In sci.space.policy message 14e34197-a6ce-4edc-b525-b88b09f76d94@w17g20
00yqh.googlegroups.com, Wed, 8 Dec 2010 23:48:30, Quadibloc
posted:

On Dec 8, 11:30*pm, |"
wrote:

Maybe ok for some hardware but not for fleshware.

It's the degree of acceleration that could be a problem for our frail
mortal flesh - not the velocity reached at the end. 16,000 mph is
orbital velocity (going around the 24,000 mile circumference Earth in
90 minutes), and that will have to be reached eventually. Of course,
to launch people into orbit, that implies a _really long_ railgun. And
it also needs to open to the atmosphere at a high altitude, so that
the air doesn't look like a brick wall to the vessel.

Since gravity is down, and the acceleration is nearly horizontal, 3g
of acceleration plus gravity is felt as about 3.16g (square root of
10) instead of 4g by the passengers. If we suppose that this can be
tolerated by the astronauts and passengers to be transported, this
acceleration of about 30 m/sec^2 would be required to be endured
for... 50 thousand minutes or 833 hours? Either I've made a mistake
somewhere, or this really is quite impractical. The ramp would have to
girdle the Earth several times; I was thinking in terms of one perhaps
400 or 1,000 miles long - a prodigious engineering undertaking, to be
sure, but not one that would be positively ludicrous.

On any spherical homogeneous body, a horizontal acceleration of one
local gee gets you to orbital speed in half a radian and to escape speed
in a full radian. See http://www.merlyn.demon.co.uk/gravity2.htm#OEV.

The distances are inversely proportional to the horizontal acceleration.

You can confirm the order-of-magnitude by watching an Ariane 5 launch
videocast; most of the accelerating, at a rather few gee, is (as can be
seen) done horizontally, and ISTR that there is a sufficient indication
of the horizontal distance covered under power.

Likewise, STS drops its ET well before UK.

Also, the time for a circular orbit depends only on the mean density
below orbital height.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links;
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