FLORA LICHTMAN, HOST:
You remember the Jetson family from Orbit City, right? Always flying off to school or the mall in their own pod. Well, this week, Elon Musk, another kind of space man, is trying to bring that pod travel down to earth. He unveiled designs for a high-speed transit system called hyper-loop. He says it would whisk you from San Francisco to Los Angeles in 30 minutes.
That means traveling at 700 miles per hour. So how does hyper-loop work and will it work. Our next guest is here to tell us just that. Tim de Chant is a senior digital editor at NOVA and he joins us from WGBH. Welcome to the show.
TIM DE CHANT: Thanks for having me.
LICHTMAN: Okay. So give us the real - this has been all the buzz this week. Give us the real deal. Could this work physically?
CHANT: Physically it does seem to be possible. There might be some changes that need to be made, but by and large, people think that theoretically that this actually could work.
LICHTMAN: Break it down. How would it work?
CHANT: Well, he envisions two tubes running down Interstate 5 in California and those tubes would be sucked clear of most of their air. They would be lowered to one-one thousandth of an atmosphere of pressure and that would reduce wind resistance in the tunnel for the capsules that would travel through. And these capsules would be made of, in theory, probably some lightweight material and along the bottom, they'd have some skis that would kind of work like the air hockey part that he mentioned.
So there would be a turbine compressor in the very front of these capsules that would feed the remaining oxygen in the tubes down through little holes in these skis, and that would create about half a millimeter to 1.3 millimeters of lift and that would keep the capsules gliding down these tubes. And as you said, over 700 miles an hour.
LICHTMAN: And so the pressure differential is actually the thing that's propelling them?
CHANT: No. That's what some people were speculating early on. But, in fact, what's driving them is a linear motor. So linear electric motors work similar to standard electric motors except kind of they're cut open and laid flat. So what they would be doing is he'd assemble, I think, two and a half miles of linear motors to get the cars up to speed.
And then, because of the low wind resistance in these tunnels, he's only need a booster linear motor about every 70 miles or so.
LICHTMAN: I gotcha. So the pressure, getting rid of the air gets rid of drag.
LICHTMAN: But you still have to push some air out of the way, right? What about heat from that process?
CHANT: That's true, yeah. So one of the concerns is that these air cushions that they're running on are such high pressure in that there'd be so much friction there that you'd be generating a lot of heat. Now, Musk's solution is to use and advanced aerospace alloy called Inconel that they use in their SpaceX rockets. And he thinks this will deal with some of that heat.
But it remains to be seen if the heat transfer from these skis to the rest of the structure could be dealt with in such a way that would keep the cabin comfortable for passengers.
LICHTMAN: Yeah. I mean, speaking of that, I mean, 700 miles per hour seems pretty fast. Is he talking about having barf bags in the pods, too?
CHANT: No word on that yet, but I'm sure you'd need them. The force would be up to half a G, depending on the turn and the acceleration. So that's quite a bit.
LICHTMAN: I mean, I can't even envision what that's like. Are people's cheeks going to be flapping back?
CHANT: I don't think it would be quite that much. I saw somewhere that half a G is about going 0 to 60 between 6 and 7 seconds so that's a reasonably fast car, but it's certainly not among the fastest cars today.
LICHTMAN: And this is an old idea, actually. Is that right?
CHANT: It is. Yeah. The hyper-loop, from what I see of it, is kind of a hybrid of three different approaches to high speed transit. The first obvious one is high-speed rail, which he's kind of pitting hyper-loop against. The other one is what's called a vactrain. So again, this idea of an evacuated tube where you have low air pressure and that would facilitate cars zipping through.
And then, kind of a hybrid of two other ones. One's called a MagLev or the magnetic levitation trains and those are propelled by the linear motors that he's proposing in using in hyper-loop. And then also this air cushion idea where he's supporting the capsules on skis. That was actually first proposed by a French engineer back in the 1960s and the U.S. Department of Transportation experimented with these trains that were levitated on cushions of air and run down monorail type guide rails in the West, again, back in the 1960s and '70s.
LICHTMAN: But this would go, I mean, almost double the speed, right, of any of these?
CHANT: It would, yes. So right now, the current speed record for any kind of train is the Japanese MagLev and they've run that up to 311 miles an hour.
LICHTMAN: And this around 700.
CHANT: Yeah. He's actually saying that it could go up to 760 miles an hour, which one of the sources I spoke with was a little concerned about, because depending on the temperature of the air inside the tube, even though it's at very low pressure, the speed of sound is constant at different pressures. So depending on the temperature in that tube, 760 miles an hour may, in fact, exceed that and then you might be pushing kind of sonic waves in front or create a miniature sonic boom within the tunnel, which could probably wreak all sort of havoc.
LICHTMAN: Wow. What was this about passengers carrying water in the pods?
CHANT: So, yeah, I'm not sure if passengers would be carrying water, but I know the capsules would be, and he has an elaborate setup where he'd be using water to cool the skis and some of the other parts and then he would be storing the steam on the train or on the capsule and then they'd have swap that out when they got to the next station.
So there's certainly some complicated logistics involved in keeping this running.
LICHTMAN: Yeah, that's a lot of water, right, that would be...
CHANT: It is, yeah.
LICHTMAN: ...wash - for swapping.
CHANT: I don't remember off the top of my head how much there is, but it certainly would be a large amount that you would have to carry along, which, of course, would affect the efficiency of the system.
LICHTMAN: Elon Musk, I think, described this as a sort of cost effective solution. What are people saying about that?
CHANT: Pretty much universally people are saying that his estimates are very optimistic. He's saying about $6 billion he could get this thing built. But one of the biggest things that people have pointed out is that he only allocated $1 billion to acquiring land or leasing land for additional right of way for the tracks.
So even though I-5 is a very straight freeway, there are going to be points where it's going to turn or it enters a city and the turns are too sharp even at the lower 300 mile an hour speeds he's proposing running there. So you'd need to have much more gradual turns. And to do that, you're going to have to buy land from somebody. And given how expensive it was for the California high speed rail, to purchase bits of land for their first section, I can't imagine he's going to be able to get away with it for a billion dollars.
LICHTMAN: Well, let's go to the phones. Daniel in Ellensburg, Washington, welcome to Science Friday.
DANIEL: Yes, thank you. I see one major drawback to the situation is things can go wrong because, you know, nothing's perfect. So you have a tube that's basically has the vacuum in it and something goes wrong, breaks down or even an earthquake, you're going to have to drain the whole system and, you know, get the people out. You can stations, you know, so far apart, you're still going to have, you know, something's going to happen between.
LICHTMAN: Good point. What about that, Tim? How would you deal with maintenance?
CHANT: That's correct. It's one of the things that he kind of glossed over a little bit. You know, I think he said that, oh, don't worry, the trains really can't get stuck and if there is a loss of pressure within the cabin, that they'll have oxygen masks and they'd figure out some way to rescue them. But it's not really clear how a capsule that's stuck, say, would get rescued. Or if there was a rupture - one of the bigger concerns from someone I spoke with was that if there is in fact a rupture on the line, you're going to be moving from one one-thousandth of an atmosphere of pressure to one atmosphere of pressure. And that's a really, really big difference. And so something going 700 miles an hour traveling into that would essentially be like hitting a brick wall.
LICHTMAN: Oh, wow. I also read that the design only leaves a tiny, tiny amount of space between the skis and the tube wall, is that right?
LICHTMAN: Is that a problem?
CHANT: Again, one of my sources, Dean Peterson, who's worked on super-conducting magnets and Maglev trains at Los Alamos National Laboratory, when I spoke with him about this, that was one of the things he raised, is that the half a millimeter to 1.3 millimeters of lift that these air cushions would provide is a really tight tolerance. So you'd have to make sure that you're welds are incredibly precise and that your tubes are manufactured to a very exacting standard. If we want to...
LICHTMAN: Is there - go ahead.
CHANT: I was going to say, if we want to compare this to, say, what Maglev trains run at, generally they run between one centimeter and 10 centimeters of clearance from their track, which still sounds tight but it's obviously orders of magnitude more margin for error there.
LICHTMAN: Has this conversation prompted anyone to step in, and do you get the sense that this is going to happen or could happen?
CHANT: I get the sense that this very well could happen. A lot of people are very excited about this. And whether anyone actually steps up and does it, that's another matter. This is going to be very expensive to build, even on kind of a large scale prototype sort of situation. And so I think Elon Musk may find himself fulfilling his second partial promise in saying that, you know, maybe in five years he'll step in and build the full scale working prototype to show that it can be done.
LICHTMAN: You know what's amazed me about this news, is just how interested the public seems to be in it. It's really captured people's imaginations. I mean, it sounds really cool but I think people also have gotten onboard. Have you noticed that?
CHANT: Yes. I think it sparked a really interesting conversation. You know, a lot of times when you bring up high speed rail in this country, it kind of evokes a divisive mood in people. Some people are very much for it, others very much against it. And this, this is something that's kind of futuristicy(ph). And of course, Musk being a salesman knew that attaching a low price tag to it would help it get some traction in the media, I'm sure.
And I think that - I think that people are really intrigued by the idea. Again, it's kind of that Jetsons sort of feel that you had in the introduction. And I think that's right. It's the concept of sitting down in a tube and then getting essentially shot down that tube and being hundreds of miles away in a half an hour. It's got very much the feel of the future about it.
LICHTMAN: Yeah, it does. And he said it would be only for $20, right?
CHANT: He did, although if you look closely at his - at the proposal that he put forth, the $20 I believe only recoups the initial capital costs, so the $6 billion that he put out there. So of course if it goes over cost, you know, that projection's out the window. And the six billion is amortized over 20 years, so he's allowing himself two decades to get paid back for the $6 billion outlay. But what it doesn't include are things like maintenance or operational costs.
LICHTMAN: Well, that's where we have to leave it. Thank you so much for joining us today.
CHANT: Thanks for having me.
LICHTMAN: Tim De Chant is senior digital editor at NOVA.
NPR transcripts are created on a rush deadline by a contractor for NPR, and accuracy and availability may vary. This text may not be in its final form and may be updated or revised in the future. Please be aware that the authoritative record of NPR's programming is the audio.