope, it seems like extrasolar planet discoveries have been rolling in constantly. But this week at the American Astronomical Society meeting, there were several big announcements.

The first was the discovery of the smallest exoplanetary system yet, containing the smallest planets known. The star in question is a red dwarf, and none of its three (known) planets is larger than the Earth. One of them is about half Earth’s radius – approximately the same size as Mars.

The second announcement was of the discovery of an object orbiting another star that seems to have a vast ring system – larger even than Saturn’s majestic companion rings! Astronomers found the rings when they passed in front of their planet’s star, dimming its light. I think the truly amazing thing about this discovery is not just that our telescopes can detect transits of rings, but that the scientists analyzing this event tracked the variation of sunlight shining through the rings and discovered that these rings, like Saturn’s, have gaps. Gaps in ring systems form when the ring particles get into an orbital resonance with another orbiting body: the second body’s gravitational tugs push the ring particle at just the right frequency to knock it away from that orbital radius, clearing out a gap. Furthermore, computer models indicate that rings around planets are generally unstable – they spread out and disperse. Saturn’s rings, for instance, would not have lasted to be the age that they are – if not for the presence of shepherd moons. My point is this: in order for this extrasolar planet to have rings, especially rings with gaps, it must have moons.

Third, and most exciting in my opinion, there has been a survey of star systems imaged with a gravitational lensing technique, and it concluded that there are more planets in our galaxy than stars. Put another way: on average, every star has at least one planet! Astronomers used to wonder: is the Solar System exceptional in the universe? And, if so, what made it so special? Now, there are more and more indications that planetary systems like ours are not just out there – they’re downright common!

The thing that makes exoplanet research so fascinating to me is the sheer variety of worlds discovered. There are so many stars out there, and so many planets, that it seems almost harder to imagine a world that can’t happen than a world that might. And some of the newly discovered worlds might give George Lucas or Gene Roddenberry a run for their money! Nothing drove this point home to me more than an astronomy lecture I attended a few years ago, in grad school: the speaker talked about M dwarf stars, and how the “habitable zone”^* of some of those stars would be at such small orbital radius that a planet in that zone would be tidally locked – orbiting once per day, always pointing one hemisphere towards the star. But, continued the speaker, we have discovered exoplanet orbits with rather high eccentricity – and those worlds would “rock” back and forth around their tidal equilibrium. On those worlds, you could stand on a beach and watch the sun rise over the ocean…then, a few hours later, the sun would reach its zenith, turn around, and sink right back down to set at the same point on the horizon!

Then, a few weeks later, I heard another speaker talking about Gliese 581g – alias “Zarmina” – shortly after its (potential) discovery. This planet, if it truly exists, lies smack-dam in that habitable zone^* but would be locked to its star, so one hemisphere is always day and one is always dark. Naturally, many sci-fi fans attached themselves to the idea that only the strip of land near the terminator would be habitable. (io9 even posted a bunch of whimsical concept art from the hypothetical Zarmina Minitry of Tourism.) But in this lecture, I learned that the climate on such a world would likely make it even stranger – rather than being habitable in a twilight band circling the globe, the world would be encased in ice with a liquid sea directly beneath its sun: the astronomer called this “eyeball” Earth. What strange and intriguing cultures might arise on such a world?

And that’s not all. There are more known exoplanets orbiting binary stars, for instance. And some more space missions designed to hunt for – or investigate existing – exoplanets are advancing through the design process. Who knows what we will find in the future?

Chances are, if you can imagine it arising from the physics we know, it does exist out there. Now the questions become: how can we explore these places? And how many other explorers are out there, looking back at us?

* I find the term “habitable zone” bothersome, because we have coined the term based on a single data point. However, the alternative “liquid-water zone” is misleading, because we know that there is liquid water in our outer Solar System. (Heck, Europa may even be habitable, we don’t know!) But “liquid-surface-water zone,” which is what astronomers really mean by this term, is just awkward.

In grad school, I became a big fan of NIAC (the NASA Institute for Advanced Concepts) and the Office of the Chief Technologist. These wings of the NASA organization support research into far-flung, visionary technological concepts. They are the parts of NASA pushing for the kinds of research that will usher in the next generation of space exploration.

The new NIAC call for proposals is out. Interestingly, this time it includes a specific call for “citizen science.” So, if you’ve got some crazy ideas for spacecraft technology…why not try for it?