Date: Mon, 26 Oct 92 05:01:42 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #345 To: Space Digest Readers Precedence: bulk Space Digest Mon, 26 Oct 92 Volume 15 : Issue 345 Today's Topics: Clinton's bad posting etiquette Dyson sphere Recognizing a Dyson sphere if you saw one Voyager Family Portrait (2 msgs) Welcome to the Space Digest!! Please send your messages to "space@isu.isunet.edu", and (un)subscription requests of the form "Subscribe Space " to one of these addresses: listserv@uga (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle (THENET), or space-REQUEST@isu.isunet.edu (Internet). ---------------------------------------------------------------------- Date: 26 Oct 92 06:01:35 GMT From: Eric Loeb Subject: Clinton's bad posting etiquette Newsgroups: sci.space The errors that caused the recent Clinton campaign material to appear on this list were entirely my own. Together with John Mallery I am managing a non-partisan campaign information service for all of the campaigns. This is an official project of the MIT Artificial Intelligence Laboratory, so there are naturally a great many bugs to be expected. The Clinton campaign happened to post at a time when we had several bugs that were, as you now know, conspicuous. I hope that those of you who are sending rude personal remarks to the Clinton address on the subject of his breach of etiquette will learn to think. Your actions are absurd. Meanwhile, we have seen several examples of feedback from the network into speeches, the Clinton health care policy, and even some of the points made in the debates. Efforts to clog the mailboxes of the campaigns are as clever and productive as shouting over a quiet but thoughtful public speaker. The Bush mailbox is still clogged, and at this point I can only ask the culprits to get some kind of life, however minimal. Your infantile, vitreolic complaints about the blindness of these posts will only ensure that no rational policy maker will ever bother to look any closer. Eric Loeb MIT Artificial Intelligence Laboratory 1992 Presidential Campaign Information Service ------------------------------ Date: 26 Oct 92 04:06:06 GMT From: Steve Masticola Subject: Dyson sphere Newsgroups: sci.astro,sci.space jmc@SAIL.Stanford.EDU (John McCarthy) writes: >Isn't it time someone did some high school physics as to how much air >would be required? >Let r be the earth's distance from the sun. >r = 93e6 miles = 1.5e11 meters Wouldn't it be a lot more convenient to make the sphere of a radius such that its surface gravity is 1G, rather than placing it way out at 1 AU radius? If solar gravity at 1 AU radius is 6.1e-4 G, then you'd need a radius of .025 AU (3.75e6 kilometers or 2.3e6 miles) to get 1G acceleration at the surface. Gravity would be more conveniently close to Earth's for habitation of the outside surface, and materials costs would be much lower (about 6.1e-4 times as much material needed to make the Dyson sphere.) There would, of course, be a much greater problem of unwanted heating of the surface of the Dyson sphere at that distance. We can assume that any civilization capable of building the sphere so that it doesn't collapse, controlling the position of the star inside, elemental transmutation on a massive scale, etc. could direct the waste heat where it wanted it. Here's one way they might do it. To avoid atmospheric heating, the waste heat from the star could be transmitted into space through cold targets in "chimneys" through the atmosphere. Perhaps the entire inner surface of the sphere could be made reflective, and power generation would occur in space outside the Dyson sphere and its atmosphere. There is, of course, the problem of compressive loads on the sphere: they'd be much higher at .025 AU. If my math is right, the compressive loads are inversely proportional to the radius of the sphere, so you'd have to cope with 40 times as much compressive stress. But, again, there may be a way out... Another crackpot idea (as if _any_ of these ideas were anything _but_ crackpot :-): how about if the sphere was inflated? Balance the gravity of the star by gas pressure inside the sphere. The sphere could be much weaker then. But I can't see a way of keeping the gas from collapsing into the star, unless you were to build the thing inside the photosphere, which would make the surface uninhabitable due to stronger gravity. You also couldn't have the open chimneys with an inflated Dyson sphere; you'd have to channel the energy out through something solid, or cap the chimenys. But since you won't be living on the surface, who cares about waste heat, and why build the chimneys anyway? :-) - Steve "where are those repelatrons and gravpolarizers when I need them?" masticol@cs.rutgers.edu. ------------------------------ Date: 24 Oct 92 18:33:37 GMT From: train@ccwf.cc.utexas.edu Subject: Recognizing a Dyson sphere if you saw one Newsgroups: sci.astro,sci.space In article <1992Oct19.055005.24078@infodev.cam.ac.uk> sl25@cus.cam.ac.uk (Steve Linton) writes: >You`re looking for a body with a diameter of a few AU's radiating a black-body >spectrum at a few hundred K, for a total power output roughly the same as that of >a star. The spectrum might not be spot on, and deviations from black-body would >like very unlike anything you might expect naturally - might have very sharp >spikes, or sudden chops. I may be wrong about this, I forget the aprroximate size of a dwarf star and don't have a book near me at the moment, but a sphere with a diameter of 2 AU's wouldn't be anything near the size of a dwarf star would it? I thought dwarf stars, at least white dwarfs, were about the size of the Earth. Well, if I am mistaken, feel free to correct me. This stuff I will know for sure next semester when I take my astrophysics class. -- ******************************************************************************* * "My neural pathways have become accustomed | Alton R. Pouncey II * * to your sensory input patterns." | train@ccwf.cc.utexas.edu * ******************************************************************************* ------------------------------ Date: Mon, 26 Oct 1992 03:58:16 GMT From: Ed McCreary Subject: Voyager Family Portrait Newsgroups: sci.space In article <1992Oct25.153622.15780@engage.pko.dec.com> moroney@ramblr.enet.dec.com writes: >In article <1992Oct25.054001.27008@elroy.jpl.nasa.gov>, baalke@kelvin.jpl.nasa.gov (Ron Baalke) writes... >>If by chance you happen to visit JPL, the family portrait images are >>on one of the walls of Von Karman Auditorium across from Voyager 3. > >Voyager 3? A third probe whose mission got cancelled after it was built? What >would its mission have been? > nope, it was a backup that wasn't used and later became a mockup to test ideas on during the mission. -- In the midst of the word he was trying to say,|McCreary@sword.eng.hou.compaq.com In the midst of his laughter and glee, |Me, speak for Compaq? He had softly and suddenly vanished away--- |Yeah, right. For the Snark *was* a Boojum, you see. |#include ------------------------------ Date: 26 Oct 92 13:22:38 GMT From: Ron Baalke Subject: Voyager Family Portrait Newsgroups: sci.space In article <1992Oct25.153622.15780@engage.pko.dec.com>, moroney@ramblr.enet.dec.com writes... >In article <1992Oct25.054001.27008@elroy.jpl.nasa.gov>, baalke@kelvin.jpl.nasa.gov (Ron Baalke) writes... >>If by chance you happen to visit JPL, the family portrait images are >>on one of the walls of Von Karman Auditorium across from Voyager 3. > >Voyager 3? A third probe whose mission got cancelled after it was built? What >would its mission have been? > No, this Voyager 3 is a full scale replica of the Voyager spacecraft and is not a real spacecraft. It runs along the entire length of one wall of the auditorium (or at least is used to, the Magnetometer boom was recently removed so that a mockup of the Magellan spacecraft could be stored next to it), and is often used as a backdrop during interviews with the news media. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | If God had wanted us to /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | have elections, he would |_____|/ |_|/ |_____|/ | have given us candidates. ------------------------------ id AA13236; Sun, 25 Oct 92 21:31:45 EST Received: from crabapple.srv.cs.cmu.edu by VACATION.VENARI.CS.CMU.EDU id aa22052; 25 Oct 92 21:19:45 EST To: bb-sci-space@CRABAPPLE.SRV.CS.CMU.EDU Xref: crabapple.srv.cs.cmu.edu sci.astro:27707 sci.space:50236 Newsgroups: sci.astro,sci.space Path: crabapple.srv.cs.cmu.edu!cantaloupe.srv.cs.cmu.edu!rochester!udel!darwin.sura.net!spool.mu.edu!agate!stanford.edu!CSD-NewsHost.Stanford.EDU!CSD-NewsHost!jmc From: John McCarthy Subject: Re: Dyson sphere In-Reply-To: max@west.darkside.com's message of 25 Oct 92 19:22:44 GMT Message-Id: Sender: news@Times.Stanford.EDU Reply-To: jmc@cs.Stanford.EDU Organization: Computer Science Department, Stanford University References: Date: 25 Oct 92 14:30:13 Lines: 45 Source-Info: Sender is really news@CRABAPPLE.SRV.CS.CMU.EDU Source-Info: Sender is really isu@VACATION.VENARI.CS.CMU.EDU Isn't it time someone did some high school physics as to how much air would be required? Let r be the earth's distance from the sun. r = 93e6 miles = 1.5e11 meters Let v be the orbital velocity of the earth. Let y = 3.16e7 be the year in seconds. We have v = 2 pi r/y = 3.0e4 m/sec Let g1 be the acceleration due to solar gravity at the earth's distance from the sun. We have g1 = v^2/r = 5.9 e(-3) m/sec^2 = 6.1e(-4) g, where g is the gravitational acceleration on the earth. At the earth surface we have 15 lbs/in^2, i.e. there is 15 lbs of air above each square inch. Because of the lower gravity at the s surface of the Dyson sphere, we need proportionately more air to get the same pressure, i.e. we need 15/(6.1e(-4)) = 2.5 e4 lb/in^2 = 25,000 pound per square inch of air. This is 1.7e7 kg/m^2. The total air required is obtained by multiplying this by 4 pi r^2, getting 4.9e30 kg. The mass of the sun is 1.99e30 kg which isn't enough. Ah, but suppose we can get by on pure oxygen at 3 lbs/in^2. Then we only have to convert half of the sun's mass to oxygen. Seems entirely feasible for those who can build the sphere in the first place. I have not put as much work into checking the arithmetic as I would for a published paper. -- John McCarthy, Computer Science Department, Stanford, CA 94305 * He who refuses to do arithmetic is doomed to talk nonsense. ------------------------------ End of Space Digest Volume 15 : Issue 345 ------------------------------