[jmyeet]

Vacuum travel in a a tube does actually make sense. It may not be viable (yet?) but the idea is sound.

A big problem is a breach in your vacuum. Keeping the atmosphere out is expensive.

But what if where you’re building it has no atmosphere and is geologically stable or dead? Then a lot of problems go away. You don’t even need a tunnel necessarily.

Yet another reason why colonizing the Moon makes 1000x more sense than the romantic pipe dream of the red planet.

[mstipetic]

Colonizing the moon makes sense because you can easily build hyperloop on it?

[moffkalast]

If you have a helium 3 reactor, yes.

[parasense]

> Vacuum travel in a a tube does actually make sense. It may not be viable (yet?) but the idea is sound.

I'm not sure the idea will be viable, ever. Too many problems, not enough rewards.

For example, the problem of a vacuum tube developing a leak. The leak would start an implosion, which then propagates down both directions of the tube at mach-1 speed of sound. The implosion would resemble the continuous crushing of a soda can down the entire length of tube. The outside pressure at sea level compared to the inside (lack of) pressure is too great to be safe for passengers or cargo.

The above problem could in theory be solved using air locks spaced apart to have a chance to mitigate the destruction to a few kilometres where the leak happened. But the idea is not very feasible, the air-locked segments would be several kilometres long, enough to slow a transport capsule to a safe halt, yet long enough to get ahead of the mach-1 speed of implosion. High speed sensor networks would have to cover the the hyper-loop ad infinium.

And don't get me started on material science, in particular thermal expansion of steel. The only way to deal with thermal expansion is by using expansion joins. The problem with expansion joints, see the above part about leaks. The entire track of (above ground) tubing would have to deal with significant expansion/contraction. Like for Dallas <--> Austin the expansion would be well in excess of ~100's of ft.

Then comes the energy requirements to pull and maintain a hard vacuum in very long & wide tubes. The closest thing that comes to mind is the Large Hadron Collider, but that pulls a vacuum by cooling the narrow tube down to cryogenic temps... it's not the same. Hyper-loop would require HUGE amounts of energy to maintain the vacuum. It would be more energy put in than profit that comes out, unless of course the hyperloop is transporting some kind of high value merchandise like kilos of cocaine or whatever. The economics simply isn't there, the engineering isn't there, it's pretty much a terrible idea.

The only good argument for the Hyperloop is a logical fallacy, called "argument from authority". Put another way, the argument goes: since Elon Musk is so amazing, we can suspend our disbelief and trust the idea on the sole basis of whatever perceived accolades (the authority) Elon Musk has gained by being a billionaire entrepreneur. Sure, Elon's a cool dude, very smart, tenacious, etc... but that doesn't stop hyperloop from being a terrible idea.

[bluGill]

> The leak would start an implosion

Depends on the materials, but most materials have very different characteristics and won't implode. Leaks are seen in modern vacuum systems all the time, and implosions are rare. I've personally caused a leak in a vacuum system when I disconnected the vacuum hose from the pump - air rushed into the hose and no implosion!

> in particular thermal expansion of steel. The only way to deal with thermal expansion is by using expansion joins

After some thought (I've been thinking about them for a while), there are two solutions: first go far underground where the temperature is stable year round. Put the tube inside something that you do careful HVAC in to ensure there is no temperature changes. Both make the whole system even more insanely expensive than what it already is. I have zero confidence in expansion joints unless we replace them yearly which means the whole is even more insanely expensive.

Throw enough money at it and I think engineers can solve the engineering problems. However nothing changes the fact that it is insanely expensive no matter how you look at it.

The real problem isn't engineering though, the real problem is political: you can't get enough money to build the thing, and if you even try you will discover that nobody will let you build it in their backyard.

[jmyeet]

> The leak would start an implosion

This is a science fiction trope with no basis in reality. The pressure differential is one atmosphere to zero atmospheres which is functionally equivalent to one atmosphere to two atmospheres or what you get from diving 10 meters into the ocean.

The Apollo LEM had a shell that was pretty equivalent to aluminum foil in places. One atmosphere to zero atmospheres is the sort of thing you can plug up with duct tape.

[parasense]

Here is your reality: https://youtu.be/Zz95_VvTxZM

You're not entirely wrong however. There is effectively one atmosphere differential at sea level, but framing the difference that way is at worst intellectual dishonest, or at best a rather naive understanding. In actual reality there is a very long tube, and all the surface area is under pressure. In metric is 10,000 kg per square meter, multiplied by all the square meters down the length of tube. Of course this simplified understanding ignores the weight of the transport capsule inside, which causes a momentary higher differential. And, the hyperloop won't work at sea level, as others have pointed out, it would have to be underground to avoid thermal expansion issues... meaning higher pressure.