Depends on the train-to-tunnel area ratio surely? If it's a close fit like the London underground you'll get a lot more drag on a train at 100k feet than you would on a plan at 100k feet.
Commercial aircraft fly at ~30,000 feet which is ~30% atm vs ~1% atm at 100,000 feet. That’s edge of space territory, but sill a long way from LHC style vacuums.
PS: In terms of force it makes little difference as you go to ever lower fractions, but it’s much harder to maintain and pump down the pressure as you keep going lower.
I think they were referring to the fact the air has to move out of the way, and in a tunnel there's less space for the air to move to, thus the drag is higher especially if the cross section of the vehicle is near the cross section of the tunnel.
It’s something to consider, but you need actual numbers to do so. Are we taking 1/3 Atmospheric pressure and 3 inches of clearance vs 1/300th atmospheric pressure and 3 feet of clearance.
Really, nobody is going to build a system where this is a significant issue past the design stage. So, IMO it’s a consideration but a non issue.
You're making a good point, but: What's the effect of leakage in both systems? And don't you need a bit larger pipes for a hyperloop? Other than that I do think the tech is applicable.
It’s mostly a question of cost. High pressure systems are only economic if they transport far more material than they leak, but some minor leaks are fairly trivial. If you talking coarse aka 7,600 micron aka 7.6 torr aka 1% atmospheric pressure you gain most of the value moving a train through an evacuated tube while still being able to use cheap and very fast pump systems to deal is lots of slow leaks. Making that kind of a vaccum tube even easier to maintain.
The LHC however deals with high vacuume becase they need particles to travel hundreds of miles without encountering any atmospheric particles. That would let trains reach orbital velocity without issue, but would be horrifically expensive.
Basicly 100% to 1% vacuume is considered rough/coarse and it cheap. 1% to 1 micron is the middle ground which is increasingly difficult but still not that bad. Under 1 micron aka High vacuume is expensive and mostly the realm of science experiments.
According to the cern website it is actually 50km but on a much smaller pipe. The total volume 15000 cubic meter. For a 11 feet wide tunnel it would be about 1.7 km long.
So the tunnel the LHC is in has a circumference of 26.7 km. But the LHC has two parallel beam lines running in opposite directions. I assume that’s where the discrepancy between our numbers came from. But both beam lines are in the same vacuum vessel.
Keeping a vacuum over a length of hundreds of km is pretty hard, and in fact, has never been done.