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Living in the Future

Dan Goodchild

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All air would be removed from the tube system to eliminate friction and we are told that human passengers would only feel the G-forces they already experience in a traditional vehicle.

How exactly are they going to bypass physics? I don't remember a lot from science class, but I'm pretty sure that gravity still exists in a vacuum. :unsure:


Edit - I think I get it... the acceleration would be a flat increase over several minutes. I'd guess it'd take around 10 minutes to get the module moving to 4000 mph w/out putting undue G's on the passengers.



A few other issues I see:

  • I doubt it'll end up being as cheap as they claim b/c they'll need tons of space to load and unload each tube. Pretty much an airport's worth of space.
  • The first time some drunk-driver crashes into a support pole there's going to be issues. If some kind of safety system doesn't stop every car in that tube at that split second, at the exact same speed, there'll be a crash and casualties.
  • And if they do all stop instantaneously, what's the effect on the human body of going from 4000 to 0 in a split second. I'd imagine that your safety harness would just cut you in half.
  • And what about the effects of weather on the tubes? I'd expect that they'd expand and contract during extremes.
Edited by Chrome
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4,000 mph in a maglev capsule in a single, continent-wide hope-it's-flawless unleaking vacuum tube?


You first.


I'd prefer George Jetson's vacuum tube transport system. For that matter (like Chrome) I want one of those flying cars...



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Edit - I think I get it... the acceleration would be a flat increase over several minutes. I'd guess it'd take around 10 minutes to get the module moving to 4000 mph w/out putting undue G's on the passengers.

For fun:

1 mph = 0.5 m/s, so this is 2000 m/s or so.

Sports car 0-60 mph in 6 sec is 30 m/s acceleration in 6 s or 5 m/s/s (0.5 g).

At that rate, 0-4000 mph takes 400 s (7 minutes) and covers some 400 km (250 mi).

Then you can sit at a steady speed for about 40 minutes, covering another 2700 mi.

Then decelerate at 0.5 g (gentle relative to cars) to a stop.

3200 miles in 54 minutes at sports car accelerations.


If you kept to only 0.25 g (0-60 in 12 sec), acceleration would take 800 s (13 minutes) and cover 500 mi. With 33 minutes of cruise and then deceleration, this is 3200 miles in 59 minutes.

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SaintRigger, on 15 Jul 2013 - 2:52 PM, said:

Except maybe emergency stopping - I'm curious about that part.


4000 MPH leaves a hell of a skid.

200km at 1g, 20km at a not-really-survivable 10g. There is no emergency stopping in any traditional sense, but with a signal system (like on existing trains) they could stop within a hundred miles or so with a few minutes notice.


The bigger problem may be energy dissipation. The ends of the line are going to need to be heavily built so that the magnets can deal with the reaction force from acceleration/deceleration. Unless the system is similarly built throughout, the magnets in the middle may not be sufficiently anchored to stop the train.


[400t of train (small TGV) at 2000 m/s is a kinetic energy just under 1 TJ. Dissipating that over 200km, you get something like 5 MJ per meter -- roughly a side-by-side line of tractor-trailers crashing into the magnets at highway speed. (Wikipedia claims 1 MJ is 2 tonnes at 72 mph, so a 3-meter-wide 36 tonne truck would produce 5 MJ/m impact at about 50 mph.) That sort of structure seems doable, but will require a fair bit of maintenance and monitoring.]

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I think he's overhyping it. It doesn't need to be continent wide and 4000 mph to be useful.


LA to SF or NYC to Washington DC at 750mph would be enough to create radical changes in thinking. For that matter, Denver to the major ski areas at 350mph would be quite useful as well.

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