Ooh, how I wish I could buy put options on the Hyperloop. Because unless they solve the thermal expansion problem -- and there is no feasible solution on the horizon AFAICT -- they will fail.
I am assuming that you are talking about the thermal expansion of the tubes (ducts ?). A long time ago, the rails making up train tracks used to have gaps every few meters to accommodate thermal expansion (same problem). Modern rails in high speed train tracks are welded into one continuous bar that can be over a kilometer long. The trick is to stretch the rail just enough and then pin it down - kind of like a slightly stretched rubber band. That stretch can accommodate thermal expansion.
That's a good direction to pursue, but CWR (continuous welded rail) segments are only a few kilometers long at most. That, plus the fact that the cross-section of a rail is much less than the cross-section of a hyperloop tube, makes the tensile stress at the ends of the rail small enough that they can be managed by anchoring the ends of the rail to the rail bed.
The tensile stress at the ends of a hyperloop track would be orders of magnitude higher if you tried this approach. I haven't done the math, but I'd suspect you'd need an anchoring system comparable to what you see on large suspension bridge cables, if not more. Not only that, but I suspect you'd start to reach the limits of what steel can structurally sustain. With this solution, you've got a O(100km) long tube that is not only under vacuum but now also under enormous tension. Before this can be considered a viable solution someone needs to do the math on that, and AFAIK no one has.
Hmmyeah, but the result is so-so, it experiences a few troubles in the warmest days of the summer and trains (especially high-speed trains who both need perfect rails and put more strains on them) have to be speed-limited or in a few cases even cancelled.
Isn't space super-cold? I mean, if you pull air out of a tube, the stretched air absorbs calories (–or cools down, which is the principle of a fridge with other chemicals and a liquid/gas transition). So can this effect keep the metal cold?
Space isn't cold. It has very low temperature. These are not the same thing.
Because space has extremely low density thermal radiation doesn't really work very well... it's very hard for a vehicle in a vacuum to dump heat...there is no medium to receive the energy!
> Space isn't cold. It has very low temperature. These are not the same thing.
That's news to me. What do you think "cold" means if not a synonym for "low temperature"?
> Because space has extremely low density thermal radiation doesn't really work very well... it's very hard for a vehicle in a vacuum to dump heat...there is no medium to receive the energy!
No, that's completely wrong. It is very easy to radiate heat into space as long as your radiator is not pointed at the sun. What you can't do is convect heat away, which makes it hard to transfer heat from the hot part of a spacecraft to the cold part. But getting rid of the heat once you've transferred it to a radiator is really easy. In fact, some parts of a spacecraft need heaters to keep them warm if they don't get sun exposure.
Not a good analogy. One of the main Hyperloop points it is to have near vaccum inside the tubes, which will reduce air resistance and allow faster speeds, otherwise it's just a train inside a tube. This means they must be totally sealed, so no gaps allowed.
So... you put in a flexible air tight seal in the tube. It will have to be modular anyway. Doesn't seem that challenging or cost prohibitive. A quick google turns up NASA projects that were looking into flexible airlock seals.
It won't be a complete vacuum though? I mean it doesn't have to be. Even removing 70% 80% of the air would greatly reduce drag. Plus don't they also need safety systems in case of issues so the tube segments can be locked and re-pressurized without damaging the train?
Drag reduction is, I think as important as decreasing the shock wave generated by breaking the local speed of sound. Partial vacuum does both. Not sure how to optimize for cost and reliability of construction vs max sped
Not to mention all of the logistical problems with building and maintaining a low pressure tube.
People think high speed rail is expensive? Wait until you see how expensive Hyperloop is going to be per mile.
PS - And I haven't even touched on safety/evacuation problems with the concept. That quadupled the cost and size of the Eurotunnel for comparison, how can we assume it won't bloat the Hyperloop's size/cost/complexity?
And so it does? However you feel about the executives and history of Hyperloop, I think it's important that companies like this exist and try things like this.
You know what's expensive and was once unfeasible? Strapping thousands of tons of fuel to a rocket and launching it into space. And yet...
> I think it's important that companies like this exist and try things like this.
They're not trying anything at this point, they've raised enough money for at most 5km worth of high-speed tracks (proper 350km/h graded tracks) and no rolling stock.
What about R&D output? Even if the company goes broke, they / their research can be purchased and used in the future. They might only produce new materials that they sell the patents for upon going bankrupt. Their engineers and scientists will develop and learn, and move on to other firms if Hyperloop becomes insolvement, and take that knowledge with them.
But those problems can be solved. Maybe. Even if they're not, the research is important to tell us what does and doesn't work.
We build massive dams to stop rivers and invest billions into complex rockets that need to carefully control explosions in order to get people and cargo into space.
If one company can build a simple 10 ~ 20km tube between two major travel points in some country, it will be an invaluable proof of concept worth way more than the initial investment.
Just because something is hard doesn't me we shouldn't try.
Any problem can be solved with unlimited funds. The question isn't if it is possible, it is how much good can be done with that same money elsewhere (opportunity cost).
For example, one mile of Hyperloop or five miles of conventional high speed rail? One mile of Hyperloop or two miles of Monorail? One mile of Hyperloop or investments into more efficient aircraft?
That's a rather offensive thing to claim. He has actually accomplished a lot and pushed two or three industries forward.
Personally I don't think Musk is a "dummy" as you do, but I do feel sometimes his passion doesn't always address real world civil engineering limitations. The Hyperloop is technically very possible, thus isn't "dumb," it is just building it at scale (and addressing consumer safety, etc) that may be a challenge.
What's unsolvable about it? Every bridge I've ever been on has had a little gap for expansion. Just make a little gap every 5km, cover the outside with rubber that stretches across the two sides, boom, you are done. The cars float on a little air pressure cushion and don't normally use their wheels, so there wouldn't even be a bump.
Could you have an outer tube with concrete and expansion joints, then a membrane on the inside that maintains smoothness but expands/contracts as the tube moves?
Remember, it's not enough to be smooth. You have to be:
1. Smooth (on the inside) and
2. Straight and
3. Strong (enough to bear the stress of having a multi-ton vehicle passing within a few millimeters at 700MPH) and
4. Long (300 miles at least) and
5. Airtight for that entire length, and
6. Cost-effective.
It is that combination of features that no one has ben able to even begin to tell a story about how they would make it work in the face of thermal expansion.
Space shuttles would have similar challenge (actually in reverse) - how to protect sealed air inside a closed cylinder from almost absolute vacuum outside in an environment where heat and cold are extreme; the cylinder being fabricated from overlapping conjoined pieces.
Thanks for sharing. They seem to be convinced about the viability albeit concluding that it may need bigger diameter pipes and the speed would be little slower.
No alarms on thermal expansion, structural integrity etc.
