marcum%nescorna@Sun.COM (Alan M. Marcum) (03/26/88)
There's an interest editorial in the latest _Air & Space Smithsonian_, dicussing the "permament lunar base" vs "Mission to Mars" issue. Recommended reading. --- Alan M. Marcum Sun Microsystems, Technical Consulting marcum@nescorna.Sun.COM Mountain View, California
hubcap@hubcap.UUCP (Mike Marshall) (04/04/88)
The same issue of Air&Space contains an article entitled "Resist the Pull of Mars" in which the author talks about "The dark far side of the moon..." being a good place to conduct " ...sensitive radio astronomy... without interference from terrestrial signals." Since this is a credible magazine, I should give the guy the benefit of the doubt and assume he is talking about the period of time that the moon appears full from the perspective of the earth, but that's not how it reads. -Mike Marshall hubcap@hubcap.clemson.edu ...!hubcap!hubcap
josh@topaz.rutgers.edu (J Storrs Hall) (04/04/88)
-> The same issue of Air&Space contains an article entitled "Resist the -> Pull of Mars" in which the author talks about "The dark far side of the -> moon..." being a good place to conduct " ...sensitive radio astronomy... -> without interference from terrestrial signals." -> Since this is a credible magazine, I should give the guy the benefit -> of the doubt and assume he is talking about the period of time that the -> moon appears full from the perspective of the earth, but that's not how -> it reads. One of the common meanings of "dark" in colloquial English is "unknown", as in "darkest Africa", something the poster was possibly in the dark about. "The dark side of the moon" simply means the side facing away from the earth. --JoSH
jlg@a.UUCP (Jim Giles) (04/04/88)
The moon always has the same face toward the earth. That is, it rotates with the same period as it orbits the earth. The 'far' side of the moon was therefore often called the 'dark' side because it was unknown to human experience until spacecraft went there. The term is similar to the use of 'dark' with respect to Africa (it wasn't a racial slur but a reference to the fact that much of the African contenent was unknown to europeans even to the beginning of this century). Just as Africa is still often called the 'dark contenent', people also still often refer to the 'dark side' of the moon. It is true that a base on the far side of the moon woud be a reasonable place toconduct radio astronomy because the moon would block all the earth-based radio noise. Many astronomers feel that such a moon base would be a much more important goal than manned trips to Mars. J.L.G.
sw@whuts.UUCP (WARMINK) (04/04/88)
In article <1290@hubcap.UUCP>, hubcap@hubcap.UUCP (Mike Marshall) writes:
: The same issue of Air&Space contains an article entitled "Resist the
: Pull of Mars" in which the author talks about "The dark far side of the
: moon..." being a good place to conduct " ...sensitive radio astronomy...
: without interference from terrestrial signals."
: Since this is a credible magazine, I should give the guy the benefit
: of the doubt and assume he is talking about the period of time that the
: moon appears full from the perspective of the earth, but that's not how
: it reads.
Surely the "dark far side" of the moon is always shielded from *terrestrial*
signals, regardless of whether it is actually dark or not at the time: it
always faces away from the Earth.
--
------------------------------------------------------------------------------
"We demand rigidly defined areas of | Stuart Warmink, APT UK Ltd.
doubt and uncertainty" (Vroomfondel) | <ihnp4>!whuts!sw
-----------> My opinions are not necessarily those of APT UK Ltd. <-----------beryl@oresoft.UUCP (Beryl Gray) (04/04/88)
In article <Apr.3.18.23.48.1988.13258@topaz.rutgers.edu> josh@topaz.rutgers.edu (J Storrs Hall) writes: >-> The same issue of Air&Space contains an article entitled "Resist the >-> Pull of Mars" in which the author talks about "The dark far side of the >-> moon..." > >-> Since this is a credible magazine, I should give the guy the benefit >-> of the doubt and assume he is talking about the period of time that the >-> moon appears full from the perspective of the earth, but that's not how >-> it reads. > >One of the common meanings of "dark" in colloquial English is >"unknown", as in "darkest Africa", something the poster was possibly >in the dark about. "The dark side of the moon" simply means the side >facing away from the earth. >--JoSH Can we adopt the old Bob Heinlein convention of calling it "Farside?" -- Beryl Gray "Clear writers, like fountains, do not seem so deep uunet!oresoft!beryl as they are; the turbid look the most profound." -Walter S. Landor
karn@thumper.bellcore.com (Phil R. Karn) (04/06/88)
> ... The dark far side of the > : moon..." being a good place to conduct " ...sensitive radio astronomy... > : without interference from terrestrial signals." Yes, it's a great idea. In fact, it's already been done. Only it was an unmanned probe in lunar orbit instead of a manned base on the surface. The spacecraft recorded its observations during the time it was shielded from earth, and it relayed them back down when earth was visible. I really wish people would stop clutching at straws, looking for every possible application of their pet man-in-space project when many (if not most) of the tasks can be done far more cheaply and effectively with unmanned spacecraft. In the case of lunar-shielded radio astronomy, lunar orbit makes a lot more sense than the lunar surface for several very good reasons: 1. You need communications channels back to earth. A radio telescope on the far side of the moon would need relay satellites in lunar orbit for this purpose. These satellites would themselves have to transmit within view of the far side of the moon, possibly polluting the very spectrum you spent so much to view in a pristine state. On the other hand, a telescope in lunar orbit can provide its own store-and-forward relay. It need not transmit anything at all while it is actually observing. 2. You need power. This is much easier to obtain in orbit, since solar panels will be illuminated for roughly half of each orbit. On the surface, you will almost certainly need nuclear power sources to carry you through the long 2-week lunar night. Thermal control is also much easier in orbit. Of course much of a surface station could be buried to help level out the day/night temperature fluctuations, except for the antennas -- and these are likely to be very susceptible to severe thermal-induced distortions. 3. You need large antennas. You can build truly awesome arrays in zero-gee that require very little mass. Not quite as easy even in 1/6 G. Even Arthur C. Clarke originally conceived of his geostationary satellite relays as being manned. Fortunately, technological developments (and some economic common sense) have made that romantic notion unnecessary. Phil
dunc%moria@Sun.COM (duncs home) (04/06/88)
In article <1022@thumper.bellcore.com> karn@thumper.bellcore.com (Phil R. Karn) writes: > ... >1. You need communications channels back to earth. A radio telescope on >the far side of the moon would need relay satellites in lunar orbit for >this purpose. These satellites would themselves have to transmit within >view of the far side of the moon, possibly polluting the very spectrum >you spent so much to view in a pristine state. On the other hand, a >telescope in lunar orbit can provide its own store-and-forward relay. It >need not transmit anything at all while it is actually observing. There's no reason a relay satellite couldn't store and forward in exactly the same way. >2. You need power. This is much easier to obtain in orbit, since solar >panels will be illuminated for roughly half of each orbit. On the On the surface solar panels are illuminated for roughly half the time too. Yes, you have to store the energy longer, but you have planet worth of raw materials to assist. In return you get to make uninterrupted observations for as long as you choose. The orbital observatory spends half the time with the Earth shouting in it's ears and half the remainder with the Moon between it and whatever it's interested in. >surface, you will almost certainly need nuclear power sources to carry >you through the long 2-week lunar night. Thermal control is also much >easier in orbit. Of course much of a surface station could be buried to >help level out the day/night temperature fluctuations, except for the >antennas -- and these are likely to be very susceptible to severe >thermal-induced distortions. Could you explain again why having the antenna cycle from sunlight to shade every few tens of minutes provides better stability than having it happen every two weeks? >3. You need large antennas. You can build truly awesome arrays in zero-gee >that require very little mass. Not quite as easy even in 1/6 G. Probably true. On the other hand, it's probably easier to get all the bits pointed in the same direction when they're mounted on a large common platform. --Dunc
dep@CAT.CMU.EDU (David Pugh) (04/07/88)
In article <48414@sun.uucp> dunc@sun.UUCP (duncs home) writes: >1. You need communications channels back to earth. A radio telescope on >the far side of the moon would need relay satellites in lunar orbit for >this purpose. ... Why do you need a relay satellite? We lay cables across the ocean, which is surely a rougher environment than the Moon. No current, no marine life, and no corrosion. The temperature extremes on the Moon shouldn't be all that difficult to handle. I can see laying fiber-optic cable using technology from derived wire-guided missiles: fire a missile containing 100+km cable, go to whereever it lands, splice the cable to a new missle, etc. Repeat 20 times.... -- "Fools are always at the bottom of David Pugh the food chain." Cesare, _Elf Defense_ ...!seismo!cmucspt!gpa!dep
compton@silver.bacs.indiana.edu (David Compton) (04/07/88)
In article <48414@sun.uucp> dunc@sun.UUCP (duncs home) writes: >>2. You need power. This is much easier to obtain in orbit, since solar >>panels will be illuminated for roughly half of each orbit. On the If you would think about it, a satellite could be in sunlight almost all the time(e.g.) a polar orbit. This makes it a better alternative than the ground based nuclear plant. dave -- compton@silver.bacs.indiana.edu ihnp4!inuxc!iuvax!silver!compton compton@silver.UUCP compton%silver@iuvax.cs.indiana.edu
karn@thumper.bellcore.com (Phil R. Karn) (04/07/88)
> If you would think about it, a satellite could be in sunlight > almost all the time(e.g.) a polar orbit. Not really. To do what you want for an appreciable length of time, you want a "sun synchronous" orbit phased over the terminator. This is actually pretty easy to do with the earth (almost every launch from Vandenburg goes into sun-synchronous orbit, though usually not over the terminator). But a sun-synchronous lunar orbit is much more difficult because of the moon's far more irregular gravity field, and because of the earth's proportionately larger perturbations. I was thinking of a lunar equatorial orbit mainly because it's much cheaper to get there. Phil
jmckerna@polyslo.UUCP (John L McKernan) (04/07/88)
In article <1022@thumper.bellcore.com> karn@thumper.bellcore.com (Phil R. Karn) writes: >I really wish people would stop clutching at straws, looking for every >possible application of their pet man-in-space project when many (if not >most) of the tasks can be done far more cheaply and effectively with >unmanned spacecraft. Fact 1. For as long as Homo Sapiens Sapiens has existed, we have expanded our range of habitation, or sought to fill uninhabited land. Conclusion 1. Man's future is in space and on other planets. Fact 2. A human being has more capabilities than any of his machines, by orders of magnitude. It is short sighted and an oversimplification to say that people should not go into space. Any reasonable space program requires both a strong manned and unmanned program. John L. McKernan. Student, Computer Science, Cal Poly S.L.O. -------------------------------------------------------------------------------
fiddler%concertina@Sun.COM (Steve Hix) (04/08/88)
In article <1335@PT.CS.CMU.EDU>, dep@CAT.CMU.EDU (David Pugh) writes: > In article <48414@sun.uucp> dunc@sun.UUCP (duncs home) writes: > >1. You need communications channels back to earth. A radio telescope on > >the far side of the moon would need relay satellites in lunar orbit for > >this purpose. ... > > Why do you need a relay satellite? We lay cables across the ocean, > I can see laying fiber-optic cable using technology from derived > wire-guided missiles: fire a missile containing 100+km cable, go > to whereever it lands, splice the cable to a new missle, etc. Why make work for yourself? Take a line-of-sight bearing in the direction of your transmitting statioon that can see Earth. Place a relay on the horizon at that bearing. Repeat until you can see the transmitting station. Use lasers to transmit data from the observatory to the downlink station (uplink? I get confused easily.). No weather to degrade the laser signal, no kids on tricycles to knock over the relays. Set up two or three relay paths for redundancy. Save fiber optics for your lunar cable TV network. (To make it harder to bootleg programming, of course.) seh
james@bigtex.uucp (James Van Artsdalen) (04/08/88)
IN article <1384@silver.bacs.indiana.edu>, compton@silver.UUCP (David Compton) wrote: > If you would think about it, a satellite could be in sunlight > almost all the time(e.g.) a polar orbit. This makes it a better alternative > than the ground based nuclear plant. I am not an astronomer, but it seems to me that if it is useful to place an observatory on the far side of the moon so that Earth isn't radiating at the telescope, it would also be useful to place the observatory to avoid the Sun shining on it. Is this not the case, or am I missing the benefit of placing an observatory on the moon? -- James R. Van Artsdalen ...!ut-sally!uastro!bigtex!james "Live Free or Die" Home: 512-346-2444 Work: 328-0282; 110 Wild Basin Rd. Ste #230, Austin TX 78746
jwm@stdc.jhuapl.edu (James W. Meritt) (04/08/88)
In article <1782@polyslo.UUCP> jmckerna@polyslo.UUCP (John L McKernan) writes: >Fact 2. A human being has more capabilities than any of his machines, by orders > of magnitude. How about "A human being is more versatile than any of his machines so far" A phrase like "more capabilities" is subject to misunderstanding. i.e. if the capability in question is lifting rocks, a crane does that real well. "We" (assuming not a netted AI) are just more versatile - we do ANYTHING!!! Disclaimer: Individuals have opinions, organizations have policy. Therefore, these opinions are mine and not any organizations! Q.E.D. jwm@aplvax.jhuapl.edu 128.244.65.5
jwm@stdc.jhuapl.edu (James W. Meritt) (04/09/88)
In article <1481@bigtex.uucp> james@bigtex.UUCP (James Van Artsdalen) writes: >IN article <1384@silver.bacs.indiana.edu>, compton@silver.UUCP (David Compton) wrote: >> If you would think about it, a satellite could be in sunlight >> almost all the time(e.g.) a polar orbit. This makes it a better alternative >> than the ground based nuclear plant. >I am not an astronomer, but it seems to me that if it is useful to place >an observatory on the far side of the moon so that Earth isn't radiating at >the telescope, it would also be useful to place the observatory to avoid the >Sun shining on it. Is this not the case, or am I missing the benefit of >placing an observatory on the moon? I am afraid that I cannot envision a point which is both hidden from the earth and hidden from the sun on the surface of the moon, unless you mean in a hole. Where did you mean? Disclaimer: Individuals have opinions, organizations have policy. Therefore, these opinions are mine and not any organizations! Q.E.D. jwm@aplvax.jhuapl.edu 128.244.65.5
karn@thumper.bellcore.com (Phil R. Karn) (04/09/88)
> I am not an astronomer, but it seems to me that if it is useful to place > an observatory on the far side of the moon so that Earth isn't radiating at > the telescope, it would also be useful to place the observatory to avoid the > Sun shining on it. Is this not the case, or am I missing the benefit of > placing an observatory on the moon? The question dealt specifically with RADIO telescopes, not optical ones. The idea is to use the moon to shield radio telescopes from the intense din of artificially generated signals coming from the earth and near-earth orbit. If you are doing very low frequency observations I suppose the moon would also help shield against most of the naturally generated signals coming from the earth's atmosphere (e.g., lightning) and the region of space near the earth. (VLF through HF astronomy would in any case have to be done from space to get past the earth's reflecting ionosphere, as would microwave astronomy much above 20 Ghz or so in order to avoid atmospheric absorption). Although the sun does emit radio frequency energy, it emits proportionately far more at infrared and visible wavelengths than does the earth. Thanks to things like FM, VHF and UHF TV broadcast transmitters, the earth already rivals the sun at meter wavelengths, and when the radars crank up at Arecibo, Goldstone or Haystack, the earth becomes one of the brightest objects in the entire galaxy at the right frequencies and directions. Since the earth's atmosphere doesn't scatter RF like it does visible (especially blue) light there's no problem in operating surface radio telescopes during the day. Of course, in space or on the airless moon there is no optical scattering either, so you can also operate optical telescopes during the day. You just put a baffle around the front, like the one on the Space Telescope. In fact, with small antennas operating at VHF frequencies it's actually easier to "see" the hotter parts of the galaxy than it is to "see" the sun. The sun may have an effective noise temperature at VHF of a hundred thousand kelvin vs a few thousand for the galactic center, but the hot parts of the galaxy are much larger and fill much more of the antenna's beamwidth. I can easily see the difference when I aim my amateur satellite antenna (14 element yagi on 145 Mhz with GaAsFET preamp) first in and at right angles to the galactic plane. However, to really "see" the sun takes somewhat larger antennas (so the sun fills more of the smaller beamwidth) and this is in fact a very common method for evaluating the performance of large antennas. Phil
f12012ag@deimos.unm.edu (Chang H. Park) (04/09/88)
In article <1022@thumper.bellcore.com> karn@thumper.bellcore.com (Phil R. Karn) writes: >> ... The dark far side of the >> : moon..." being a good place to conduct " ...sensitive radio astronomy... >> : without interference from terrestrial signals." > >Yes, it's a great idea. In fact, it's already been done. Only it was an >unmanned probe in lunar orbit instead of a manned base on the surface. >The spacecraft recorded its observations during the time it was shielded >from earth, and it relayed them back down when earth was visible. > >I really wish people would stop clutching at straws, looking for every >possible application of their pet man-in-space project when many (if not >most) of the tasks can be done far more cheaply and effectively with ^^^^^^^^^^^ Are you sure about this??? -------------------------------| It seems to me that long term observations of some objects would be easier to carry out on the moon, as opposed to a satellite. (Which would be orbiting the moon....at times having the moon itself eclipse the very object under observation!) >unmanned spacecraft. In the case of lunar-shielded radio astronomy, >lunar orbit makes a lot more sense than the lunar surface for several >very good reasons: > >1. You need communications channels back to earth. A radio telescope on >the far side of the moon would need relay satellites in lunar orbit for >this purpose. These satellites would themselves have to transmit within >view of the far side of the moon, possibly polluting the very spectrum >you spent so much to view in a pristine state. On the other hand, a >telescope in lunar orbit can provide its own store-and-forward relay. It >need not transmit anything at all while it is actually observing. Come on! This is a weak argument. For one thing, the same store and forward technology could just as easily be used for the moon to earth relay satellites. >2. You need power. This is much easier to obtain in orbit, since solar >panels will be illuminated for roughly half of each orbit. On the >surface, you will almost certainly need nuclear power sources to carry This may be true...but what about running cables to the other side of the moon to carry electricity while the telescope is in the lunar night. Several solar power arrays would keep the telescope powered continuously. Superconducting cables would help...even to the point of eliminating the need for a relay sat. in orbit. Just place your communications antenna on the earth-facing side of the moon! >you through the long 2-week lunar night. Thermal control is also much >easier in orbit. Of course much of a surface station could be buried to >help level out the day/night temperature fluctuations, except for the >antennas -- and these are likely to be very susceptible to severe >thermal-induced distortions. > [....] > >Phil Just thought I`d say something. The radio telescope on the moon is a great idea. Even if people use it as an excuse for getting men & women in space, so what! What`s wrong with that? Isn`t that the goal we all have...or am I being silly Let`s explore the possibility of having both oribiting and surface telecopes. Ollie Eisman - N6LTJ -- SEDS-UNM : Students for the Exploration and Development of Space Box 92 Student Union, University of New Mexico, Albuquerque, NM 87106 (505) 277-3171
karn@thumper.bellcore.com (Phil R. Karn) (04/11/88)
> It seems to me that long term observations of some objects would be > easier to carry out on the moon, as opposed to a satellite. (Which > would be orbiting the moon....at times having the moon itself eclipse > the very object under observation!) You're forgetting that a base on the moon's surface would also be eclipsed by the moon itself. Once an object set, you'd have to wait 2 weeks, not just 12 hours, to see it again. From lunar orbit you'd have even less time to wait. (Please don't tell me about siting bases on the moon's poles. You'd not be shielded from the earth, which was the whole point of this exercise, and a single base would never see half of the sky). Not that many astronomical observations require such long and uninterrupted views of a single object. Remember that the Space Telescope will be similarly limited, yet it will still be a very powerful instrument. > Come on! This is a weak argument. For one thing, the same store and > forward technology could just as easily be used for the moon to earth > relay satellites. Agreed. But if you need lunar satellites for communications, why not just put the instruments there too? > This may be true...but what about running cables to the other side of the > moon to carry electricity while the telescope is in the lunar night. Now YOU'RE way out on a limb (weak pun unintended) here. Ever hear of the engineer's corollary to Occam's Razor? The simplest and cheapest way to do job reliably is usually the best way. > Just thought I`d say something. The radio telescope on the moon is > a great idea. Even if people use it as an excuse for getting men & > women in space, so what! What`s wrong with that? Isn`t that the goal > we all have...or am I being silly Now we come to the real heart of the matter. You're now admitting what I said in my first item, that everyone was falling all over themselves trying to find some practical excuse, no matter how stretched, for putting as many people in space as possible. Isn't this exactly the mistake NASA made with the Shuttle? Obviously it didn't learn much the first time, because now it's doing it all over again with Space Station. Look, I really *do* enjoy manned missions. I was one of the few people around here to see Challenger blow up on the TV in real time, because the major networks (and most other people) had long tired of shuttle launches by then. Not me. But at least I try to be up front about it -- I admit that I enjoy manned missions strictly for entertainment and/or educational value. My share in a Shuttle launch is a lot less than a movie ticket. But I don't try to rationalize that sending up seven people is the best way to launch a communications satellite, or conduct earth resources photography, or any of a long list of things that have been done perfectly well and far more cheaply (if with less glamor) with unmanned launchers. The one aspect of the STS-51L mission that really did require a human presence in space was the part everyone was looking forward to -- Christa McAuliffe's science lesson. The shuttle is admirably suited to this sort of thing, which is completely worthwhile if inspires youngsters into careers in engineering or science. But don't kid yourself -- for the vast majority of practical space applications, you're a lot better off in the long run by going after the simplest and most direct approach to the problem, and only VERY rarely does this require humans in space. Phil
fiddler%concertina@Sun.COM (Steve Hix) (04/12/88)
In article <211@aplcomm.UUCP>, jwm@stdc.jhuapl.edu (James W. Meritt) writes: > In article <1481@bigtex.uucp> james@bigtex.UUCP (James Van Artsdalen) writes: > >I am not an astronomer, but it seems to me that if it is useful to place > >an observatory on the far side of the moon so that Earth isn't radiating at > >the telescope, it would also be useful to place the observatory to avoid the > >Sun shining on it. > I am afraid that I cannot envision a point which is both hidden from the > earth and hidden from the sun on the surface of the moon, unless you > mean in a hole. Where did you mean? A large Farside telescope would have 14-day-long nights...this would give you a place to make very long exposures with reduced tracking efforts, no weather to worry about, no local light pollution sources, and less vibration from local truck traffic. seh