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Comment by UnoriginalGuy | Hacker News Reader

I've not read anyone claiming that the Hyperloop is technologically infeasible. It re-uses a lot of known concepts and will likely work.

Most of the concerns I've read are about construction costs, safety (e.g. escaping a stuck hyperloop train), failure modes (e.g. what if the tunnel suddenly floods with air from e.g. an earthquake), practicality (the Hyperloop trains as envisioned don't support wheelchair access, and don't have toilets), and similar civil engineering challenges.

If a hyperloop were designed to transport cargo/mail then I think that would "solve" most of the perceived problems (except maybe construction cost). But transporting people adds a whole new vector of complexity to the concept.

Again the core concepts of the hyperloop are likely sound. The thing would work if we built it. But it doesn't mean it will ever be built and even if it is, that any passengers will ever be able to utilise it commercially.

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The trip is short, short flights have the same issue with restrooms as you aren't allowed to use the restroom while taxi-ing or during takeoff/landing, which can easily pass 30-40 minutes, especially if there is a line to use the restroom after a delayed takeoff.

It is a pod, so wheelchair access will involve stowing the wheelchair, just like a car or seated bus.

Not all wheelchair users can leave the wheelchair for a normal seat though. They can't use cars, but the ADA won't allow the hyperloop to exclude them.

Why does the ADA allow airplanes, then?

Looks like I was wrong- people who can't leave the chair in their own will be lifted out on planes. I should have realized that they don't sleep in their chairs so they must be able to leave them :/ This is a pretty slow operation though - it would be a real challenge to do this without ruining the throughput numbers proposed. In my experience they don't leave the chairs for cars or buses (buses have space for chairs or offer paratransit, they use adapted vans and wheel the chair in instead of a normal size car).

Be serious. If it's an emergency you can of course use the toilet on an airplane.

It's just a safety precaution and have seen it ignored many times before.

The issue with hyperloop is that there are no options if there is an emergency which makes the idea impractical.

> I've not read anyone claiming that the Hyperloop is technologically infeasible

Then you need to read this:

http://www.leancrew.com/all-this/2013/08/hyperloop/

TL;DR: thermal expansion is a show-stopper.

Yes the columns are underdesigned. That's typical of paper designs for elevated railways. Compare fictional drawings of monorails with the many real ones.[1] The Tokyo Haneda monorail has held up well through several earthquakes. Assume the Hyperloop will need comparable sized columns. They're bulkier than the Hyperloop conceptual drawings, but they work.

The expansion joint problem is probably solvable. Take a look at some standard piping expansion joint options.[2] A "bumpless" expansion joint is an unusual requirement, but one could probably be designed. Two tubes slipping over each other with an interior lining of braided mesh might do the job. The SF BART tunnel under the bay has huge rubber expansion joints. It survived the 1989 earthquake with no damage.

The larger Hyperloop design (3.3m diameter) is probably more useful than the little (1.43m diameter) one. The smallest successful bizjet is about 1.5m diameter.

Emergency exits will be a big problem. In practice, some form of emergency access every half mile or so will probably be necessary. Eurotunnel has a cross-passage between the tubes every 375 meters.

[1] http://monorails.org/ [2] http://www.flexicraft.com/

> A "bumpless" expansion joint is an unusual requirement, but one could probably be designed.

Not just bumpless. It also has to be sealed against a large negative pressure differential. Those two requirements together take you into unexplored engineering territory.

> The SF BART tunnel under the bay has huge rubber expansion joints.

Not even remotely comparable. That tunnel is two orders of magnitude shorter than the HL, the walls aren't smooth, they don't have to sustain a vacuum, and the thermal gradients are much smaller underground.

> Two tubes slipping over each other with an interior lining of braided mesh might do the job

And what provides the vacuum seal?

> The expansion joint problem is probably solvable

Sure, but the interesting question is: can it be solved without prohibitive cost. The jury is still very much out on that.

> Emergency exits will be a big problem

Why do you think so? Pressure-sealed doors are a solved problem.

There are vacuum-rated expansion joints.[1][2] They have metal rings integrated into the flexible component to prevent inward collapse.

Interior tube smoothness remains a problem. The Hyperloop air bearings float at only 1mm ± 0.5mm. Even fixed joints with that tight a tolerance are difficult. Anything other than plain tube (access hatches, etc.) will have to present a totally smooth inside. Not impossible, but runs up the costs.

[1] http://www.ethylene.com/flexijoint.php [2] http://www.garlock.com/en/products/style-204-evs

The conclusion of that article actually doesn't seem to be that the Hyperloop is technically infeasible - only that the original spec does have issues, and it glossed over those issues.

"I’m not saying that the problems with Hyperloop can’t be solved. Money, time, and talent can solve any problem that doesn’t involve breaking physical laws, but I wouldn’t put my money, time, or talent in the hands of someone who takes me for a fool."

The biggest problem in my opinion is lack of capacity for the induced demand a working hyperloop would create. A single train can carry the 4-hour capacity of an LA-SF hyperloop.

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