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« If You Prick Me, Do I Not Bleed? | Main | Disaster »

A Space Elevator Blog

Really. Boy, talk about specializing.

Posted by Rand Simberg at October 18, 2003 12:33 PM
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I hope they have a lot to report on in the next few years.

Posted by B.Brewer at October 18, 2003 01:17 PM

I'm curious about something. How does the space elevator concept compare to building a linear accelerator large enough to launch payloads? Is that comparing apples to apples, or would each be useful for different purposes?

Posted by Alan K. Henderson at October 18, 2003 10:38 PM

They are starting up big. Single-stage-to-tether would be much easier sell. Like the one outlined on

Posted by at October 19, 2003 04:05 AM

Alan: an em-gun launcher and a space elevator are totally different animals. The latter can be used to launch anything, while the former can only launch payloads that can withstand several hundred to several thousand Gs of acceleration. The primary barrier for the former is the materials-engineering challenge (which I believe can be overcome, sooner or later), while the primary barrier for the latter is the environmental impact (which I believe cannot be overcome). The payloads of an em-gun launcher would have to exit the barrel at roughly mach 27; the resulting sonic boom would likely kill anything with eardrums over an area of hundreds of square miles. About the only plausible place to conduct such launches would be Antarctica, which doesn't result in the most useful of orbits.

Posted by Nathan Koren at October 19, 2003 11:48 PM

Heinlein may have been right about building rail guns on the Moon. No sonic boom problem there, and only one-sixth gee. Sound would travel through the crust - would that present a problem for lunar colonists?

I've heard that a rail gun could be suitable for (survivable) human launch if it were built long enough. Assuming that the launch site is on the equator in the Ecuadoran Andes (and not without seismograph-triggered shutoff switches for that tectonically active location), how far east would the rail gun have to extend?

Posted by Alan K. Henderson at October 21, 2003 12:03 AM

With apologies to Rand for diverting the thread, I'll have a post answering that question later today.

Posted by Jay Manifold at October 21, 2003 09:13 AM

It's up. Graze on over.

Posted by Jay Manifold at October 21, 2003 12:40 PM

Alan, it's high school physics.


Desired V=8000 m/sec
Assume a=100 m/sec^2 (a little over 10 g)

Then t=80 sec
d=100 * 80 * 80 / 2 = 80,000 m = 80 km

Now, 10 g over 80 seconds is survivable, but can be harmful. With 5 g, the rail will be 4 times longer - 320 km.

Posted by Ilya at October 22, 2003 09:20 AM

With 5 g, the rail will be 4 times longer - 320 km.
Your first calculation is correct, but this one is large by a factor of 2.

If you solve v = at for t and plug that into d = (at^2)/2 you'll find that

a = (v^2)/2d and

d = (v^2)/2a;

the final velocity is the squared term, while acceleration and distance are both linear.

Posted by Troy at October 22, 2003 10:47 PM

...actually, I should have said "reciprocal" instead of "linear". :-/

Posted by Troy at October 22, 2003 10:48 PM

Can anybody help!
Trying to find out if a standard .45 caliber automatic pistol will actually fire / work on the moon??
thank you for your time.

Posted by scotty at January 7, 2004 03:51 PM

Can anybody help!
Trying to find out if a standard .45 caliber automatic pistol will actually fire / work on the moon??
thank you for your time.

Posted by Scotty at January 7, 2004 03:52 PM

Sure a .45 caliber pistol will work on the moon. Some people thing that you need oxygen for a gun to fire, but that's not true. Everything you need for the bullet to go bang is inside the bullet, no need to add air. The smokeless powder used in bullets detonates rather than combusts. There are a couple of things to keep in mind however. If the pistol is left in the cold too long the lubricants will freeze and the gun will jam up. (This happens even on earth in very cold conditions.) Second, if the gun is left out in sun the lubricants will vapourize and primer in the bullets might get hot enough to go off in the gun without the trigger being pulled, similar to when bullets are thrown in a hot fire.

P.S. In a shamless, self-promoting plug, I will mention that I've written on problems with building a space elevator in my own blog which can be reached by the URL below.

Posted by Ronald Brak at October 2, 2005 07:20 PM

D'oh! I just replied to a comment that's nearly a year old! Oh well, maybe Scotty checks every week or something to see if anyone's answered his question.

Posted by Ronald Brak at October 2, 2005 07:47 PM

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