Date: Sat, 31 Oct 92 05:01:34 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #360 To: Space Digest Readers Precedence: bulk Space Digest Sat, 31 Oct 92 Volume 15 : Issue 360 Today's Topics: Comet Collision (6 msgs) Galileo High Gain Antenna Geo Bush: Claiming revelance , getting phasered HRMS for ETI (2 msgs) lunar phases Magellan Update - 10/30/92 pocket satellite receivers (was Re: Query Re: pluto direct/ o Re:Swift-Tuttle Comet a threat to earth? REPOST! UN Space/Moon Treaty?! Strategy for new generation of telescopes Surveyor landings (was Re: QUESTIONS: Apollo, Earth, Moon) Swift-Tuttle Comet a threat to earth? 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: 30 Oct 92 15:14:00 GMT From: Dave Jones Subject: Comet Collision Newsgroups: sci.space,alt.sci.planetary Lines: 35 X-Newsreader: TIN [version 1.1 PL6] Source-Info: Sender is really news@CRABAPPLE.SRV.CS.CMU.EDU Source-Info: Sender is really isu@VACATION.VENARI.CS.CMU.EDU John Black (black@breeze.rsre.mod.uk) wrote: > Maybe a near comet approach could be a good thing. I did a rough calculation > and estimated that there must be something of the order of 10 to the power 11 > metric tonnes of water. Maybe in 130 years time somewhere on the Earth could do > with some water, eg the interior of large continents affected by drought. I > know that one of the effects of the greenhouse effect is to make sea levels > rise, but that is salt water, no good for crops, and still would be hundreds of > miles from a continental desert region. The comet presumably is almost pure > water and therefore would be ideal for crops, drinking etc. > OK, I'll bite. 10^11 tonnes of water is a lake about 30km on a side and 1 meter deep. I imagine Lake Eyre, in Australia, has about that much, when it has any water at all, and it evaporates PDQ. Not much help. > So if in 130 years technology is sufficiently advanced, it could be possible > to alter the orbit of the comet so that it goes into a stable orbit around the > Earth. The trick then would be to "chip" bits off the comet and "land' them > in the appropriate region of the Earth. This would be the most difficult bit > since viz the probable cause of the Tunguska event (see previous article on > comet hitting Earth) you would end up doing the equivalent of nuking the region > The comet could also be an almost infinite supply of water for lunar bases if > there are any by then. > Notwithstanding other comments about linear-vs-exponential-vs-synergistic change, the fact is that if you have the ability to do 45 mi/s velocity changes on comets, then you also have the ability to do other things closer to home: like moving icebergs bodily into the Sahara, excavating artificial inland seas etc. Or just plain replanting all the flora that were lost to desertification in the first place..... -- ||)))))))))))))))))))))))))))))))))))))|Puff the Magic Dragon ||)))))))))))))))))))))))))))))))))))))|Lived by the sea ||Dave Jones (dj@ekcolor.ssd.kodak.com)|Who knows what's in the autumn mists ||Eastman Kodak Co. Rochester, NY |In the mind of Yadallee? ------------------------------ Date: 30 Oct 92 15:31:03 GMT From: Dave Jones Subject: Comet Collision Newsgroups: sci.space,alt.sci.planetary Dave Jones (dj@ekcolor.ssd.kodak.com) wrote: > John Black (black@breeze.rsre.mod.uk) wrote: > > Maybe a near comet approach could be a good thing. I did a rough calculation > > and estimated that there must be something of the order of 10 to the power 11 > > metric tonnes of water. Maybe in 130 years time somewhere on the Earth could do > > with some water, eg the interior of large continents affected by drought. I > > know that one of the effects of the greenhouse effect is to make sea levels > > rise, but that is salt water, no good for crops, and still would be hundreds of > > miles from a continental desert region. The comet presumably is almost pure > > water and therefore would be ideal for crops, drinking etc. > > > OK, I'll bite. 10^11 tonnes of water is a lake about 30km on a side and > 1 meter deep. I imagine Lake Eyre, in Australia, has about that much, when > it has any water at all, and it evaporates PDQ. Not much help. > Whoops! Make that 316 km on a side and 1 m. deep. Still not a lot by most standards: try 100km on a side and 10m deep, and compare with the Great Salt Lake, though Lake Eyre may still be good.... Anyway, neither blooms the desert, except on a strictly local basis. One day, I'm going to sit down and work out if Asimov's Martian Way really would have worked....soft land a chunk of Saturns Rings on Mars, when just getting into Earth orbit takes 90% of your starting mass? Hmmm....... -- ||)))))))))))))))))))))))))))))))))))))|Puff the Magic Dragon ||)))))))))))))))))))))))))))))))))))))|Lived by the sea ||Dave Jones (dj@ekcolor.ssd.kodak.com)|Who knows what's in the autumn mists ||Eastman Kodak Co. Rochester, NY |In the mind of Yadallee? ------------------------------ Date: 30 Oct 92 18:16:16 GMT From: Ken Arromdee Subject: Comet Collision Newsgroups: sci.space,sci.misc,rec.arts.sf.science In article amon@elegabalus.cs.qub.ac.uk writes: >You are guilty of the classic fallacies of extrapolation. The first >fallacy is an overestimate of short term advance. The second is the >underestimate of the long term. Both are due, in part, to linear >thinking, straight line extrapolation. Technological capabilities and >knowledge are accumulating exponententially. If you make a linear >extrapolation in a particular field, you will tend to "draw a line" >of some slope that seems "reasonable". But the problems invariably >turn out to be more difficult in your field than you actually >believed. So the exponential will for some period of time grow >slower (lesser slope) than your line, but when it finally does cross >it... There was a non-fiction article in Analog (a science fiction magazine) around 1960. The author pointed out exactly what you do here: lots of ideas about the future are extrapolated linearly. He graphed the maximum speed that human beings could travel at, as an example, and showed that it increased faster than even an exponential. The curve also showed, however, that (by extrapolation) humanity would surpass the speed of light by the year 1985. I believe that in the 1980's he (or someone, anyway) wrote another article recognizing the existence of S-shaped curves that eventually level off. The moral is that some barriers can't be found by extrapolation from points before the barriers have any significant effect. It's legitimate to argue that advances require solving a difficult or impossible problem; just noting that you can graph past that point is not an answer. (How do you conclude that technological capabilities are accumulating exponentially, anyway?) -- "the bogosity in a field equals the bogosity imported from related areas, plus the bogosity generated internally, minus the bogosity expelled or otherwise disposed of." -- K. Eric Drexler Ken Arromdee (UUCP: ....!jhunix!arromdee; BITNET: arromdee@jhuvm; INTERNET: arromdee@jyusenkyou.cs.jhu.edu) ------------------------------ Date: 30 Oct 92 18:15:47 GMT From: Doug Mohney Subject: Comet Collision Newsgroups: sci.space In article , amon@elegabalus.cs.qub.ac.uk writes: > >The capabilities of 130 years from now are really and truly outside >the realm of science fiction. We can't extrapolate that far ahead at >the current rate of advance. The exponential is rising so fast now >that knowledgeable projection and hard science fiction are almost >indistinquishable and cover the same time frame: no more than 30-50 >years in the future. > >In 2126 we'll be able to do just about anything we care to do with >that oversized snowball. As to what that might be, I fear my crystal >ball is bit cloudy today. Dateline: O'Neill News Service, October 31, 2125 Subject: Szabo Asteroid Miners, LunaOne Space Resources race to claim comet. :-) Play in the intelluctual sandbox of Usenet -- > SYSMGR@CADLAB.ENG.UMD.EDU < -- ------------------------------ Date: 30 Oct 92 17:49:06 GMT From: Mark Evans Subject: Comet Collision Newsgroups: sci.space komarimf@craft.camp.clarkson.edu (Mark 'Henry' Komarinski) writes: : : There is a greater change of dying from a train wreck or a car accident than : getting plowed by the comet. : Another thing to consider: How big is this comet? It doesn't have to hit : us to do some major damage. YOOGE tidal waves, earthquakes, knocking : the earth out of it's orbit, etc. Y'know...minor worldwide disaters. And what do you think it is made of (neutronium???) the gravity produced from a 10km iceberg is minimal. -- ------------------------------------------------------------------------- Mark Evans |evansmp@uhura.aston.ac.uk +(44) 21 565 1979 (Home) |evansmp@cs.aston.ac.uk +(44) 21 359 6531 x4039 (Office) | ------------------------------ Date: 30 Oct 1992 12:51 PST From: SCOTT I CHASE Subject: Comet Collision Newsgroups: sci.space In article <1992Oct30.174906.20091@aston.ac.uk>, evansmp@uhura.aston.ac.uk (Mark Evans) writes... >komarimf@craft.camp.clarkson.edu (Mark 'Henry' Komarinski) writes: >: >: There is a greater change of dying from a train wreck or a car accident than >: getting plowed by the comet. >: Another thing to consider: How big is this comet? It doesn't have to hit >: us to do some major damage. YOOGE tidal waves, earthquakes, knocking >: the earth out of it's orbit, etc. Y'know...minor worldwide disaters. Actually, I think that if you just average the deaths per year over 100 millions years or so, the odds of getting killed by a comet or meteor is several times higher than the annual odds of dying in a car crash. NASA recently reported such a calculation. Of course, the difference is that a meteor kills billions of people all at once, but only once every few 10 million years or so. -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: 30 Oct 1992 11:54 PST From: SCOTT I CHASE Subject: Galileo High Gain Antenna Newsgroups: sci.space,sci.astro In article <1992Oct29.191642.1@stsci.edu>, zellner@stsci.edu writes... > >> and 2) would this help the engineers at all? > >Very doubtful. They know what the problem is, they just can't find any >way to fix it. That's too strong a statement, I believe. They certainly have a model of the problem which they are using to try to fix it. But I don't think that it's possible to do more than go with a likely candidate. There is little doubt that the HGA failed to open. But *why* is didn't open - what got it stuck - is a matter of some speculation. That's why it is not possible to say with any confidence whether the various attempts to fix it will work or not. -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: Fri, 30 Oct 92 18:24:07 -0600 From: pgf@srl05.cacs.usl.edu (Phil G. Fraering) Subject: Geo Bush: Claiming revelance , getting phasered In article <29731@life.ai.mit.edu>, Clinton for President <75300.3115@compuserve.com> writes: |> |> FOR IMMEDIATE RELEASE |> October 20, 1992 |> |> GEORGE BUSH'S DRUG WAR: CLAIMING VICTORY, COVERING UP LOSSES |> [Statement by Bob Boorstin, Deputy Communications Director] |> |> George Bush just doesn't get it. He's shown time and time again he |> doesn't understand America's economic problems. Now he's showing |> again he doesn't understand America's drug problem. >etc. |> Bill Clinton will lead a national and international crusade against |> drugs. He knows we have to tackle both demand for drugs and the |> supply of drugs. He sees the drug problem from a personal |> perspective, not a political one. And he knows we can do better than |> George Bush's cynical, failed drug war and attempted coverup. >Let's beam George Bush into a wall. Actually, Bush understands it about as well as Clinton, who hasn't really said what he'd do besides "get tougher." I sorta wonder what that means with the Bill of Rights in the state it's in today. Thankfully the only Ferengi in the race has made sounds about how it's obsolete, and if it's in the way, change it! In short, dudes, I feel nothing but contempt for all of this non-space-related political arguing, so haul it off of sci.space before I get nasty with the photon torpedoes. Besides, everyone knows these coersive states are not the way of the _true_ Klingons... -- Phil Fraering pgf@srl0x.cacs.usl.edu where the x is a number from 1-5. Phone: 318/365-5418 SnailMail: 2408 Blue Haven Dr., New Iberia, La. 70560 --------------------- Disclaimer: Some reasonably forseeable events may exceed this message's capability to protect from severe injury, death, widespread disaster, astronomically significant volumes of space approaching a state of markedly increaced entropy, or taxes. The world will end tomorrow. NASA scientists note that this was the way the system was designed to operate. - From the Nov. Focus in Sky and Telescope, on a hypothetical NASA press release on something hitting the Earth... ------------------------------ Date: 30 Oct 92 18:18:25 GMT From: Stanley Friesen Subject: HRMS for ETI Newsgroups: sci.space,sci.bio In article <1992Oct30.023542.4610@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes: |In article <1346@tdat.teradata.COM> swf@tdat.teradata.com (Stanley Friesen) writes: | |> This last is an extremely unlikely requirement. The basic upshot of the |> Urey experiment and its follow-ups is that organics form spontaneously |> under most non-oxidizing 'medium-energy' conditions. The presence of |> organics in interstellar dust clouds just confirms this basic ubiquity. | |The Miller-Urey experiment is widely acknowledged to be irrelevant, |as it assumed an atmosphere that likely bears little resemblance |to the early earth. Specifically, methane and ammonia are unlikely |to have been abundant in the early atmosphere, as they are destroyed |within centuries by UV light. That is why I specified 'and follow-ups'. Almost every variant atmosphere that was either reducing or 'neutral' has yielded organics. The results do *not* depend particularly on the exact original chemistry - though the exact set of organics produced does vary with the initial conditions. |When performed with more reasonable gas mixtures, the experiments have |much lower yields. And, in any case, all that these experiments |indicate is that some of the basic molecules of life are rather stable |(and, importantly, that others are not), not that a particular source |is where they first came from. They show them to be formed under a wide variety of conditions, so they are liekly to be present on most otherwise suitable planets - perhaps from *multiple* sources. In short, it is more *lack* of organics is more extraordinary, and thus more unlikely, than thier presence. |The unstated assumption here is that life would *not* have had a hard |time originating back then. We simply don't know enough about how |life started to say this. Not really, the all I was talking about here was the fact that our oxidizing atmosphere destroys all unprotected organics. | |Au contraire! Our ignorance about origin of life is profound, and |very little progress has been made in dispelling it. There is no |really plausible model for the origin of life. We're missing at least |one, and possibly several, fundamental ideas. | Have you read Cairns-Smith's "Seven Clues to the Origin of Life"? I consider that to be an extremely plausible model (though the best reasons are not in that, now out-of-date, book). Also, one could argue, based on the usual defnitions of life, that the recently produced self-replicatinf RNA molecule *is* alive, and thus we *have* made life in the laboratory. (Of course the exact definition of life in the boundry cases is decidedly difficult, so one could also make a case that it is not alive). -- sarima@teradata.com (formerly tdatirv!sarima) or Stanley.Friesen@ElSegundoCA.ncr.com ------------------------------ Date: Fri, 30 Oct 1992 19:51:02 GMT From: Paul Dietz Subject: HRMS for ETI Newsgroups: sci.space,sci.bio In article <1357@tdat.teradata.COM> swf@tdat.teradata.com (Stanley Friesen) writes: >|Au contraire! Our ignorance about origin of life is profound, and >|very little progress has been made in dispelling it. There is no >|really plausible model for the origin of life. We're missing at least >|one, and possibly several, fundamental ideas. > Have you read Cairns-Smith's "Seven Clues to the Origin of Life"? > I consider that to be an extremely plausible model (though the best > reasons are not in that, now out-of-date, book). Cairns-Smith's ideas are very imaginative, but are supported by almost no evidence. In particular, no one has ever demonstrated that clays -- or any other crystals -- can propagate genetic information. The fact that such speculations are taken seriously shows how blocked the field has become. > Also, one could argue, based on the usual defnitions of life, that the > recently produced self-replicatinf RNA molecule *is* alive, and thus > we *have* made life in the laboratory. (Of course the exact definition > of life in the boundry cases is decidedly difficult, so one could also > make a case that it is not alive). Sure, we've made RNAs in the laboratory -- using purified, chiral tri(?)phosphorylated nucleotides, which (correct me if I'm wrong) are extracted from biological sources. Prebiotic Miller-Urey type experiments have not, to my knowledge, ever produced nucleotides, nor have they produced anything but racemic mixtures of mostly biologically irrelevant molecules. The monomers of RNA are sufficiently complicated that it is quite implausible they could have arisen without some prior evolution. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Fri, 30 Oct 1992 10:23:49 GMT From: Jan Spitzkowsky Subject: lunar phases Newsgroups: sci.space Please help, I need an algorithm for calculating the lunar phases. I need it for computing the red letter days, most of them depend on the moon like Easter. Thanks in advance Jan ------------------------------ Date: Sat, 31 Oct 1992 05:57:26 GMT From: Ron Baalke Subject: Magellan Update - 10/30/92 Newsgroups: sci.space,sci.astro,alt.sci.planetary Fowarded from the Magellan Project MAGELLAN STATUS REPORT October 30, 1992 1. Magellan continues to operate normally, performing a starcal (star calibration) and desat (desaturation of the reaction wheels) on each orbit and transmitting a carrier plus 40 bps X-band signal. 2. No commanding of the spacecraft is planned for today or the weekend. Magellan continues to pass through the shadow of Venus during the apoapsis portion of each orbit. 3. The craft has completed 5982 orbits of Venus, just 18 orbits from the 6000 mark. 346 orbits have been completed in Cycle 4. Since the science requirement is to collect gravity data on at least one out of every four orbits, we have about 86 orbits of gravity. This represents about 70 degrees of longitude out of the 360 degree coverage planned. ___ _____ ___ /_ /| /____/ \ /_ /| 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: 30 Oct 92 09:52:22 GMT From: John C Sager Subject: pocket satellite receivers (was Re: Newsgroups: comp.sys.hp48,comp.sys.palmtops,sci.space I got some information on the GESSA device. It appears that they use the NavCore V GPS receiver module from Rockwell-Collins. John C Sager Mail: B67 G18, BT Labs Email: jcs@zoo.bt.co.uk Martlesham Heath Tel: +44 473 642623 IPSWICH IP5 7RE Fax: +44 473 637614 England ------------------------------ Date: Fri, 30 Oct 1992 17:53:59 GMT From: Henry Spencer Subject: Query Re: pluto direct/ o Newsgroups: sci.space In article <1992Oct30.163302.15547@rcvie.co.at> se_taylo@rcvie.co.at (Ian Taylor) writes: >>... aerobraking at Pluto. > >How about aerobraking at Neptune first? For the Nth time, folks, Neptune is nowhere near Pluto. Nothing of any useful size is anywhere near Pluto. Any braking done must be done at Pluto; otherwise the trip times are simply too long. >While I'm here, anyone know if a gravity assist trajectory can be used to >*reduce* speed? Yes... but a gravity assist around *what*? -- MS-DOS is the OS/360 of the 1980s. | Henry Spencer @ U of Toronto Zoology -Hal W. Hardenbergh (1985)| henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 30 Oct 92 16:34:20 GMT From: Erik Max Francis Subject: Re:Swift-Tuttle Comet a threat to earth? Newsgroups: sci.astro,sci.space sheaffer@netcom.com (Robert Sheaffer) writes: > I should think that, given that a comet consists largely of ice and > other volatiles, even one good-sized H-bomb placed directly into the > nucleus would pretty much eliminate any "threat to earth". Seems it > would be mostly vaporized and scattered. Splitting it up might not help, if those chunks still hit the Earth. A million million-kilogram chunks of ice and rock isn't very much less dangerous than a single trillion-kilogram chunk. It would have to be separate into considerably small pieces so that any pieces that _do_ still hit the Earth burn up in the atmosphere with little surface damage. The best bet is to use a device to _nudge_ it out of the way, not to blow it to bits. That just isn't practical. ---------- Erik Max Francis Omnia quia sunt, lumina sunt. Coming soon: UNIVERSE _ | _ USmail: 1070 Oakmont Dr. #1 San Jose CA 95117 ICBM: 37 20 N 121 53 W _>|<_ UUCP: ..!apple!uuwest!max Usenet: max@west.darkside.com 464E4F5244 | ------------------------------ Date: Fri, 30 Oct 1992 17:50:12 GMT From: Henry Spencer Subject: REPOST! UN Space/Moon Treaty?! Newsgroups: sci.space In article <1992Oct29.204147.16685@bnr.ca> stu5s33@bnr.ca writes: >I am looking for information concerning the "Moon Treaty" or some sort >of treaty drafted by the UN dealing with "...the Use of the Moon >and Other Celestial Bodies". Why bother? Nobody's ratified it, and nobody's likely to. In particular, US support of it is stone cold dead, thanks entirely to the efforts of the late lamented L5 Society. -- MS-DOS is the OS/360 of the 1980s. | Henry Spencer @ U of Toronto Zoology -Hal W. Hardenbergh (1985)| henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 30 Oct 92 18:57:02 GMT From: Garry Holmen Subject: Strategy for new generation of telescopes Newsgroups: sci.space,sci.image.processing In article <1cn3lmINNe9l@oly.cs.ubc.ca> yking@cs.ubc.ca (Yossarian Yggy King) writes: > >I saw a talk last week by Dr. Geoff Hinton, and he mentioned that he'd >been involved in some work (though maybe only peripherally, I'm not >sure) on building neural nets to learn how to correct for optical >defects in large lenses. I've probably got this wrong, but it was >something like having the net learn the distortion parameters for each >point on the lens, which are then corrected with a secondary lens that >is distorted in real-time as the image is gathered to correct for the >distortions in the primary lens. > He said in passing that the neural-net corrected lenses >rivaled the resolution of the Hubble scope. Obviously (I think) you >can only correct for distortions, not attenuations, by the atmosphere >... once you've lost information you can't get it back. >-- >Yggy King | Thinking the world should entertain you leads to boredom >UBC Comp Sci | and sloth. Thinking you should entertain the world leads >B.C., Vancouver | to bright clothes, odd graffiti and amazing grace in >Canada | running for the bus. -- Ann Herbert One should note that neural nets are not 100% accurate on the predictions that they can make. A good net usually has an accuracy somewhere between 80 - 90%. And when a neural network isn't correct the results can vary wildly. This is the big disadvantage of neural nets.... noone can guarantee error bounding. So while these new telescopes should be better than existing telescopes I would be hesitant to compare them to Hubble. Except when it comes to $$$$ 8). PS: You should also be able to use neural nets to enhance Hubble images. But as a word of caution : Anytime you distort data to achieve results that you deem desirable you can lose valuable information outside your interest. Garry Holmen ------------------------------ Date: Sat, 31 Oct 1992 06:03:43 GMT From: Ron Baalke Subject: Surveyor landings (was Re: QUESTIONS: Apollo, Earth, Moon) Newsgroups: sci.astro,sci.space In article <1992Oct30.033908.1@fnalf.fnal.gov>, higgins@fnalf.fnal.gov (Bill Higgins-- Beam Jockey) writes... >I've played Lunar Lander (being a relic of the compter dark ages >beforre Flight Simulator and Sim City), so I can appreciate the >usefulness of a throttlable engine. So how did Surveyor manage to >land? I recall a big solid-fuel motor and small liquid-fuel "vernier" >engines. Was there a computer playing Lunar Lander on board? Was >there a radar altimeter? Or did they just get the probe to >*approximately* zero velocity with the big motor, and build it >extra-sturdy to survive a drop? How does this compare with the scheme >Luna 9 used to land, which I understand was rougher? > The Surveyors fired a solid rocket motor at 96 km to cancel most of its horizontal velocity, causing the spacecraft to descend towards the Moon's surface. The solid rocket motor was then ejected, and a radar altimeter was used to feed a computer for a closed loop control of three thrusters to further reduce the descent velocity. At 4.3 km above the surface, the three thrusters were shut off, and the spacecraft simply dropped the remainder of the way down, landing at a velocity of 11 km/hour. >(I recall that one of the Surveyors was moved after landing with the >verniers.) You are thinking of Surveyor 6 in 1967. It became the first spacecraft ever to be launched from the surface of the Moon when it fired its thrusters for 2.5 seconds, lifting the spacecraft 3 meters high at a slight angle. It landed 2.5 meters away from its original landing spot. ___ _____ ___ /_ /| /____/ \ /_ /| 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: Fri, 30 Oct 1992 19:04:36 GMT From: "Stephen F. Schaffner" Subject: Swift-Tuttle Comet a threat to earth? Newsgroups: sci.astro,sci.space In article <1992Oct30.165026.9268@ccu.umanitoba.ca>, youngs@ccu.umanitoba.ca (Scott D. Young) writes: |> |> According to the data I have seen (I will try and find the reference), |> a comet 1 mile in diameter moving at an averge orbital velocity (what |> ever tht means) would cause a crater 40 miles diameter, and destroy |> everything for 100 miles. 400 million cubic *miles* of dirt would be |> thrown up into the tmosphere, nd stay there for up to 1000 years, |> blocking 98% of solar radition. As someone else put it, "You die, I |> die, everybody dies". That seems like rather a lot of dirt. Unless I'm confused (which I frequently am), to get it all out of a 40 mile diameter crater you'd need a crater 300,000 miles deep. Now *that's* a crater I'd like to see (provided I didn't have to be around while it was being made, of course). -- Steve Schaffner sschaff@unixhub.slac.stanford.edu The opinions expressed may be mine, and may not be those of SLAC, Stanford University, or the DOE. ------------------------------ End of Space Digest Volume 15 : Issue 360 ------------------------------