Hey! Ret, thanks for joining in. I’m no engineer, but I have researched this quite a bit and, quite frankly, was initially hopeful that something like this was possible, though the skeptic in me started to question of few things and my opening post was a little bit of what I uncovered.
So let me address your points as best I can…
Vacuums definitely wouldn’t transfer heat through the tube, but wouldn’t do anything to prevent uneven heating on the outside.
Here is a pic of the scaled-down prototype. It was about 1000m (1km)’ long and about 1/2 the diameter of the planned full-scale version.
Now here are a couple of thermal imaging pics taken on an average 75 degrees F day:
Here is a shot of the bottom where the temp near the bottom was about 66F
And here is a shot of the same area close to the top where the temps near the top reach about 86F (the pic shows 28C)
Now, obviously, the gradient between the top and the bottom is about 14F. now given the expansion properties of steel, given the thermal gradient, in this case, the top of the tube over 1km would stretch about 4" longer than the bottom. Probably not even noticeable. However, 381miles long and the difference will be about 300’ (though again, that’s just a 14F difference between the top and bottom).
Not sure I understand this…?
If the passenger module is traveling at 700mph (150mph faster than a 737), a shift of just a few inches would likely be felt as several G’s of force. I mean, it’s not like a passenger plane where the wings act like springs and absorb most of the shock when buffeted by pockets of dense air. The car will be moving through a steel tube.
Perhaps, this I’m really not sure of…But, I would argue that a 381-mile long tube, if it had escape doors, what, every 100 yards would mean 6705 doors and 6705 chances for leaks? I mean a plane might have 2-3 doors over it’s 100’ length?
The other problem is that passengers would be a vacuum tube. Unless the entire tube was pressurized (or it could be sealed up in separate sections) and smaller sections pressurized, you wouldn’t be able to open the doors anyway.
It’s not that this problem cannot be overcome, it’s just that the simplicity of the idea is getting increasingly more complex and expensive.
Presumably, the passenger “cars” would be light, so they could float on the mag-lev rail. With almost no air in the tube, the car wouldn’t have to be built like a plane as the car would’t experience air friction. If it flew at 700 miles an hour into a pocket of air, it would be like driving a car into a pool at high speed. Compared to the vacuum, air would be incredibly dense.
Obviously a 1/2" hole created by something the size of a .50 caliber round wouldn’t lead to a catastrophic failure. I think we can say that sensors in the tube would detect changes in pressure and the cars in the tube would stop (though at 700mph one would think that a safe stop would take several miles). So, you may be right, as long as there wasn’t a car near the breach of a newly created bullet hole, the cars could be brought to a stop.
However, a catastrophic failure, say from an explosive could potentially kill everyone in the tube, or at the very least injure everyone. Remember it’s a vacuum. If the tube were breached air would rush in at extremely high speed to fill the void all the way down the length of the tube, in both directions from the breach. Given the cars would fill the tube, they would likely be pushed into each other by incoming air.
The cars wouldn’t even have to be moving. The air rushing in would, and I just guess now because I really don’t know, but I’d guess that air would travel down the vacuum tube at incredible speed. Sort of like water rushing into a submarine deep underwater.
Perhaps, we’ve solved more difficult technical challenges as humans…However, I think you underestimate the incredible pressure that would exist in a tube of that size with no air in it…
This is what happens when the atmosphere pushes down on a railroad car.
Again, neither of us are engineers, but given the research I’ve done, I can’t imagine it would be possible given a tube of this size, temperature gradients involved and the precision fit necessary to maintain a vacuum.
It would be one thing if we were talking about a tube 1000m long tube. That would be hard. But LA to SF is 613,000m!
Again, air rushing in would likely push all the cars in the tube towards each end causing collisions. If the cars become stuck (or held in place with braking systems, and there were air on one side and a vacuum on the other, air squeezed past the cars would likely be rushing so fast it would tear the cars apart.
Any engineers here?
What do you think, am I wrong?