Seriously, it is easy to put together a some sketches, a couple animations, and a cost estimate based on handwaving. Actually proving the feasibility of a large scale engineering project using unproven and novel applications of technology is another thing entirely. And based on even cursory knowledge of large scale construction projects, I cannot figure out how the get a cost of under US$6B; even with mass production, the raw materials and fabrication cost should exceed this, never mind the labor, upkeep, and right-of-way costs.
This. Though prices are dropping, just the cost for the solar panels he envisions, much less the actual structure, land costs, etc. would be a significant fraction of the $6 billion.
Batteries. Something that Musk knows a little bit about.
Sure. But it’s not like Musk doesn’t have a little bit of experience in running fairly large projects. No, his expertise is not in civil engineering, so there’s probably a grain of salt to be taken there. But the cars are not obviously more difficult than an electric car or rocket, so I’m willing to give him a pass there.
Can you give a back of an envelope sketch of your alternate estimate? I’ve looked for costs of structures with similar characteristics, such as bridges, dams, and oil pipelines, but it’s difficult to correlate.
The solar arrays are sized at 285 megawatts peak. For such a highly mass produced system, $2/W installed cost should be doable, so it’s only a bit more than a half-billion dollars. Maybe not even that, these days.
And how exactly are you braking this thing? What do you brake against? The cars are floating on an air cushion for normal operation. The linear induction motors are 70 miles apart so you can’t use them for emergency braking. You can’t deploy wheels at 760 mph. Do you just lay down some type of sled like skid pads and start scraping along the bottom of the tube?
Either the entire length of the tube needs to be lined with a material that can take the friction of an emergency stop or else you are going to need to replace entire sections of tube every time emergency stop is used.
the PDF merely says “mechanical brakes will be on each car”, theres no details.
Thats just one example but it seems theres a lot of fundamental problems have been handwaved in the proposal.
Another problem is the design of the doors to be both safe from explosive de-pressurization and able to quickly unload / load the car. Seeing as there is no aisles they open up a large number of doors along both sides of the car. People in other sites have pointed out that the outward opening gullwing doors are a very very bad idea for a pressurized design.
the paper explains that there would be a need for wheels to be used at low speeds, and retracted airplane style for high-speed mode. Brakes can be placed on that. Plus the front facing compressor can be stopped or even reversed to function as an air brake. In fact, because the design calls for a vehicle whose diameter is smaller than the tube diameter to avoid sonic pressure waves from developing, I suppose that an airbrake that deploys to cover most of the inside of the tube would work quite nicely, even at 100 Pascals.
That is what I had in mind. The inside of the tube is smooth and skidpads should work quite well.
It’s steel. You don’t need any special lining. The cars are 3,100 kg and hit 312 m/s top speed, so there’s around 151 MJ of KE. Steel has a heat capacity of 466 J/kg-K. If we imagine that a 500 K rise is acceptable (not even orange hot), then we have 233,000 J/kg of total heat capacity. Divide out and we get 650 kg of steel, or 0.081 m^3. Assume a depth of 1 mm* and a skid width of 20 cm, and we get 406 meters to spread the heat long.
Even allowing for factors like more energy being dissipated at high speed than low (which could be corrected for anyway using the air bearings), there’s plenty of area to dissipate heat into. The cars are spaced 37 km apart so there’s no collision risk.
I’m not sure if the depth figure is optimistic or not. However, even if it is off by a factor of 100, we would still be ok–it means we’d need 1 m of skids an 8 km to slow down.
I don’t see why that’s a fundamental problem. It’s only 1 atmosphere on the inside. The cars will be light, but don’t need to shave every last gram the way airplanes do. The doors can be overbuilt for their purpose to give a nice safety margin. Gullwing doors aren’t the only possibility, anyway.
Its not just the heat, what about abrasion? Check the PDF, The air skis have 0.5mm to 1.3mm clearance in normal operation. Any debris left over from emergency braking is going to be a very bad thing for the next car that comes through at 312 m/s. They’d have to stop and clear out each tube very carefully after each use of the emergency brakes.
Filling the entire tube with a deployable airbrake and reversing the compressor might do the job for the initial deceleration then deploy some kind of skid pads at lower speed then drop the wheels for the final deceleration once it gets below 100 MPH. Still I’d like to see someone work out the actual mechanism and total time to stop from 760 mph.
I see no reason why there should be significant abrasion as long as the pad material is chosen carefully and the temperatures are kept under control. Disk brake rotors don’t abrade significantly in use. Brake pads can create dust, but it certainly depends on the material and may not even matter.
Still, the air brake is a reasonable idea. There are lots of possibilities here. The proposal certainly isn’t fully fleshed out.
OK. So you figure out a way to bring the system to a complete stop.
Now you’ve got a tube filled with stopped capsules filled with people stretching all the way from San Francisco to Los Angeles.
If it’s a major emergency that made a section of the tube unsafe or cut power supplies, you need to get the people out of the capsules and out of the tubes. You can’t leave them there for days or even very many hours. Even if it is a less serious emergency that will still require an indeterminate amount of time to resolve, you need to do something about the people.
What will be the logistics? Will there be emergency exit doors from the tube? Will there need to be rescue crews stationed every x number of miles?
No it isn’t. Has any kind of “air ski” riding system ever been attempted at such speeds ?
I think the cost estimates are wildly inaccurate and until they build a test track with unmanned cars they probably have no idea what the real costs and issues are.
Sure, there will be emergency exits every X miles. It’s along a busy corridor so I’m not sure you need specialized rescue crews. The cars will have powered wheels so they can travel to the next exit (at low speed).
There aren’t actually that many cars in the tube at any one time (about 30 at most). And they’re spread out enough not to overload any one rescue department.
Air bearings are probably military research, it’s just their sort of thing.
I understand that California was looking at high speed transport, and that’s why this idea was created- but I don’t think California is the place to build it. Too expensive, too hilly, too earthquaky.
Having the device centered in Chicago makes sense- you could have a branch go to New York, and another head south to St Louis.
Easier construction out East, and a more plausible user base of intercity commuters.
Pity, this would be perfect for that fairly flat [or gently rolling[ terrain between the Appalachians and the Rockies. I would kill to not have to drive those long interminable flat states; Road sucks, flat and LOOK ! Cows!. sigh [Though we did spot an eagle sunning itself on a fence post in Nebraska or one of those flat states out west last time we drove to Calfornia. Maybe Wyoming? it had long straight roads, fenced in pastures and cows. Lots of cows. Not too many people, though.]
I would love to put my car in a pod, if we could sit in the car. How long would it take to go from St Louis to someplace like the other end of Wyoming? Just schlorp us along and we could nap in the seats. Maybe 2 vehicles per pod?
And you could conserve land and put the pylons between the 2 roads of the interstate system. They have rest areas in the median with access to either side, so you could do it with pod stations too.
Or maybe sell the surplus to the grid in the daytime and buy it back at night.
‘Solar panels don’t work at night’ (and for that matter, the also common ‘wind turbines are useless because the wind isn’t always blowing’) is a bit like saying that "Oil isn’t always squirting out of the ground’.
So having emergency escape doors that could be opened from inside the tunnel (without requiring superhuman strength) wouldn’t interfere with the required continuity or smoothness of the tunnel? Would having rubber gaskets around the doors be a problem? How about handles, latches, and opening devices?
I also wonder if a pod became disabled inside the tunnel, would they have some sort of tow truck?
As for the TSA-style screenings, it’s true that a bomb won’t kill many people. 28 maybe, possibly 56 if you time it right.
Set of the bomb as you pass next to or under the right building or freeway bridge, you might get a few more.
But a bomb that ruptured a tube would inconvenience many millions of people.
It’s exactly this sort of detail x 1000 that makes Musk’s proposal ludicrous.
In principle, yes, it could work. But putting that principle into practice requires a tremendous amount of engineering work because there will be thousands of little unexpected hitches that will emerge when you actually start building the thing. High-speed rail is the result of 200 years of incremental innovation. The problem domain is very well understood. Most of the engineering work has already been done, and any hitches that emerge are going to be relatively small.
HyperLoop (what a stupid name) is a completely untested technology. Basically all Musk has are some back-of-the-envelope calculations that say it’s theoretically possible. There are literally tens of thousands of little engineering problems that need to be solved before this thing would be ready to carry human passengers. Solving those problems will take decades and drive the cost through the roof.
All Musk is done is demonstrate his own naivete as an engineer.