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How would you like to get around in a vehicle that “never crashes, that’s at least twice as fast as a plane, that’s solar powered, and that leaves right when you arrive, so there is no waiting for a departure time”? Sounds a little too good to be true, but that is precisely what serial entrepreneur Elon Musk’s is aiming to do with “Hyperloop,” an as-yet-mysterious form of transportation he has proposed. Furthermore, the Hyperloop would be shockingly cheap: A path between San Francisco and Los Angeles would cost only about $6 billion to build, according to Musk—a tenth of the estimated cost of the proposed California bullet train. If it were anyone but Musk making these claims, people would likely assume he was loony and ignore the hype. But after his amazing success leading companies that build electric cars (Tesla) and private spacecraft (SpaceX), his big talk is giving some people big hope for a transit revolution.

One big question about the Hyperloop is what exactly it is. Musk has been cagey, describing the idea as a “cross between a Concorde, a rail gun [an electrically powered launcher], and an air hockey table.” Some people have assumed that it will be based on an evacuated tube system, like one put out by a company called ET3. That unproven plan would levitate and propel vehicles with magnets, sending them through a tube at 4,000 miles an hour. 

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But earlier this week, Musk tweeted that a design mooted by John Gardi was the closest anyone has gotten so far. His design features two-meter-wide pods propelled by air jets, rather than a vacuum. 

The Hyperloop might be a revolution in cross-country transport, but Musk says he won’t reveal the much-talked-about design until August 12th. Until then, we asked several transportation experts to give their opinions on whether or not the Hyperloop could be the future of transport technology. Here is what they said about some crucial parts of the idea:

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On using a pressurized tube:

Roger Goodall, professor of control systems engineering at the University of Loughborough: I assume he is thinking about carrying the vehicles along by pressurized air, and if the air is moving along the tube then this removes aerodynamic drag force that resists motion; however large amounts of energy are still needed for the pressurization, i.e. you don’t get something for nothing! It’s also worth noting that creating compressed air can be very inefficient, because as it’s pressurized it heats up—the heat is then lost and the pressure drops.

John Harding, former chief maglev scientist for the U.S. Department of Transportation: I have heard it is sort of meant to be like a pneumatic tube, but you would need a fair amount of air in there to push the vehicle and that would require a long distance and a tremendous amount of energy to get it going. Everyone says they are going to use green energy, but you would need an enormous collection area to get the amount needed; it couldn’t just be over the ride way.

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Jim Powell, co-inventor of super-conducting maglev and head of Maglev 2000: “It is not practical. The air friction on the walls of the tube would be fantastically high. You would need huge pumping power. And then as you travel along, the air pressure would drop so you would have to have a series of compressors along the way—which couldn’t actually be in the tube. So the air would have to be extracted, and reinjected into the tube at a higher pressure to make up for the pressure losses. I hate to say it, but it doesn’t make any sense.”

On using an evacuated tube:

Tony Morris, president of American Maglev: To evacuate a tube like that you would need something that really sucks.

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Morris [on if the tube cracked and you had to maintain the vaccum]: If you cannot get rid of the air, then that drag will be massive, and it will manifest in heat (think rocket re-entry). If you cannot get rid of the air, then you will have a lot of trouble getting about 200-300 mph and dealing with that heat. If there was a sudden loss of the vacuum, then that would make the capsules heat up like mad as they slow down. 

Harding: Apparently he says it’s not a vacuum system, and if he is going to go that fast it is going to be difficult to do that without an incredible amount of energy. If it is going to be an open system, you are looking at a max speed of 300 mph due to the aerodynamic drag. If it is faster, obviously then he would have to operate it in an evacuated tube like the ET3 system. But then that is not really viable due to the safety problems involved. In an airplane going that fast you get a problem and you can drop down to a lower altitude. In an evacuated tube what could you do?

On the path of the tube:

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Morris: When you do the math on this, even at 150–200 miles an hour, the track has to be really very straight because you can’t expose people to that much g force. You’d have to buy land, you’d have to tear down houses, you’d have to build over communities. If you are going from New York to LA, what happens if St. Louis is in the way?

Harding: If you are in the tube, and it is off by the slightest amount when it is going at top speed, then that would cause a sideways acceleration. It has to be incredibly straight. You can’t avoid things. 

You can’t afford to stop at intervening places either. So if it isn’t even going to stop in your town then why let it go through it? The stations would have to be very far apart to let it accelerate and decelerate. 

The usual response to “How do you expect to reduce travel time?” is “Go fast and avoid curves.” That sounds great except what do you do when you reach the Rockies—do you go around them, over them, or through them?

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Powell: If one part of the system settles a few inches down relative to another part of the system and you are traveling at 1,000 miles an hour the car would hit the wall of the tube. You not only have to have a very straight tube, but it can’t move for any reason. 

On cost:

Harding: Then there is testing it. That is a real problem with high-speed systems. With low-speed systems you can build a track a couple of miles long and test it. With high speed you need some distance to get up the right speed and then distance to run the test. This test facility would be extremely expensive in itself. If they use a smaller track [as ET3 say they will], then they would have to accelerate the car faster than any human being inside could tolerate, but then that doesn’t test for the effect of putting a person in it. 

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Harding [On media reports that say it would cost only $100 from New York to LA]: “Is that right? (Laughs.) Well, that is certainly where he is hard to believe.”

Harding: If they got the kind of money the military has then you can do it. It is always possible to build something if you are prepared to spend the money.

Goodall: I see Musk is claiming a tenth of the cost compared with the SF-LA high-speed rail system, which I can’t believe is based on solid facts.

Powell: $6 billion translates into a about $10 million a mile. I don’t think that is possible. I really don’t think that is possible. 

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On safety, usability, and comfort:

Morris: I just can’t get past the human factors. Not only what would this do to you and me, but what the effect be on an 80-year-old or an 8-year-old experiencing those g forces?

Harding: When people say anything is something-“proof” I feel very skeptical about that. Things they say can’t happen invariably do happen. 

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Powell: If you are in a tube above ground, containing that kind of load for 500 miles or so exposed in that way is very vulnerable. 

A crash is like Concorde hitting a mountain.

Harding: There couldn’t be an attendant in a six-person car, so if something goes wrong then you are on your own. That would be very scary. That is another thing: you got to convince people to use the thing. I wouldn’t want to be first in, put it that way. If something goes wrong then you are stuck in a small vehicle in a tube and there is going to be no way to preserve your life for any length of time. 

Harding: You would have to have disabled access and a restroom as well, but there would be no space in a six-person car. How would you accommodate that?

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Morris: The US standards are that standing and seated passengers cannot be exposed to more than 0.1g in any direction at any time. Passengers with seat belts can be exposed to 0.25g (or in an emergency). This would be a killer for this concept, so they will have to find a way around what is basically a human factors safety issue.

Powell: You would need very thorough screening for getting on board. Anyone with an explosive could destroy not just the vehicle, but also the whole tube. It’d be a great attraction for terrorists. And so that causes lots of time delays like at airports. The overall total time to travel would not be much less.

On whether it can actually work:

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Industry observer and maglev proponent Larry Blow: There we go again, with fantastic performance predicted, at a ridiculously low cost, without a shred of hardware proof—he’ll be re-imagining basic physics, from what I’ve seen in the past.

The combination of fantastic system characteristics being touted, presumed benefits and minimal cost is just too difficult to believe. And just from my own knowledge, I do not think it could practically be achieved.

George Masie, fluid dynamics expert at Maglev 2000: “If somebody other than Musk had proposed this, I would say it’s very suspect,” Maise says. “I really have no idea how you do this.”

Harding: I can’t imagine he is a total fool. I wonder if it is his idea or somebody else’s. I wonder who his supporters are, if they are people that can really do this.

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Morris: I just cannot imagine how you could do this.

Powell: I think people are excited by new ideas and there is nothing wrong with that, but I think that these ideas need to be looked at very seriously and objectively not just from a, “Geez wouldn’t this be wonderful if it could happen?” but from a real mechanical engineering perspective. My feeling on the Hyperloop is that this process has not taken place.

Originally from Scotland, Claire Cameron is an intern with Nautilus and a recent graduate of Columbia Journalism School.

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