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 ; Mon, 23 Apr 90 01:43:06 -0400 (EDT) Message-ID: <4aAdL8u00VcJEGh042@andrew.cmu.edu> Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Mon, 23 Apr 90 01:42:33 -0400 (EDT) Subject: SPACE Digest V11 #304 SPACE Digest Volume 11 : Issue 304 Today's Topics: 'Soviet Space' exhibit at Boston Museum of Science Re: Drake Equation (was Re: Interstellar travel) Re: Pegasus launchers, space-going DUCT TAPE Re: Radar (was Re: Drake Equation Re: Drake Equation (was Re: Interstellar travel) Re: Drake Equation power frequencies equation of time needed Re: Drake Equation (was Re: Interstellar travel) Dyson spheres? Re: Fatal voltages Pegasus launchers, space-going DUCT TAPE ---------------------------------------------------------------------- From: davidbrierley@lynx.northeastern.edu Date: Sun, 22 Apr 90 18:10:51 EST To: astronomy@bbn.com, space@andrew.cmu.edu Subject: 'Soviet Space' exhibit at Boston Museum of Science Source-Info: From (or Sender) name not authenticated. From June 1 to September 23, 1990 the Museum of Science in Boston will be sponsoring a special exhibition entitled 'Soviet Space.' Some of the items in the exhibit are full-scale models of Sputnik 1 (the first man-made satellite) and Lunakhod 2 (a moon rover); components of Luna 24 (the last unmanned probe to the moon) and the Vega probe (which explored Venus in 1984 and Comet Halley). Also featured will be a five meter model of the MIR orbiter. The exhibit will also include space suits, tools, and food from the Soviet space program. Technical experts from the Soviet Union will also be on hand throughout the exhibit for lectures, questions, etc. Please note: I do not know what effect, if any, the situation in Lithuania will have on the exhibit. For more information: Museum of Science Science Park Boston, MA 02114-1099 (617) 723-2500 P.S. The exhibit 'Space Spinoffs,' focusing on technology that developed as a result of space research, ends this Tuesday, April 24. David R. Brierley Northeastern University ------------------------------ Date: 23 Apr 90 02:13:25 GMT From: calvin.spp.cornell.edu!johns@cu-arpa.cs.cornell.edu (John Sahr) Subject: Re: Drake Equation (was Re: Interstellar travel) In article <1990Apr22.154923.24834@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes: >In article <1990Apr21.195116.4258@calvin.spp.cornell.edu> johns@calvin.spp.cornell.edu.UUCP (John Sahr) writes: [] >>1) 60 Hz is much lower than the "plasma frequency" of the ionosphere >>(greater than about 1 MHz everywhere on the Earth). > >The plasma frequency of a plasma with electron density N (in units of >eletrons per cubic meter) is 56.35 N^{1/2} Hz. The formula above yields the radian-frequency. The plasma frequency in Hz is 9 sqrt(N) Hz (The "9" is approximate, should be 8.977297....) Radian frequencies should be marked as 1/sec or sec^-1, which is not the same as Hz. For a nice intro to plasma physics, see the text "Introduction to Plasma Physics and Controlled Fusion" by Francis Chen (2nd edition is MKS, 1st edition is cgs). -- John Sahr, | Electrical Engineering - Space Plasma Physics johns@alfven.spp.cornell.edu | Cornell University, Ithaca, NY 14853 ------------------------------ Date: 23 Apr 90 00:12:00 GMT From: crdgw1!sixhub!davidsen@uunet.uu.net (Wm E. Davidsen Jr) Subject: Re: Pegasus launchers, space-going DUCT TAPE In article cobbhs@AFSC-SSD.AF.MIL ("HENRY S. COBB, 1LT.") writes: | Does the Space Shuttle carry duct tape? You better believe it. The | In-Flight Maintenance (IFM) kit contains a whole bunch of | hardware-hacker stuff, including voltmeters, breakout boxes, patch | cords, black electrical tape, and "grey tape", the official NASA term | for space-qualified duct tape. I hope it includes "ductile soft iron fastening materials" (bailing wire), too. That might be particularly useful in low G, since it has a useful rigidity in addition to strength in tension. Good for holding something "right there." -- bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen) sysop *IX BBS and Public Access UNIX moderator of comp.binaries.ibm.pc and 80386 mailing list "Stupidity, like virtue, is its own reward" -me ------------------------------ Date: 23 Apr 90 00:46:25 GMT From: mailrus!news-server.csri.toronto.edu!utgpu!utzoo!henry@tut.cis.ohio-state.edu (Henry Spencer) Subject: Re: Radar (was Re: Drake Equation In article <1990Apr22.014025.4826@calvin.spp.cornell.edu> johns@calvin.spp.cornell.edu.UUCP (John Sahr) writes: >>In order to detect ICBMs, these radars would have to have ranges of >>about 2 or 3 times that of regular radars... > >...Even for the DEW-line radars, it may be pointless to increase the >power. Consider that the "E-region horizon" is only 1100 km away (you >can see a 100 km tall mountain from 1100 km), and ICBM trajectories >are fairly low... I think you're a little confused. First, DEW-line radars, ICBM-warning radars, and OTH radars are three entirely different systems. The DEW line is an old bomber-warning network. Second, both DEW and the BMEWS ICBM-warning radars are ordinary microwave line-of-sight radars that largely ignore the ionosphere. Third, ICBM trajectories are quite high in most cases, as "depressed trajectory" paths reduce payload (although they are considered in defense planning because they also reduce warning time). -- If OSI is the answer, what on | Henry Spencer at U of Toronto Zoology Earth could be the question?? | uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: 22 Apr 90 15:49:23 GMT From: rochester!dietz@rutgers.edu (Paul Dietz) Subject: Re: Drake Equation (was Re: Interstellar travel) In article <1990Apr21.195116.4258@calvin.spp.cornell.edu> johns@calvin.spp.cornell.edu.UUCP (PUT YOUR NAME HERE) writes: >To the extent possible, the power grids are "in phase" across the USA. >However, 60 Hz probably isn't such a great place to go looking for >radio sources. > >1) 60 Hz is much lower than the "plasma frequency" of the ionosphere >(greater than about 1 MHz everywhere on the Earth). The plasma frequency of a plasma with electron density N (in units of eletrons per cubic meter) is 56.35 N^{1/2} Hz. The electron density of the solar wind is roughly around 10^6 m^-3; of interstellar space, perhaps 10^4-10^-6 m^-3. Looking for low frequency leakage from alien power grids is, therefore, futile -- space is opaque at those frequencies. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: 21 Apr 90 23:45:32 GMT From: unhd!rmk@uunet.uu.net (Robert M. Kenney) Subject: Re: Drake Equation In article <7149@timbuk.cray.com> lfa@timbuk.cray.com (Lou Adornato) writes: >>The point that people are forgetting is the impracticality of advanced >>civilisations using radio signals, especially if they're technologically >>advanced enough to have colonised other worlds and thereby need to keep in >>contact. We are acting like American Indians a couple of hundred years ago > Native Americans >>looking for smoke signals from a neighboring tribe to indicate they're >>presense when they're using CB radios. > > >I'm certainly willing to conceede that there are things in the universe >that we don't understand. However, I'm not sure I can accept that >there's an information medium that can travel through a vacuum at (or >faster) than light over long distances, of which we are completely >ignorant. How about gravity waves? As far as I'm concerned, we're not too far(couple of centuries, at most) from having G-wave communications ourselves. Just a consequence of finishing the GUT, which could be any day now. -- ----------------------------------------------------------------------- Robert M. Kenney uucp: uunet!unhd!rmk USNH Computer Services Nearnet: rmk@unh.edu Kingsbury Hall, UNH BITNET: R_KENNEY@UNHH ------------------------------ Date: 23 Apr 90 00:54:17 GMT From: mailrus!news-server.csri.toronto.edu!utgpu!utzoo!henry@tut.cis.ohio-state.edu (Henry Spencer) Subject: power frequencies In article <21959@nuchat.UUCP> steve@nuchat.UUCP (Steve Nuchia) writes: >To include a shred of space relevance, which power distibution >scheme is currently in vogue for the space station? ... DC. For a while they were planning an insane 20kHz system, which would have meant custom-building everything from wiring to lightbulbs. When they abandoned that as a cost-cutting measure, I guess it would have been humiliating to admit the mistake, so they went straight to DC instead of using the aviation standard of 400Hz AC. -- If OSI is the answer, what on | Henry Spencer at U of Toronto Zoology Earth could be the question?? | uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: 22 Apr 90 17:23:30 GMT From: bbn.com!grossman@bbn.com (Martin Grossman) Subject: equation of time needed I'm looking for the equations (or tables) of time that will give me how many minutes and seconds the sun is fast/slow during the year. This is going to be used on a microprocessor (8031) hooked upto a sundial. PS Do the equations take into effect height ? PS Do the equations take into effect latitude ? PS Do the equations take into effect logitude (ie how far away I am from the centerline of the eastern time zone) ? Please send reply via email to grossman@bbn.com ------------------------------ Date: 22 Apr 90 18:11:29 GMT From: nuchat!steve@uunet.uu.net (Steve Nuchia) Subject: Re: Drake Equation (was Re: Interstellar travel) In article <2323@wrgate.WR.TEK.COM> dant@mrloog.WR.TEK.COM (Dan Tilque) writes: >steve@nuchat.UUCP (Steve Nuchia) writes: >>spectral lines are at 50 and 60 Hz (remember, not all the ... >>choosing the optimally fatal frequency than we did). >Is this a figure of speach or is some low frequency actually fatal? One thing about power grids -- they reach into homes, where they occasionally come into contact with children, pets, electricians, whatnot. Different frequencies of AC, in contact with the body, differ in probability of serious injury. 60 Hz is just above the saddle in the 50% fatal voltage level curve, 50 Hz is closer. The fact that they also use twice the voltage we do for standard residential service is probably a more important factor in the different electrocution statistics, which I don't have handy (and which are skewed by the fact that the Europeans *know* getting shocked is more dangerous than we do.) If we had it to do over again, 400 Hz would have been a much better choice. At the time though, the extra complexity in the rotating machinery placed a low upper bound on the frequency. Today's utility generators are plenty complex; wouldn't be a big deal. Changing over would. Nothing about low frequency *radiation* is particularly hazardous. To include a shred of space relevance, which power distibution scheme is currently in vogue for the space station? I wonder if shock hazard is one of the things they are considering in making the choice? The RF they were proposing is (somewhat) less hazardous in direct contact, but it is a lot more likely to find a leakage path to the case, than DC or 400 Hz. I don't know which is the best choice, but I suspect it's 400 Hz. Given that the human specimens selected for space duty are in superb condition, and that they are isolated from communicable diseases once on station, electrocution has to rank pretty high on the list of mission-critical medical contingencies. Contamination of the air supply, eg by a small fire, and burns from experiments or fires are about the only other things that are likely (ignoring EVA for the moment). Minimizing electrocution risk would seem to be worth a few kilograms mass. ------------------------------ Date: 22 Apr 90 18:46:42 GMT From: sun.udel.edu!salamon@vax1.udel.edu (Andrew Salamon) Subject: Dyson spheres? So whats a dyson sphere? Magic in my Mind | /Andrew/ Music in my Heart | soi-disant Bleydion op Rhys Laughter in my Soul | salamon@sun.acs.udel.edu And...A Sword in my Fist (sigh) | ------------------------------ Date: 22 Apr 90 20:01:26 GMT From: usc!cs.utexas.edu!news-server.csri.toronto.edu!qucdn!gilla@ucsd.edu (Arnold G. Gill) Subject: Re: Fatal voltages In article <21959@nuchat.UUCP>, steve@nuchat.UUCP (Steve Nuchia) says: > >whatnot. Different frequencies of AC, in contact with the body, >differ in probability of serious injury. 60 Hz is just above >the saddle in the 50% fatal voltage level curve, 50 Hz is closer. You are going to have to explain this one to me a little bit better. I guess I was always under the mistaken impression that the dangers of electricity have a lot more to do with voltage and the amount of current that that voltage can pump through a person (0.1A is supposedly the fatal current level). What effect can frequency have? ------- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- | Arnold Gill | | | Queen's University at Kingston | If I hadn't wanted it heard, | | BITNET : gilla@qucdn | I wouldn't have said it. | | X-400 : Arnold.Gill@QueensU.CA | | | INTERNET : gilla@qucdn.queensu.ca | | -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- ------------------------------ Date: 22 Apr 90 14:01:00 PDT From: "HENRY S. COBB, 1LT." Subject: Pegasus launchers, space-going DUCT TAPE To: "space" I N T E R O F F I C E M E M O R A N D U M Date: 22-Apr-1990 13:38 PDT From: HENRY S COBB, 1LT COBBHS Dept: CLFP Tel No: 643-2504 TO: _MAILER! ( _DDN[SPACE@ANDREW.CMU.EDU] ) Subject: Pegasus launchers, space-going "duct tape" In all this discussion of possible launch aircraft for Pegasus, I haven't seen anyone mention OSC's _actual_ plan: they are accepting bids for a (used) passenger airliner, jumbo-jet class. OSC expects to wind up with a Lockheed L-1011. The airlines don't like them any more, because they are relatively rare and therefore comparatively expensive to support. This makes them cheap to acquire; I heard rumors that OSC thought they could get one for some $3-5 million, an order of magnitude less than the price new. The "launch-a-rocket-from-a-dirigible" idea was tried as far back as the late '50's. Look it up under the name "rockoon" (from rocket-baloon). In the rockoon concept, the baloon was expendable, but high-altitude baloons aren't all that expensive (under $1 million per shot, if memory serves). And now to duct tape: Yes, Apollo 13 was saved by duct tape (among other things). Why did they have duct tape when they needed it? Probably for the same reason Mary Shaefer's tool crib stocks it -- the stuff has a million uses, and can save your bacon if you're smart enough to improvise. Nobody ever said NASA was dumb. Does the Space Shuttle carry duct tape? You better believe it. The In-Flight Maintenance (IFM) kit contains a whole bunch of hardware-hacker stuff, including voltmeters, breakout boxes, patch cords, black electrical tape, and "grey tape", the official NASA term for space-qualified duct tape. Cheers... --Stu Round up the usual disclaimers ... (COBBHS @ AFSC-SSD.AF.MIL) ------------------------------ End of SPACE Digest V11 #304 *******************