Aucbvax.5481 fa.space utzoo!decvax!ucbvax!space Tue Dec 15 04:10:29 1981 SPACE Digest V2 #60 >From OTA@S1-A Tue Dec 15 04:01:46 1981 To: SPACE@MIT-MC Reply-To: Space-Enthusiasts at MIT-MC SPACE Digest Volume 2 : Issue 60 Today's Topics: Laser launch systems Sub Orbital Launch Skyhook Stability Linear accelerators as launchers. interest rates & launching lasers specific thrust of materials Cables in space the Gap interest rates & launching lasers Elevators, fuel Ultimate limits Shuttle's wings Shuttle's and laser launching system laser launching systems ---------------------------------------------------------------------- Date: 14 Dec 1981 0724-PST From: Jim McGrath Subject: Laser launch systems To: space at MIT-MC Although there does seem to be some similar points between laser weapons and a launch system, the launch system is far more practical. Certain advantages are as follows: 1) Launch from a high elevation. This decreases fuel costs but, more importantly, decreases the amount of atmosphere you have to punch through. 2) Launch in good, calm, weather. You can take your time when launching, just as shipmasters of old did. Keep a shuttle in reserve for an all weather transport. 3) Use several lasers (which can be time-shared between different payloads) for launching. This reduces the need for a continous beam from a single laser. 4) Use different pathways for the laser beams. If the beams are firing in burst mode, then this reduces the effects of blooming considerably. 5) Use a nuclear power plant, selling excess power to the electric grid. This is actually a far more cost effective idea than most of the comments so far indicate. For instance, launch only during the night - that way the power demand curve is evened out, and little extra costs are incurred. Use the day for repairs. It also gives you fantastic night launchings if you can see the beam! The ideal site would be in southern US or Mexico, hooked into a large power grid, at a high elevation and with clear, calm weather at night. Any suggestions from folks down thataway? Jim PS Note that while I am more confident that the system would work, I am still not totally convinced. Any document out there with hard, crunchy, numbers? ------------------------------ Date: 14 Dec 1981 0725-PST From: Jim McGrath Subject: Sub Orbital Launch To: space at MIT-MC An interesting article appeared in ANALOG magazine a year or so ago on sub orbital launching. Throw something up into the air at relatively low speed. In near space it encounters a linear accelerator which transfers momentum from itself to the payload, placing it in orbit. The accelerator itself stays in orbit either via ion drive, solar sails, or momentum transfer from incoming payloads to earth. Couple this with a laser launch system and you have a more effective combination. We could do it in a 10-15 year time frame (it all depends on how big you want the facility). Will we have a beanstalk by then? Probably not due to the greater materials (in technology and volume) requirements of the latter - you will need an accelerator in order to develope space sufficiently in order to let you get anywhere with skyhooks. Jim ------------------------------ Date: 14 Dec 1981 0734-PST From: Jim McGrath Subject: Skyhook Stability To: space at MIT-MC There appear to be large technical problems with skyhook stability due to two factors. First, the skyhook is vertically unstable. That is, small displacements will not tend to be corrected. I do not believe there is a similar horizontial stability problem, but there is another difficulty due to the fact that a skyhook is a very long and thin structure, with the primary strength criteria for construction being compression, not shear. If the structure suffers a horizontial shock, then the energy will be transmitted as a wave throughout the structure, potentially causing a lot of damage. First, are my fears grounded? Second, can we get materials that have both compression and shear characteristics we want? Finally, can we use feedback in order to dampen some of these problems (remember that the speed of light is a serious limitation here). Jim ------------------------------ Date: 14 Dec 1981 0741-PST From: Ted Anderson Subject: Linear accelerators as launchers. To: space at MIT-MC CC: jpm at SU-AI The real problem faced by any linear accelerator used in a orbital launch system is that all practical lengths lead to rather large accelerations. This is due to the fact that for a given length (l) and required final velocity (v) the average acceleration is v^2/2/l. Plugging in some sample numbers we have low earth orbital speed of 8 km/s, and say our accelerator is 10 km long. This gives an acceleration of 320g. This is unacceptably high for people and other relatively fragile cargo. Note that the laser scheme mentioned recently had and acceleration of 10g for 90 seconds. This gives a length of 400 km. This still causes soem problems but you don't have to build a track thats 400 km long. Ted Anderson ------------------------------ Date: 14 December 1981 1144-cst From: Bill Vaughan Subject: interest rates & launching lasers To: POURNE at MC, Leavitt at USC-ISI Cc: SPACE at MC, VaughanW Whether you set the generator up in Baja or Utah is probably immaterial. The fact remains that the utility buying your excess power is going to have to accept a 100% reduction whenever you want to launch a spacecraft. That means you are not selling that utility any base load; you are selling peaking power - so the customer will only buy it when it is needed, not the rest of the time. Your power plant will actually be producing salable power less than 25% of the time. This will reduce return on investment substantially. As far as equity taking the place of interest: this is true only to the extent you can convince investors that their equity will increase at a rate greater than the interest rate. (By the way, those investors are precisely the venture capitalists that Leavitt advocates avoiding. ?? ) It is true that the American investor is a perennial sucker, but will they go for this? Maybe - if you can produce a convincing (and nonfraudulent) prospectus. Anyway, my only point was that financing costs would be greater than fuel costs. I still think that's true. ------------------------------ Date: 14 Dec 1981 1452-CST From: Jonathan Slocum Subject: specific thrust of materials To: space at MIT-MC What Hans neglected to explicate in his reply concerned how one determines what theoretical thrust is. The basic information is partly there already, but some dummies like me might not be able to piece it together. I shall not pretend to be as facile as he is with the numbers (or the physics) but here is a sketch of the limitations. Thrust is determined by the velocity and mass of the combustion products; velocity is determined by (combustion) temperature as well as the molecular weight of the exhaust products. Therefore, the higher the temperature, the higher the thrust (in chemical reactions, of course, the mass is constant). With each fuel/oxidant combination, one can determine the temperature at which the combustion products decompose (e.g., water -> hydrogen + oxygen at around 3,000K as I recall) in an endothermic reaction -- which reduces temperature, hence exhaust velocity. As it turns out, hydrogen is the best possible chemical fuel; as an expert would put it, it has the highest possible "specific thrust" (probably has something to do with its binding energy, resulting from chemical reactions within the innermost electronic shell, which Hans was talking about). Therefore, a hydrogen-burning engine operating at 3,000K is as good as you can possibly get in principle; the Shuttle engines approach this limit, thus we are near the theoretical limit w.r.t. chemical engines. ------- ------------------------------ Date: 14 Dec 1981 13:43 PST From: Wedekind.ES at PARC-MAXC Subject: Cables in space To: Hans Moravec at CMU-10A (R110HM60), space at MIT-MC cc: Wedekind.es Thanks for a clear explanation of some of the technical issues re space cables. To reiterate, the figure I gave in my original question for the minimum characteristic length (~3k mi) of any potential cable material is all wet, because it assumed no tapering. I was next going to bring up coriolis forces on the cargo and atmospheric turbulence but first I better get ejukated.. please tell me what references you have besides the Clarke and Sheffield books. Jerry ------------------------------ Date: 14 Dec 1981 1623-PST From: Stuart McLure Cracraft Subject: the Gap To: space at MIT-MC cc: dist at SRI-UNIX !n067 1530 14 Dec 81 BC-G(Newhouse 006) By PATRICK YOUNG Newhouse News Service WASHINGTON - Four astronomers think they have found a great cosmic hole largely devoid of galaxies in a place so far from Earth that light takes more than 360 million years to bridge the gulf. The gap itself isn't what has surprised their fellow scientists. It's the size that has astronomers, cosmologists and astrophysicists puzzled. ''Since we see large clusters of galaxies, one would expect to see gaps,'' says David Schramm of the University of Chicago. The area is some 300 million light-years - roughly 18 quadrillion miles - in diameter and 180 million light-years deep. (A light-year is the distance light travels in a year, or about 5.9 trillion miles.) A gap that big doesn't fit easily into current thinking. ''Existing theories of the distribution of matter in the universe can't quite explain the discovery,'' says John Huckra of the Smithsonian Astrophysical Observatory in Cambridge, Mass. ''There is still some doubt whether it is real.'' But if the gap is real - and new work suggests it is - it should provide a deeper understanding of how galaxies formed some 1.5 billion years after the birth of the universe. It may even shed some new light on the Big Bang itself, that gigantic explosion believed to have begun the universe we know some 10 billion to 20 billion years ago. The universe is populated by galaxies, which tend to cluster together. These galaxy clusters also tend to be grouped into what are called superclusters. In between are vast regions of space containing little matter. ''We would like to know how galaxies and galaxy clusters formed,'' says Robert Kirshner of the University of Michigan in Ann Arbor, a member of the team that discovered the gap. ''At the beginning, we think, everything was homogeneous with matter evenly distributed. Somehow we have to account for how the structure of the universe formed. If we understand how this structure grew from early times to present, we could infer what happened at the beginning.'' Until now, the largest known gap was about 60 million light-years across. The new gap appears five times larger, and it takes up far more space than the largest known supercluster of galaxies. The new hole was discovered by Kirshner, Augustus Oemler Jr. of Yale University, Paul L. Schechter of the Kitt Peak National Observatory in Arizona, and Stephen A. Shectman of the Mt. Wilson and Las Campanas Observatories in Pasadena, Calif. The four, using telescopes at Kitt Peak, the Smithsonian's Whipple Observatory in Arizona and Mt. Palomar in California, were conducting a survey to determine the distance of galaxies far from Earth. They were able to observe galaxies up to 40,000 times fainter than the naked eye can see. The hole was inferred from three samples of galaxies that formed a triangle in the area of the constellation Bootes. In each sample, the gap began about 360 million light-years away and continued outward to 540 million light-years. Preliminary results from more than 100 areas studied within that triangle has since supported the gap's existence. Viewed from Earth, the patch of sky appears small. ''If you hold a garbage can lid up at arm's length, it's that big a piece of the sky,'' Kirshner says. But because the region is so far away, the hole actually represents about 1 percent of the observable universe. Thousands of galaxies should be found there. Yet the four astronomers find 10 times fewer than expected. ''To have found a population density of less than three times average would have been a rare find,'' Schechter says. ''But finding that the density is about 10 times less than the average is exceedingly hard to understand.'' The gap intrigues scientists trying to fathom the birth and evolution of the universe, for it goes to some basic issues in cosmology. Although matter does clump in galaxies and galaxy clusters, overall the material of the universe is evenly distributed. ''Two of the most fundamental questions in cosmology today are: Why, on the large scale, is the universe so smooth; and why, on the small scale, is it so bumpy,'' Schramm says. Kirshner and his colleagues continue to investigate whether matter might exist in the gap in some form other than normal galaxies. Two unlikely possibilities are as great clouds of gas or as unusually tiny, faint galaxies, making the gap a ''place where all the galaxies are pygmies.'' ''That in itself would be surprising,'' Kirshner says. BJ END YOUNG nyt-12-14-81 1831est ********** ------- ------------------------------ Date: 15 December 1981 03:55-EST From: Jerry E. Pournelle Subject: interest rates & launching lasers To: VaughanW at HI-MULTICS cc: POURNE at MIT-MC, SPACE at MIT-MC, VAUGHANW at MIT-MC, Leavitt at USC-ISI It seems clear to me that one could launch on off-hours, or otherwise schedule to the convenience of customers for power. I see no reason at all why clever scheduling cannot manage to sell a lot of power and simultaneously get a lot of stuff into orbit. Example: an electric furnace steel plant, given the low cost of labor in certain areas, plus a break on power, might well forgoe the third shift, leaving one shift for launch and two for selling power to a steel plant; or, if I can assure you I'll deliver your power during the hours of 8Am to 8PM, you're likely to buy; and I'll have 12 for launching. I fail to understand why we must have a rigidly scheduled system. Unless, as Alex points out, we can't launch at night because you can't see where you're going... ------------------------------ Date: 15 December 1981 0410-EST (Tuesday) From: Hans Moravec at CMU-10A (R110HM60) To: space at MIT-MC Subject: Elevators, fuel CC: Hans Moravec at CMU-10A Re skyhook stability - The anchored kind is VERY stable vertically - after it is constructed the bottom end is anchored to the ground, and the top end (as much as 70,000 miles beyond synchronous orbit) is ballasted with a counterweight which tries to escape centrifugally, and puts the entire cable at design tension. When a payload travels on the part of the cable below synch orbit, its weight (decreasing as the payload rides up into lower g, higher centrifugal heights) merely removes some of the load on the anchor - the cable above the load feels no change in the forces on it, the cable below the payload has its bias stress temporarily lessened. Coriolis forces are also no problem - they just cause the cable to lean a tiny bit. Careful payload scheduling can minimize the long term induced sway. The cable is so thin for its length that payloads simply thrusting up and down on it cause no material shear forces to speak of - just a little local bowing. Unlike a weight on a taught catenary, the anchored skyhook is a constant tension system. Resonances are another issue; Pearson's first two papers in the reference list below conclude that all serious oscillations can be easily avoided. Some ascent/descent speeds excite resonances, but if you accelerate through those speeds quickly, the vibrations don't have time to build up. Re hydrogen/oxygen as the best chemical fuel - actually hydrogen/fluorine is a little better. The HF reaction product is heaver than the H2O of the shuttle's engines, but the greater reaction energy more than makes up for it. Of course both the fuel and the exhaust vapor are very unpleasant to man and machine - and the reaction is very hot. Still its one of the major fuels used in high power chemical lasers. The very highest specific impulse from a chemical reaction undoubtedly comes from the recombination of atomic hydrogen. H + H -> H2 both liberates a lot of energy and has a very light, thus high velocity for the energy, reaction product. Storing the monatomic hydrogen until it's needed represents a still unsolved packaging problem, however. Possibly the hypothetical metastable metallic hydrogen is an answer to this problem too. Here are the elevator references requested: Y. Artsutanov, V Kosmos na Elektrovoze (To the Cosmos by Funicular Railway), Komsomolskaya Pravda, July 31, 1960 (contents described in Lvov, Science 158, p 946, November 17, 1967). J.D. Isaacs, A.C. Vine, H. Bradner, G.E. Bachus, Satellite Elongation into a True "Sky-Hook", Science 151 p 682, February 11, 1966 and 152, p 800, May 6, 1966. Y. Artsutanov, (The Cosmic Wheel), Znanije-Sile (Knowledge is Power) No. 7 p 25, 1969. J. Pearson, The Orbital Tower: A Spacecraft Launcher Using the Earth's Rotational Energy, Acta Astronautica 2, p 785, September/October 1975. J. Pearson, Using The Orbital Tower to Launch Earth Escape Payloads Daily, 27'th IAF Congress, Anaheim, Ca., October 1976. AIAA paper IAF 76-123. J. Pearson, Anchored Lunar Satellites for Cis-Lunar Transportation and Communication, European Conference on Space Settlements and Space Industries, London, England, September 20, 1977. in Journal of the Astronautical Sciences. H.P. Moravec, A Non-Synchronous Orbital Skyhook, 23rd AIAA Meeting, The Industrialization of Space, San Francisco, Ca., October 18-20, 1977, also Journal of the Astronautical Sciences 25, October-December, 1977. J. Pearson, Lunar Anchored Satellite Test, AIAA/AAS Astrodynamics Conference, Palo Alto, Ca., August 7-9, 1978, AIAA paper 78-1427. H.P. Moravec, Skyhook!, L5 News, August 1978. H.P. Moravec, Cable Cars in the Sky, in The Endless Frontier, Vol. 1, Jerry Pournelle, ed., Grosset & Dunlap, Ace books, November 1979, pp. 301-322. R.L. Forward and H.P. Moravec, High Wire Act, Omni, Omni publications international, New York, July 1981, pp. 44-47. ------------------------------ Date: 15 December 1981 04:56-EST From: Jerry E. Pournelle Subject: Ultimate limits To: FONER at MIT-AI cc: SPACE-ENTHUSIASTS at MIT-MC Ultimat limits to matter: 42 Reference: Hitchhiker's Guide to the Galaxy... ------------------------------ Date: 15 December 1981 05:05-EST From: Jerry E. Pournelle Subject: Shuttle's wings To: David.Smith at CMU-10A cc: SPACE at MIT-MC But can't they always land on Easter Island...?? ------------------------------ Date: 15 December 1981 05:10-EST From: Jerry E. Pournelle Subject: Shuttle's and laser launching system To: BRUC at MIT-ML cc: SPACE at MIT-MC Art Kantrowitz is the new Chairman of the L-5 Society and will be writing on laser launch systems for the L-5 News. (Subscribe by sending $20 to L-5 1060 E Elm Tucson AZ 85719) (I don't get paid nothing nohow for L-5 News) NASA has a decision to make: operate stuff, or develop advanced technology? There's a conflict. Worth thinking about. ------------------------------ Date: 15 December 1981 05:11-EST From: Jerry E. Pournelle Subject: laser launching systems To: LRC.SLOCUM at UTEXAS-20 cc: SPACE at MIT-MC After all, there are people who believe the Earth is flat; znd I expect that gunpowder weapons were "controversial" for a long time, especially amongst experienced pikemen./ You want to be your life on Tsipis, go ahead. ------------------------------ 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.