"Robert J. Bradbury" wrote:
>
> Hal wrote:
>
> > And for long distances, the problem is the necessary tunneling depth.
> > A train from NY to LA would be over 250 miles deep at the center.
> > The deepest hole which has ever been dug was less than 10 miles
> > deep, and that was a massive effort drilling straight down.
>
> Its far worse than that, as you go deeper it gets much warmer.
> I believe the deepest mines now have problems with plastic
> deformation of the rocks and explosions where the pressure
> can expel weakly bonded rocks. So you have to line the tunnel
> with a strong material.
You also cannot go beyond the crustal lithosphere in depth. Once you hit
the zone between the crust and the outer mantle, you are dealing with
molten rock. The NY to LA route also has to deal with upwellings,
especially the major western US upwelling that peaks in the Yellowstone
area, but is actually a bit of a ridge from north to south that is
between 20-50 km below the surface. You would need VERY active cooling
to establish a hardened tube through this zone and maintain it. Needless
to say, it would be an interesting terrorism target to destroy.
Geological history shows that this upwelling has flooded most of the
western US with lava at different periods. Since we got into this
discussion, I think, as an alternative to the threat of using aircraft
as terrorist weapons, I think this kinda rules it out.
This sort of system may work fine on the moon, where there are no
tectonics of any consequence, but I think that any such tube system
would have to remain pretty close to the surface on earth, using
geothermal power generated to overcome frictional losses, either from
rolling on track or via magnetic levitation.
You would also have to deal with drag from vacuum pressures. Since you
can never produce a perfect vacuum, there will be some gas within the
evacuated tube that will compress in front of a train capsule and expand
behind it, thus producing a drag on the system.
This archive was generated by hypermail 2b30 : Fri Oct 12 2001 - 14:40:57 MDT