Category Archives: Research

My Presentation Philosophy

Hello again, Blogosphere!

I spent last week in Toronto at the annual AIAA Guidance, Navigation, and Control Conference. This is a huuuuuuuuuuge conference of engineers from academia, military, and industry all presenting papers about their research. So, I got to see a lot of Powerpoint presentations. (Okay, okay, supernerds, there were some PDFs and Keynotes. But “Powerpoint” is pretty much like “Kleenex” these days.) And an awful lot of the presentation slides I saw looked something like this:

Fine, right? I mean, this is a technical venue, full of super-brainy engineers. We want the facts, ma’am, just the facts, in all their glorious mathematical detail, and style means nothing. Right?


The first rule anyone will ever tell you about giving any kind of presentation is to know your audience. And if I’m in the audience at a conference like this, then I’m spending a full day listening to technical talks and you have only twenty minutes to make me think that your research is as cool, interesting, or relevant as the title made it sound when I picked it out of the lineup that morning. Because I’m still holding the conference program in my hand, and I have a notepad and pen ready to jot down research ideas the last cool presentation made me think of, and I might have my laptop in my bag, so I’m not at a loss for things to do if you’re not very exciting. In other words, not only do you need to convey your technical material, but you also need to keep me interested and/or entertained, at least enough to keep me listening to your technical stuff.

It’s a tall order.

I’ve been told that I do a good presentation, though, so I’m going to share a bit of my philosophy for what a technical presentation should be like. Here are the points that I start from:

  1. Nobody wants to see lots of equations. Some are necessary, sure, and they can be a great way to add technical gravitas, but a 20-minute presentation is a much better time to show off results, pictures, movies, hypotheses, conclusions, possibilities, tricks, and excitement. And if the conference is like GNC, requiring a paper with each presentation, then all the equations go in there, anyways. The oral presentation is for highlights, not derivations.
  2. These presentations come in the middle of a solid block of otherwise identical presentations that are going to blur together in the audience’s minds. So, they need to be distinctive. In other words, a bit of flash and polish goes a long way. Also, attention-grabby things like pictures and movies are good, but not if they’re just thrown together in a clip-art sort of way. (There’s good attention to grab, and bad attention to grab!)
  3. Slides are visual aids. I mean both “visual” and “aids.” Think about both of those terms: slides are supposed to be for showing the audience things. And the slides in a live presentation are not supposed to be completely independent of the presenter: you should refer to them, but you are the one giving the presentation.

As an example of my own style, allow me to go through my recent GNC presentation slides and point out my thoughts on their layout, style, and content. If you want to follow along, most of the presentation itself is here on YouTube:

Continue reading My Presentation Philosophy

Research update: Multibody Dynamics Simulator

When I’m not doing silly things like constructing languages, writing science fiction, or biking through the Great Smokey Mountains, I have a research job in a Cornell spacecraft engineering lab to maintain. Mostly, that stuff doesn’t go on my blog because it ends up on our research group web site or in published journal articles and conference papers. But I’ve hit a milestone, and I think it’s pretty cool.

I hand-coded, from scratch, a multibody dynamics simulation package for Matlab. Continue reading Research update: Multibody Dynamics Simulator

NASA, High Technology, and Me

You know why I’m most excited about President Obama’s proposed budget for NASA? High-powered technology research programs. Hey, our space program really ought to be synonymous with high tech!

At an industry forum today hosted by NASA’s Office of the Chief Technologist, several new research programs, open challenges, and collaborative initiatives got rolled out – and my research group’s projects were, literally, a poster child for NASA!

In this presentation on small spacecraft technologies, you can see a picture of Cornell’s CUSat spacecraft on page 5…concept pictures and graphs that I developed for my flux-pinned spacecraft project on pages 7 and 15…a picture of me in front of the Zero-G aircraft in page 15, along with a picture of my labmates with our equipment in microgravity…and the citation slide lists this post on my blog.

I’m thrilled – as a guy who’s passionate about space exploration and passionate about combining weird physics and radical engineering to make sci-fi technologies into reality, I’m really psyched to see innovative programs like NIAC come back from their funding graves and a new NASA focus on enabling technologies that will help make our space exploration dreams into exciting realities.

Time for space enthusiasts to lobby hard for the new budget on Capitol Hill!

Hey, Joe! What’s your research about?

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:

I demonstrate flux pinning

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 processContinue reading Hey, Joe! What’s your research about?

My research appears in ‘Avatar!’

First: great movie, literally awesome visuals, stunning effects, good acting and execution, fun alien creatures, who cares if it’s a retelling of Pocahontas.

What I absolutely did not expect when I finally got to see James Cameron’s ‘Avatar’ yesterday afternoon was to see my own research appear in the movie. Granted, it doesn’t take a front-row seat and it doesn’t play any major plot roles. As I was driving home with my girlfriend (a fellow aerospace engineer), we got into a discussion about how this was a reasonably hard sci-fi movie. None of the technologies seem particularly farfetched: ducted-fan helicopters exist on Earth at a low technology readiness level (TRL), as do exoskeleton power suits. 3D glassy computer displays aren’t a stretch, nor are hovering VTOL aircraft on a low-gravity world. The flight to Alpha Centauri takes 6 years, meaning some reasonable sort of sublight propulsion. The ship Sully arrives on even has rotating segments, big radiators, and solar collectors. The avatars themselves don’t even seem too crazy, since we keep hearing about advanced prostheses that can be controlled by a user’s thoughts. (I’ll reserve judgment on mixing alien and human DNA until we have real alien DNA on hand.) Nor does a planetwide neural interface – though I have to wonder what selective pressures would cause such a thing to evolve – given that we have bacterial, fungal, and other life forms on Earth that can split and recombine, blurring the distinction between organisms.

But surely, I thought, those floating mountains are ridiculous. Visually stunning, yes, and great for those 3D flying scenes. But physically ludicrous.

Pandora's Hallelujah mountains

We are led to believe, in the movie, that these mountains float against the force of (albeit reduced) gravity because there is an exceptionally strong magnetic field generated on Pandora. Cameron even gives us direct evidence of that field: you know how iron filings align themselves with a magnetic field, like that of a bar magnet?

Iron filings aligning themselves with magnetic field lines

Well, the magnetic field on Pandora is so strong that geologic formations align themselves with the magnetic field. The field is so outrageously strong that whatever iron content is in Pandoran minerals – most likely not 100%, even if those rocks are pure hematite or magnetite or something like that – is sufficient to make rocks suspend themselves against gravity in the shape of the magnetic field lines:

A field that bends rock to its will!

I know for experience that this might not necessarily be impossible, for a sufficiently strong magnetic field. After all, in my lab is a whopping-big NdFeB rare-Earth magnet about the size of a margarine tub, and even when it’s contained within its sarcophagal wooden box, I can get six-inch steel bolts to suspend themselves, against gravity, at a 45° angle in its field. So, for a sufficiently strong magnetic field, this flux-line rock formation is not at all out of the question, believe it or not!

How about the mountains themselves? Couldn’t the magnetic field strong enough to make these “flux arches” also levitate mountain-sized chunks of rock?

Well, I thought, surely not if it is solely the repulsion of like magnetic poles that is responsible. After all, Earnshaw’s theorem says that the familiar field sources that drop off with distance, like gravity, electrostatic attraction, and magnetostatic attraction, cannot be arranged in a passively stable configuration. If you don’t believe me, then I set for you a challenge: get some ordinary bar magnets, and lay them out on a table. Try to arrange them in such a way that they are within a few centimeters of each other, but the attraction of opposite poles and repulsion of similar poles cancel out so that the entire arrangement sits on the table without moving. (For safety’s sake, do not do this with the rare-earth magnets I mentioned above, because when you fail at the challenge, the magnets will jump towards each other with substantial force. Rare-earth magnets are brittle and will shatter if that happens, sending neodymium shrapnel flying around – if they didn’t pinch your fingers when they impacted.) You will find that no matter how hard you try, no matter how many friends you get to hold the magnets in position and simultaneously release them, no matter how you angle them and tweak them, you won’t ever be able to prevent at least one of the magnets from attracting or repelling some other magnet. The whole arrangement will either fly apart or collapse together. You might think that in 3D you’d be able to come up with some super-clever configuration that is stable, but, in fact, if you move beyond the two dimensions (and three degrees of freedom) of the table top the situation gets far worse, because all the bar magnets try to align themselves with one another in 3D. So, a combination of purely magnetic and gravitational forces cannot result in a stable configuration of those mountains.

“But, ha!” you say. “You must be wrong! You said that a combination of gravitational field sources can’t be in a stable arrangement, and clearly, the planets of our solar system have been stably orbiting each other for four billion years! And I’ve even seen those Levitron tops – magnetic tops that stably levitate against gravity, just like those mountains!

The Levitron: just two magnets, one inside a spinning top

The key difference between a Levitron or an orbit and the bar magnets on a table top are that they are dynamically stable. They require motion to preserve stability. Stop the planets from orbiting, and they will fall into each other and the Sun. Stop the Levitron from spinning, and it flops over – aligning itself with the magnet in the base – and drops to the ground. So, for Pandora’s mountains to levitate like that, they must be spinning or moving in some way. It might be the case that, if they were at Pandora’s equator, the repulsive magnetic force actually “cancels out” the low gravity of the moon enough that the mountains are actually in circular orbits about Pandora’s equator. But that situation is dynamically tricky, requiring exquisite balances of forces – and I would estimate from the different sizes of floating mountains that they have different magnetic mineral contents, so the balance between gravity and magnetism would be different for each mountain and each would have a different orbit. Doesn’t work.

So what’s the answer? Well, it’s all in those little gray crystals the imperialist human colonists of RDA are after. Unobtainium.

An unobtainium crystal, unobtrusively levitating. Wait, what?
An unobtainium crystal, unobtrusively levitating. Wait, what?

Above is a picture of an unobtainium crystal from the movie. It’s levitating above some crazy sci-fi antigravity contraption, that holds it stably up in the air where people can poke at it, spin it, pluck it out of midair and play with it before putting it back in exactly the same spot again. Now, wait a minute – where have I seen this behavior before? Oh, right. My research lab.

A rare-earth magnet levitating over a high-temperature superconductor

That is a picture I took of a NdFeB magnet, stably levitating over the high-temperature superconductor yttrium barium copper oxide, or YBCO. (For scale, the magnet is 3/4″ across.) You can do everything with that magnet that they do with the sample of unobtainium in ‘Avatar.’ Leave it alone, and it happily floats in midair. Poke it, and it rocks a little before going back to its equilibrium position. Give it a twirl, and it’ll spin over the YBCO – and if the magnet isn’t cylindrically symmetric, it’ll eventually stop spinning and settle down again. Pull it away from the YBCO, and you can put it back later and watch it float in exactly the same midair spot as when it started. You can even pin different sizes and shapes of magnets – all stable against gravity. This whole setup would work perfectly if the magnet was on the table and the YBCO was doing all the floating, too. It’s all because the magnet induces currents in the YBCO that are not opposed by any resistance – “supercurrents” – which generate their own magnetic fields that then interact with the magnet.

“Wait,” you ask, “that magnet is just a magnet. The supercurrents make magnetic fields. I thought you said that magnetic field sources couldn’t be arranged in a stable configuration! It’s Earnshaw’s Theorem again.”

That would be an astute question. The answer is that, in this case, the superconductor doesn’t have a fixed magnetic field. As the magnet moves around – let’s say it starts to fall from its equilibrium position, because gravity is pulling on it – then its motion causes the supercurrents in the YBCO to move around. The new distribution of supercurrents gets superimposed on top of the previous distribution of supercurrents, with the net result that the magnetic field from the YBCO tends to push back on the magnet, keeping it in its original position. It’s as if the field lines of the magnet get stuck, or trapped, in the volume of the superconductor. The effect is called “magnetic flux pinning” for that very reason, and it happens with Type II, or “high-temperature” superconductors. (If you know about Meissner repulsion, flux pinning is related but not the same.) So, that blue-glowing antigravity generator in the RDA command center, with the levitating sample of unobtainium, is very likely just a magnet. And the Hallelujah Mountains are just a scaled-up version of the magnet and YBCO in my lab.

But, you probably noticed from that photo, the YBCO has to be below liquid nitrogen temperature in order to superconduct and exhibit flux pinning. Clearly, Pandora is not at cryogenic temperatures, which pretty much pegs “unobtainium” as a room-temperature superconductor – a type of material that is highly sought-after in research labs today, and would indeed be extremely valuable. That means that the Hallelujah Mountains on Pandora likely consist of large deposits of unobtainium, which are flux-pinned to the stupendously powerful magnetic field lines coming from that field sources on the planet. This explains the value of unobtainium, how the mountains levitate the way they do, and why the floating mountains are so close to the flux arch structures.

There’s another interesting link between ‘Avatar’ and flux pinning. Remember how I said that the effect of flux pinning is as if a magnet’s field lines get stuck within the superconductor? Well, if you had a good electricity and magnetism course, that notion might sit uncomfortably with you, because you were probably taught that “field lines” or “flux lines” are not physically real, but are a good visualization tool for magnetic fields, which exist everywhere around a magnet and not just in neat little looping lines. Well, you’d be right, but things tend to get kind of weird inside superconductors. Magnetic fields are quantized just like everything else, and it is these magnetic flux quanta that get “stuck” inside the YBCO. In fact, they actually get trapped on impurities within the YBCO’s crystal structure. You might think that these quanta of magnetic flux would be called “fluxons,” but because they correspond pretty well to magnetic field lines, papers on superconductivity and flux pinning tend to throw around several names for them – like “flux lines,” “field lines,” and “flux vortices.” That last name likely comes from the fact that, in the superconductor, each of the magnetic field lines induces a little loop of electric current that races in a circle around the flux line, like a little vortex. The sum total of all these little currents adds up to the distribution of supercurrents that gives us flux pinning.

In ‘Avatar,’ every time they fly near the flux-arch structure, they talk about a “flux vortex.” It sounds like your classic sci-fi trope of combining sciency-sounding words. (“Invert the phase capacitors!”) But, hmm…maybe, just maybe, that’s not mere technobulshytt after all!

I’m pretty convinced that all this isn’t accidental. The filmmakers had every intention of unobtainium being a room-temperature supercondcutor and the floating mountains being flux-pinned to the field source within the planet. Because I know that this is not the first article on the web about it! But the fact that it’s my own research in this movie: now that is cool! (For the uninitiated, I’m working on using flux pinning to assemble and reconfigure modular spacecraft. More info on my web site and my research group web site. You can also check out Youtube videos of me demonstrating flux pinning and our microgravity experiments with flux-pinned spacecraft mockups from last summer.)

Of course, ‘Avatar’ doesn’t get it all right. And they shouldn’t be expected to. I know from my research that flux pinning is a very short-range effect; getting those mountains to levitate would require a (probably literally) mind-bogglingly powerful magnetic field. Not something I’d expect to see from a planetary dynamo. Nor would a dipolar magnetic field within Pandora explain the flux arches: those are clearly centered on a magnetic field source at the surface of the world. And if the field source is powerful enough to get the rocks to bend around and follow field lines – all the aircraft, armor suits, guns, mobile lab trailers, and equipment carried by the human scientists and soldiers probably has more than enough ferromagnetic metal content to be ripped towards the field source. And that doesn’t even account for this happening:

Oh, well. But, speaking as someone who hopes that our future space program will involve spacecraft build out of components that “levitate” near each other without touching, but still acting as if they are mechanically connected, I would sure love to see some room-temperature superconductors and floating mountains!

research news

My lab’s recent microgravity flights gave us some good data to demonstrate that we’re not totally crazy with this flux-pinned spacecraft idea. In fact, it actually works. We were able to get mockup CubeSat-sized spacecraft to pin together without touching, and use magnetic fields to form a non-contacting hinge.

An article just appeared in the Cornell Chronicle about our stuff.

We’ll be applying to fly a refined experiment on the Vomit Comet next summer, as well, through the NASA FAST program. (Check out the link to our video on the FAST front page!)

on healthcare and research

I have two things to write down some thoughts about.

First, while I do some of the more mechanical computer modeling work during the day, I’ve been listening to a lot of NPR streamed over the Tubes. Today, I learned some factoids that basically break down as follows:

  1. If you figure out how many people in America get health care and the quality of care they recieve, you find that we actually have the most “rationed” healthcare system of industrialized nations. That is, in a country with omg-we-can’t-have-that single-payer healthcare, or even anything not as vile and disgusting as that, more people get the care they need when they need it than in the USA.
  2. If you figure out how much health care costs in this country, and compare it to the cost of health care in other countries – not just premiums, mind you, but tax money that goes into health care as well – you find that Americans have the most expensive health care system in the world.

If you’re thinking what I’m thinking, it’s that the GOP is neither morally nor fiscally responsible; and that they are not really “conservative” in any actual definition of the word. If you’re not thinking that, you’re probably a Republican and have just pegged me as a pinko commie godless bleeding-heart Massachusetts liberal. (I will give you three of the words in that phrase, contend that there’s nothing wrong with at least those three, and the rest I contest.) In fact, I am merely a scientist and engineer, and I know how to read numbers and am willing to make policy decisions based on data. I’m also insulin-dependent diabetic, and would seriously appreciate a much lower cost and more assurance of the efficacy of the treatments just keeping myself alive.

Second, I have been hoping to come up with some good theoretical results to present in a conference paper on my research later this summer, and it just hasn’t happened. I’ve been too busy with other work-related things, and now I’m in a summer internship at NASA and don’t have the time to spare, so results are not going to be forthcoming before the paper deadline. This leads me to conclude that I much prefer being an experimentalist to being a theoretician. The reason is that labs sometimes go the experimenter’s way, and sometimes they don’t – but part of that is uncontrollable. The experimenter can, though, usually sift through data to find some useful results. Even negative results are useful. Any results at all will at least shed light on the techniques employed. If theoretical work doesn’t go the theoretician’s way, however…you are just left with a theoretician staring blankly at a piece of paper with a lot of scratchwork. And a lack of results just means that the theoretician hasn’t done the right thing or worked hard enough yet.

In other words, I have no results and it’s my own damn fault. I can’t even blame fault apparatus, numerical noise, or experimental error. I just didn’t do enough, or the right kind of, work. And that just makes me less motivated to continue this line of inquiry.