From: jeff davis (jrd1415@yahoo.com)
Date: Tue Sep 25 2001 - 22:04:32 MDT
--- "Robert J. Bradbury" <bradbury@aeiveos.com> wrote:
"Its far worse than that, as you go deeper it gets
much warmer.
<snip list of daunting technical problems/details>
Though if you do it right, you can produce a lot of
energy this way."
Ballistic subterranean trains (I've always referred to
them as underground tube trains) is one of my favorite
ideas, since 1965. Close to the top of the list. So
I'll likely come back again for a more detailed
treatment. But for now, a few quick comments.
-------------------------------
A terrific treatment of this subject, particularly
regarding the current status of no bull, real world
implemention,
The Evolution of Transport
Jesse H. Ausubel and Cesare Marchetti
can be found at:
http://phe.rockefeller.edu/TIP_transport/
Ausebel and Marchetti are good. I would further
recommend their
Elektron: Electrical Systems in Retrospect and
Prospect
which can be found at:
http://phe.rockefeller.edu/Daedalus/Elektron/
-----------------------------
Getting your propulsion from gravity is a pleasant and
elegant idea, but an unnecessarily limiting. Robert's
obsevation that geothermal energy can be tapped as a
source of energy is a useful idea, but one should
consider whether tunneling to a depth where the temp
is high enough for energy generation is worth the
problems that result from having the tunnel at so
elevated a temp. Perhaps the tunneling technology
could be used to tap geothermal energy, but I think
that because of the depth/temperature/pressure
problem, particularly as it complicates the train
implementation, that the two challenges--tunnels for
trains and tunnels for tapping geothermal energy--
should be considered separate undertakings.
Now consider that the same theory that says you get
all your gravitational energy back, because the
operation is frictionless, also allows you to recover
(linear induction propulsion and then braking with
superconducting components) a substantial fraction of
the energy, above and beyond the gravitational
contribution, that you use for propulsion. Thus the,
IMO, most practical arrangement has the trains
speeding along at a relatively shallow depth.
Amara Graps noted in the last treatment of this idea
that the equations of motion for dropping through the
earth are equations of simple harmonic motion.
Except for a tunnel straight through the axis of the
planet, or circular at some depth in the equatorial
plane, there will be side thrusts on the train. I
have always depicted such a train as a cylinder of
circular cross-section in a tube to match. In this
configuration, if the train is free to rotate in the
tube, and the bottom of the train is heavier than the
top, it will "bank" (rotate in the tube) in response
to side-thrust. Thus, as long as the side-thrust does
not come on too abrubtly, passengers will experience
what feels exclusively like a downward force.
Finally, consider that, as you approach orbital
velocity, the true downward force (not the apparent
downward force if you're banked in response to side
thrust) approaches zero, so that except for
side-thrust you approach weightlessness. Then as you
approach excape velocity, the centripital force on the
train, experienced by the passengers in the inverted
train as "downward" force, gradually increases until,
at escape velocity, it is again one g. Fom one g
downward at zero mph, gradually diminishing to zero g
at 17,500 mph, and thence gradually returning to one g
"downward" (outward actually) at 25,000 mph.
Fun Stuff.
Best, Jeff Davis
"Everything's hard till you know how to do it."
Ray Charles
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