Getting to space is all about rockets, but people are trying to figure out other methods that could carry payloads to orbit and beyond. Railguns, airplanes, tethers and more. Today we’ll talk about alternative methods of spaceflight.
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Fraser Cain: Astronomy Cast Episode 482: Alternative Ways to Space.
Welcome to Astronomy Cast, 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. I’m Fraser Cain., publisher of Universe Today. With me – as always – Dr. Pamela Gay, the Director of Technology and Citizen Science at the Astronomical Society of the Pacific and the Director of CosmoQuest. Hey, Pamela, how’s it going?
Pamela Gay: It’s going well. How’s it going for you, Fraser?
Fraser Cain: It’s going great. Something just arrived for me that I’ve been waiting a long time for and I’m gonna hold this up so the people who are watching the live stream can see it. It is a Falcon Heavy – I think it’s a resin-printed Falcon Heavy – that’s been spray painted silver and this was provided to me by Oli Braun, who has sort of made a cottage industry of making these 3-D printed models of Falcon rockets and they’re awesome. He makes bigger ones, smaller ones, different configurations.
Check out his website. Do a search for Oli Braun, Falcon rocket. He’s got a really cool collection. I’ve seen a bunch of these starting to show up. So, he’s clearly sending these all out to the YouTubers, but mine got caught in shipping for a long time because it had to go from Germany to Canada. But I’m so glad that I got it and it will take a place of honor on my shelves that I have behind me when I’m shooting. So, thanks a lot, Oli.
Getting to space is all about rockets, but people are trying to figure out other methods to carry payloads to orbit and beyond; railguns, airplanes, tethers, and more. Today, we’ll talk about alternative methods of space flight. Alright, Pamela, this is one of those regularly requested topics that I get on the Guide to Space at Universe Today, things like that. People are always like they’re just frustrated at the tyranny of the rocket equation and, for good reason. If Earth was any more massive, we would barely be able to launch off of this planet at all.
Pamela Gay: Well, we’d barely be able to support our human body structure if there was too much more gravity.
Fraser Cain: But I mean like you know when you consider like when you look at a rocket and how much of it is made up of fuel and how much is left over for payload, there is not – it is a gigantic amount of it and that you can just barely eke out enough positive thrust to get into orbit and the fact that we can even do it at all is kind of magical. If we lived on a more massive planet, we would be stuck and so rockets suck.
Pamela Gay: And the thing is that – as much as we all get frustrated with rockets and how all of the space goes to fuel instead of to cargo – it turns out they’re the most tractable for getting things to space because – well, everything else you run into composite, tensile strength issues. So, we either have to deal with rocket equation or we have to deal with the fact that steel can crush under its own weight.
Fraser Cain: Right. I think someone did the math one time. I forget what the size was but you could build whatever is the maximum possible height of a skyscraper and it’s something like–
Pamela Gay: One and a half kilometers.
Fraser Cain: There you go, one and a half kilometers, yeah, and we’re very close to that height and then, beyond that – And, of course, this is you know only going up. This has nothing to do with going sideways at 28,000 kilometers per hour, which is what orbit really is. It’s not about going up. It’s about going sideways. But people have been very creative, right? So, what are some of the interesting ideas that people have come up with to try to get to space – and maybe even move around in space – that isn’t a chemical rocket, that isn’t a controlled explosion in the way that rockets are?
Pamela Gay: The ones that we most often hear about, think about, and wish about is the idea of either building a space elevator or a space tether system where – in the one case – you have a pretty much permanently connected, carbon nanotube, wire of some sort that extends up past geosynchronous orbit, has its center of mass at geosynchronous orbit, and then drops down to somewhere along the Earth’s equator.
And then you can simply have things go up and down the cable just like any old elevator and life is good and it’s not a lot of power and the issue is we can’t get there from here yet because we just can’t build big enough, thick enough, strong enough, carbon nanotube rope, wire, cable. Whatever you want to call it, we can’t build it yet.
Fraser Cain: Yeah. The strongest structure that’s been proposed so far or the strongest building material is like carbon nanotubes – which are incredibly strong and could theoretically be strong enough to be able to support this – but people can’t craft carbon nanotubes beyond a couple of centimeters long. Still, the material science hasn’t caught up. But let’s say that we could. What would a space elevator look like and what would be sort of the savings and the economics of that?
Pamela Gay: Well, physically what it would look like is find yourself preferably a nice mountain along the equator and you would want to build from geostationary orbit downwards because upwards that’s harder.
So, you slowly ideally have robots that are working away from geosynchronous orbit to keep the center of mass at geosynchronous orbit, build upwards with something that’s big and heavy so that it doesn’t have to go up very far, build downwards with this cable of uniform thickness, and then build just like a normal, everyday elevators on either side of this that theoretically the best way to do it would have the two of them counterbalance each other on this cable.
So, as one goes down, the other goes up. And, if you were watching that, my hands went in entirely the wrong direction. The idea with the space elevator is to take what we know how to do and what we’ve known how to do since the 1800s and just use mass to balance things out and go up and down simultaneously. This is the same way ski lifts work, the exact same way that cable cars work. You just string things along the string equally separated.
Fraser Cain: Right, and because you’re using some kind of elevators that would be going up and, at the same time, going down, they would be balancing each other and then essentially the only thing you’d be paying for is the friction in the system. You’d probably use electricity. It would be electrically powered elevators that would be going up. Now, it would take it a long time. It would take it like the better part of a week to get from low Earth orbit up to geosynchronous but – once you’re up there – then you can freely float off into the solar system and the actual energy cost was fairly low.
But you know there’s a lot of people that are trying to work on space elevators. There’s LiftPort Foundation and there’s a bunch of these other people.
Pamela Gay: And they’re getting federal funds. They’re getting supported by governments because if someone can figure out the technological breakthrough that’s needed – and that’s all it is we think is a technological breakthrough. We don’t think there’s any reason that you shouldn’t be able to make cables out of carbon nanotubes. We just don’t know how. If someone can solve this problem, they’re gonna solve a whole lot of different problems by having this super strong fiber.
Fraser Cain: But one thing that’s great is this idea would actually work a lot better on Mars or on the Moon. For those places, the kinds of materials that we can build today work just fine. You could build one out of say Kevlar rope, Spectra. You could build various kinds of materials that we have today and you could build a lunar elevator on Mars and that would actually be a great place. You build your elevator. You bring up your lunar material and either transfer it to Earth or send it off into the solar system – the same thing with Mars. So, it feels like those are actually gonna be the places we’ll see these elevators happen before Earth.
Pamela Gay: And having one at the moon would make a whole lot of sense. It’s fairly low gravity. It’s just a nice, simple way to do it. We’re already working on space stations not too far away from there. We’re gonna start building things in lunar orbit soon enough. So, let’s capture that asteroid, bring it in with all the materials we need, and just start building.
But here on Earth, it turns out that the idea that does make more sense than a space elevator – because the other problem with space elevators is they kind of eat a lot of space through low Earth orbit – because you have to constantly maneuver around them. With something like a space tether, you can have something in low Earth orbit that is constantly rotating and has essentially whips coming off the two sides that balance each other off and – when they come through the atmosphere –you fly. You match their velocity. You get hooked in. Then they whip you around and release you into orbit.
Fraser Cain: I’m sort of imagining this kind of rotating chain kind of that’s just turning in the atmosphere and one end of the chain is coming through the atmosphere while the other end is high up and then they just turn around and you can just catch a lift.
Pamela Gay: Get hooked on. Skyhooks is the way Kim Stanley Robinson has referred to them in some of his books.
Fraser Cain: Yeah, and they had them in ‘70s as well. They had a really sort of great way to approach it in ‘70s.
Pamela Gay: So, with the skyhook, you still have issues with atmospheric drag. You still have to get fairly high up in the Earth’s atmosphere to get hooked on, but they eat less space around them so they’re not interfering with a bunch of other spacecraft and they’re this good compromise between using normal airplanes that require atmosphere to function for their engines and then getting stuck into orbit rather quickly.
Fraser Cain: There are a couple of downsides with these tethers. One is that every time that you connect onto them and the skyhook and you grab a little bit of momentum from them, you’re gonna be bringing it down into the atmosphere and – as we know – the deeper you get into the atmosphere, the more the Earth is trying to interfere with it with its atmosphere and bring it back down. So, how would they deal with these kinds of situations?
Pamela Gay: You do have to have periodic counter engines to lift things up. You have to do that anyways because of all the friction that you get from low Earth orbit because there’s still some atmosphere there. And you can hook on from both sides. You can return things to the Earth this way and so when you look at this, you can balance it out. More likely than not, you’re just going to have thrusters on it that keep it in its correct orbit.
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Fraser Cain: There’s a couple of really interesting ideas with this – I bet you didn’t even know about this because literally the news just came out a couple of days ago when we were recording – this idea of an air breathing ion engine or air breathing electric thruster. So, it is – and ISA has actually tested this out – it’s like an ion engine except right now ion engines use little particles of xenon and they fire them out and they use electricity so you can carry less fuel.
They figured out how to have one of these engines bring in atmospheric particles – like air – and then accelerate those out using electricity. And so because it’s you know as long as you have it down in the atmosphere at a certain point, you don’t need to give it any propellant – any fuel. It brings in its fuel from the air. It uses electricity. It uses solar panels to accelerate those particles and so they think that you get a very low altitude satellite that it’s low enough that it can get air particles in and then accelerate those out fast enough to keep itself outside of falling back down to Earth.
And so right now, instead of having thrusters that you have to send new rockets up to the International Space Station and things like that, you can have these air breathing electric thrusters, which are just – It’s such a fantastic idea. I’m just so excited about it. But the other thing just to mention as well is this idea that you can actually use the Earth’s magnetic field with these tethers as well – that you can run electricity through them and that then you can actually get a positive boost – and vice versa. You can let the thing dip down and generate electricity into your tether. So, there are a lot of options to get these things going.
Pamela Gay: And using the tethers to generate electricity is something that’s actually been tested out and so we know these basic concepts work. We just haven’t constructed them yet. And one of the things you have to think about when you’re constructing them is these are things that are going to dip in and out of the atmosphere and they’re going to go around the Earth every roughly 90 minutes, which means they’re gonna cut through nations that may not want skyhooks cutting through their air. So, this is part of why we haven’t built these things yet is we do have to take into consideration not everyone wants their atmosphere invaded by a skyhook.
Fraser Cain: Right. Well, let’s talk about railguns.
Pamela Gay: Okay – so, railguns. You also may have heard them referred to as mass drivers. These are systems where you – on a small object like the moon – you build a large track on the surface and just accelerate outwards. From the Earth, you want to build in at an angle and launch yourself out the top of a mountain. And the idea is you accelerate along an extraordinarily long track and – at the end of the track when you pop off the end – you’re at the velocity you need to get into orbit.
You are then, of course, going to have to fire engines once you get to that distance farthest from the surface to keep yourself in orbit and not come back down ballistically, which we talked about a lot last week. And with a railgun, all of this is done with electricity. This is the same technology that the Six Flags Mr. Freeze ride in a lot of US amusement parks uses to accelerate your rollercoaster car.
Fraser Cain: I didn’t know that. Those are railguns for people?
Pamela Gay: Yes. The way this happens is a pulsed magnetic field that accelerates you forward and it switches where on the track the acceleration is to constantly move you faster and faster and faster forward. You can actually build railguns fairly easily if you feel like it using coils of wire and car batteries and then use a refrigerator magnet in a PVC pipe. So, take a PVC pipe. Wrap it and wrap it and wrap it and wrap it and wrap it with wire. Hook it up to a car battery and it will happily fire small magnets for you. This is a great way to make small children quite dangerous using electricity.
Fraser Cain: This sounds like a thing you’ve done.
Pamela Gay: It is and it’s fun.
Fraser Cain: Let’s talk a bit about then the pluses and minuses. As you said, these are electrically powered. So, you can hook them up to the energy grid on Earth and use that as a way to launch your payload off into space. But what about the accelerations involved?
Pamela Gay: The first problem is actually that hooking it up to the electrical grid. At Six Flags – when they were first setting up Mr. Freeze – they realized that all of the park lights would flicker when they fired off the ride and they had to build massive banks of capacitors and that was just to accelerate up a rollercoaster hill. And the City of Austin – when I was in graduate school – the area around the Pickle Research Center would get brownouts whenever they were testing the railgun they were building there for military purposes.
These suckers require vast amounts of energy and in those two applications – one was military, “Let’s replace tank cannons with railguns” and the other one was just an amusement park ride. And if that’s browning out your power grid, you’re gonna need a dedicated power plant if you’re trying to get to orbit. So, the power consumption is actually kind of problematic. But you’re right, gravity is also a problem. With mass drivers, they’ve figured out that you can build some with fairly realistic, “We can build something of this size to launch mass.”
Fraser Cain: Cargo.
Pamela Gay: Yeah, cargo is the appropriate word because that cargo is going to pull 10 to 20 Gs, which means that something that normally perceives itself as weighing 100 pounds is going to perceive itself as weighing 1,000 to 2,000 pounds. So, you need stuff that’s really non-crushable – like seriously non-crushable – and that’s problematic. Humans can’t quite handle that. So, with humans, they have been trying to figure out systems that were only pulling a couple to a few Gs and now we’re starting to look at systems that are tens of kilometers long in order to launch to significant velocity.
Fraser Cain: Yeah, I’ve heard that you would need things that are several hundred kilometers long where the slope of this rises up significantly – as high as a mountain – to actually launch you out. The other issue, of course, is that you need orbital velocity, but you’re still in the Earth’s atmosphere and so you get to enjoy what say returning astronauts get to enjoy when they come in – and we’re gonna be talking about that in our next episode – but that you’re gonna hit the friction of the air.
Pamela Gay: And that makes it look like there’s fire surrounding you, which is a bit disturbing. And so here you are. You’re getting accelerated to fairly high Gs. You then see everything outside your capsule appear to be on fire and this has the double effect of you don’t just need to have enough velocity to reach orbit; you need to have enough velocity to not get slowed down too much by the atmosphere. And one of the ways they’ve looked to overcome that particular problem is to just make the tunnel 20 kilometers into the atmosphere.
Fraser Cain: Which reminds me of that conversation we had about the height of a tower.
Pamela Gay: Yes, yes.
Fraser Cain: Right?
Pamela Gay: And the thing is people really want to build that tower and I think my favorite, “Oh, oh, that’s not gonna work” is the idea of building a tower all the way to geosynchronous orbit because if you could build a tower all the way to geosynchronous orbit, you just let go of things at the top and they’re going at orbital speed.
Fraser Cain: But that’s a space elevator.
Pamela Gay: They are actually thinking skyscraper, no counterweight, just build the building.
Fraser Cain: But we have nothing that could have that kind of compressibility, right? So, that’s crazy talk.
Pamela Gay: Yes, but it’s amusing crazy talk.
Fraser Cain: Oh, okay, great. Well, as long as the crazy talk is amusing. Alright, so we’ve talked about tethers. We’ve talked about space elevators. We’ve talked about railguns. What about I mean are there other alternative ideas to get to space?
Pamela Gay: There’s the idea of a space gun. This is another one of those things that people have played with the technology for and sometimes this gets combined with other technologies. The idea is you have a long essentially gun barrel – except much bigger – and you use it to channel your thing. And just like with an actual bullet – where the bullet doesn’t have any engines attached to it – the explosion takes place behind the bullet and the expansion of that explosion behind the bullet drives the bullet down the barrel.
The idea with the space gun is you don’t actually have the engines, the rockets, any of that. You instead get accelerated out this tube by some sort of an effect behind you. This has occasionally – in some of the things I’ve been reading – gotten combined with the idea of a scram jet or a ram jet. So, you have the initial acceleration that takes place that gets you from zero to some significant velocity.
Once you’ve achieved that initial significant velocity, scram jets and ram jets use the shape of their engines to take a large amount of air, compress it down, and then channel an explosion within the nozzle. If you’re within a tube, you can effectively have your bullet vehicle be that center of the scram jet engine – where the shape of your vehicle determines the physics of the scram jet – and then behind you is where all of the reactions are then taking place. I personally find this idea a bit terrifying.
Fraser Cain: Yes, again for cargo.
Pamela Gay: Yeah. So, there’s lot of creative minds out there looking for crazy talk solutions to the rocket equation.
Fraser Cain: We should talk a bit about some more hybrid approaches, for example, things like what’s happening with the Stratolaunch. I don’t know if you’ve been following. This is the launching rockets from aircraft – which is sort of an interesting halfway point. This isn’t a new idea. There are the Pegasus rockets which are launching from – I think they’re launching from 747s or something like that. And so there are examples of rockets that are air launched and there are benefits to that as well.
Pamela Gay: And we’ve been building these essentially droppable rocket planes since before we even went to orbit. This was the original experimental suborbital flights. They would carry something up to fairly high altitude on the bottom of a big old plane, drop this little tiny essentially horizontal rocket with tiny wings, fire those engines, and pop up until you could see the darkness of space, and then come back down and land like an airplane.
Today, we take the same model. You see the suborbital version with Virgin’s Galactic’s plans and we also have other projects. There’s SkyCat is one of the most well-known where –instead of taking things up and giving them a fair amount of velocity with an airplane – you just take them up with a balloon, get them significantly high, and then release them. You have a whole lot less air to fight against. You still have to create all of the velocity, but you have less air to contend with.
Fraser Cain: And I think that those are great ideas, but the problem is they have a lot of moving parts. You know you have to have a rocket. You have to attach to a balloon. It has to go to a certain point. It has to release at the right moment and be able to finish the rest of its mission. And I think now maybe 10 years ago, this made a lot of sense, but now we’re looking at what’s happening with SpaceX, with the BFR.
I mean the cost for launching 250,000 kilograms, 250 tons to low Earth orbit, is gonna be on the order of $7 million is I think what they’re saying. So, it kind of just deeply changes the economics, but you probably won’t ever be able to go any cheaper than that. That is the price of fuel at that point because these rockets are fully reusable. But it definitely kicks the can down a couple of decades on what are some alternative ways that we can get to space, that if the BFR is gonna be as cheap as they say, the need to come up with these alternative methods are not gonna be as great.
Pamela Gay: And I think there will always be rocket scientists and architects and construction engineers playing with these crazy what feels like science fiction ideas because we like to dream. We like to dream big. I’ve been really amazed at how many of these ideas are actually coming out of Russia and Eastern Europe. There’s a certain allowed creativity in this kind of engineering for even the most normal, staid engineering type.
We want to find new and creative ways to go to space. A space elevator eventually will be – if it can get built somewhere probably not here – the cheapest way to go up and down. But until then, it looks like – well, I think Elon Musk – as you said – with the BFR may have found the way.
Fraser Cain: Yeah, absolutely. Alright. Thanks, Pamela. We’ll see you next week.
Pamela Gay: Sounds great, Fraser. Bye, bye.
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Duration: 28 minutes