Date: Mon, 5 Mar 1990 17:40-EST From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #52 Contents: Edward Wright Re: Dropping a cable on the moon Jim Smith Communication on Luna S Schaper Re: CQ Moon Don Lindsay Re: Dropping a cable on the moon John Roberts Lunar synchronous orbit Chris Neufeld Re: CQ Moon Chris Neufeld Re: CQ Moon Marc Ringuette Re: CQ Moon Henry Spencer Re: CQ Moon Henry Spencer Re: CQ Moon ------------------------------------------------------------ Date: Fri, 2 Mar 90 11:31:38 CST From: "Edward V. Wright" To: lfa@vielle.cray.com, mikew@neptune.fx.com, space-tech@CS.CMU.EDU Subject: Re: Dropping a cable on the moon >The DoD types have all sorts of wire guided missiles and torpedoes in >development or in use. Given the low surface gravity on the moon, it wouldn't >take that much of a rocket to send out a _LOT_ of cable. The problem I forsee is in actually *landing* the cable on the Moon. (Plus, do you really want to be firing a missile at the other base?) Think of the problems involved in laying an undersea cable: even there the cable occasionally breaks during the laying process and has to be hauled back up for repairs, and the cable-laying ships don't travel at nearly the speed of a rocket. I think it would be safer to lay your cable from a surface vehicle. >So, the question is, is 100km longer than line of sight on the moon? That depends. How high a tower are you willing to build? Keep in mind, the Moon has a smaller radius than the Earth, so the horizon is a lot closer. Are you planning to use glass or plastic fibers for the cable? How flexible are glass fibers? Plastic is going to be expensive on the Moon and may be susceptible to outgassing and long-term radiation damage. Of course, if you don't need ultra-high-speed data links, maybe you don't need fiber optics at all, just old- fashioned aluminum cable. (Just thinking out loud here, folks.) ------------------------------ Date: Fri, 2 Mar 90 15:08:18 -0500 From: 6079 Smith J To: space-tech@DAISY.LEARNING.CS.CMU.EDU Subject: Communication on Luna If you're willing to build a mighty tall tower, you can just use line- of-sight repeaters. Or you can build a lot of short ones. The numbers are as follows, where R is the radius of Luna (about 2400 miles? That's a guess, folks, I don't have any books here). x = R ( sec(theta) - 1 ) where x is the height of the tower, and theta is the angle you space your repeaters at. If you use R=2400 mi, for instance, you get a height of about 9 miles for 72 towers to cover the equator and a strip 100 miles each side. If you want the towers 500' high (reasonable) you need 720 of them. Of course, mountains and such make things both easier and harder. Probably, orbiting reflectors are the way to go. You're already pretty heavily into space before you worry about lunar-surface communication, so redundant satellites shouldn't be a problem. So let's get there, already! 4-aminobiphenyl, hexachlorobenzene/Dimethyl sulfate, chloromethyl methylether/ 2, 3, 7, 8-Tetrachlorodibenzo-para-dioxin, carbon disulfide/Dibromochloropane, | James W. Smith, University of Arkansas | jws3@uafhcx.uark.edu | chlorinated benzenes / 2-nitropropane, pentachlorophenol / Benzotrichloride, strontium chromate/1,2-dibromo-3-chloropropane/Watch it run straight down..... ------------------------------ Date: Thu, 1 Mar 90 09:14:21 CST From: S Schaper To: orbit!bungia!nic.MR.NET!DAISY.LEARNING.CS.CMU.EDU!mnr@pnet51.orb.mn.org Subject: Re: CQ Moon Place an Advanced TDRSS at the L4 and L5 positions, if this does not adequately cover the moon, then use the L2 and L1 if necessary. The LFO - Lunar Farside Observatory (let's get that budgeted NOW!) and the normal, Ride/Quayle manned base will not be at the same location. The manned base will liely be where the resources are particularly good, such as possibly the poles if water is found (ice) or at a spot where the mass driver would be particularly efficient (the limb?) And we don't want to kick up dust onto the mirrors. Plus we need to relay the data flow from the LFO, which has earthlike planet resolving capability out for some light years using current technology. UUCP: {amdahl!bungia, uunet!rosevax, chinet, killer}!orbit!pnet51!schaper ARPA: crash!orbit!pnet51!schaper@nosc.mil INET: schaper@pnet51.cts.com ------------------------------ Date: Fri, 2 Mar 1990 16:58-EST From: Donald.Lindsay@MATHOM.GANDALF.CS.CMU.EDU To: space-tech@CS.CMU.EDU Subject: Re: Dropping a cable on the moon I have good news and bad news. The good news is that there are fiber-guided rockets, which tow several kilometers of fiber. Clearly, the stuff can be made rugged. Also, yes, we are on the verge of being able to lay repeaterless transoceanic cables. The bad news (aside from mass) is that radiation makes fiber slowly lose its transparency. The nuclear industry has had some success in "bleaching" these cables back to usefulness (with high powered lasers). On the Moon, I would assume that a good long lifetime was important. Lunar satellites sound better and better. Don ------------------------------ Date: Fri, 2 Mar 90 19:42:28 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@CS.CMU.EDU Subject: Lunar synchronous orbit >From: Richard Schroeppel >To: space-tech@cs.cmu.edu >Subject: Lunar-synchronous satellite >The earth is in synchronous orbit around the moon. >From a particular place on the moon, the earth >oscillates about a constant position in the sky. >(The oscillation is because the moon's orbit is >an ellipse.) >Rich Schroeppel >rcs@la.tis.com That does not follow. You can't say that the synchronous orbit around a small earth satellite is equal to the distance to the center of the earth just because the satellite may keep one side facing earth. If I got the calculations right, synchronous orbit around the moon would be about 88500km from the center of the moon. This ignores effects from the earth, which could affect the orbit. (Does it? My intuitive guess is that an object in such an orbit would oscillate across a line between the moon and the earth. Obviously, I've never had a course in orbital mechanics. Any good textbooks?) John Roberts roberts@cmr.ncsl.nist.gov [[ Yes, the earth certainly does affect it! You have to be either directly between the earth and moon (the L1 point, I think) or on the other side (the L2 point), if you want a synchronous orbit. -- Marc ]] ------------------------------ Date: Sat, 3 Mar 90 10:01:16 EST From: Christopher Neufeld To: space-tech@CS.CMU.EDU Subject: Re: CQ Moon Brian P. McCarty writes: > The premise is this: suppose somebody buts a base on the moon (Base A) > and somebody (not nessisarily a different organization) puts another > base on the moon. The bases are beyond line-of-sight radio communication. > [this would be less than the los distance on Earth since the Moon > "curves faster", but if you insist on a distance, 1000kM] > How would these two bases communicate with each other? (which > they might want to do even if one or both are not manned) > > Since I don't think the Moon has a usable ionosphere, here are some ideas: > Strange, I have this vague memory that you can bounce signals off a component of the lunar atmosphere, but I'm not sure of this. > #1:Landline (either copper or fiber-optic [preferred]). > Would meteor damage be a threat? (a 1cm diameter cable would have an area > of 10000m^2). > Probably not. It would be interesting, though, if somebody would provide data for the number of significant meteor hits which accumulated in 'n' years and the exposed surface area for that Ranger piece brought back, or any other piece of hardware which has been on the moon's surface. >How much bother to bury it? Don't forget about any repeaters > needed. > Probably too much bother. To lay the cable, you just have to drive from one base to the other at, say, 20 km/h playing out the cable behind you. This could be done in a matter of days. Compare digging a trench 1000+km long, laying the cable, and filling it in. That would take a lot of manpower, and would be seen as profligate use of expensive resources when the surface cable is so easy. >Which gives option 1.5, have some radio repeaters placed between > the two bases. > This would probably be more practical than copper wire, but less practical than fiber-optic. Copper wire would weigh a lot (1000 km of 1cm diameter copper weighs 700 tons, while the same length of 1mm glass fiber weighs about 2 or 3 tons). Fiber optics would probably have much higher bandwidths than radio repeaters, which would be manufactured on the earth, and dropped off by the same vehicle which would have laid down the fiber. The real question is bandwidth. If you just want to exchange greetings on Sundays, the radio repeater is probably cheaper. If you want to use the nearside Cray to process data from the farside radio satellites, you'd probably want the fiber-optic link. > #2:LLO (Low Lunar Orbit) sat. If the bases were farther apart, they might > not be able to see the sat. at the same time. I'm sure message storage > and forwarding could be used for routine messages, but what if real > time conversation was needed? The satelite might not be in either bases view. > This might be solved with enough sats in orbit, assuring that at least one is > usable by both bases. > You'd need three satellites for full coverage. That's a bit expensive. > #3:Lunosynchronous Orbit. I'm not sure the dynamics or even the possibility of > LSO, but if it could be parked anywhere above the "equator" of the > moon, the two bases could always be in contact, even if on opposite sides of > the moon (given arbitrarily high antennas, again, I don't know the dynamics of > LSO). Can anyone enlighten me on the physics of LSO? > You can place relay satellites at the earth-moon L1 and L2 points. L1 lies about 55000km from the centre of the moon, on a direct line to the earth. L2 lies about 63000km from the centre of the moon, on a direct line away from the earth. Both points move a few hundred kilometres over a period of a month because of the eccentricity of the moon's orbit. Because these points are unstable Lagrange points in the earth-moon direction, the satellites would require active station-keeping with thrusters, or maybe some clever gimmick. L4 and L5 are viable, but they are as far from the moon as the earth is, so would only be practical for relaying messages to farside, where an earth-based relay station is of no practical use (and here I'm cheating a bit, because an earth-based station could probably still send messages to L2 because of the distance it is from the moon, and the positions of geosynchronous satellites). A practical system for lunar communication would probably put two radio repeaters near the nearside-farside boundary; one on each side of it. The earth would relay all nearside-nearside messages, and nearside-farside messages would go nearside-earth-repeater-repeater-L2 satellite-farside. If signal propagation time is a problem, more lunar satellites would have to be launched, but that is expensive at the moment. > #4:Earth Relay:An Earth station would simply relay the message. Assuming that > the delay is acceptable and niether base is on the "dark side" (bad name, > but we are stuck with it) this would work. > Please, let's call it the far side. > Brian P. McCarty (N9IWP) > bitnet:UCSBPM@UWPLATT > internet:UCSBPM@UWPLATT.EDU -- Christopher Neufeld....Just a graduate student | "I always think there's neufeld@helios.physics.utoronto.ca | a band." cneufeld@pro-generic.cts.com | Prof. Harold Hill "Don't edit reality for the sake of simplicity" | (The Music Man) ------------------------------ Date: Sat, 3 Mar 90 10:46:36 EST From: Christopher Neufeld To: space-tech@CS.CMU.EDU Subject: Re: CQ Moon It seems that in my last message I was doing the effective equivalent of comparing message drums and smoke signals for a future Bell Canada upgrade. The extremely low atmospheric pressure on the moon allows another option which should outperform radio repeaters and fiber optics handily. Try laser repeaters. We need fibre optics on the earth because other things get in the way, like air, clouds, and intervening buildings. On the moon you could place a few laser repeaters in convenient lines of sight. The bandwidth would be comparable to that in a fibre-optic line with lighter apparatus. Lunar mountain ranges would be a nuisance, because of the difficulty of placing the laser repeaters, but if necessary that can be circumvented by putting a repeater on each side of the mountain, and firing a fibre optic link ballistically over the mountain to connect them. The stations would then talk to each other by sending messages along fiber optic lines to the station laser communications assembly, bounce to a couple of repeaters, maybe pass through a fiber optic line, and on to the receiver. Turnaround time should be comparable to light travel time, and faster than a pure fiber optic link because of the lower speed of light in glass. If you can use extremely low bandwidth communications, the wavelike nature of light will become significant at wavelengths comparable to the radius of curvature of the moon, so you can send radio signals over the horizon if you don't mind doing it around 200Hz. This has the advantage of using no additional equipment at all, but you have baud rates worse than a 1975 modem. Question for the materials scientists: does anybody know the vulnerability of fiber optics to particle radiation such as is present on the moon's surface? The LDEF experiment in which the military put fiber optics in LEO might be of some interest, but atomic oxygen could be the dominant contributor to the visible degradation of those samples. Would anybody care to estimate the usable lifetime of a fiber optic cable on the lunar surface, barring mechanical stresses (like some idiot stepping on it and ripping the cable)? -- Christopher Neufeld....Just a graduate student | "I always think there's neufeld@helios.physics.utoronto.ca | a band." cneufeld@pro-generic.cts.com | Prof. Harold Hill "Don't edit reality for the sake of simplicity" | (The Music Man) ------------------------------ Date: Sat, 3 Mar 1990 12:47-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Re: CQ Moon > Try laser repeaters. We need fibre optics on the earth because other > things get in the way, like air, clouds, and intervening buildings. On the > moon you could place a few laser repeaters in convenient lines of sight. Sounds good, especially since there's a very cheap laser repeater available: a mirror. What's wrong with using a series of mirrors to provide the equivalent of direct line-of-sight? I bet it would work great. I'm imagining a zig-zag line of mirrors atop the highest features of the lunar terrain, connecting the two stations. The only potential killer I can think of is if the mirrors would have to be prohibitively flat, but I doubt that. ==== What I'd really like, though, is some more details on how a laser based communications system would work. This is relevant not just to lunar bases, but to communicating with small space vehicles. Does anyone have some information they could share, or a reference that I could look up? \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ /// Marc Ringuette /// Carnegie Mellon University, Comp. Sci. Dept. /// \\\ mnr@cs.cmu.edu \\\ Pittsburgh, PA 15213. Phone 412-268-3728(w) \\\ /////////////////////////////////////////////////////////////////////// ------------------------------ From: henry@zoo.toronto.edu Date: Sat, 3 Mar 90 18:54:34 EST To: space-tech@CS.CMU.EDU Subject: Re: CQ Moon > #1:Landline (either copper or fiber-optic [preferred]). ... > Would meteor damage be a threat? (a 1cm diameter cable would have an area > of 10000m^2). How much bother to bury it? Don't forget about any repeaters > needed. One would certainly use fiber for this: it's lighter and smaller and has much higher capacity. Repeaters would not be a big deal; last I heard, the phone companies considered repeaterless transatlantic fibers to be a realistic near-term objective, although they aren't quite there yet. I'm not sure about lunar-surface meteorite numbers, but burying the cable a small distance should not be a problem in lunar regolith. The hassle of laying it, not to mention the sheer mass of great lengths of cable, work against this approach, however. > Which gives option 1.5, have some radio repeaters placed between > the two bases. This is also a hassle, because it means the equivalent of microwave-relay towers. Tall towers are easier to build on the Moon, but on the other hand the towers also need to be taller, since the surface curvature is greater. From a 100m tower, the lunar horizon is only about 19km away, so even pushing things, a 1000km distance requires about 30 relay towers. >#2:LLO (Low Lunar Orbit) sat. If the bases were farther apart, they might >not be able to see the sat. at the same time... This is a general problem with any low-orbit comsat system: many birds are needed to get continuous coverage. There is also the problem of keeping them up. The Moon's gravitational field is very lumpy, and things left in orbit generally end up crashing on the surface eventually. SSI's lunar-polar-orbiter RFP specified capability for orbit corrections roughly monthly, as I recall. (This was an unusually bad case, mind you, because the mission -- gamma-ray spectrometry -- requires the lowest practical orbit.) >#3:Lunosynchronous Orbit... There is no lunar analog of Clarke orbit. The Earth's gravity gets in the way too much. However, you can park something at one of the in-line Lagrange points and get continuous coverage of one hemisphere. Actually, better is a "halo orbit", orbiting around the Lagrange point in a plane perpendicular to the Earth-Moon axis. Such orbits are not completely stable, and require occasional small corrections, but they're close. I believe stability against perturbations is better than at the Lagrange points themselves. ISEE-3 was stationed in an Earth-Sun halo orbit for some years. There is a disadvantage in that the satellite does not look stationary from the ground, but there is the bonus that a halo orbit around the far-side Lagrange point is large enough to be in line of sight from the Earth. >[Side note: is there an "Equator" of the Moon? A North and South Pole? >How about Greenwhich and the International Date line? In short, is there a >coordinate system for the Moon?] There are well-defined coordinate systems, but there is no time-zone system. Lunar expeditions to date have run on Eastern Standard/Daylight Time for mundane practical reasons. :-) >#5:Bounce the signal off the Earth. Since people... >can bounce signals off the Moon, I imagine it would not be hard for two >organizations to do the reverse... The downcomings of this >are the same as [Earth relay]. Actually there is an added problem: the signal you get back is very weak. Barring military applications, it is invariably better to "bounce" a signal off an active repeater rather than a passive reflector. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ From: henry@zoo.toronto.edu Date: Mon, 5 Mar 90 16:56:18 EST To: space-tech@CS.CMU.EDU Subject: Re: CQ Moon > >How much bother to bury it? ... > Probably too much bother. To lay the cable, you just have to drive from > one base to the other at, say, 20 km/h playing out the cable behind you. > This could be done in a matter of days. Compare digging a trench 1000+km > long, laying the cable, and filling it in... The phone company and others have gadgets that lay cable *underground* as they go, doing everything automatically; think of sort of a specialized tall-and-skinny plow with a cable feed. One might wonder how uniform the lunar regolith is at suitable depths, though. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ End of Space-tech Digest #52 *******************