trc@houca.UUCP (10/28/83)
Does anyone know anything about the idea of using high-powered laser beams to launch space craft from earth? My understanding of it is that the craft would carry a load of water, (or some similar substance) that could be super-heated and expelled. Obviously not as elegant as a space elevator, but I wonder if a space mounted laser system might not be a good way to take a craft up from some altitude (perhaps transfer it from low-earth orbit). I suspect that this would be primarily used for un-manned cargo ships, at least at first. (Those high-powered lasers can *sting* if they should be mis-aimed slightly!) Note that this might be feasible even if today's lasers couldnt punch all the way to the bottom of the atmosphere. Thus, "star wars" technology is not required. The lasers would be powered by "free" solar power, of course. For a LEO to a geosynchronous orbit, I would think that little more than a modified industrial strength laser and some highly accurate aiming equipment would be needed. (Remember that one of the difficulties with the "star wars" concept is that the intended targets might take evasive action or use protective shielding - something *our* intended targets would presumably not do!) It wouldnt seem to take too many bucks to put up such a sattelite, and then most anything we put up with the shuttle (perhaps even those ETs?) could be boosted on up for little cost. Evenually there might even be a "ferry" craft, from LEO to geosynch. A space station could be built around the laser launcher. This, if feasible, is something that doesnt require the large investment or even as much new technology as a space elevator would require, and so would be a good "stepping stone" into space. Does anyone know enough about rockets and the properties of water, to do some calculating of how much water would be needed to do various things? Some interesting examples would be taking the ETs up from LEO to a secure orbit, taking a craft from earth to LEO, or all the way to a non-decaying orbit. If the beam could punch through the atmosphere, could we power commercial rocket-planes with this technology, at high altitudes? Tom Craver houca!trc
eder@ssc-vax.UUCP (10/28/83)
28 October 1983
Laser propelled rockets have been studied by NASA and aerospace
contractors in the past. For the ground-to-orbit regime, the design is
rather simple in principle (note that a rocket is simple in principle too)
What you have is a block of solid material, such as wax or ice, with some
black material in it (i.e. it absorbs the wavelength the laser operates atihnp4!houxm!hogpc!houti!ariel!vax135!cornell!uw-beaver!uw-june!eli
From: eli@uw-june.UUCP
Newsgroups: net.math
Subject: New question about primes
Message-ID: <694@uw-june>
Date: Fri, 28-Oct-83 17:28:37 EST
Article-I.D.: uw-june.694
Posted: Fri Oct 28 17:28:37 1983
Date-Received: Mon, 31-Oct-83 03:52:04 EST
Organization: U. Washington, Computer Sci
Lines: 12
I was wondering if anyone had a >simple< proof of the following fact,
For all n > 0, there exists a prime, p, such that n <= p <=2n
I already have a rather complicated proof based on the Prime Number
Theorem... I'm looking for an easier one -- possibly based on the sieve
of Aristophenes.
Please mail to me. I will chew, digest and post.
... uw-june!eli
1828
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