Date: Tue, 20 Oct 92 05:03:51 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #329 To: Space Digest Readers Precedence: bulk Space Digest Tue, 20 Oct 92 Volume 15 : Issue 329 Today's Topics: DCX Status? Dyson Spheres and Cosmic Spaghetti (2 msgs) Earth's two moons Mars & Magellan Images Mars Direct to be Briefed at NASA Johnson. Nuclear Power / FAQ (2 msgs) Weather satellites & preventing property damage 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: 20 Oct 92 02:58:43 GMT From: "Simon E. Booth" Subject: DCX Status? Newsgroups: sci.space Sorry I can't quote but: The paper on the DC-X is facinating. Is the prototype going to be flown manned or unmanned?? There is a reference to a "near-crash" during a shuttle landing. When did this take place?? Simon ------------------------------ Date: Tue, 20 Oct 1992 00:55:36 GMT From: "Richard A. Schumacher" Subject: Dyson Spheres and Cosmic Spaghetti Newsgroups: sci.astro,sci.space The original poster is referring to a speculative article by Niven in which he discusses various designs of artificial worlds of many sizes and styles, including but not limited to the Ringworld. The torus described there (basically a piece of spaghetti a few km in minor radius, occupied inside) has nothing to do with the later "Smoke Ring" novels. ------------------------------ Date: 19 Oct 92 23:33:48 GMT From: Anthony Frost Subject: Dyson Spheres and Cosmic Spaghetti Newsgroups: sci.space >> Niven proposed a different form of this which was sort of >> neat. Instead of multiple O'Neil colonies, you just build >> one that's extensible. You extend it until it wraps all the >> way around. If it's thin enough (say, ~10km with a 1AU >> radius) the rotation stresses are negligible. So you can >> spin it for gravity. > Nope. Niven had to invent > yet-another-impossibly-strong-material for his ringworld. > Scrith, I think he called it. > Oh! Re-reading, perhaps Alan means the ring is a torus, and > spins around its small circle. In that case the stresses > *are* negligible, but it wasn't Niven's ringworld. The design for this is mentioned in a Niven article "Larger Than Worlds" which I've got in a collection called "A Hole In Space". The design is credited to a Pat Gunkel who apparently called it a "topopolis". The tube can go round the sun multiple times with the inner loops providing power to the outer ones. In fiction, the nearest structure is "The Way" in Greg Bears Eon and Eternity. "Larger Than Worlds" covers structures from O'Neill colony sized things through Ringworlds, Discworlds and Stellar Dyson spheres to galactic sized shells... Anthony ------------------------------ Date: 19 Oct 92 13:33:46 GMT From: "Mr. L.T. Killip" Subject: Earth's two moons Newsgroups: sci.space In article , cocking@csugrad.cs.vt.edu (Cara Cocking) writes: > > I took an astronomy class in high school and my teacher told us that > Earth really has two moons but that the other one can't be seen unaided > because it's a lot smaller and farther out. > > I've been telling some people that Earth has two moons but no one > believes me. Could someone please confirm this? > I used to have this opinion too. Sometime in the seventies I read a newspaper article which claimed that an asteroid named Toro (number is in the four thousands I think) was actually a moon of the earth with about a 9-million-mile radius orbit. For some time I went around telling people about this. Then I found out that later calculations of the orbit had made this seem less true. The orbit was still fascinating though. It seems that Toro has (fairly distant) encounters with Earth, Mars and Venus on a semi-regular basis and that as a result its orbit varies rather a lot. As I remember it (corrections please) the orbit has several fairly stable states and that every ?20000 years a particularly close encounter with one of the planets flips the orbit into another of those states. The only analogue I know of is the Saturnian shepherd moons which swap orbits every now and then but this is much more complicated. ______________________________________________________________________ Les Killip JANET : killip@uk.ac.liv.csc Computer Science Dept, Internet : killip@csc.liv.ac.uk University of Liverpool, P.O. Box 147, Phone : 0(or 44)-51-794-3700 LIVERPOOL L69 3BX United Kingdom ______________________________________________________________________ | The right of Mortuarius the Extremely Violent to be identified as | | the author of this posting has been very persuasively asserted by | | him in accordance with the Copyright Designs and Patents Act 1988 | ---------------------------------------------------------------------- ------------------------------ Date: 20 Oct 92 12:43:45 GMT From: Ron Baalke Subject: Mars & Magellan Images Newsgroups: sci.space,sci.astro,alt.sci.planetary ========================== MARS & MAGELLAN IMAGES October 19, 1992 ========================== Two Mars images and line drawings of the Magellan spacecraft are now available at the anonymous ftp site at ames.arc.nasa.gov. The Mars images are in both GIF and JPEG format, and show two views of the Mars globe as constructed by USGS from the Viking Orbiter images. ftp: ames.arc.nasa.gov (128.102.18.3) user: anonymous cd: pub/SPACE/GIF files: mars1.gif mars2.gif cd: pub/SPACE/JPEG files: mars1.jpg mars2.jpg The "Magellan" drawing is quite accurate. The "VGRAM" drawing has been used frequently in Magellan publications, but actually represents an early spacecraft design. In the flight hardware, the attachment of the propulsion thrusters was to a separate "propulsion equipment module", rather than to the bus itself, as VGRAM shows. The Magellan images are available in GIF format and as Macintosh StartupScreen files. cd: pub/SPACE/GIF files: magellan.gif vgram.gif cd: pub/SPACE/MAGELLAN/CAPTIONS files: magellan.bin (Macintosh StartupScreen files, MacBinary) magellan.hqx (Macintosh StartupScreen files -> BinHex) vgram.bin (Macintosh StartupScreen files, MacBinary) vgram.hqx (Macintosh StartupScreen files -> BinHex) ####### ___ _____ ___ /_ /| /____/ \ /_ /| 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. ------------------------------ Date: 19 Oct 92 23:48:35 GMT From: Pat Subject: Mars Direct to be Briefed at NASA Johnson. Newsgroups: sci.space I saw something in the local trade rrag that Zubrin was invited down to Johnson to brief on Mars Direct. some Associate director had heard him brief on Lunar direct at WSC and wanted more. Anyone know if the meeting went off and how the impressions went? ------------------------------ Date: 19 Oct 92 23:59:00 GMT From: SCOTT I CHASE Subject: Nuclear Power / FAQ Newsgroups: sci.space In article <18OCT199218394394@zeus.tamu.edu>, i0c0256@zeus.tamu.edu (IGOR) writes... > >Nuclear power is to heat some fluid in order to get something out of it. >How to heat it up ? put a lots of fissile materials all together so that >the neutron population increases exponentially, the heat comes from the >energy given away by the nucleus that is splitting ( fission process). >In order for this reaction to occur more than once, one has to reach the critical >mass.. the main problem is to control this neutron population, if it is not >done one has a bomb... This is not quite right. First of all, if your sample of fissile material has an exponentially increasing neutron population, then you might want to prepare to meet your maker. It's gonna explode. Secondly, critical mass is necessary in order to have a self-sustaining reaction - i.e., an explosion (if not moderated). If you have less than critical mass, then the probability that a given neutron will cause the release of a second which goes on to participate in a new reaction is less than one, but still non-zero. That is, each spontaneous fission induces a small, exponentially dying chain reaction with a damping factor given by how close to 1.0 the probability is. For slightly less than critical mass, many reactions may be induced by each neutron. Your lump of material gets warm, stays warm, but does not explode. But if I understand correctly, the nuclear power used in spacecraft is not a fission reaction. It is a quantity of radioactive material which stays warm due to it's decay. The mechanism depends on the material, but basically, it depends on the lump of material absorbing the energy of the particles emitted in the decay. -Scott -------------------- Scott I. Chase "It is not a simple life to be a single cell, SICHASE@CSA2.LBL.GOV although I have no right to say so, having been a single cell so long ago myself that I have no memory at all of that stage of my life." - Lewis Thomas ------------------------------ Date: 19 Oct 92 23:31:26 GMT From: Paul Dietz Subject: Nuclear Power / FAQ Newsgroups: sci.space In article <19OCT199211295353@rigel.tamu.edu> i0c0256@rigel.tamu.edu (IGOR) writes: >>In article <18OCT199218394394@zeus.tamu.edu> i0c0256@zeus.tamu.edu (IGOR) writes: > Perhaps you could throw up somewhere else sir, because It is my belief > that the Sp100, the topaz or the nerva project are nuclear power > related projects. If you are not convinced of that why don't you come > beginning of january in albuquerque at the space nuclear power > symposium, you might learn things. As for the RTG's how can one > compare decaying materials to fission controlled technology..... How can I compare RTGs to fission? Well, perhaps it is because the original poster was asking about how nuclear power was used in spacecraft. Right now, nuclear fission is *not* used in spacecraft. RTGs are. If he had asked about how nuclear power could be used in spacecraft, or will be used in spacecraft, well, then a discussion of fission would be appropriate. > Why so many people feel threatened when one does not give their > answers as the good one? Glad you asked. In your case, it was because you gave a baby-talk cutsy lecture in nuclear physics that was substantially in error. Aside from ignoring RTGs, the bit about "controlling the neutron population being the main problem" is just ridiculous. Control of space reactors, at least the electric-power-producing variety like SP-100 or Topaz, is the least of their problems. The real problem is materials that can stand up to the necessary temperatures (which have to be high to drive thermoelectric generators or rockets), and do so reliably for long enough times. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 20 Oct 92 02:26:28 GMT From: Robert P Dale Subject: Weather satellites & preventing property damage Newsgroups: sci.space In article jbh55289@uxa.cso.uiuc.edu (Josh 'K' Hopkins) writes: > I think hurricanes are the only major natural >disaster we can predict reliably enough that people take it seriously and far >enough in advance to do much good. I dunno... Major tornadic outbreaks are well forecast and publicized usually, although the warnings aren't always heeded (Wichita/Andover 1991.) Rob -- Robert P. Dale <> rdale@attserv.atms.purdue.edu Toledo, OH <> 74010.302@compuserve.com Meteorology/Emergency Services <> N8GSK@K9IU.IN.USA.NOAM ------------------------------ End of Space Digest Volume 15 : Issue 329 ------------------------------