Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Fri, 11 May 90 01:42:55 -0400 (EDT) Message-ID: Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Fri, 11 May 90 01:42:26 -0400 (EDT) Subject: SPACE Digest V11 #386 SPACE Digest Volume 11 : Issue 386 Today's Topics: Re: Dirigible launchers (was Re: Pegasus launchers, space-going DUCT TAPE) Re: launch windows Re: Looking for a good telescope Re: why there are no ETs Hubble Space Telescope Update - 05/10/90 (Forwarded) Radioactive Shuttle? Re: Terraforming Venus (was: Manned mission to Venus) Re: Re: Dyson spheres (long) Re: Manned mission to Venus (long) ---------------------------------------------------------------------- Date: 10 May 90 11:47:23 GMT From: mcsun!ukc!edcastle!hwcs!adrian@uunet.uu.net (Adrian Hurt) Subject: Re: Dirigible launchers (was Re: Pegasus launchers, space-going DUCT TAPE) In article <1990Apr27.155920.16673@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >In article <33838@sequent.UUCP> cliffw@crg1.UUCP (Cliff White) writes: >>why reject the B-1? >>It's fast, new, designed for dropping things... >>and has no useful current mission that i've heard about... > >The B-1 is not particularly fast, actually. With occasional exceptions, >military aircraft have been getting slower over the past 20-30 years, as >people came to realize that high supersonic speeds are of very little use >for most military missions. That's the B-1B you're thinking of. Are there any of the prototype B-1A's still around? Even the B-1B can go faster and higher than a B-52, although in its military role it probably wouldn't do so. The B-52 can't go beyond Mach 1; the B-1B can; and the B-1A could go at Mach 2. The B-52 can't get over 50,000 feet; both B-1 types can get over 60,000 feet. "Keyboard? How quaint!" - M. Scott Adrian Hurt | JANET: adrian@uk.ac.hw.cs UUCP: ..!ukc!cs.hw.ac.uk!adrian | ARPA: adrian@cs.hw.ac.uk ------------------------------ Date: 11 May 90 02:39:53 GMT From: winter@apple.com (Patty Winter) Subject: Re: launch windows In article <1990May9.164912.5907@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >In article <1990May9.025512.14415@melba.bby.oz.au> gnb@bby.oz.au (Gregory N. Bond) writes: >>And why is there any launch window at all for satelites, shuttles and >>stuff? An orbit is an orbit, and the only reference point is the >>earth, no? > >The Sun matters too, and that's the reason for a lot of launch windows >in one way or another. What I've been trying to figure out (and some of my friends say the same) is why there was a "launch" (release) window for HST. I would've thought NASA would want it released while they were in visual communication with the shuttle. What gives? Patty -- ***************************************************************************** Patty Winter N6BIS INTERNET: winter@apple.com AMPR.ORG: [44.4.0.44] UUCP: {decwrl,nsc,sun}!apple!winter ***************************************************************************** ------------------------------ Date: 10 May 90 17:12:18 GMT From: hplabsb!dsmith@hplabs.hp.com (David Smith) Subject: Re: Looking for a good telescope In article <1990May9.172227.7629@ingres.Ingres.COM> sid@friday.Ingres.COM (Sid Shapiro) writes: >Hi folks, I hope this is the right place to ask this... >I'm looking for a good telescope for under $1000. What are the >possibilities? Are there any? Must I go to $2000 or more? Are there >any places that I might look for used scopes? Watch the want ads. A fellow I met placed a "telescope wanted" classified ad, and got two good bites. The second came after he had already bought the first. He passed the lead on to me, and I bought the scope. Seeing that you're from the SF Bay area, I'll depress you by saying that you missed a great opportunity last Saturday. The San Jose Astronomical Association held its annual (or apparently now semiannual) swap meet and auction. My, were those prices depressed! (And now you're really depressed.) A brand new 8" Dobsonian built by Earl Watts (excellent reputation) got no takers at $300 minimum bid. Earl waived the minimum bid, and it sold at $175. Other scopes went cheaply, as well. The bidders pretty much already had good telescopes, and weren't motivated to bid the prices up. Finders and eyepieces went for a higher fraction of value. I am told that Earl Watts runs a telescope making workshop every Friday night in Berkeley. Send me a note if you want his number. -- David R. Smith, HP Labs dsmith@hplabs.hp.com (415) 857-7898 ------------------------------ Date: 10 May 90 04:41:46 GMT From: bfmny0!tneff@uunet.uu.net (Tom Neff) Subject: Re: why there are no ETs In article <482@megalon.UUCP> acad!megalon!peb@uunet.UU.NET (Paul Baclaski) writes: >It just occured to me that one of the possible reasons we have not >discovered extraterrestrial intelligence in the universe is that they >have created full fledged virtual reality systems and feel no need to go >exploring space because they have enough fun exploring the inner space >of their collective minds. I'm not sure how serious this was intended to be, but it has the same flaw as all the other "they're not seen because they don't want to be" arguments: it assumes that ALL civilizations come to the identical conclusion. All it would take is one exception, or one ACTIVE exception at any time in the history of the cosmos, to flood the galaxy with lifesigns even if 95% of the beings in the galaxy were "SETI dark matter" sitting plugged into nine dimensional Nintendo games. I still like my explanation. When you achieve interstellar travel or communication, someone comes along and kills you. Fits the nature of the universe, i.e., a real bitch. ------------------------------ Date: 10 May 90 16:32:52 GMT From: snorkelwacker!usc!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov!baalke@tut.cis.ohio-state.edu (Ron Baalke) Subject: Hubble Space Telescope Update - 05/10/90 (Forwarded) THE NEW YORK TIMES -- MAY 10 "Old Error Stalls Focusing of Space Telescope" By John Noble Wilford "An error made years ago in planning has set back efforts to focus the Hubble Space Telescope and delayed by at least another week an attempt to take the first picture of the heavens with the $1.5 billion instrument." Revised commands radioed to the telescope tonight could result in the first picture being snapped Wednesday according to the Times. If a second test becomes necessary, the picture may be delayed another two days. Wilford says engineers found that a pointing error of half a degree caused by use of an outdated star chart had been programmed into the telescope computer. The Times report states that the first picture should magnify objects about as well as fairly large Earth-based telescopes while later pictures will be able to see objects out close to the edge of the universe seven times clearer than the largest ground telescopes. The first test photo subject is a 3-billion year-old star field, Theta Carina, the "Ship's Keel", some 1,260 light years away. * * * * * * * * WASHINGTON TIMES -- MAY 10 "Math Mistake Points Hubble Wrong Way" "A simple math mistake -- somebody added when he should have subtracted, or vice versa -- caused the Hubble Space Telescope to miss its target stars and point to the wrong spot in the heavens, embarrassed scientists said yesterday." The Times quotes Hubble deputy manager Jean Olivier saying, "when we were trying to point the telescope to the center of a pretty rich star field with a high probability of acquisition, we were really off to one side of that." The story says because of this error, the first picture from the telescope won't be taken until sometime next week. * * * * * * * * WASHINGTON POST -- MAY 10 "First Space Pictures From Jittery Hubble Telescope Still Several Days Away" By Kathy Sawyer "After two weeks in orbit, the Hubble Space Telescope has not shaken its opening-night jitters and is not expected to return its 'first light' images to Earth until at least next Wednesday, its handlers said yesterday." The Post story cites Hubble oscillation and jitter problems and describes the math error committed by Space Telescope Science Institute staff in correcting a 1954 sky chart for use by the telescope fine guidance system. Sawyer then quotes from the STS-31 post-flight crew press conference and mission specialist Bruce McCandless, "this is not your garden variety satellite. What you're seeing now are the first efforts in working our way through the things which are zero-gravity and orbit related" and couldn't be tested before launch. Sawyer cites the astronauts' plea that the public and media maintain patience while the telescope team tackles start-up problems. Ron Baalke | baalke@mars.jpl.nasa.gov Jet Propulsion Lab M/S 301-355 | baalke@jems.jpl.nasa.gov 4800 Oak Grove Dr. | Pasadena, CA 91109 | Go Lakers! ------------------------------ Date: Thu, 10 May 1990 08:31 EDT From: SIMMONS DONALD F <27000%AECLCR.BITNET@vma.cc.cmu.edu> Subject: Radioactive Shuttle? To: I have recently heard that while in space, the belly of the shuttle picks up radiation from the sun, so much so that after the shuttle has landed they check it with a geiger counter before the astronauts can disembark. Anyone know anything about this? Donald Simmons 27000@aeclcr ------------------------------ Date: 10 May 90 14:11:07 GMT From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!watserv1!maytag!watdragon!watyew!jdnicoll@ucsd.edu (Brian or James) Subject: Re: Terraforming Venus (was: Manned mission to Venus) I think using Saturn's rings as H2O fodder for terraforming Venus is a Bad Idea. There are other sources of ice in the Solar System, and destroying a beautiful ring sytem unecessarily seems wrong. Kind of similar logic to national parks or historic buildings. The Rings have a value where they are. JDN ------------------------------ Date: 10 May 90 16:43:22 GMT From: helios.ee.lbl.gov!hellgate.utah.edu!mailrus!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca!neufeld@ucsd.edu (Christopher Neufeld) Subject: Re: Re: Dyson spheres (long) I was asked where the numbers came from. I'll summarize here, and send the calculations to John through e-mail. Unless otherwise indicated, all values are for a sphere at 1 AU. The Sun is taken to shine at 1.4 kW/m^2 at a distance of 1 AU. In article <9005100040.AA08237@cmr.ncsl.nist.gov> roberts@CMR.NCSL.NIST.GOV (John Roberts) writes: > >>From: usc!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca!neufeld@ucsd.edu (Christopher Neufeld) >>Subject: Re: Re: Dyson spheres? > >>The Sun subtends 6.8E-5 steradians of solid angle from the inner >>surface of the sphere (at 1AU). Assuming that the radiation from any >>element of the sphere is isotropic (I don't know how good an assumption >>this is), the Sun catches 1.1E-5 of the reradiation, which raises the >>surface temperature of the Sun by much less than 1 degree. > Angle subtended is projected area divided by distance squared. The radius of the Sun is 700000km, the distance is 150000000km. So, any individual element on the inside surface of the sphere, assuming it radiates equally in all directions over the 2pi steradians available to it, casts 1.1E-5 of its radiation onto the disk of the Sun. The rest of the radiation misses the Sun and hits another part of the sphere. So, the Sun's temperature has to increase, so that the power output is 1.000011 times its former value. This corresponds to a temperature increase of about 0.05 degrees. >There's a much simpler approach, which I would have a greater tendency to >trust: > I did it this way first, but thought my other argument was more intuitive. >If >we assume that the power output of the sun is constant, that everything acts >like a black body, that the current temperature of the sun is 5000K, that the >temperature of space is about 3K, and that the inside surface of the Dyson >sphere is 500K, then putting a Dyson sphere around the sun will raise its >surface temperature by about 1/8 of a degree K. > Close enough to my value not to make a difference (I'm a physicist, so if they agree to within a factor of ten, I'm happy). >If I got the calculations right, a blackbody Dyson sphere at 1AU would be >heated to about 400K rather than 500K. > Yes, that's right. And at 1.4 AU, it would be 335K, at 2 AU it would be 280K, which is close to freezing. >Upon further consideration, I don't think the re-radiated heat will help >to inflate a sphere of black body material which radiates equally to the >inside and to the outside. Consider the situation you described (I think it >was the nonreflecting surface): as you pointed out, the sphere in steady-state >must radiate to the outside the same amount as the solar energy directly >incident upon its inner surface - about 1400 W/m^2 at 1AU. It also radiates >the same amount to the inside. According to my earlier spherical integration, >the perpendicular force vector from this radiation is reduced by a factor of >2 because the surface radiates in all directions. > Yes, all right. I got the same result. >The inside of the sphere >absorbs 2800 W/m^2 (half from the sun, half uniformly distributed over a >solid angle of 2*pi sr from the rest of the inner surface of the sphere). > Ah hah! And half more from the radiation TO the inner volume of the sphere. That's 1 (from the Sun), 1/2 (from radiation from other parts of the sphere hitting it), and 1/2 more (from the radiation it is sending to other parts of the sphere). >The >surface of the sphere thus experiences an outward force of 1.5 times that >of the solar flux alone, and an inward force of .5 times the solar radiation >pressure. The net result is that the sphere experiences no more outward force >than if the surface radiation were ignored. (Again, if the inner surface is >reflective, the situation is different - but the black body formula has to be >modified.) > Well, outward force of 2 times that of the solar flux, and an inward force of 1/2 the solar momentum flux. Putting this back into the equations, the acceleration of gravity at 1 AU due to the Sun is 5.95E-3 m/s^2. The force per unit area of the solar radiation pressure at 1AU in the Dyson sphere is 6.9E-6 N/m^2. This means that the surface of the sphere could be held up by radiation pressure if it had a mass density of 1 kg per 960 m^2 of area. >I didn't quite follow how you got some of your numbers - more detail might >be helpful. > Hope this helps. > John Roberts > roberts@cmr.ncsl.nist.gov -- Christopher Neufeld....Just a graduate student | "Spock, comment?" neufeld@helios.physics.utoronto.ca | "Very bad poetry cneufeld@pro-generic.cts.com Ad astra! | captain." "Don't edit reality for the sake of simplicity" | ------------------------------ Date: 10 May 90 04:30:28 GMT From: bfmny0!tneff@uunet.uu.net (Tom Neff) Subject: Re: Manned mission to Venus (long) Several points. * Why wouldn't powersats work for supplying a Venus base? Radar gets through. * You can always dig. I know, I was the one with the snide remark a few months back -- "if you want to live in a basement, how much does it matter which planet the basement is on," but even so -- if you HAD to go to Venus for some reason, you could dig. * The way things are going, top priority may be terraforming the Earth before we get to the other planets. :-) * Regardless -- Mars before Venus. Mars could be settled with a century's work. Venus may take a millenium, and I'm not sure why anyone would care. * The one reason NOT to colonize the planets is lebensraum. We added three billion to Earth this century. We can trash any biosphere you give us. There is no substitute for learning to manage our planet sensibly. -- "UNIX should be used :: Tom Neff or as an adjective." -- AT&T :: ...uunet!bfmny0!tneff (UUCP only) ------------------------------ End of SPACE Digest V11 #386 *******************