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The Next Best Thing to a Space Elevator



 
 
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  #1  
Old December 8th 10, 10:35 AM posted to sci.space.policy
Quadibloc
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Default The Next Best Thing to a Space Elevator

Well, I'm glad that my speculation that a railgun, even on Earth, is a
useful step in obtaining very cheap access to space seems to have some
validity, as the same idea is being studied by those who should know
what they're doing:

http://www.nasa.gov/topics/technolog...tallaunch.html

This news item dates from September.

The scheme proposed, though, appears to involve the railgun-assisted
launch of an aircraft, which will then launch a rocket from a high
altitude. It is not clear to me that a railgun will really benefit an
aircraft that much, since aircraft are already much more economical
vehicles than space rockets. But then, a railgun that accelerates its
payload to 600 miles per hour is much more modest than one that
accelerates it to 16,000 miles per hour.
  #2  
Old December 9th 10, 07:30 AM posted to sci.space.policy
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accelerates it to 16,000 miles per hour.

Maybe ok for some hardware but not for fleshware.
  #3  
Old December 9th 10, 08:48 AM posted to sci.space.policy
Quadibloc
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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.

John Savard
  #4  
Old December 10th 10, 11:45 PM posted to sci.space.policy
Dr J R Stockton[_92_]
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Default The Next Best Thing to a Space Elevator

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;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
  #5  
Old December 11th 10, 02:47 AM posted to sci.space.policy
Quadibloc
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Default The Next Best Thing to a Space Elevator

On Dec 10, 3:45*pm, Dr J R Stockton
wrote:

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.


Ah. So 10 degrees of longitude will do at three G, based on this and
your later statement. I would have thought time was inversely
proportional to acceleration, and distance is proportional to time
squared... ah, yes, but times the acceleration, so that cancels out
one factor of the time.

John Savard
  #6  
Old December 11th 10, 02:23 PM posted to sci.space.policy
Ian Stirling[_2_]
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Quadibloc wrote:
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


There has been research done in the 60s on maximum that 'motivated
voulenteers' can take.
It's coincidentally around 9000m/s delta-v over a range from 15G-25G.

This is prone, immersed in fluid IIRC, but the link I had has gone
dead.

They basically centrifuged people at constant high G, until they tapped
out.


  #8  
Old December 14th 10, 07:51 AM posted to sci.space.policy
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On Dec 8, 11:48*pm, Quadibloc wrote:
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.

John Savard


On the bright side such set ups would be shorter on Mars or
the Moon. Of course, such a set up would require a industrial
base on either I'd think.

Any chance to use a mountain range as the range? I suppose
Asia would the only place of it?

Given that astronauts survive rocket shots I think shorter
systems around 200 miles maybe possible. Provided
they can take the turn as they start to go more upwards.

coffee is ready....................Trig
  #9  
Old December 14th 10, 03:41 PM posted to sci.space.policy
Ian Stirling[_2_]
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Default The Next Best Thing to a Space Elevator

Ian Stirling wrote:
snip
No - fighter pilots GLOC at around 10g - in fighter aircraft seats.
Prone, it takes a bit more.


Also - in principle - you don't actually have to be concious to be
launched into space.
(though I question if that's a good idea)
  #10  
Old December 14th 10, 07:12 PM posted to sci.space.policy
Pat Flannery
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Default The Next Best Thing to a Space Elevator

On 12/14/2010 6:41 AM, Ian Stirling wrote:
Ian wrote:
snip
No - fighter pilots GLOC at around 10g - in fighter aircraft seats.
Prone, it takes a bit more.


Also - in principle - you don't actually have to be concious to be
launched into space.
(though I question if that's a good idea)



Really odd weapon design with prone pilot pulling 20 g's:
http://www.luft46.com/bv/bvrmist.html
Brought to you by Blohm und Voss, home of innovative aircraft design:
http://texasbestgrok.mu.nu/archives/062630.php

Pat
 




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