Category Archives: NASA

Money matters

The whole public debate about sequestration, cutting the deficit, and stimulating the economy is looking in the wrong directions. The broad solutions are simple: (1) the federal government should not spend as much as it does in relation to its income; (2) the government should target its fiscal policies in a way that makes the US economy expand. The details, of course, are where everybody bogs down.

I’m an engineer. I like to solve problems by looking at data and figuring out where to apply pressure to a system to get it to do what I want. Clearly, where I apply that pressure matters: it’s better to target the big-ticket items than the small fry. This approach means, simply, that cutting federal discretionary spending is almost completely irrelevant. Instead, proposals for managing federal spending should be looking at cutting things like the military. (This is one good thing about the sequestration plan: it forces the issue of cutting our ludicrous amount of military spending.) The politicians resistant to touching the military budget sometimes argue about the number of jobs involved – not just soldiers, but civilian contractors to the military. We wouldn’t want to hurt the economy by cutting military spending, right? Well, as it turns out, the military budget is not well-correlated with GDP growth. One reason for this result might be that, while the military is certainly interested in investments, infrastructure, advanced technologies, and new medicines – all things that can make for jobs and growth in the wider economy – the military also isn’t exactly interested in sharing those things with the civilian community through a commercialization process. It wants to invest in itself alone. This does not help make the economy grow. So, there is plenty of room for cuts in the military budget (and plenty of room to remain comfortably secure, too).

A well-crafted budget plan should also look at diverting spending towards programs that have the greatest positive impact on our economy and society. Yes, I’m talking about increasing some areas of federal spending as part of a deficit reduction solution. That’s because of multiplier effects – sometimes, the government can take actions that reverberate throughout the economy and generate positive benefits for everybody: jobs and wealth for citizens, increased tax revenue for governments. Win-win!

Increasing spending happens to be about the same in deficit and revenue terms as cutting taxes, but the multiplier effect from tax cuts isn’t going to be much to help. They provide some amount of economic growth, but there are a lot of studies that show that the effect is less pronounced than changes in government spending. Here is a good article outlining both sides of issue. In my opinion, the preponderance of evidence is that most economic growth for every dollar cut from federal taxes is lower than the economic growth from boosting spending. However, even the studies that don’t agree with me tend to show that most of these actions have multipliers up to about 1.6 – for every $1 of taxes cut or spending increases, GDP grows by $1.6. As long as this number is greater than 1, there’s a positive effect on the economy, but a 60% return on investment may take a while to have positive effects in society at large.

Fortunately, there are some slam-dunk areas where a little government investment goes a long way. One example is highway infrastructure investment: it may not be sexy, but it apparently carries a multiplier greater than two! This means the if the federal government cut $2 from the Pentagon budget, but invested $1 in the Eisenhower Interstate Highway System, then not only would the deficit shrink by $1 but the economy would grow by $2! (Plus, we would have bridges that don’t fall down.)

Even highway spending, though, isn’t as good as the government could do.

There’s this one government program that happens to provide a staggering return on investment, and is hugely popular with all demographics, but doesn’t really get a lot of federal budget love. It’s called the National Aeronautics and Space Administration. (I bet you were wondering when I would say something about space!)

For every $1 that the government spends on NASA, it spends about $200 on other things. But for every $1 the government spends on NASA, the economy grows by….well, a Freakonomics panel says that the economy grows by $8 – an 800% return on investment. A Rutgers University report posted on the Johnson Space Center web site puts the return at $7 (not just for NASA, but for research and development in general, as well). And here’s a link to a 2002 article that suggests that for $64 million of investment from the government through NASA, private companies received a “value-added benefit” of $1.5 billion, making a ratio of over 1 to 23. If a broker came to you offering an investment account with a historical 2300% rate of return, wouldn’t you take it? Purely as an engine of economic investment, without getting into any of the scientific, technological, or sociological benefits, NASA is a tremendous success!

Certainly, our national representatives should be engaged in a thoughtful and difficult discussion over what programs to reduce and which to expand. If they are smart about it, though, they should look at preserving – or even enhancing – those programs that benefit us the most. They should look at the data and target their actions.

Therefore, cut defense – I have enormous confidence that the Pentagon will successfully figure out how to prioritize. Cut some entitlements – there are certainly bloated programs out there. But fund infrastructure. Fund research and development. Fund the NSF, NOAA, NIST, DOE, and USGS. And fund NASA!

That’s no moon…

While somewhat facetious, this petition on makes an excellent point. With investment in space-related technology, science, and development,

the government can spur job creation in the fields of construction, engineering, space exploration, and more.

Ever dollar the federal government spends on NASA boosts the United States GDP by a much larger amount, with estimates ranging from 2 or 3 dollars to 14. (That’s anywhere between a 100% and 1300% return on investment. Any number there is a fantastically good deal.) Of course, the pure economic return doesn’t come close to capturing the effects of new technologies and inspirational missions.

If you got a laugh out of the Death Star petition, like I did, I’d suggest that when you’re done chuckling you take a look at this one, instead, or learn about advocacy groups like Penny4NASA and The Planetary Society.

What’s the deal with Lagrange Points?

You may have read about rumors that NASA is considering building a space station at a place called the “Earth-Moon L2 Point.” The “L” is short for “Lagrange,” and this is one of the places in space known as a “Lagrange Point.” Unless you’re familiar with the basics of orbit mechanics, you may be wondering – who the heck is Lagrange, and why does he have points in space? More to the point (ha!), why is NASA interested in building a space station there?

To explain what a Lagrange Point is, I’m going to take you through a couple analogies.

Imagine you are standing on the top of a perfectly rounded, symmetric hill.

Right where you are, the ground is flat and level. You don’t feel any forces moving you one way or the other: you are in equilibrium. But if you take a step in any direction, the ground begins to slope and a force pulls you out further away from the top of the hill. The magnitude of this force is your weight, times a factor that accounts for the angle of slope:

The force always pulls you out from the center of the hill. Let’s call this direction r, for “radial.” There’s another direction on the hill, the “circumferential” direction c – this is a direction that always takes you walking around the hill in a circle. There is no component of force pulling you in this direction.

From physics classes, you are probably familiar with the idea of potential energy. Potential energy is a quality associated with points in space, and we express that quality with a single number measured in joules. Where I am sitting, space might have a potential energy of six joules, and where you are standing space might have a potential energy of ten joules. This energy comes from sources like gravity or magnetism. The difference in potential energy between two points tells us how much work it takes to move something from one point to the other: if I want to visit you, I need to spend four joules of energy. If you visit me, you actually get four joules out of the deal, which you can spend on something else (such as moving faster).

Potential energy has a direct connection to force. If you are in a place which has a high potential energy, and nearby is a place with low potential energy, you will feel a force pushing you towards the lower-energy spot. Mathematically, we say that the force is equal to the gradient of the potential energy. So, on this hill, the top of the hill has the most potential energy (we’ll call it zero, though) and there is less and less energy as we move off in the +r direction. In the c direction, the potential energy is always the same, depending on your current position in the r direction. If you go up the hill, in the direction –r, you will go towards higher potential energy and the force of your weight will work against you. You could imagine making a topographic map of the hill, only instead of the contour representing different heights, they represent different potential energy levels.

If you were to let yourself go and slide down the hill, your total energy would be about constant. You may recall the definition of kinetic energy: mv2/2, where m is your mass and v is your speed. The sum of potential and kinetic energy must stay the same, so as you roll and your potential energy drops, your kinetic energy (therefore, your speed) will rise. The equation for your total energy will have the pieces from both, though: E = U + K = –mgrsin(theta) + mv2/2. Notice that in this equation we have one term that depends on our position in space and on term that depends on our speed.

Got the hill down? Great. Now I’m going to stick you someplace else!

Suppose we go and find a merry-go-round, and we convince the operator to clear out all the horses and chariots and stuff so that it’s just a big, flat, rotating disk. Let’s also put a curtain around the outer edge, so that we can’t see outside from within. Then, you go and stand in the very center and we slowly start rotating the disk until it reaches a constant, slow angular velocity.

In the exact middle of the disk, you will notice very little. However, take one step away – in the +r direction – and you will begin to feel a centrifugal force: a force that you perceive as pulling you outwards. But thinking about forces in rotating reference frames is hard, and we’ll immediately get into pedantic debates about which forces exist and which don’t. So let’s think about energy again!

The disk is flat, so every point on it will have the same gravitational potential energy – it doesn’t really matter what that energy value actually is, since it’s differences in potential energy that are valuable, so let’s call it all zero. As you walk in the +r direction, you will have kinetic energy from two sources. First, there is your own motion, which contributes energy mv2/2. Second, there is the energy you have from spinning in a circle, because your feet are on the disk. If the spin rate w of the disk is slow enough, you might not notice it, but it’s there – and the energy is mr2w2.

Your total energy, therefore, is U + Kmr2w2mv2/2. Now–

Huh. Wait a second. That equation has a term that depends on your position in space and a term that depends on your speed. The piece that depends on speed is exactly what we had on the hill, too!

The piece that depends on position doesn’t quite look the same as it did on the hill. However, it has one very similar property: when you move out in +r, the value of that term changes. And, therefore, the magnitude of your speed v must change to keep the total energy constant! We can debate about whether centrifugal or centripetal forces are real, but effectively, the equation for your total energy behaves in the same kind of way on the spinning disk as it does on a hill. Effectively, your entire kinetic energy trades back and forth between the “translational” mv2/2 part and the “rotational” mr2w2 part, just as on the hill it traded between K and U.

So let’s call mr2w2 your “effective potential energy” on the disk! It behaves just like any other kind of potential energy – gravitational, magnetic, chemical, whatever – would, because it is energy that depends only on your position in space, even though it’s actually kinetic energy. We could even make a contour map of the effective potential energy.

Okay, then. Lagrange points, right?

Imagine the Earth and the Moon, sitting in space near each other. Don’t worry about orbital motions yet – just pretend that the two are fixed. Each body has a gravitational field, which we can visualize by a contour map of potential energy levels: far away from both the Earth and Moon, an object would fall generally inwards toward them, with potential energy decreasing as it goes in. The closer an object gets to either body, the stronger the gravitational pull, so the contour lines must be spaced closer together. And somewhere in the middle, the gravitational force of the Earth and Moon will balance each other exactly, so there is a level spot in the potential energy map.

This isn’t the whole story about bodies in space, though, because the Earth and the Moon aren’t fixed. They orbit around each other. An object we place near the Earth and Moon will also orbit around them. And because of that orbital motion, the energy of the object must include a component from rotation – which we can incorporate into the effective potential energy map around the Earth and Moon. Picture sitting in a spaceship somewhere “above” the Earth-Moon system that rotates at the same rate as the Moon orbits the Earth, such that from your perspective the Earth and Moon appear fixed in space. Then the effective potential energy map must have a component accounting for that rotation, just like on the merry-go-round. The map will look something like this:

Notice that there are five places on the map where the “topography” is locally flat – meaning that there is no net force acting on an object there. Between the Moon’s gravity, the Earth’s gravity, and the objects’ own orbital rotation, objects in those locations are at equilibrium!

These are the Lagrange points, and this is what makes them special: place a satellite at a Lagrange point, and it will stay there.

The reason why these points are attractive places to put a space station is because it’s easier to get to Lagrange points from the Earth’s surface than it is to go all the way to the Moon – and vice-versa.  In terms of our effective potential energy map, we have to cross fewer contour lines to get from the Earth to, say, L2 than we do to get to the Lunar surface. Every time we want to cross a contour line, we gave to make our spaceship gain or lose kinetic energy, and that means firing the engine – so crossing fewer contour lines directly corresponds to using less propellant or power.

If NASA located a space station at L2, then it could launch crews to the station with a smaller rocket than it would need to put the same crew on the Moon. NASA could also launch exploration vehicles and extra fuel to the station, so that the crew could eventually shuttle from the Earth to the station, and then take the station-to-Moon express from that point, at their leisure.

So: The reason why a station at L2 is exciting is not that L2 is an especially exciting place, but that the station would be part of a larger space exploration architecture. Not just flags and footprints, but more stations and vehicles and astronauts!


They’ve Still Got It

I pulled my car into my lot today, and as I walked over to the mailbox, I passed three young kids from the apartment complex. One of them asks me, “do you work for NASA?!

(There’s a NASA meatball sticker on my car bumper.)

“I used to,” I told them.

“Wow! What did you do when you worked for NASA?”

“You know the new Moon rover?” I reply. “It has six legs with wheels on the ends, and a bubble on top for the astronauts to sit in.”


“I helped work on the suspension system for those wheels – so the rover can climb over big rocks while it drives.” My hands were crabbing their way over imaginary Moon boulders.

“That is so cool!

People in this country generally fall into two categories: those who love NASA, and those who think NASA needs to be even more ambitious and capable than it already is. In media, the phrase “NASA scientist” lends a researcher more weight than the simple moniker “scientist.” NASA means achievement, technical wizardry, and the impossible made possible. The entire organization is about the best and brightest coming together to make small steps into giant leaps.

NASA doesn’t fly people on its own spacecraft any more, and one of the greatest NASA heroes just departed the Earth for the last time. But the mere mention of the Space Agency still enthralls these kids in my parking lot. Let’s make sure that legacy continues.


Stoking our Curiosity for Other Worlds

In the wee hours of last Monday (Eastern US time), a jubilant Mission Control erupted at the successful landing of the Mars Science Laboratory “Curiosity.”

Curiosity has demonstrated some amazing technological feats. Now, that portion of its mission is nearly over, and the rover will go over to science operations. The hair-raising, fist-pumping, frenzy-whipping part is done – but it’s been great practice!

While the MSL entry, descent, and landing system may seem harebrained and silly, it is in fact quite conservative and driven by fundamental engineering decisions. The engineering triumph of this system demonstrates to me how spacecraft engineers can set extraordinarily technically ambitious goals and achieve them in dramatic fashion. The JPL engineers who devised it are the types of people who design a device to last for three months and find it still happily ticking away six or eight or more years later. This thing was going to work. The toughest part was probably selling the concept to the NASA brass!

So, now we’ve got reinforcing knowledge that we can aim for the stars and hit them (well, planets, anyway). Let’s set out with some crazy-ambitious goals! And let’s set out for some places that let us answer fundamental questions.

This is my core disagreement with the NASA Decadal Survey, which prioritizes a Martian sample return mission above all else: such a sample return will advance the sub-sub-field of Martian geochemistry an incremental amount. This is not an ambitious enough goal to meet our demonstrated engineering capability! I don’t want to discover evidence that some place may have been habitable sometime in the distant past – I want to go someplace where we discover life because it’s staring right back at us.

Not so long ago, I proposed a mission concept for a subsurface probe to Jupiter’s ice moon Europa. Europa is intriguing because we already know that it has liquid water, and we already know that it has a strong energy source from Jovian tides – both of which are key ingredients for life as we know it! Even better, there are certain surface features on Europa, which – if our best models for how those features form are correct – are conduits from outer space to the ocean beneath. I suggested that we might develop a space vehicle that conducts a high-wire act above one of these exposed ice fractures, dropping probes down into the ocean below.

Soft landing on a Europan double ridge

Continue reading Stoking our Curiosity for Other Worlds

The kind of technology that NASA needs to embrace wholeheartedly

I’m always happy to learn that NASA is conducting new technology demonstrations – and the recent success of an inflatable heat shield is no exception!

Inflated heat shield (from SpaceRef)

Congress has determined that NASA should follow the 1960s vision of space travel: you launch in a vehicle, you travel through space in that same vehicle, and you land in that vehicle. Sounds all nice and cozy, except that the last five minutes of your trip require a heat shield, which is massive – eating into the amount of food supplies, scientific instruments, and astronauts you can launch in the first place. Until the moment of re-entry, the heat shield is just dead weight, doing nothing and eating into the mission planners’ mass budgets. This whole architectural problem is one of the big reasons why I favor assembling interplanetary exploration vehicles in space and then taxiing up and down to those vehicles with capsules, instead of trying to take capsules to the Moon, asteroids, or Mars.

How about if your heat shield didn’t have such a huge mass? And how about if your spacecraft could stow it neatly away, so that its size and shape wasn’t a design driver of the launch vehicle or capsule shape? Some of those problems wouldn’t be so bad.

This is a big step towards opening up more flexibility for mission architects. I hope the technology finds its way onto some real missions in the near future!

People’s Reactions to the MSL Landing System Bother Me

On 5 August, the Mars Science Laboratory Curiosity will attempt its landing on the Red Planet.

MSL is an exciting mission, the biggest rover we’ve ever sent to Mars, packed full of science experiments and capabilities, and it’s going to start things off with a daring landing detailed in this NASA PR video:

I highly recommend fullscreen...

For more information about MSL, I strongly suggest these blogs.

Something that bugs me about MSL, though, is how every time the Internet hears about it, there’s a slew of commentary about how terrible an idea the landing system is. (For a good example, look at the comments on Gizmodo’s blurb about the above video.) People wonder why the system has to be so complex, sometimes asking what happened to the “KISS” (“Keep It Simple, Stupid!”) philosophy of engineering. Others lament how risky the landing system seems. Still more wonder why Curiosity can’t bounce down like the Sojourner or MER rovers did. I’ve even heard some of the mission scientists express reservations about the “skycrane” part of the landing process.

This thing is, each stage of this landing system was driven by engineering requirements. The guys at JPL didn’t just think one day, “hey, you know what would be cool? Landing by rappelling from a jetpack!” This is, in fact, the best solution that the engineers came up with for landing something as massive as the Curiosity rover on Mars.

Let’s look for a moment each successive step in the process:

  1. The heat shield. A lander screams in towards Mars at several kilometers per second – more than orbital velocity. Then we want to get it through an atmosphere, and, really, there’s no choice in the matter: as soon as we hit the atmosphere, we get friction with air molecules. A lot of friction. Friction that superheats our spacecraft. So, we’d better put a heat shield on our vehicle!
  2. The parachute. The heat shield gets our spacecraft down to about Mach 2, but if we were to rely on it the whole time we wouldn’t slow down enough before smacking into the Martian surface. We’ve got to get the speed of our vehicle down, and one of the obvious (and lightweight!) ways to do this is by deploying a parachute. (This is actually the part of the process that boggles my mind the most. Deploying a parachute at Mach 2! Yikes! Yet this is what our last three Martian rovers have all done, successfully.)
  3. Jettisoning things. After we deploy the parachute, the heat shield is just dead weight pulling us down. We want to get the most out of our parachute that we can, so we drop the heat shield away with some pyrotechnic charges. When we don’t need the parachute any more, we’ll similarly cut it loose.
  4. Retro-rockets. Mars’ atmosphere is so thin that even the combination of a capsule heat shield and a parachute doesn’t slow the probe down enough to land safely! Earth’s atmosphere – about a hundred times thicker than Mars’ – is fine for this. We can stuff astronauts in a capsule that rides the parachute all the way down, and doesn’t even need to drop its heat shield. But on Mars, even after the parachute gets our falling vehicle to terminal velocity, we still need to do something to slow it down! So we fire some rockets downward, killing off the rest of our speed. And the rover hangs in midair, about twenty meters above the planet surface. Up until this point, the MSL and MER landing sequences are basically the same.
  5. Rappelling. Finally, we need a way to get down that last few meters to the surface. On the Pathfinder, Spirit, and Opportunity vehicles, we popped airbags out on all sides of the lander and just let them go, inspiring egg-drop competition participants everywhere. But Curiosity is simply too big for this to work: it would be like taking our egg drop and substituting a paperweight for the egg. The rover would squish the balloons, still smashing itself against the hard ground. Another option might have been to have MSL sitting on a platform which descends on rockets all the way to the surface, like Phoenix or the Viking landers did. But the platform you would need to do that properly would end up being big enough that you’d have to go tell the JPL robot-builders to make a smaller rover. So instead, we just lower the rover down on a rope, and as soon as the rover registers touchdown, we fly the rocket platform away.

The controllers we will need to get the skycrane to work are really nothing to fear. They are not fundamentally different from the controllers that keep launch rockets pointing up when our probes leave Earth in the first place. But beyond the general terms, analogous robotic piloting happens all over on Earth – from military drones to quadrotors in research labs. As a dynamics and control engineer, I think this design would have been a challenge – but easily within our capabilities. And in terms of overall complexity, this isn’t any worse than, say, a Space Shuttle launch, or the entirely robotic X37-B.

More fundamentally, though, what bothers me about all the criticism and concern about the MSL landing system is one of philosophy. We should be giving wild ideas a shot – experimental technologies, unconventional science experiments, risky missions. That is how we advance the state of the art: by pushing the envelope. If that means that once in a while our rockets explodes or our space probe smashes into a planet, then so be it. I have no problem with seeing NASA try something innovative a fail once in a while!

You see, we didn’t ever start with the Right Stuff. We learn the Right Stuff. And this is how we learn. We simply need to be willing to accept that fact if we want to go forwards.

This makes me a *little* happier about the SLS

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.