Re: ballistic subterranean trains

From: Party of Citizens (
Date: Thu Sep 27 2001 - 23:06:04 MDT

On Thu, 27 Sep 2001, Spike Jones wrote:

> > Spike Jones wrote:
> >
> > > Nowthen, since we are talking about frictionless evacuated tunnels,
> > > an acceptable solution would be to build the tunnels at a constant
> > > depth of about 4.5 km. Such could theoretically be built. After
> > > the car descends to that depth, regardless of the shape of the
> > > path down there under these assumptions, it would be travelling
> > > at about 300 meters/sec, so the trip from anywhere to anywhere
> > > would be at speed about competitive with current airline travel.
> > Party of Citizens wrote: Mag lev trains now travel > 300 mph. How fast
> > would they travel in a
> > vacuum tube? Why 4.5 km deep? Why not on the surface?
> Party it was merely an entertaining mental exercise. We postulated
> an evacuated frictionless tube since it would not need an electromotive
> force to move the train. The train would fall to its destination. I
> chose
> a constant depth of 4.5 km since the train would be going about
> 300 m/sec at that depth, a perfectly arbitrary value for a cruise
> velocity. Of course it is easy to drive a maglev train. But it is
> cool to imagine getting there by gravity. spike

No objection from me. But even if you get your propulsion from gravity,
you still have to keep the craft away from touching the vacuum tube. So
why not use mag lev for that purpose and for propulsion as well? If you
can get it up to V1, orbital velocity, the passengers will experience
weightlessness. On the way to that speed I suppose the g forces will be
formidable. As somebody said it could be practical on the Moon. In that
case I guess you could also use mag lev to launch space craft from the
Moon. Arthur C Clark had a technical paper along those line from the 50's-
a space catapult for the Moon.


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