Aucbvax.5438 fa.space utzoo!decvax!ucbvax!space Fri Dec 11 03:37:00 1981 SPACE Digest V2 #56 >From OTA@S1-A Fri Dec 11 03:28:28 1981 SPACE Digest Volume 2 : Issue 56 Today's Topics: Shuttle's wings Shuttle's and laser launching system laser launching systems Meteor showers Penthouse, please.. ---------------------------------------------------------------------- Date: 10 December 1981 1040-EST (Thursday) From: David.Smith at CMU-10A (C410DS30) To: space at mit-mc Subject: Shuttle's wings Message-Id: <10DEC81 DS30@CMU-10A 104051> The shuttle's wings are as big as they are because the Air Force won the argument with NASA. The AF wanted the ability to fly up to 1,000 miles cross-range on reentry. This is needed in the event that a shuttle launched into a polar orbit from Vandenberg has to come down after one orbit. ------------------------------ From: BRUC@MIT-ML Date: 12/10/81 11:12:09 Subject: Shuttle's and laser launching system BRUC@MIT-ML 12/10/81 11:12:09 Re: Shuttle's and laser launching system To: Space-Enthusiasts at MIT-MC First, the research on the laser launching system was done by Avco Everett Research Labs. I've asked them for a report, and if and when I get it, I will report some of its results here. Next, I don't know too many technical details of the system, but Dr. Kantrowitz did mention a few. The system they were designing would have put a one ton capsule into orbit (at 10 g's). It would have required a one gigawatt (average power input) laser. Currently, the unclassified record is two megawatts (probably average power output). In any event, getting something that big would require many lasers operating in parallel. The cost of operating the system is that of the power plus whatever maintenence. At 10 g, orbit is achieved in about 90 seconds, so the system requires 25000 kwh per ton in orbit. At 10 cents/kwh, that's $2500. As far the politics of developing the shuttle went, NASA's decision to go with the shuttle at the time was OK. Laser technology was nowhere near the levels it's at now. Mass drivers would have plausible. Ditto for the big dump booster idea. It's understandable why they didn't pursue any more esoteric system, but that doesn't make it any less of a shame. Avco isn't working on the laser launch system anymore, and they should be. The research should still be happening, but the threat it poses to the shuttle via the powerful critics of the shuttle is still signifigant. I suppose that once the shuttle is operational and in heavy demand, we can really start pursuing all these launch systems energetically. But then, there probably won't be any money for research on advanced designs (OMB is trying to cut all such research from NASA's budget.) ------------------------------ Date: 10 Dec 1981 1158-CST From: Jonathan Slocum Subject: laser launching systems To: space at MIT-MC It occurs to me that a laser launching system can be considered to be just another use of a high-power laser weapon, in that the operational characteristics are essentially identical. Rather than melting the skin of the vehicle, of course, one hopes to heat/vaporize some substance that exhausts at a high velocity. But there are some very serious problems with this approach. To quote from the most recent issue of High Technology (v. 1, no. 2, Nov/Dec 1981, pp. 79-80): As the evidence indicates, there's no consensus of opinion on the feasibility of laser weapons. The technological issues are complex and far from settled, and they present a major challenge for scientists and engineers. Building a large enough laser, while by no means a trivial task, is probably the easiest step; even such pessimists as Tsipis [MIT] and Callaham [CMU] concede that high laser powers appear to be attainable. The most serious problems arise in reliably directing high powers onto a small enough area of a distant, moving target for a long enough time to do lethal damage. The atmosphere presents a complex set of problems. Although it looks transparent, the atmosphere isn't transparent enough for high-energy lasers. Even clear air absorbs a tiny fraction of the light going through it, and any absorption at all can be a serious source of trouble when trying to transmit millions of watts of light. That slight absorption is enough to heat the air a little, and as the air is heated it expands, reducing its density. As density decreases, the refractive index of the air in the beam path decreases, in effect making the air into a negative lens, spreading out the beam -- an effect called "thermal blooming." Atmospheric turbulence and a variety of other effects can also make laser beams wander off their targets. The next paragraph goes on about focussing problems (insuring sufficient energy presence/density at the target) which arise even in space. A recent Sci. Am. article dwells on the focussing/tracking issues, which are a source of some controversy. But the big, perhaps insurmountable problem for earth launches would appear to be atmospheric distortion. Unless the atmosphere is darn-near 100% transparent at some wavelength for which we can induce a substance to lase at extraordinary power levels, or we can find a way to make and sustain large tubular holes in the air, it ain't-a-gonna-work! ------------------------------ Date: 9 Dec 1981 2039-EST From: G.RONNIE at MIT-EECS at MIT-AI Subject: Meteor showers To: ota at S1-A Has there been some kind of meteor shower going on in the past 3 or 4 weeks? I ask because during this time I have seen an excess of meteors shooting across the sky. ------------------------------ Date: 10 Dec 1981 18:51 PST From: Wedekind.ES at PARC-MAXC Subject: Penthouse, please.. To: Space-Enthusiasts at MIT-MC cc: Wedekind.es I think it was OMNI where I saw the space elevator idea; they would run on cables which are anchored on the equator and extend somewhat past the geosynchronous orbit (22,000 miles?), where there is a big weight tied at the end to keep them stretched tight. If I remembered that much right, a few picky technical problems come to mind. The first is that it requires very strong cables - able to support at least 3,000 miles of their sea level weight by my calculations. I don't remember if the OMNI article was presented as speculative science or out-and-out fiction; does the idea seem ridiculous now, ridiculous for the near future, or just forevermore ridiculous? Jerry ------------------------------ End of SPACE Digest ******************* ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.