Astronomy Cast Ep. 101: Advanced Propulsion Systems

0:00It's the 365 Days of Astronomy podcast, coming in 3, 2, 1. Astronomy podcast, episode 101, for Monday, August 11, 2008.

0:32Advanced Propulsion Systems. Welcome to AstronomyCast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain. I'm the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University, Edwardsville. Hello, Pamela. Hey, Fraser. We're into the three-digit numbers. I know, I know, three digits. At the time people are hearing this, I'm sitting on sunny Hornby Island, enjoying the proceed meteor shower.

1:03And I'm in upstate New Hampshire doing the same thing. Well, there you go. The wonders of recording into the future.

1:12All right. So last week we talked about rockets, how they work, how they go boom, their limitations. And this week we're going to look at the future of propulsion systems. Every other way that people have theorized might be able to get us around the solar system and even the galaxy. And not all of them are realistic, but we're going to go there anyways. We'll go there anyways, yeah. So from ion engines that are already working to explore the solar system, to the prototype solar sails, to futuristic technologies like magnetic sails and bussard ramjets.

1:46I hope I pronounced that right. This is how we'll travel to other stars. Okay, Pamela. So last time we talked about rockets, we got, you know, that essentially if you boil it down, a rocket is throwing stuff out of the back of the rocket. And thanks to conservation of momentum, you move in the other direction. So these advanced technologies use a completely different laws of physics, right? Well, laws of physics are generally kept constant. That's one of the nice things about the universe.

2:17But they use different techniques to try and accelerate themselves, although there is one exception, and that's the rail gun, in which case you're still throwing stuff out the back end of the aircraft, but you're accelerating it in really cool ways. Right. But at the end of the day, all of this stuff is more advanced forms of sitting on a chair on ice throwing rocks, right? Pretty much. There's a few exceptions where you start doing things like playing with the Earth's magnetic field and using it to accelerate yourself, in which case you're just... Or people are throwing rocks at you.

2:48Well, yeah, that's true too, but yeah. It can move you. Okay, all right. Well, let's talk about one that really exists, and that's ion engines. So what is an ion engine? An ion engine is basically a device that takes atoms and then ionizes them, removes a few electrons, and this gives them a charge. And if you have a charged particle in a magnetic field, you can get the thing to move. And in fact, you can get it to move really, really fast. This is essentially a particle accelerator's work.

3:19Now, if you start throwing really fast-moving particles out the back end of your spacecraft, you can, admittedly with a very small acceleration, because you're only throwing particles out the back end, you can move yourself forward. And there's a few caveats, though. If you strictly throw the ions out the back end of the spacecraft, what you're going to do is slowly create a cloud of charged particles behind your spacecraft, and you're also going to slowly charge your spacecraft. So you have the positive ions going out the back end,

3:51you're keeping the negative electrons, and this causes you to eventually start electrostatically attracting yourself to your exhaust jet. So you have to remember to also fling the electrons out. You just throw them out in a different way so that they meet up outside the spacecraft, and you end up with neutral spacecraft and neutral cloud of exhaust. Right. So this is where we've got this formula, the mass times velocity, right, to determine your momentum.

4:22And in this case, you're taking very small masses, but you're accelerating them at enormous velocities, and you're using that to accelerate the spacecraft. How efficient is this compared to a rocket? This is like the absolute most efficient way that currently works that we have to accelerate ourselves. So if you look at the way we generally quantify efficiency, we look at something called the specific impulse. And for a solid rocket, it has a value of about 250.

4:53For an ion thruster, you're looking at more like 3,000. You're also looking at getting about 3 megajoules per kilogram of fuel out of solid rocket fuel, whereas you get about 430. So, again, more than 100 times the number of megajoules per kilogram of fuel. Okay. So why don't we have ion engines launching from the ground? Why don't we just have great big ion engines, and they're pushing with a lot less fuel and launching up into space? Well, this is where the whole it-doesn't-accelerate-you-very-fast part comes in.

5:27To get off the planet Earth, you have to start off with a force that is sufficient to fight against the gravitational pull of the planet Earth. And if you don't have a force right off the bat, if you don't have an acceleration, a change of momentum right off the bat that is greater than gravity holding you down onto the planet Earth, you're never going to get anywhere. And with ion thrusters, I can sit in my chair that has wheels and fire ions all day long.

5:58And they have so little mass that pretty much no matter how fast I, holding a device that fits in my lap, fling ions, I'm never going to overcome the force of friction in the wheels of my chair, which is kind of a sad statement. Right. I think someone mentioned that the force you feel from an ion engine would be the equivalent of the weight of a piece of paper on your hand. So if you hold a piece of paper, that's how much force the ion engine is actually putting out.

6:32So how can the ion engines get... Because I know some of the fastest spacecraft in the solar system have gone with ion engines. How does that work then? Well, what you do is you get somewhere where the force that's on you right now is a lot less. So decrease the force on something, and then it becomes much easier for the initial ion to be able to get you moving a little bit. Or you just start off with an initial velocity, and you increase that initial velocity using the ion engine. So you have to somehow get past the gravitational pull that you have to overcome to get yourself going.

7:05And then you have to make sure that the drag that's on you is exerting less of a force than the ions are able to overcome. Once you're out in space, you're pretty much good to go. Right. There's no friction out there. There's no friction out there. So just get yourself past Earth's orbit, and then start firing the ion drives. This is where we use chemical rockets to launch things initially into space. Sometimes stick a booster on them to get them a little bit further away from Earth's orbit, and then start firing the ion drives.

7:36And the other thing is time. Yeah. Like I know that some of the spacecraft, like Deep Space One, just kept its engine firing for the better part of months on end to reach high velocity. So, you know, that little force of a piece of paper really adds up over time. In fact, Deep Space One, no, I'm sorry. New Horizons? Smart One. Smart One. Smart One, which was the ESA's spacecraft that visited the moon. It used an ion engine, and it slowly increased its orbit around the Earth and increased its orbit,

8:06and finally it got to the point. I'm making little hand motions here of it orbiting the Earth. And it finally got, its orbit was so big that it was included the moon, and then it slowly slowed its orbit back down, and finally it was orbiting the moon. And it did that on a tiny amount of fuel. It just took like a month. Yeah. And so these are things that we're using. Smart One had one. The space electric rocket test was the first example of using one, and that was back in the 1970s. Deep Space One used one.

8:37Artemis. Dawn, which was one. Dawn has one, yeah. Yeah, and so these are out there. They're being used. You just have to be patient with them because it takes time to get yourself up to the speed you want to be going. And the limit of this, I know, was thought about for a mission that would explore all of the icy moons of Jupiter. It would be a very powerful ion engine, relatively speaking, with a huge nuclear generator, and it would be able to power a fairly powerful ion engine that could then have the spacecraft drop into orbit around each of Jupiter's icy moons,

9:17explore them from orbit, and then launch itself back out of orbit of the moon, onto the next one, back down into orbit. And, you know, that's the kind of technology that it's going to take to be able to do some of those kinds of missions. So, you know, we're going to see a lot more ion engines in the future for planetary exploration. Yeah, one of the biggest problems that we're facing right now is America, at least, doesn't have any small nuclear fuel sources for any spacecraft that are sitting in reserve not being used. The military has pretty much snapped up any of them that are left, or at least any of the fuel sources that were left.

9:50And we aren't currently running any reactors that are producing new nuclear fuel sources for us. So this is a problem that needs to get solved, but hopefully the answer will come in the not-too-distant future. Okay, so ion engines, same concept, sitting on a chair, throwing rocks. So what else sort of fits in that same concept of hurling things off of you at great velocity? Well, the buzzard ramjet that you mentioned up at the head of the show is perhaps one of the strangest,

10:26at least to me, imaginings of a way of flinging things out the back of your craft that has been devised. Here the idea is basically you put the interstellar media equivalent of a snowplow at the front end of your spacecraft, and you scoop up hydrogen fuel from the space between stars, and using magnetic fields, compress this ionized hydrogen down into tighter and tighter and tighter coils until it starts undergoing thermonuclear reactions.

10:59And then you use that nuclear reaction to fire hot things out the back end of your spacecraft and move yourself forward. Now, when this idea was first come up with, people didn't know just how little stuff there are between the planets. And it was thought that this would be a cool way to move around the solar system. And then we realized there's like nothing between the planets. So really the only way to make something like this happen in our solar system, or in general when you're not in the thick part of the interstellar medium,

11:29is to precede space with hydrogen. So you basically fire out a stream of hydrogen and you somehow make it go where you want your spacecraft to go. And then the spacecraft confines itself to the stream of hydrogen, which means you can't make any navigational changes as you go, which is a bit sad if you're an explorer because you're confined to your hydrogen trail. Right, but you are essentially gathering hydrogen, building a star at the middle of your spaceship, and then using the heat and temperatures to blast out an exhaust.

12:03Yeah, and the other little problem with this is really hydrogen doesn't like to undergo fusion. So it becomes much harder than was originally thought using the mix of material that's between the stars to get your nuclear reactions going. Right, I think nuclear fusion has always been 30 years away. Yeah, and if space was filled with nothing but deuterium and tritium, which have extra neutrons in them,

12:35this would be easy, but it's not. Right. Okay, any other methods of hurling stuff off of your spaceship to move? Well, there's all sorts of crazy ideas out there. One of the crazier ways of doing this is, well, to use antimatter. I thought this was kind of funny. You basically go out and you find yourself a few positrons, find yourself a few antiprotons.

13:08Or make them. Yeah, you make them. You don't find them generally. And you confine them in a magnetic field. And then you go up into space carrying your carefully confined in a magnetic field pot of antimatter. And whenever you want to accelerate yourself, you release a little bit of your antimatter and let it react with some non-antimatter. So you mix a positron and electron, for instance. And this gives off a huge blast of energy and you somehow funnel this energy out the back end of your spacecraft.

13:41Now, this is essentially the purest form of energy generation possible, right? There is no more efficient way of creating energy than mixing matter and antimatter together. Right. As long as, like, anti-neutrino is not going to help. But, yeah, mixing electrons and protons, the most efficient way we have of creating any sort of energy. It's just rather hard to control. And the confinement systems that you have to use are rather heavy. And so you're building something that, once to explode, is extremely weighty and trying to get it off the surface of the planet safely.

14:13So we aren't trying to build this currently. No, and I think that, you know, I'm not sure what the numbers are, but I'm sure, you know, even with all of the particle accelerators out there building antiparticles for years, you still wouldn't get much of, you know, much of an explosion even if you tried to put all of that. Right, right. I mean, you need to turn antimatter production into this gigantic scale economy. But I think that would solve the problem of being able to get you off the ground and get you around in space

14:46if you could somehow come up with a way to make as much antimatter as you needed. It would just be, you know, expensive in terms of energy, right? Because it takes an enormous amount of energy to make antimatter in the first place, and then you would then burn it to get yourself around. But it would be very lightweight. I mean, you could carry, well, like just a few grams of antimatter to get a rocket up into space, right? Yeah, that's entirely true. The question is, do we really want to expend the energy necessary to build that little tiny amount of antimatter?

15:20Because the amount of energy that goes into creating that antimatter far, far exceeds the amount of energy that you get out of the nuclear reaction. Right, but if weight is your absolute issue, then antimatter might be the way to go. It's in the future. All right, okay, so anything else where we're throwing stuff off the spaceship? Well, there's also, we talked a little bit about nuclear drives last episode, and they come in a couple of different types of forms. One of them is you simply have a nuclear reactor, and this is what we mentioned last week.

15:54And nuclear reactors run really, really hot, and you use them to heat up something else that you use as a propellant. Now, the other alternative is you just have a nuclear drive, and you fling bits of the stuff from the nuclear drive out the back end of the spacecraft. So this is something that we're kind of sort of looking at in different ways, but it's, again, we don't have a lot of nuclear reaction research going on.

16:24One of the ways that they've considered is building a tokamak reactor, which is where you have plasma that is confined in magnetic fields. It gets extremely hot. Nuclear reactions go on within the plasma. Pressures build up. You release the pressure to move the spacecraft forward. But tokamaks are big devices. They weigh a lot. And the amount of energy that's going to come out of them, and more importantly, the amount of energy needed to confine the plasma, doesn't make them practical. Right, aren't those kinds of reactors just barely energy neutral here on Earth?

16:59They're not even energy neutral. Yeah, yeah, here on Earth in gigantic facilities. I can't even imagine the engineering that would be required to put it on a spacecraft. But it's part of our fusion dream for the future. Yeah, absolutely, yeah, yeah. And then Mr. Fusion in my car. That'll come later. Okay, and also there's rail guns? Yeah, rail guns are kind of cool. We actually had some of these back in Austin when I was a grad student. The Pickle Research Center had them that they were developing for military purposes.

17:33And rail guns are just one of these cool devices. You basically take a couple of, well, rails, and you run magnetic fields down them. And you can greatly accelerate bits of metal down these rails. And you can get things going at large enough velocities that it starts to become interesting as projectile weapons to the military. They just haven't figured out how to build one of these things that is actually the size of a tank. They're working on it. Someday in the future, we may have tanks with rail guns instead of your more classic turrets.

18:06Here the idea is you basically have a set of rails. You run a magnetic field down them. And you accelerate chunks of metal or anything else that happens to conduct electricity out the back end of your spacecraft. This is pretty much exactly the sitting on the ice throwing rocks way of accelerating yourself. Right, and this is one of the thoughts about how to move an asteroid because a lot of asteroids are made of metal. So you would clamp one of these rail guns to the side of your asteroid that you want to move.

18:38And then you just start mining the asteroid, sticking the pieces onto the rail gun and blasting them away. And each load that you fire off would move the asteroid a tiny little bit or give it some thrust in the direction that you want. And here, basically, what's kind of cool about the idea of doing this with asteroids is every bit of metal that you fling out into outer space is a little bit more space for the human being to live inside. So you get where you're going and you end up with a progressively larger house to live in as you do it.

19:09Right. So, and eventually, I guess you would use up all of your fuel. You know, you would, if you just kept flinging it out, you would eventually run out of a spaceship. But it would definitely be an effective way of moving you from point A to point B. And what do you want to do with the shell of asteroid once you get there? Anyways, you might as well use it all up. Exactly. Hollow it out, live inside. So I think that'd be great. Okay. Well, have we exhausted all of the ways of flinging stuff off here? I think we have. I think we're now on to flinging things at ourselves, which is a bit more traumatic.

19:43Right. Exactly. So we think again to our poor person on the ice, shivering cold, throwing stuff off. Has run out of projectiles, has run out of snowballs, but all of his friends are now quite angry and now start throwing their snowballs back. And so there have been some ideas that have been proposed where you are catching stuff from space that's moving and using that as a way to get you moving. So solar sails, I think, are the classic example of this, right?

20:16Yes. And this is one of these technologies that everyone understands how it works. We're pretty sure it will work and no one has done it yet, which is kind of frustrating. But it was so close, though. It was so close. And we almost did it. There was a private initiative involving the Planetary Society that was looking at trying to figure out how to make this work. And the only problem is that their spacecraft, Cosmos 1, and this was also done in collaboration with the Russian Academy of Sciences, it failed.

20:48So they did a submarine launch, which is kind of cool. Launched it on a rocket, but the rocket didn't carry the spacecraft all the way into space. So we weren't able to test it. Right. But what are the underlying physics that are in play here to make a solar sail work? Okay. So the idea is you take something shiny, something that is highly, highly reflective and not going to absorb the sunlight and get hot. And you make a giant sail out of it, just like you'd make a giant sail to collect the wind.

21:19In this case, what you're collecting is the light. And when the light hits and reflects off of the mirror, it imparts momentum to the mirror and the mirror moves. So the light is bouncing. So when light is hitting like a mirror or even just me, when I'm out in the sun, I'm actually being buffeted by the sun. Yeah. Yeah. Yeah. The sunlight that hits you when you're standing outside, different wavelengths of light are going to react with you in different ways.

21:52The infrared light, you're generally going to absorb and get hotter. But the red light, the blue light, things like that, that allow me to see you when I look at you, these are colors of light that are hitting your clothes, hitting your skin and bouncing off. And that reflected light is what I'm able to see with my eye. Now, with the solar sail, the reflected light is not only allowing anyone who happens to be out looking at the solar sail to see it, but it's actually imparting enough momentum if the sail is big enough that it's able to get the sail moving.

22:22And just like anyone who's ever tried to use a sailing vessel, a small little, I don't know, sailboat on your local lake, over time, you figure out that even though the wind is only blowing in one direction, you're able to steer, you're able to move around, and you can go pretty much anywhere you want on the lake just by making tack changes. And you can do the same thing with a solar sail. So, a lot of the plans for how to make these have things that look like crazy wind spinners, the little things you stick out in your garden that have a bunch of petals to collect the wind.

22:58And these have a bunch of steerable petals to collect the sunlight. And the way it works is you go in whatever direction is the angle halfway in between the direction the light comes in on and the light goes out on. So, if you have your mirror straight on facing the sun, you're going to move straight away from the sun. Now, if you tilt your mirror 45 degrees, you're going to go at 45 degrees away from the angle the light is coming in.

23:29It's the laws of angle coming in equals angle going out, and you move at an angle that's between those two angles. It's a neat way to be able to steer. It's a neat way to be able to get around. And the reason we're not using it, even though you basically don't have to worry about your fuel running out because the sun's just going to sit there for a while, the reasons that we're not doing this are twofold. First of all, there's this whole problem that we're a bit scared that in the process of trying to unfurl the sail, something bad will happen.

24:00Any of you who've been following the International Space Station or many other missions, in fact, know that one of the things that happens fairly frequently is when you're trying to unfurl a solar panel or even a telecommunications boom has happened with one of the Mars explorers. Things get stuck periodically, and you have to go out and shake them and beat them and point them at the sun to get them to change temperatures and all sorts of radical things to get them to fully expand. Well, with a solar sail, you're dealing with extremely thin material that tears easily, a complex truss system that has to weigh next to nothing.

24:38And if things don't unfurl correctly, you can't steer, you may not be able to move. There's all sorts of ways that your technology could fail you just in the unfurling process. The other reason we don't use this is the ability of these things to work falls off as the square of the distance from the sun, which is a fancy way of saying the further you are away from the sun, the less able to move you become. So if you want to get to Venus and you don't mind tacking into the sun, or more importantly, you want to get back from Venus or Mercury, good technology.

25:12If you want to go out and visit Pluto, not the right choice to be making unless giant laser beams, perhaps attached to a shark, that we don't currently have the technology to build are employed to artificially accelerate your solar sail, which is now, I guess, a laser sail. Right. So same deal. You would seed your route with laser beams, and then as your solar sail went by, you would zap it, and it would accelerate and accelerate and accelerate.

25:43And I guess one of the cool things about this on the upside is that a solar sail could theoretically go close to the speed of light because that is the maximum velocity. That's what velocity of the light is hitting it at, right? Yeah. And here, the only trick is how much light can you hit the solar sail with before either you ionize it. It's a problem. You're shooting laser beams. Yeah. Yeah. Yeah. Get it just right.

26:13Right. Or you can imagine this technology might perhaps work much more effectively in a really dense star cluster. But even then, how far can you go in a straight line accelerating before you hit a star? That's also a problem.

26:27And I think people have a bit of a misunderstanding about how the solar sails would work because, you know, you mentioned this, that it's very much like a sailing ship. You know, you think of a solar sail sort of starting by the sun and then zipping in a straight line out of the solar system. But the reality is that you would put these into orbit, just like Earth is in orbit around or Mars is in orbit around the sun. And then you would tilt the sails one way and it would push you into higher and higher orbits away from the sun.

26:59You'd still be circling the sun, but then you could push it, push the sails, tilt the sails the other way, and it would actually slow you down and drop you into lower and lower orbits. So the same solar sail would either let you raise your orbit to visit the outer planets or lower your orbit to visit the inner planets. So there's no problem with using the solar sail to move down towards the sun or back up, you know, away from the sun. And just like with a sailing craft, you can't move straight toward the sun, but you just tack left and right and eventually you get there.

27:31Yeah, you're essentially using the photons to either slow down your orbit to drop you into lower and lower orbits or you're using it to speed up your orbit to rise you up into higher and higher orbits. Yeah, really cool technology. Now, there's kind of a similar technology, which is a magnetic sail, right? Yeah, and this is another one of those things that sounds really cool until you start realizing, wow, I have to build something really, really big. The idea here is if you take a loop of wire, in this case a jignormous loop of wire, and you run electricity through it, it's going to generate a magnetic field.

28:11Now, magnetic fields can be used to track or repel things. Anyone who's played with refrigerator magnets knows that you can both scoot them across the counter by making them repel each other or lift something up off the kitchen counter using a magnet in the opposite orientation. Well, here, space is filled with magnetic fields. You have lots of opportunities to either accelerate or repel yourself from some object's magnetic field, like the Earth's magnetic field, the sun's magnetic field. And the other cool thing is space is filled with moving charged particles.

28:45And moving charged particles interact with magnetic fields in neat ways. So you take your loop of wire, and if you know that there's a wind of ionized particles, you can use that wind of ionized particles interacting with your magnetic field to deflect yourself in the direction you want to go. You simply set up your magnetic loop so that it's at a right angle to the moving particles, and you move in that right angle. It's kind of cool.

29:15It's basically physics 102, second semester E&M. I'm going to be torturing engineering students with this next semester, and little do they know they'll be forced to understand magnetic sails. Loop of wire, charged particles, off you go. Problem is, when you're in the parts of space that are kind of low on the charged particles, when you're not near a star that has a large magnetic field, just like with the solar sail, the further you get from the sun, the further you get from a source of ions, the less ability you have to move forward.

29:46And it's a bit harder to cede space with ions than it is to just shoot hydrogen out there if you'd rather do the ramjet instead. Right. Okay, well, I think there's one last paradigm that we'll look at, which is, you know, we've got a guy sitting on the ice throwing snowballs. We've got the people throwing snowballs at that person, and I guess you've got more of a collaboration thing with a person sitting on the ice, and a skater comes by, and they grab, hold hands, and the skater gets them moving, and I guess the skater slows down.

30:18So I'm thinking you're talking about space tethers here. Right. So there's a couple different things that are both referred to as space tethers. One of them is far cooler to me than the other. And this is the idea of you take a large heavy object, a piece of ballast of some sort, and anchor it in orbit somewhere. And then you attach a really long, thin cable made of like carbon nanotubes or something to it. And you set the whole thing spinning so that this tether just shoots straight out the same way that happens if you start spinning rapidly with a long rope in your hand.

30:52The rope's going to shoot out. Now, if you put this object in a high enough orbit and you have a long enough tether, the end of that tether just might dip down into the Earth's atmosphere to a point where you can match its velocity and you can match its altitude with some sort of fancy airplane. So you go up with your fancy airplane and you attach to your fancy airplane a capsule of some sort that you can shoot out. And you match speeds with the tether, just like if you were trying to match speeds with a refueling jet.

31:24And you attach your little capsule onto the tether. Now, you have to do this at the exact moment that the tether is pointed directly at the Earth. It's kind of scary to think about all the you have to do it just rights that are involved in this. But then you get your capsule attached to the tether and it's going to be so big, so massive. And the ballast in the center is rotating so quickly that it's not going to care about the capsule that just got attached. It's going to keep swinging on by.

31:55This is sort of like trying to grab onto a rapidly spinning Ferris wheel. You don't weigh anything compared to the Ferris wheel and you're just going to get lifted up to the top of the spin. Well, in this case, the top of the spin, it might be another thousand kilometers off the surface of the planet Earth. And that's kind of cool. And you can almost imagine an entire system of these where we have the ballasts with tethers attached at a whole series of different orbital heights such that periodically they line up just right for you to jump from one tether to the next until you reach perhaps the moon, perhaps extremely high orbits, and then use them as jumping off points.

32:35Again, not something we've built. Again, something quite scary that we don't have the technology to do just yet. In this case, it's the building of the long tethers that we just don't quite have the ability to pull off. But it's a neat idea. And you mentioned there was another concept as well? There's another concept, and this is where the whole let's abuse E&M comes in again, electromagnetism. In this case, we have a planet with a magnetic field. And if you run current through a wire, that also generates a magnetic field.

33:05So one of the ideas is you take a spacecraft, run a really long wire off the end of the spacecraft, and as that wire moves through a magnetic field, it generates a current. The current that's generated generates its own magnetic field. These two magnetic fields work against each other and can cause a spacecraft to drop out of orbit or rise into a higher orbit depending on just where you are in the Earth's magnetic field. And that's kind of cool. And that's actually been tested.

33:35It's been used to basically deorbit part of a Delta rocket. They threw something into space with a tether test unit on it that they didn't care about. So if it didn't work, everyone wouldn't be upset. And it worked. They were able to deorbit a spacecraft using a tether. Awesome. Yeah. Well, I can't wait for all these technologies to show up. You notice we didn't mention anything about warp drives? Yeah, that's not going to happen. Yeah, not going to happen.

34:06These are the ones that the laws of physics permit. All right. Well, thanks, Pamela. And just one last reminder that you're going to be at DragonCon at the end of August. So if anyone's going to be there, I know you're going to be doing a live episode of AstronomyCast. Phil Plait's going to be there and a lot of other people. There's going to be some really great presentations at the podcasting section. So check it out. And the International Year of Astronomy is going to have their own booth. If you're trying to figure out where Phil or I are, we will keep our schedules at the International Year of Astronomy booth.

34:40And you can find out more about astronomy and figure out how to find Phil and I. All right. Well, we'll talk to you next week, Pamela. Sounds great. Talk to you later, Fraser. Bye-bye. You are listening to the 365 Days of Astronomy Pod.

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