[withinboredom]

Sure.

If you put it above ground, you are a few short bullets from killing everyone in the loop. Hitting a wall of air in a vacuum at hundreds of miles per hour is going to be like hitting a brick wall. Ask any reentering spacecraft.

The same problem exists underground, the weakest points being the stations themselves which can be bombed.

A failure in the system itself (even just a power outage or malfunctioning equipment) would mean people suffocate inside after a matter of minutes.

So, sure, it is possible to create it, but it is impossible to make any sort of safety guarantees. In other words, literally any other mode of transport would be safer, including a hydrogen-filled dirigible.

So, sure, the concept itself might be possible, but an engineer doesn't concern themselves with possible. That is for scientists. An engineer considers what is realistic AND possible, because that is an engineer’s job: to make the possible real. This cannot be real; literally no regulator would ever sign off on it.

[yellowapple]

> So, sure, it is possible to create it, but it is impossible to make any sort of safety guarantees.

Right, because cars and planes and trains and boats and bicycles and footpaths and airships all famously have 100% perfect safety track records, right?

[withinboredom]

They have mitigations. If a plane breaks down, it can glide. If a regular vehicle breaks down, it can be moved off. If a train breaks down, people can just get off the train. On a hyperloop, where are they going to go when surrounded by a vacuum? What about whatever is behind them also waiting?

There are no mitigations and the only option is death. Maybe you can repressurize the tubes ... assuming there is power to do so ... to evacuate people. This is the main issue, there is no air outside your vehicle. If a window breaks (see: airplanes where this happens every so often) everyone inside is dead. No discussions, no second chances.

That's the problem. The main problem and you can't engineer around it. There are no emergency procedures because if you have an emergency, you are dead; and there will be emergencies.

[yellowapple]

> Maybe you can repressurize the tubes ... assuming there is power to do so

Fail-open air valves are a thing.

> to evacuate people

Emergency exits are a thing.

> If a window breaks

Why would a shuttle in an underground vacuum tube have windows?

> The main problem and you can't engineer around it

Pretty sure people said the same thing about most of the modes of transportation I mentioned above.

[ENGNR]

There are mitigations though. Assuming you have sensors in every segment, you could detect the vacuum ahead deteriorating and brake.

Equally, if the train stopped in an emergency, the valves around it could fail safe to open and let the atmosphere back in. The train has to be pressurised anyway so a small delay there isn’t unreasonable

[withinboredom]

Sure. I'll play. I assume those sensors are always powered and never malfunction and so, now the train is stopped in a vacuum. What now? How do we get the people out, and all the trains behind them now also stopping. If the tracks are below ground, where is the nearest valve that can open? Given some parameters to chatgpt, because I can't be bothered to do the math myself, it takes ~5 minutes to fill a 500m section with air. So, that assumes a 500m sealable section with an independent valve. So, there would need to be some kind of system that can seal a section on power loss or breach, without a train running into in-progess.... so, 500m sections are too small. The sections need to be ~5km which would take nearly an hour to fill with air that won't kill you instantly. So, if there were structural integrity issues with the train, everyone is guaranteed to die. If there is a critical power loss, hope that it can scrub the CO2 out of the air for at least an hour without power. If there is a breach, hope that it isn't in your section or is at least 3 sections away.

Killing everyone in the train because someone gets in a fight and fires a gun is pretty much a non-starter. That's the real problem you got to solve. It's not like a plane where someone can fire a gun in nearly any direction without consequence to the plane, firing a gun in literally any direction on a hyperloop would mean certain death for everyone on board.

It's in a vacuum, it's not like you can drop oxygen masks. In a vacuum, your blood boils and your eyeballs are sucked out. It's a pretty shitty way to go, but you'll lose consciousness before the worst of it.

[panxyh]

You stretched 500m to 5km but kept only one valve. Why?

And presuming that whole wagon doesn't burst because a couple of bullet holes, is it unrealistic for onboard pressurized tanks to keep up with escaping air while outside is getting pressurized?

Do you mind sharing the parameters you fed GPT?

[withinboredom]

> You stretched 500m to 5km but kept only one valve. Why?

This is the worst case scenario by assuming only one valve is functioning. Theoretically, even that could break, but I'll assume there are enough redundant valves that at least one will always work.

> is it unrealistic for onboard pressurized tanks to keep up with escaping air while outside is getting pressurized?

It depends on the size of the hole. A bullet hole for an average train car size would take hours to become deadly and could easily be corrected by onboard air (depending on how much air is onboard), but a gun isn't going to cause a bullet sized hole. It is quite violent. Something like a catastrophic door failure, or derailment, would deplete the oxygen in less than a second. Basically, the inverse of oceangate; instead of everyone imploding, everyone would explode. Since I also suspect there will be valves on the vessel to handle releasing small amounts of gas enroute (to allow adjusting internal pressures to match destination atmospheric pressures), this could also get stuck open.

I suspect, if anyone were to actually do this, they would go for low pressure (like high altitude) instead of a vacuum. The speed of sound is so high, they could easily reach it in the tunnel. Further, people just need oxygen masks instead of dying a horrible death.

Nobody has mentioned this while following along with all the US hyperloop failures, so it is clear nobody has really tried engineering this thing, IMHO, and why I said my original comment about it. If someone were actually engineering the system, these are all pretty obvious things. As described in the original 1800's systems and by Elon, it is an impossible system. I used to think about this thing all the time in the '90s, so maybe I've thought too much about it.

I'm also curious about other issues, like maintaining low atmosphere or a vacuum (these were the key failures in older attempts in the late 1800's) in the tunnel in an energy efficient way. If it can't be kept, things will deteriorate at an accelerated rate, introducing catastrophic failures early in the system lifetime. There is also maintenance and inspections to consider. Not to mention that underground is already dealing with increased pressure from the earth, it also has to support it while maintaining a vacuum. I suspect above-ground tubes are probably far cheaper to build and maintain, but at that point, you might as well build a train.

Since moving to Europe, I can go pretty much anywhere in Europe in a day. Heck, I can get on a train this evening, sleep in a bed on the train, and wake up on the other side of Europe tomorrow morning for breakfast, for a little more than the cost of an average hotel room. Trains are great, well understood, and pretty fast. The problem the US has (as seen with the California high speed rail), is that they 'want it to be all US based' instead of hiring experts from across the ocean who work on these things every day. The US has no experience building high speed networks, which is part of the reason the hyperloop even has a chance at getting money. It's a collaborative Dunning-Kruger effect.

I think if the US can get to the point where they can develop high speed networks, in general, then stepping up to something like the hyperloop is a good idea. Other nations are still working on the hyperloop and they are making good progress, but I'm not as familiar with their details.

[incrudible]

> The same problem exists underground, the weakest points being the stations themselves which can be bombed.

Few if any modes of transportation are safe when bombs come into play.

[withinboredom]

Blowing up an empty train station doesn't kill everyone on a train.

[incrudible]

...which is why they don't bomb empty train stations. I'm not saying it's just like a train.

[milo256]

Huh? In what world is a hyperloop going maybe 700mph comparable to a spacecraft reentering from orbit at 17,000mph? Also, maybe there's something I'm missing but spacecraft can and do renter from orbit intact, thus proving that this problem is solvable even when the forces at play are orders of magnitude greater. Apply your safety argument to passenger airliners or even ordinary trains and you'll see that they are also "impossible to make safety guarantees" for.

[withinboredom]

> In what world is a hyperloop going maybe 700mph comparable to a spacecraft reentering from orbit at 17,000mph?

In that case, the air can just "go around" the space craft. Try pushing down a syringe with the end capped. Bet you can't do it. Now imagine that at 700 mph; you will get a lot of heat and destruction. No heat shielding will save you.

> Apply your safety argument to passenger airliners or even ordinary trains and you'll see that they are also "impossible to make safety guarantees" for.

See sibling comment.

[milo256]

You have a strange idea of what a hyperloop is. nobody says it has to be sealed around the edges like a syringe plunger.