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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. |
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The Next Best Thing to a Space Elevator
accelerates it to 16,000 miles per hour.
Maybe ok for some hardware but not for fleshware. |
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The Next Best Thing to a Space Elevator
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 |
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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. |
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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 |
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The Next Best Thing to a Space Elevator
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. |
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The Next Best Thing to a Space Elevator
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
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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
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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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