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Comment by djsumdog | Hacker News Reader

It's important to note that evacuated tubes aren't a new idea. The Hyperloop is a re-branding of Evacuated Tube Transport (ETT) that came about in the .. 80s? I think? I wonder if Musk is licensing the patents from that company or if the Hyperloop division has patented their own tech as being entirely different somehow.

Edit: Looks like Musk did negotiate with the ET3 people back in 2013

https://en.wikipedia.org/wiki/ET3_Global_Alliance#2008–prese...

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Hyperloop is a variation on the Vactrain [1], a concept that goes back a long time. The thing that made Hyperloop different was the notion that you didn't need a hard vacuum in the tube -- the air in a Hyperloop tube will be really thin, but it will be there. The other thing notable about Musk's original proposal was that the cars would float on air bearings rather than a maglev track. I think most if not all of the current experimental Hyperloop systems are using maglev technology because it works better than the air bearings would. If Hyperloop systems adopt hard vacuum in the tubes, then I think you can make the case that Hyperloop is not new, it's just re-branded Vactrain. In reality, I don't know that this distinction will make any big difference.

I personally think we will ultimately see some functional passenger-carrying Hyperloop systems, but I don't know that they will be any more successful than maglev has been to date. I don't think we will see any systems using a hard vacuum (the classic Vactrain), because hard vacuums are, well, really hard to do.

[1] https://en.wikipedia.org/wiki/Vactrain

I'm curious, what's the definition of hard vacuum?

Obviously there will be a few nitrogen molecules bouncing around in there so it seems there must be some arbitrary cutoff.

I worked with electron microscopes back in the day, for that I would say 10^-6 atmospheres. But it probably depends somewhat on your application, I don't think there is a solid definition.

There’s pretty much no such thing as a ‘hard vacuum’ in the real world. Even ultra-high vacuum systems always have particles still floating around (even space has a few hydrogen atoms per cubic metre, while the best vacuums we can produce on earth have a few orders of magnitude more particles).

At 100Pa (according to Wikipedia), the hyperloop is still a bit less than 0.1% of the pressure of the atmosphere, which is still a significant challenge given its size, expansion problems, and the risk of a small impact destroying the whole thing. The amount of energy required to pump down a hyperloop of any reasonable length (which could take days) would be immense.

I think with the expansion and impact risk, the only safe place for a hyperloop would have to be underground. Even then, I think it’s unlikely to ever really be practical.

I mean, evacuated tubes are ultimately a development of atmospheric railways, which date back to the 18th century.

There were definitely lots of proposals to put maglevs in evacuated tubes from not long after large amounts of funding started to pour into maglev design.

Strange that the hyperloop idea is to have tubes above ground, whereas the Boring company is all about tunnelling under cities.

Not that strange. Can't never get enough tubes. Underground, above ground, on mars. Before long we'll be talking about tubes in space; what's hype-er than hyper?

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