Aucbvax.5470 fa.space utzoo!decvax!ucbvax!space Mon Dec 14 03:52:43 1981 SPACE Digest V2 #59 >From OTA@S1-A Mon Dec 14 03:45:58 1981 SPACE Digest Volume 2 : Issue 59 Today's Topics: Costs of laser launch facilities hammering the dinosaurs Beam weapons, comments from Access to Energy Ultimate strengths ---------------------------------------------------------------------- Date: 13 Dec 1981 0916-PST Sender: LEAVITT at USC-ISI Subject: Costs of laser launch facilities From: Mike Leavitt To: VaughnW at HI-MULTICS Cc: SPACE at MC Message-ID: <[USC-ISI]13-DEC-81 09:16:59.LEAVITT> Actually, you must worry about interest costs in building these big facilities only if you are a "public" utility or a government. Utilities finance captial projects through bonds much more often than through new stock issues, and everything new that the government funds must be considered to be funded from the proceeds of a loan at the going short-term T-bill rate. If, instead, you are an entrepreneur, you have the option of substituting equity growth for interest as the inducement to get new capital. This is the way most new enterprises get their capital if they can avoid the venture capitalists for long enough. Mike ------------------------------ Date: 13 December 1981 12:49-EST From: Ron L. Levin To: SPACE at MIT-MC Thank you for all the replies about project Orion. These are listed in MC:USERS5;LEVIN ORION. Two people mentioned McPhee and his book "On the Curve of Binding Energy." The consensus is that it probably works, and that it may be possible to reach 10% of the speed of light in a year. A model with "equivalent" TNT explosives was tried. The advantage of Project Orion over other nuclear powered systems, is the rapidity with which nuclear fuel can be consumed. The project was terminated with the nuclear test ban treaty. ------------------------------ Date: 13 Dec 1981 1648-PST From: Stuart McLure Cracraft Subject: hammering the dinosaurs To: space at MIT-MC !a266 1741 12 Dec 81 AM-Dinosaur Deaths,480 Theory Blames Dust, Darkness for End of Dinosaurs By ROBERT LOCKE AP Science Writer SAN FRANCISCO (AP) - For perhaps two months, the Earth was wrapped in a cloud of dust so thick that the sun was obscured and temperatures over land everywhere fell below zero. Within six months, according to the new verion of a 2-year-old theory, the landscape was littered with carcasses. Species after species became extinct. Plants stopped growing and dinosaurs couldn't find enough food and died. The idea that a giant asteroid or comet, crashing to Earth and kicking up huge clouds of dust 65 million years ago, ended the 140-million-year reign of the dinosaurs was described at a meeting of the American Geophysical Union by atmospheric scientist Owen B. Toon. Toon, of the National Aeronautics and Space Administration's Ames Research Center at Mountain View, Calif., said theories of the end of the dinosaurs continue to stir considerable interest. ''It's one of the longest-standing mysteries in science,'' he said in an interview Friday. ''If it could happen to them, it could happen to us. They were the kings of the earth.'' The extinction of the giant reptiles launched the age of mammals, which survived, Toon theorizes, because they were small enough to burrow underground for warmth ''and could probably stumble across enough food,'' including dead dinosaurs. ''All the mammals were mostly mice and little things like that and that's how we survived ... But if you're a big guy like a dinosaur, you've got to find an awful lot of food,'' Toon said. ''Plus, you can imagine how dangerous it would be for a dinosaur to stumble around in the dark.'' He said cold and the inability to find food probably killed off any creature that weighed more than 75 pounds. The idea of a dust-producing collision was proposed in 1980 by a team of scientists led by Walter Alvarez of the University of California's Lawrence Berkeley Laboratory. They based the theory on geologic evidence that, about 65 million years ago, a thin layer of debris was deposited around the Earth. The concentration of certain metals in this layer is much different from that found in the Earth's crust, but about right for an asteroid. The group concluded that a meteorite, perhaps 8 miles across, caused a dust cloud that darkened the Earth for several years. Toon, with colleagues at Ames, R&D Associates of Marina del Rey, the University of Colorado and Informatics, Inc., of Palo Alto, used computer simulations designed to study volcanic ash and the atmospheres of other planets to better determine the effects of such a collision. The team presents a different picture, with shorter but more dramatic impacts. ''The duration was less than six months and possibly less than three months,'' Toon said. The crash, possibly in the ocean, would have had 10 million times the energy of the Mount St. Helens volcanic explosion last year, he said. ap-ny-12-12 2041EST ********** ------- ------------------------------ Date: 14 December 1981 02:06-EST From: Gene Salamin Subject: Beam weapons, comments from Access to Energy To: SPACE at MIT-MC, ARMS-D at MIT-MC The December 1981 issue of Access to Energy deals with beam weapons. It may or may not turn out to be practical, but you don't know until you try. The following is a quote from AtE. Only two years ago one could find articles explaining why atmospheric absorption would preclude particle beams. These forecasts (as near as we can tell from the open literature) have proved wrong; not because any physical laws have been broken, but for lack of experience with an energy threshold where other factors come into play. There have been such cases where just a little experimental physics, or the lack of it, considerably affected warfare. The secret invention of radar was not only decisive in the Battle of Britain (the entire tiny RAF fighter force always intercepted the Luftwaffe squadrons wherever they chose to approach), but it also revealed to the British that very short radio waves will propagate well beyond the horizon, rudely overruling contemporary physics and engineering textbooks. Again, no physical laws were broken, but the texts had failed to take account of a tiny, but decisive (refractive) effect of the atmosphere. The British used this effect in 1941 to bomb Berlin at night, through clouds, for unknown to the Germans, Berlin (and Western Europe) was covered by a navigational net spun from signals emitted by radio beacons in Britain. They were received on board British aircraft by the grandfather of today's electronic navigation, the "G-box", tuned to the then stunningly high frequency of 50 MHz (the band of today's commercial TV channels). The G-boxes had a detonator to destroy their most secret ingredients on impact, but it failed to explode on one of the planes shot down, and the Germans appointed a commission to top experts to investigate the puzzle. "We couldn't make head or tail of it", one of its members told this writer some years after the war. "But we unanimously concluded that it was something for training purposes only, because it was easy enough to determine the frequency to which the receiver was tuned, and we all 'knew' that such short waves could not possibly propagate beyond the transmitter's horizon." ------------------------------ Date: 14 Dec 1981 0217-EST From: HPM at CMU-20C Subject: Ultimate strengths To: foner at MIT-AI, space at MIT-MC cc: hm60 at CMU-10A Actually there are several "ultimate" limits. I was talking about normal, earth surface, conditions where all the interaction between atoms happens amongst the outer electrons. The characteristic energies are a few electron volts per atom. These few evs are the inter-atomic glue in materials, and what is liberated in energetic reactions. If you messed with the inner electrons, that would jump to tens of ev, nuclear energies are in the millions of ev, and total conversion of mass to energy gets you billions to tens of billions of ev per atom. With normal chemistry and materials science you get to tap only the one or two evs, the rest of the atom is essentially dead weight. As it happens, it takes tens of ev to lift even light atoms out of earths potential well, and this is what makes high mass ratios in rockets and cables or towers necessary: It takes the energy of tens of atoms to get just one to escape. It much easier on the moon, where a few ev per atom suffices, and much harder on the bigger planets. It takes hundred of ev to get an atom off jupiter, and a simple chemical rocket would have to have an astronomical mass ratio (but nuclear could work). Back to earth-normal: the ultimate strength of normal substances can be calculated by looking at the in-lattice bond strength between adjacent atoms, and dividing by the atom's mass. A real chunk of matter would achieve this strength only if all the atoms in it were so bonded in the direction of the stress, and if the stress were perfectly uniformly distributed over all the bonds. Normal engineering materials blow it on both counts. Grain boundaries and other lattice defects create both some inferior bonds, and cause stress to be concentrated unevenly. The overstressed regions break long before the rest of the material reaches its limits, but then the load is passed to what's left, and it all breaks. Perfect single crystals with smooth surfaces can exhibit nearly the theoretical strengths, however, and a lot of this is retained in bulk materials when single crystals are bonded together in a soft matrix (often metal) which distributes the stress among them pretty evenly. A nice intuitive way to express the strength to weight ratio of a material is called "characteristic length". It is the length of material fashioned into a constant cross-section rope that can just support itself when hung from one end in a uniform one earth gravity field. (The formula is tensile-strength/(density*1g)). Graphite, with its strong covalent carbon-carbon bonds is the best actually existing material. Its theoretical characteristic length is several thousand km. A metastable metallic version of hydrogen that can exist at room temperature might be quite a bit better because hydrogen has much less dead weight, but its existence is only conjectured. Later editions of the CRC handbook have a NASA originated table labelled "Mechanical and Physical Properties of Whiskers". The indicated whiskers are actual laboratory grown, millimeter length, single crystal rods of various substances, whose strength and density can be measured. The measured properties give the following characteristic lengths: Graphite whiskers 961 km Al2O3 whiskers 527 km Iron whiskers 162 km Si3N4 whiskers 455 km SiC whiskers 704 km Si whiskers 337 km These numbers are about 1/5 to 1/10 of the theoretical limits for the substances. By comparison we have todays engineering materials: Bulk aluminum 10 km Bulk iron 11 km Bulk steel 40 km Nylon 88 km Fiberglass 98 km Kevlar 195 km As stated in my previous message, a strength five times that of Kevlar would make earth elevator cables of varoius varieties possible. This means a characteristic length of about 1000 km; a bulk material with the graphite whisker strength above would do fine. ------- ------------------------------ 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.