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"No need for right of way" is also enough to know that none of these tube proposals are correct. You can't build a tube from SF to LA without running into right of way concerns.

socialist_coder 4957 days ago

Yeah. That is my assumption too. But all these proposals just seem to gloss over it.

edit: Jacques admitted it was an oversight.

Still, it's interesting reading these ideas even if they might not be what Elon is thinking.

jacquesm 4957 days ago

One of the central supports against patents is that engineers given a problem will all come up with roughly the same solution. So given that Elon has dropped a number of hints the question then becomes: can a bunch of engineers come up with his proposed solution before he reveals what it is.

That's a very interesting puzzle to me and I think this may be a way in which the patent office could do their reviews: ask a community of smart cookies to come up with what is in the (secret to that point) patent application, the one that gets it right gets a part of the filing fee and the patent is denied, if nobody can crack it in some set time (say 4 weeks) then the patent is granted.

There are not right of way issues if your tube is floating under water in the ocean. This also protects you from earthquake risks.

He has said that his system is like a “ground based Concorde”. His specs give you a speed of over 1200 km/h. If you're going 1200 km/h on the ground and aren't in a tube, you've got a problem.

Okay, but if you're floating under water, you've added a ton of new concerns. You're looking at a lot more than 1 atmosphere of pressure if you're under water, and a containment failure goes from stopping the transit to drowning everyone. Also you now don't have the solar panels Musk mentioned (they don't do so well underwater), and the oceans are not magically immune from the effects of earthquakes. Tsunamis can most definitely cause plenty of damage.

LA is also 17 miles from the coast, so if you're getting from downtown SF to downtown LA in 30 minutes, you've got less than 15 minutes to travel nearly 400 miles underwater in order to leave enough time to even attempt to get to LA under the deadline. You're now travelling at Mach II, almost twice as fast as Musk proposed.

If he really meant the actual downtown of Los Angeles, then there is definitely a problem getting out of there in time to make anything feasible. And all of the ground, air and underground around there is going to be an issue. Heck, http://en.wikipedia.org/wiki/Westside_Subway_Extension shows 4-8 billion just to extend a subway through part of it.

As for oceans, I think the risks are less than you think. A tsunami does great damage when it hits land, but in the open ocean you just bob a few inches. The mechanics behind that are simple - a wave coming in to shore starts to get bigger once the depth of the land is the same as the depth of the wave. Tsunamis are very deep waves.

I don't pretend to know what Musk has been hinting at. I don't see why you're clinging desperately to the "not an evacuated tunnel" constraint while dismissing other constraints you don't like, though. I assume Musk said "downtown" intentionally, since he said it twice (once for each city). Maybe his idea simply isn't feasible, given the constraints he's mentioned, but if we're going to dismiss inconvenient constraints, "Mach I without a vacuum" seems like a good place to start.

As for oceans, a Tsunami is still going to put a lot of stress on a 400-mile underwater tunnel. And at the points you get in and out of the tunnel, you're going to be at the shore anyway, where the Tsunami is its strongest. Also boats.

...but if we're going to dismiss inconvenient constraints, "Mach I without a vacuum" seems like a good place to start.

OK, let's discuss Mach 1 without a vacuum. A condition that I had not through, but which actually makes surprising sense as a design limit with the system that I am suggesting.

The Chapman–Jouguet condition says that a supersonic shock wave travels at the speed of sound in the air behind it. The ideal gas law says that this speed is almost entirely determined by temperature, not pressure. If you were to go anywhere above Mach 1, the temperature behind the shock wave gets hotter than room temperature very, very quickly. At Mach 1 exactly you should be able to maintain a thin (~0.2 micrometers is quoted by Wikipedia as the measured value) bow shock.

That shock can trap a huge pressure differential behind it, which could allow an open container to maintain normal air pressure while moving through a much lower density of air. If you are moving below that speed, the pressure differential that you maintain is much less than if you speed it up. Therefore for efficiency you'd want the vehicles to be moving at Mach 1 relative to the gas. Assuming that the gas is dragged along, this would let you actually go slightly faster than Mach 1. But if we assume that we have a lot of tunnel and occasional objects, the air would move much closer to the speed of the tunnel than the objects moving through, and therefore the top speed would be approximately Mach 1.

The exact relationship between the air pressure of the tube and the air pressure behind that flap is very complex. But with the flap design that I suggested, at pressures above 1 atmosphere there would be leakage and an opportunity to remove air. If the pressure fell below 1 atmosphere, that opportunity would disappear. Therefore the flap system that I suggested would do a good job of letting air leak out of the tunnel at about the necessary rate to maintain 1 atmosphere inside of the open containers as the speed of the whole system increases and air leaves the tunnel. (It should not be hard to design ways to bring air into the tunnel...)

This reinforces the point that the tunnel need not be evacuated, and explains why Elon said it would run at the speed that he predicted.

Turing_Machine 4957 days ago

"You're looking at a lot more than 1 atmosphere of pressure if you're under water"

There are already some very long vehicular tunnels at depth (the Chunnel, Seikan Tunnel, etc.). I don't think one atmosphere more or less would be a showstopper.

The point is that if you can deal with many atmospheres of pressure, you would just do a proper evacuated tunnel and get the benefits of lower friction, etc., instead of trying to find a way to make it work with air still in the tunnel.

The Chunnel also cost about $17 billion in today's dollars and is only 31 miles long (including the above-ground parts). I don't think this is a feasible model for long-distance transit, especially when Musk claimed a cost of $6 billion for SF to LA.

The Chunnel was also built by governments with contractors, subcontractors, sub-sub contractors and so on.

With SpaceX Elon has demonstrated an ability to reduce costs by a factor of 10 in large part by eliminating the use of contractors. If you look on the PandoDaily interview, just before the Hyperloop is discussed he was railing on about how inefficient the 405 highway expansion is. I wouldn't be surprised if he thinks that he could save an even bigger factor in that kind of public work than he did with SpaceX.

I'm not saying that he's right. I'm saying that his cost projections are extremely unlikely to start with existing construction projects as a base line.

ET3 4954 days ago

I dont know about 'hyperloop' but ET3 (tm) tubes (if placed underground) require less than 1/15th as much earth removal than a train tunnel or freeway tunnel. Our patented (US 5,950,543 and others) ET3 system optimizes tube size to strike a balance between low cost and high utility (as cars do), we use a freeway network design philosophy (not like a train track) see www.et3.com and www.et3.net to learn more.

mapt 4954 days ago

Far easier than an evacuated tunnel, though, is a tunnel built on standard-pressure hydrogen/helium. Light gasses have a much higher speed of sound, and their lower density means lower drag. A system of hydrogen-filled maglev tubes that can max out at 2500mph with freight-weight loads over long hauls would be more than a little bit valuable.