> 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.
Then you need to read this:
http://www.leancrew.com/all-this/2013/08/hyperloop/
TL;DR: thermal expansion is a show-stopper.
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.
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.
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
"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."