The issue I would most like to see progress on is thermal expansion of the the tube. The best solution I have heard is slip joints at the stations but if we're talking miles of slip, I still have a hard time imagining how that would work.
This. Thermal expansion is the show-stopper. Unless and until they solve this problem (and I don't see any practical solution) everything else is moot.
Thermal expansion is also a well known property and something that is dealt with in buildings and structures all the time. It would be a challenge, I agree, but I don't think it will be an intractable one.
There's 2-3 orders of magnitude difference in the scale of ordinary structures and the scale of the hyperloop. There may be a solution, but so far AFAICT no one has actually come up with even a plausible-sounding story. You can't simply say, well, we've solved the problem for small structures so surely we'll be able to solve it for larger ones.
Oh, so now we not only have hundreds of miles of a near-vacuum being maintained... but also hundreds of miles of a near-vacuum being maintained at a specific temperature.
And for the remaining bit of expansion it might be
possible to let the pipes slide upon/inside the pillars
and make even the terminals moveable.
So you want a hundreds-of-miles long vacuum sealed tube that is composed of movable, sliding joints.
Please tell me, what kind of magical sliding joints are you familiar with that are cheap to produce and also able to hold a near-perfect vacuum?
