🚀 go-pugleaf

Recently Scientific American ran a short article on 'evacuated
maglev', or 'e-mag', which means putting trains in a tube,
evacuating the tube, and then using magnetic levitation to propel
them.

As rocket pioneer Robert Goddard pointed out in 1909, also in
Scientific American, the lack of both aerodynamic and mechanical
friction allows even small rates of acceleration to accumulate to
very substantial speeds.  This makes e-mag the ideal system
for long-range transportation.

For example, an automobile accelerating at 1 ft/sec/sec would
require 40 seconds to reach 60 mph.  Not many owners would
tolerate an acceleration this sluggish, but if the car could keep
going at that rate it would be travelling at 180 mph after three
minutes, and at 3600 m/h after an hour.  A train travelling at
this acceleration would cover 1 mile in 100 seconds; a hundred
miles in seventeen minutes; and ten thousand miles in just under
three hours.  It would circle the globe in 4.5 hours.  Of course
faster accelerations are available -- a powerful car accelerates
at 6 ft/sec^2 -- but there hardly seems to be any point.

An e-mag train would never spend any time running at a constant
speed -- it would always be either accelerating or decelerating.
The limits are set by passenger comfort, which presumably are
symmetrical with regards to forward and backward acceleration, so
that a train would spend the same amount of time in positive and
negative acceleration.  Since the distance between two ends of a
terrestrial diameter, as measured on the surface, is about 12,400
miles, the longest point-to-point run any e-mag train is likely
to have is 6,200 miles.  (It would take 2 hours and fifteen
minutes to reach this point and pass it at a speed of 5500 m/h.)
In theory these trains could go a lot faster, but they seem to
have run out of places to go.

However, given a great circle tube, the train could run around
the globe repeatedly, building up speed to even higher levels.
As it approached orbital velocity the passengers would feel
lighter and lighter, until, after 7.3 hours of steady 1 f/s^2
acceleration and 67,000 miles of travel the train would attain
orbital speed -- 18,000 mph.  At this point the passengers and
contents of the train would be in free fail.

In other words, it is perfectly possible in theory to build a
gravity free environment underground. One can imagine free fall
theme parks, health spas, movie sets, manufacturing facilities,
hospital units, and the like.  The problem is the upfront costs.
I guessestimate building a great circle e-mag with contemporary
technology might cost a trillion dollars.  Even if technological
improvements and advantages of scale bring that cost down by
*two* orders of magnitude, it is hard to see the facility
competing with NASA, unless the upfront costs can be offloaded
onto some other function, like defense.

Free associations invited.