OT: Speed of vehicle in vacuum

e

to

t,

uld

e

of

lding

s)

Too late:

And nobody wants to be accused of copying the Swiss.

Mark L. Fergerson

e

to

t,

uld

e

of

lding

s)

It's been proposed. Better still, don't bother using any power at all, just show up at your destination (anywhere on the planet) in 2.9 minutes.

Other interesting vacuum options include a very tall pipe (not necessarily a bean stalk, it only has to penetrate most of the atmosphere), with the inside pumped out. Put your maglev stuff inside, oriented vertically, and blast off into space. Heck, it's already proven technology (sans vacuum) on many roller coasters. It just has to keep going another few ten thousand feet.

Tim

ike

y to

d)

n

at,

se

would

rse

od of

uilding

I

ays)

or this

:)

-Lasse

No more science fiction than AGW.

/:)

Just build a 10-15 mile long LIM going up the side of Everest or K-2, and evacuate it. Accelerate your cargo pod at, say, 10G and it could reach orbital velocity at 35,000 ft. ;-) (somebody ambitious will have to do the numbers for me; I'm way too lazy.)

Power it with off-the-shelf nuke plants - you'll need some substantial vacuum pumps!

Cheers! Rich

Yes, it's plausible from an engineering pov, but the ~30G deacceleration when the vehicle exits the tube would probably kill a human being unless it's significantly compromised in load carrying capacity. Cargo would be a better use. Existing designs of ablative heat shields (developed to protect nuclear warheads) would work on the way up too. Optimum location would be near the equator.

The ultimate constraint is that making the tubes follow the earth's curvature means centrifugal force countering gravity. At orbital velocity (8km/s), passengers would be weightless; at twice orbital velocity, you would have 1g with "down" being up (i.e. skyward).

So you would want the seats to be able to pivot. Once you start picking up speed, you compensate for the reduced gravity with increased forward acceleration. At orbital velocity, you would have 1g forward acceleration, with "down" toward the rear of the train. At twice orbital velocity, everyone would be upside down. Deceleration would peak at 1g, with "down" being toward the front of the train.

You can increase the total "apparent gravity" slightly above 1g, as the journey times would be quite short (at twice orbital velocity, you can circumnavigate the globe in 45 minutes).

Particularly if you push it to twice orbital speed ;)

E = (1/2).m.v^2.

At v=16000m/s, E=256MJ/kg. For comparison, TNT has 4.6MJ/kg and Dynamite

7.5MJ/kg. An average 86.6kg US male would have ~22GJ of kinetic energy, or around 5.3 kilotons TNT-equivalent.

Not really something you'd want as a lowest-bidder, fake-the-xrays project.

You probably *wouldn't* want to bury this; I suspect that an above-ground structure would be easier to make earthquake-proof.

Indeed. In a vacuum, the only per-mile energy cost is down to inefficiencies, so it's really a question of how hard you can make the vacuum.

There have been guys at MIT and other places that have devoted much of their careers to promoting and researching evacuated tunnel trains. I heard a talk by one of them more than a decade ago, it was VERY interesting. There is no technological problem to building these, starting today. The cost of such a system, however, would be quite high. It is a big tunnel project spanning the entire US, for instance! So, each coast-coast tunnel would cost, I'm just taking a WAG, hundreds of billions of $. Safety is certainly a concern, but not insurmountable. You need some kind of radar system to detect major failure of the tunnel from miles ahead, but just laying a grid of the appropriate materials in the walls of the tunnel should allow such a radar to work by making the tunnel into a huge waveguide. People now travel everyday in an environment that would kill them in a couple minutes, namely 40,000 foot altitudes. So, a hermetic craft with a life support system inside, and a way to repressurize the tunnel in case of an emergency should do. Some kind of a rescue vehicle which could travel in either evacuated or air-filled tunnels to get the people out and tow the craft back to a station would be needed.

I'm not sure we could afford such a system right now. It WOULD be good to try building such a demo system, however, and start thinking about how to pay for such a network. One good point is it will save a HUGE amount of energy and carbon release. Planes waste a HUGE amount of energy rising out of the atmosphere and then waste it all descending, not to mention pushing all that air aside at 400+ MPH. The vacuum trains could mostly passively coast from station to station, and the linear rail drive could be used to slow the train as it approaches the station, recovering the acceleration energy and feeding it back into the grid. To keep from smashing people, there would need to be miles of linear rail drive at each station, and this would cost a bundle, too.

I suspect the aircraft industries would resist a move to such a system, but it could be pointed out that they know many of the technologies that would have to be built into such craft. Especially pressurized, lightweight vehicles with life support equipment on board. Anyway, I've never heard of anybody outside these research groups that have been serious about putting such a system into place. I think you'd need a demo project better than firing ping-pong balls across a football field through plastic pipe before anybody would get serious about funding anything.

Jon