[Geezer (OP)]

Why don't we use super-tubes instead of aircraft? A super-tube is a "tunnel" (although it need not be subterranean) that has most of the air removed from it. Train-like vehicles traveling in the tubes would be accelerated to, say, 1500mph (possibly quite a bit more), and probably coast most of the way to their destination. Of course, I don't think it would make much sense for distances of less than 1000 miles.

The capital cost of something like this would be high, but the long term energy saving and reduction in air pollution would be considerable, not to mention that it would save a lot of time. As most of the friction is eliminated, the only energy consumed is the energy that goes into accelerating the vehicle and its payload, and a large percentage of that could be recovered if the system used regenerative braking.

Has anyone heard of any studies of something along these lines?

[RD]

Gravy Gravity train ...

https://en.wikipedia.org/wiki/Gravity_train

Gravity train journey times would all be the same ... https://en.wikipedia.org/wiki/Gravity_train#Mathematical_considerations

https://en.wikipedia.org/wiki/Vactrain

[Geezer (OP)]

Ah! Yes - the "Vactrain" (although you'd probably want to call it a hoover train in the UK).

Actually, despite what the Wiki page suggests, I don't think they would need to be all that expensive. In the US, the tunnel could be a concrete tube on, or near, the surface, and when you consider how much reinforced concrete goes into building freeways, I don't think it would be all that bad. I think the biggest problem is caused by any change in direction (horizontal or vertical). At the speeds required to make it worthwhile, the 'g' forces would be very large unless the rate of change was very small.

The Wiki article makes no mention of the greatest potential benefit which is the very low energy consumption per mass transported. If it's implemented properly, it operates like a big spring that only needs a relatively small amount of continuous energy to keep it oscillating, and it does not need to use hydrocarbon fuels of any sort.

[CliffordK]

One problem, of course, is that if the train compartments were punctured, it would be lethal within seconds.  It might also be quite lethal with certain tube ruptures.

Would it have some kind of forced compartmentalization so that an accident in one location would not take down the whole system?  Imagine travelling at 1000 MPH, and then hitting an air shockwave caused by a breach somewhere.

Also, I'm not sure that concrete would be impermeable enough for the high vacuum, although perhaps one could cover it with a vinyl or fiberglass or similar.

I believe all current maglev systems are active systems requiring energy input to maintain levitation.  Could one use opposing permanent magnets for levitation, and only use power for fine-tuning the levitation?  Of course, you would then need miles and miles of very powerful rare earth magnets.    Anyway, I'm doubtful that the current generation maglev trails would save a significant amount on energy.

[Geezer (OP)]

Atmospheric pressure is really fairly wimpy, so sealing it should not be such a big deal.

The main advantage is the gigantic savings because of the lack of friction loss. I think the propulsion would have to come from periodic linear induction motors in the track acting on passive conductors on the vehicle. It should be possible to achieve levitation by induction as a result of the vehicle's speed. Wheels of some sort might be OK, but only to get started.

I think you'd want to keep it pretty simple, like only one vehicle (or train of vehicles) in a tube at any time, with the "train" shuttling back and forth between two points only.

The whole idea does sound a but strange, but if we were not used to zipping around in jet aircraft all the time (that really are not all that "zippy") it probably would not strike us as all that strange at all. The development of the jet engine to its current state was probably a lot more difficult than this.

Unless we decide that travel is inappropriate and we are only going to permit "virtual travel", something like this is the next logical choice. Planes are nasty polluters, they consume huge amounts of energy, and economics prevent them from going any faster. The current high speed trains are (believe it or not) not all that much better in terms of energy consumption, and they can't go much faster either without turning into aeroplanes, so if not this, where do we go from here?

[syhprum]

Can you imagine the field day the sercurity inspectors would have when the most minor breech in the sealing of one coach would result in the death of all passengers with no hope of rescue.
If only one train could use the line at a time the cost of a trip would make the Concord seem dirt cheap in comparison.

[imatfaal]

Atmospheric pressure is really fairly wimpy, so sealing it should not be such a big deal.

The main advantage is the gigantic savings because of the lack of friction loss. I think the propulsion would have to come from periodic linear induction motors in the track acting on passive conductors on the vehicle. It should be possible to achieve levitation by induction as a result of the vehicle's speed. Wheels of some sort might be OK, but only to get started.

I think you'd want to keep it pretty simple, like only one vehicle (or train of vehicles) in a tube at any time, with the "train" shuttling back and forth between two points only.

The whole idea does sound a but strange, but if we were not used to zipping around in jet aircraft all the time (that really are not all that "zippy") it probably would not strike us as all that strange at all. The development of the jet engine to its current state was probably a lot more difficult than this.

Unless we decide that travel is inappropriate and we are only going to permit "virtual travel", something like this is the next logical choice. Planes are nasty polluters, they consume huge amounts of energy, and economics prevent them from going any faster. The current high speed trains are (believe it or not) not all that much better in terms of energy consumption, and they can't go much faster either without turning into aeroplanes, so if not this, where do we go from here?

If you hadn't already discussed it in public I would say patent it. 
1. Loss of vacuum in the tunnel would cause air friction and slow train down - but would not be catastrophic
2. Loss of cabin integrity - we already deal with that to an extent on airliners. 
3. You could run freight services that don't even need pressurize cabins - the teamsters would probably put a contract out on you
4.  Dunno how well levitation through forward velocity (I guess you are thinking along the lines of ground effect) will work in a partial vacuum
5.  You would need regular emergency flooding valves to prevent syhprum's no hope of rescue scenario.
6.  Could you work a pneumatic system such that the train is sucked forward by the same action as the air is removed.  I K Brunels first idea for mass transit used the opposite idea - trains were to be pushed by action on a "bung"  by compressed air in a semi sealed tube under the carriage.

What you really need is tunnels that float or are a few hundred feet below the ocean surface and then you can link up world hubs, and importantly the producers and the consumers.  Those hubs are already there and deal with vast numbers of containers every day

[CliffordK]

It all depends on what pressure you run the tubes at.

˝ ATM would not be immediately lethal with rapid decompression.  Would it give a person the bends?  But, it would only give a 50% reduction in wind resistance. 

Going to a lower pressure...

0.01 ATM, and wind resistance would be negligible.  However, a decompression inside the capsule would be far worse than happens in a jet.  Think of decompression in space.  How quickly could you refill the tube with air?  Perhaps within a fraction of a second if it is above ground.  Potentially more difficult, but not impossible to do in a 5000 mile undersea voyage.

Anyway, based on the Wikipedia link, the idea is already ˝ century old.  No sense in re-applying for a patent.

While convenient for moving passengers, such a system might also be able to be used with freight, if it does in fact save energy. 

Oh, also for the undersea, a few miles deep, and the pressures are pretty extreme, it wouldn't be a simple tunnel building.

[Geezer (OP)]

There might be aspects of it that are patentable, but the development time for something like this would exceed the life of the patent, so why bother. I'd rather make it all public so that nobody else can patent it! (Ooooo, I think I just did that.)
 
The cost/utilization argument is nothing like Concord(e?). You have to figure it out on the basis of passenger miles in time. Unlike Concord, there is no particular limit to the number of pasengers carried per vehicle, and the thing that killed Concord was simply the cost of fuel per passenger mile. If I'm right about this, the cost of fuel per pasenger mile is not related to the work done by the "fuel" (electric energy) - it's largely determined by the inefficiency of the conversion from from electric energy into kinetic energy and vice-versa, and those conversions are usually quite efficient.
 
I was thinking the support would have to use some sort of magnetic levitation (superconducting magnets pehaps?) or some sort of inductive repulsion method that I have not quite figured out! Ground effect would mean air pressure, and that means friction, which mucks the whole thing up.
 
I don't think the vacuum thing is such a big safety concern either. It's tricky, and emotionally supercharged, but by no means insurmountable. The "early adopters" might want to wear space-suits if they were worried about it. The way I look at it, it's pretty much the same as getting on an aircraft without a parachute, and we do that all the time because we understand the risks.
 
The idea of using it to shuttle cargo would certainly be a good way to get going. If it worked without incident for a number of years it would ease a lot of the concerns about putting people in it. I think it would be best to stay well away from any sort of underwater version until all the bugs had been worked out with land-based systems.
 
Anyway, as I said, if not this, what else?

[imatfaal]

Anyway, as I said, if not this, what else?

Ships - I like ships.

[Don_1]

I think one of the biggest stumbling blocks would be not so much technical as financial. As said, such a system would only be of use over long distances, say from NY to LA. Would such a route attract sufficient passengers to make it viable. NY to DC, on the other hand, might attract the passengers, but over such a short distance would probably be of no great benefit, since the train probably wouldn’t be able to reach high speed before having to start slowing down.

But, suppose you replace the train with a pod which might carry up to a dozen passengers. With side chutes off the main tube at major towns and cities, a pod might make the system more attractive to passengers and, therefore, more lucrative for the operator.

But there would be one major drawback, you will need two independent tubes, one east – west and one west – east. It might even be necessary to have third tube to enable rescue services to get to a breakdown or accident in the middle of the Arizona desert, just as the Channel Tunnel has an emergency escape bore.

[Geezer (OP)]

If the transit time between the ends is short enough, you only need a single tunnel. The tunnel would be equipped with airlocks and access hatches at frequent intervals so that any section could be returned to atmospheric pressure for maintenance and rescue operations.

[syhprum]

Most of the time consumed in air travel is in getting to the airport sercuity etc once you autualy get on the vehicle it makes little difference whether it travels 200 or 2000mph for trips of up to 300 miles trains or cars are often the quickest.

[Geezer (OP)]

Most of the time consumed in air travel is in getting to the airport sercuity etc once you autualy get on the vehicle it makes little difference whether it travels 200 or 2000mph for trips of up to 300 miles trains or cars are often the quickest.

I think you are quite correct. The US finally seems to be waking up to that reality. Meanwhile, the brilliant planners in our nearest town just decided to start building on the railway line that went right into the center of town. There was once an electric train that ran on that line. I wonder how long it will be before they start bemoaning the fact that they no longer have the right-of-way.

When I was a kid, Glasgow and the surrounding area had a fantastic tram system. The local government ripped it all out in the sixties in the name of "progress".

[syhprum]

When I lived in Hemel Hempstead I had to make frequent trips to Glasgow, I found that I could drive there more quickly than taking the train but the train cost slightly less and there was always the problem with the sloth police.
I well remember the trams an excelent way to travel both in London, Glasgow and Viena.

[Geezer (OP)]

When I lived in Hemel Hempstead I had to make frequent trips to Glasgow, I found that I could drive there more quickly than taking the train but the train cost slightly less and there was always the problem with the sloth police.
I well remember the trams an excelent way to travel both in London, Glasgow and Viena.

Guess what! They are putting them back in Edinburgh. Talk about "short sighted."