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Heaven Help Me, But I Sort of Love Elon Musk’s New Hyperloop Idea. (Well, at Least in Theory…)
The sci-fi buff and futurist in me just loves, loves, loves Elon Musk’s idea of building an underground hyperloop between Washington and New York. Heck, I would love the idea even if the vacuum tube connected LA and San Francisco or Houston and Dallas or Chicago and St. Louis. Even Dubai to Abu Dhabi.
Now since I live in the greater Washington DC area, I find the idea even cooler. I would love to be able to zip to Manhattan in 30 minutes. Plus, I would imagine, real-estate prices within driving distance of the stops would get quite a boost. And when there are hyperloops from coast to coast, time to get started on a space elevator.
But, but, but … the technology does not yet exist. The regulatory path to approval does not yet exist. The business case does not yet exist. The commitment for public financing does not yet exist. If we were a country that could build a project like this, I imagine we would already have a continent-spanning, high-speed rail network. And about the cost. Probably north of $300 billion. It is hard to see public financing on that scale to fund better transportation for the Acela corridor. (Oh, and it seems likely there would be additional stops, such as in Wilmington and Newark.) Didn’t the POTUS get elected by promising to help the left-behind communities in the Rust Belt and Appalachia? Musk’s idea for a city on Mars might be more realistic. (The Economist offers some conceptual problems as well as some boring, non-Boring Company transportation ideas.)
Then again, this is hardly the worst idea I’ve heard lately. (Using protectionism to “bring back” manufacturing jobs, travel bans, a solar border wall immediately pop to mind.) And I love that someone is trying to push forward rather than look backward. Anyway, Wired offers a pretty good take on the Musk hyperloop:
First, you have to get the OK from all the states and cities and municipalities involved…. To give you a sense of how big a deal getting everyone on board with a hyperloop would be, consider that just New York and New Jersey have struggled for over 20 years to reach an agreement to build a single tunnel under the Hudson River — a tunnel the region needs desperately…. Even if the feds could somehow take the lead on this one and ram a hyperloop through localities, it’s not clear who’s in charge. The Federal Railroad Administration, which handles high-speed rail? The Federal Highway Administration, which manages the roads? Who determines safety standards and holds the Boring Company accountable?…
And then there’s the little problem of moolah. Just updating the current Northeast corridor railroad — you know, the one run by Amtrak — to high-speed rail standards would cost an estimated $123 billion. Tunneling will be even more expensive…. Carving less than two miles of tunnel under New York for the Second Avenue Subway took $4.5 billion. Even if this hyperloop were entirely privately financed, it would take lots of zeroes…. Environmental effects can also strangle projects indefinitely. An extension of Washington, DC’s metro has been in the works since 1994, but was hamstrung by lawsuits alleging the project would destroy wetlands and other wildlife habitats…. Then there’s the little trouble of perfecting a technology that doesn’t exist yet. Hyperloop One, one of the many companies competing to build the first hyperloop, ran a successful test out in the Nevada desert last week. Just a few small problems: The track was 315 feet, the “train” a sled, and that sled reached just 70 miles per hour. (A completed hyperloop should hit 700.)
It’s a long way from here to there, even with “verbal government approval.”
Published in Economics, Technology
I was wondering about that myself. But it seems Musk likes the tube, so. . .
I have no idea. How does that relate to the Hyperloop?
It was 4″ pipe. And household aluminum foil.
You missed the two previous tests when they pull almost 30″ Hg and failed to implode the same car. As you point out, they then damaged the car by dropping a Jersey barrier on it from about 50′ up, and then it imploded. But you’re doing your math wrong. You converted from inches of mercury to psi alright, but you put it on the wrong side of the tank. A 23″ vacuum inside the tank makes the pressure differential 11 psi, not 3 psi.
Lots of transportation systems fail catastrophically when damaged. Cars and trains crash, and planes fall out of the sky. That’s never been a deal-breaker before.
Everything you wrote in your comments is correct, I just think this point exaggerates the challenge to the point of suggesting it’s unachievable. I took issue with it because not everybody is equipped to recognize that for themselves.
My point wasn’t that all pressure vessels would withstand a vacuum, but that a rail car designed to withstand elevated pressures would fare better than one simply designed to hold unpressurized liquids. My theory was that two tank cars that look very similar from the outside might behave very differently. Dan since commented above that the car was pressure rated to 600 psi, and I have no reason to doubt him.
You can’t keep a tube at ambient pressure if you are trying to blow air through it. In fact, trying to push that much air through a tube this size is completely infeasible. The pressure differential from the blowing end to the other end would be enormous. Skin friction inside the tube will rob the air of energy, as will bends, pods, etc. At this scale, the pressure required to make air flow through the tube at the speeds required would simply explode the end that the pump is attached to – if you could make a pump powerful enough to do it.
Think about this in scale – you have a tube maybe 500km long, but only 10′ in diameter. Pushing a significant amount of air through that will require hellacious amounts of energy and there will be a huge pressure differential from one end to the other. Think about how much force it takes to blow hard through a straw, and how little force comes out the other end compared to the effort it takes to blow.
I would say it’s un-achievable as designed. A single welded steel tube is a non-starter simply because of thermal expansion. I studied how pipelines handle this, and none of the solutions work for Hyperloop. Some pipelines have ‘Z’ bends at regular intervals to act as accordians and absorb the expansion. Some have expansion joints, but an expansion joint that works for a 4′ pipeline carrying liquids is wholly unsuitable for a 10′ pipe holding a vacuum. In addition, according to Musk the interior of the tube has to be mirror smooth. I’m trying to imagine an expansion joint that can move back and forth under thousands of pounds of force, while maintaining a perfectly smooth interior, and it seems like a very daunting challenge. And, you’d need at least hundreds of them. And since they have moving parts, you need to inspect them and replace them. If you have 1,000 of them across the length of the tube, and each one has a design life of ten years, you’d be replacing one every three days – something that would require shutting down the entire system.
Without some kind of expansion joint, imagine a curve halfway down the track – the starting point of that curve will move back and forth more than 500 feet per day – and therefore the track after the curve would move laterally 500 feet as well. Musk’s pylon design doesn’t allow for any lateral moment at all. Therefore, the design simply doesn’t work. Maybe a new design can be made to work, but that requires an entirely new cost estimate. Musk’s 6 billion was always at least an order of magnitude low anyway, but once you add all the safety features, expansion mitigation, etc, you will have created the most expensive yet most brittle and low capacity mass transit system ever made.
The difference is that when holding pressure, a spherical vessel has the force pressing outward evenly around it. Therefore, the force is distributed evenly through the surface of the sphere, and it will stay intact until the material itself tears apart.
When you are applying a compression force, the force on each part of the tube is distributed all the way around as well (think about an arch, and how the forces on the top of an arch are pushed outwards and down through the legs.). However, the big difference comes in when the force is not symmetrical, say because of a dent. Now the force applied is no longer distributed around the entire sphere, and all its strength goes away.
I’m sure you’ve tried the old trick about trying to break an egg by pressing on the ends. The egg has evolved a shape such that forces on the ends are symmetrically distributed down through the entire surface of the egg, so it’s very strong. But if you squeeze it on the side, instant smushed egg. That’s what will happen to a vacuum vessel once it has any kind of damage to its shape.
I have also done a demo for high school students where I invite one of them to stand on an empty soda can sitting on its base. If the can is free of dents and they step up very carefully, the class is amazed it will hold so much weight. Then I get another student to use a pencil and lightly brush the sidewall. Crunch.
You’ve seen designs? I assumed it was crayon sketches on toilet paper, plus a few models because investors like those.
Except it won’t, and it can’t.
It turns out that making a highway a lot wider doesn’t expand traffic capacity in a linear fashion, especially in rush hour conditions.
Going from one lane to two in one direction helps a lot – faster traffic can often route around slower, especially with limited access roads.
Going from two to three doesn’t increase capacity by 50%, though – it’s usually closer to 30%. Three to four increases a little bit, but mostly helps route around stoppages in high-use situations.
Anything past four is basically useless, and once you get to six lanes, it can often make capacity lower, due to so many people changing lanes and saturating onramps and offramps. You’re better off streamlining flow instead (fewer/larger ramps and gentler curves).
Usually, when you have a clogged four lane highway, the better option is to make a whole different four-lane highway a mile or two off to one side, going the same general direction, with a few crossing interconnectors.
Heh. The design only has to be done to the level where a politician can sign off on it. That means pretty pictures, mentions of Co2 and global warming, and some talk of ‘green jobs’. Fit all those into your ‘design’, and Bob’s Yer Uncle.
So it doesn’t need to be good – it just needs to sound good.
However, what little documentation there is does say it will be a single welded steel tube, with expansion dealt with at the end terminals. And all the ‘demonstration’ loops that have been built have been exactly that – welded steel tubes. No expansion joints in sight. Of course, you can get away with that when your ‘demonstration’ is perfectly straight and only a few hundred meters long.
So we’re taking inspiration from Genesis II now?
What next? Dual navels?
https://youtu.be/Ew0eEl6N-30
I’m both proud and appalled that I immediately got that reference.
Bloomberg media has an interesting opinion piece about the hyperloop:
https://www.bloomberg.com/view/articles/2017-08-03/elon-musk-s-hyperloop-is-doomed-for-the-worst-reason?utm_content=buffere2c12&utm_medium=social&utm_source=facebook.com&utm_campaign=buffer
By Virginia Postrel who finally realizes that the burden of over regulation slows economic growth, it also disables the governments ability to stimulate the economy, and is largely why the 2009 stimulus bill failed. (partly true – it also failed because huge portions of it where pay offs to unions – and not designed to stimulate anything other than democrat supporters)