Subject: Space-tech Digest #56 Contents: Jordin Kare Re: Lunar Surface Comm. George Ott Bobcats on the Moon George Herbert Re: Fairly Stupid Robots Vince Cate South for the winter (was Bobcats on the Moon) Henry Spencer Re: Fairly Stupid Robots George Ott Powering a Lunar Bobcat Gord Deinstadt Fairly stupid robots David Cortesi Dumb & Shivering Robots Edward Wright Re: South for the winter (was Bobcats on the Moon) Vince Cate Re: South for the winter (was Bobcats on the Moon) Gord Deinstadt Powering a Lunar Bobcat Gordon Pusch Lunar Polar Solar Power (was: South for the Winter ------------------------------------------------------------ Date: Mon, 19 Mar 90 15:49:56 PST From: Jordan Kare To: lfa@vielle.cray.com, space-tech@CS.CMU.EDU Subject: Re: Lunar Surface Comm. >From: Lou Adornato >Can anyone out there answer the following: > 1) Using present technology, how tighly can a communications laser > be focused? Is it reasonable to expect that tighter focusing in > the next 20 years, or are we at a fundamental limit? Laser range is limited (in vacuum) by diffraction, and good optics are at the diffraction limit. The only way to focus more tightly is to build a bigger mirror. There is considerable excitement in the physics world about ``super-Gaussian'' transmission and ``Photon torpedos'', both referring to ways to do better than the diffraction limit. From what I understand of the physics, these either a) do not do fundamentally better than conventional optics (they control the wavefront differently, but put no more power into the central peak of the beam) or b) require impossible initial conditions, like infinite source size or infinite energy, or c) require impractical conditions, like multi-octave swept-frequency sources, that are unlikely to be available in laser wavelengths any time soon. Proposals in category c) are also not clearly workable even if the sources _are_ available. So I wouldn't rule out the possibility of doing better, but I'd bet heavily on the diffraction limit holding in the near term. To a rough approximation, R=dD/lambda, where R is the useful range, the transmitting and receiving mirrors are diameter d and D, and lambda is the wavelength. You can do better with shorter lambda; hence, for instance, a visible laser will have a longer range than an infrared laser. On the other hand, you may be able to get a more efficient, more powerful infrared laser -- and diffraction-limited mirrors are easier to make for long wavelengths, so you may be able to get bigger mirrors.... > 2) What is the threshold of detection given the present technology? > In other words, at 10Mbps, how much power needs to come out of the > small end of my attenuation function? Again, is this fundamental or > subject to incremental improvements? Laboratory systems get to within a small factor (~3) of the statistical limit, which is effectively a few photons per bit for decent signal/noise ratio. I seem to recall a recent test that got to 20 photons/bit. Assuming ~1 eV photons, 10 Mbps would require ~few x 10^8 eV/sec, or ~10^-10 watts received. You should have a comfortable margin at ~10^-9 watts received (-60 dBm). If you start with ~100 mW (easy with current diode lasers) you have ~80 db available for link losses. Of course, I'm not including problems like scattered sunlight adding to the noise floor. > 3) What references exist for someone with limited knowledge of laser > communications technology (but with an engineering background and > enough physics to not understand eigenfunctions?). I'm talking > about transmission _and_ detection technoology, preferably line of > sight. Any number of handbooks, etc. are available about fiber optics; free-space paths are pretty rare now, so I don't know what to recommend offhand. > >Lou Adornato | Statements herein do not represent the opinions or attitudes >Cray Research | of Cray Research, Inc. or its subsidiaries. >lfa@cray.com | (...yet) > Jordin Kare jtk@mordor.uucp jtk@mordor.s1.gov ------------------------------ Date: Tue, 20 Mar 90 09:09 CST From: GOTT@wishep.physics.wisc.edu To: space-tech@CS.CMU.EDU Subject: Bobcats on the Moon First question: I know there is a 30 Watt SNAP nuke-thermal generator, what other power ratings are available i.e. what is riding with Gallileo etc? Second question: How good is the lunar soil as thermal insulation? Potential Scenario for a Bobcat On The Moon: 1. Land the Lunar Bobcat (hereafter LB), an external tank, a plug of insulation big enough to seal the end of the external tank, a aluminized mylar box big enough to fit the bobcat in, assorted science instruments and communication gear on a flat piece of the moon where the sun just rose i.e. just as the two week day begins. 2. Put the ET on it's side and chop off the lower end. Keep it from rolling by pushing soil up next to it. Set up the comm. and science gear. 3. Build a ramp into the ET and push soil inside the ET so that the LB can get in and out of the ET. 4. Push up more soil around the ET until it is buried except for the entrance ramp. 5. Start the rest of the mission, at this stage probably a mapping/surveying run around the local neighborhood. Dig up a monolith or two :) 6. When night comes, drive the LB into the ET and close the insulation plug over the door. Then deploy the mini-garage i.e. the "aluminized mylar box big enough to fit the bobcat in", drive the LB in, close the flap and wait out the night. NOTES: > You don't have to use an ET for the garage, perhaps one of LLNL's inflatable structures will do. The kernal of the idea is to use lunar soil as the main insulation material and to get around the cold by staying inside. > Given the appropriate numbers on lunar soil the energy requirements needed to keep the garage warm should be fairly simple to calculate. > Additional heaters powered by a solar/battery combination or other Nuke- thermal generators can be added as needed. As to the required intelligence of the Lunar Bobcat, I agree that it doesn't need to be able to handle every possible situation and that it should have a fallback position of calling home to ask for instructions. I would like the software set up so that the LB get's better at it's job i.e. it only has to ask the same question two or three times i.e. it learns. George K. Ott gott@wishep.physics.wisc.edu ------------------------------ Date: Mon, 19 Mar 90 17:22:27 PST From: gwh%ocf.Berkeley.EDU@lilac.berkeley.edu To: GOTT@wishep.physics.wisc.edu, space-tech@CS.CMU.EDU Subject: Re: Fairly Stupid Robots Besides using a non-space rated brain [a mac SE???] that robot would be using a thirty watt RTG [oy] for power. Do you know how little you can do with thirty watts? -george ------------------------------ Date: Tue, 20 Mar 1990 11:29-EST From: Vincent.Cate@SAM.CS.CMU.EDU To: space-tech@CS.CMU.EDU Subject: South for the winter (was Bobcats on the Moon) If you go to the North pole of the moon you can get a 6 month day. Solar power will work well even at the low angle because there is no atmosphere. You can drive around for 6 months. Then getting, off to a timed and planned start, you can spend 14 to 28 days migrating south for the winter (curve around as you go south). The moon is small enough, and there are no fences, so far. Net result is that we could drive a remote control bobcat year round. I think of it more as a remote control space buggy than a bobcat, since it will probably be very light and take awhile to push dirt around - but hey, we will have the time. If you have two of these with some remote control arms such that you can use one to work on the other you may even be able to keep them both working for some time. -- Vince ------------------------------ From: henry@zoo.toronto.edu Date: Tue, 20 Mar 90 12:23:06 EST To: space-tech@CS.CMU.EDU Subject: Re: Fairly Stupid Robots > > If I were trying to use off-the-shelf hardware, I think I'd opt for the > > heated garage. > > Would this have to be a heated *and pressurized* garage, or would radiant > heating suffice? Just keeping the thing warm suffices. In fact, pressurizing it is probably a bad idea, because that brings up the question of what you pressurize it with. Oxygen is a bad idea, given its corrosiveness... and the better gases -- nitrogen etc. -- are hard to find on the Moon. What one might do is insulate the garage well and put a small isotope generator in it, both to provide a bit of base-load power during the night and to keep the thing warm. Daytime activity can be solar-powered. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Tue, 20 Mar 90 13:57 CST From: GOTT@wishep.physics.wisc.edu Subject: Powering a Lunar Bobcat To: space-tech@CS.CMU.EDU X-VMS-To: IN%"space-tech@cs.cmu.edu" Some mention has been made of running the lunar bobcat on solar power. What are the advantages of solar power over radioisotope power in this case? Which has a higher power per lb. launched from Earth? How do the systems compare with regards to reliability? George K. Ott university of wisconsin HEP dept. gott@wishep.physics.wisc.edu ------------------------------ Date: Tue, 20 Mar 90 16:04:20 EST From: Gord Deinstadt To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: Fairly stupid robots My, what a lot of responses! :-) From: uunet!uiucuxc!convex.com!ewright (Edward V. Wright) >Are you talking about off-the-shelf robots? Are there really >robots available that can reproduce themselves? No, as I said that was my ultimate goal. But in the meantime I would be delighted to have robots on the moon that could disassemble and reassemble each other, and that had interchangeable parts, so as long as there are spare parts they can fix each other. (And cannibalize when budgets are cut.) From: Joe Beckenbach > Why not simply let each be solar-powered? This would be pretty unwieldy for the little guys (robots) building the moonbase. Wouldn't you find it inconvenient to drag around, say, ten square metres of solar cells with you? But... it might be the solution for the robots that have to travel long distances, like the ones building laser relay towers. They won't be in as crowded an environment anyway. (I know, a 20 lb/ 10Kg robot doesn't need 10 sq m of solar cells; I scaled it up.) > Yeah, that's it. Put up instruments, a couple of small propulsion >experiments, a commsat or two, and a batch of robots all on one bus. Put >this in orbit around Luna, and then send each item on its way, like >blowing dandelion seeds. This is beautiful imagery. From: uunet!wishep.physics.wisc.edu!GOTT >How large and intelligent does a robot have to be to be useful for >setting up a lunar base? >Would a semi-intelligent bulldozer do the trick or do we need something >with some sort of arms? What are the early tasks that need to be >accomplished? I see a need for three types of robots. 1. A truck (solar powered, see above). 2. A backhoe (more flexible than a bulldozer - used for all kinds of heavy lifting and moving). 3. A "monkey", ie. a small thing with high-dexterity effectors for doing fiddly tasks like repairing other robots. From: uunet!zoo.toronto.edu!henry >Remember that you need either (a) plenty of power to run heaters, (b) a >heated garage, or (c) robots built to soak at cryogenic temperatures >during the lunar night. Or d) insulation plus an active cooling system. Not practical? Too bad, it would be neat having warm-blooded robots! :-) From: uunet!vma.CC.CMU.EDU!SISKMP@VUCTRVAX.BITNET >Personally, I favor the "semi-autonomous" theory of operation, where Bif the >fairly stupid robot checks in with his mentors whenever he encounters anything >beyond his scope of "reasoning." I hate to see projects stalled because we're too ambitious in our software designs. I don't know what AI is capable of these days, but for Lunar work and a short design cycle I'd even settle for simple remote control, which is why I said the robots could be slow. Semi- autonomous would be better if it is available more or less off-the-shelf. -- Gord Deinstadt gdeinstadt@geovision.UUCP ------------------------------ Date: Tue, 20 Mar 90 13:38:16 PST From: David Cortesi To: space-tech@pyramid!CS.CMU.EDU Subject: Dumb & Shivering Robots On Mar 19, 5:04pm, uunet!zoo.toronto.edu!henry wrote: > If I were trying to use off-the-shelf hardware, I think I'd opt for the > heated garage. Hardware that is *exposed* suffers cryogenic temperatures. How much lunar soil does it take to mitigate that? In other words, what would a passive-solar heated garage look like? Or at least, a garage that was warmed during the 14day by the sun, then had its temperature minimally maintained by a 30-watt RTG over14night? Mainly, if you set your toytown down just past dawn, could they build their own garage before sunset? ------------------------------ Date: Tue, 20 Mar 90 13:10:49 CST From: "Edward V. Wright" To: Vincent.Cate@SAM.CS.CMU.EDU, space-tech@CS.CMU.EDU Subject: Re: South for the winter (was Bobcats on the Moon) Jerry Pournelle's Lunar Society spent considerable time working on a lunar bulldozer very much like the proposed Bobcat. They called it the Go-cart. It was an ATV-type vehicle with a waldo on the front. It was designed to be teleoperated from Earth: autonomous most of the time, but call for help when you encounter something that you don't understand. As far as migrating from one pole to another, I think you may be overestimating the distance a vehicle can cover, over unexplored terrain, in a day. The Moon is about 6000 miles in circumference, we're talking a 3000-mile trek, so 100 to 200 miles per day. That doesn't sound very fast, but as I recall the proposed Martian rovers cover only a fraction of that distance in a day. You could probably improve on that some, but only at the risk of losing vehicles. (I'd plan on some attrition, anyway. There are a *lot* of holes on the Moon.) It might be better just to land two groups of robots, one at either pole. Operate each group of robots for six months at a time. Or build a tower that's tall enough for its top to be in sunlight all the time. The robots spend 6 months of the year roaming free and 6 months tethered to the base of the tower, doing work around the base camp and getting their power from extension cords. ------------------------------ Date: Wed, 21 Mar 1990 12:20-EST From: Vincent.Cate@SAM.CS.CMU.EDU To: space-tech@CS.CMU.EDU Subject: Re: South for the winter (was Bobcats on the Moon) >It might be better just to land two groups of robots, one at either >pole. Operate each group of robots for six months at a time. Or >build a tower that's tall enough for its top to be in sunlight all >the time. The robots spend 6 months of the year roaming free and >6 months tethered to the base of the tower, doing work around the >base camp and getting their power from extension cords. This reminds me of another idea I had: Another option is to spend 6 months at the pole and then run around near the pole to stay in the sunlight the other 6 months. How big a circle you have to make depends on which part of the year it is - the closer to the six months where you don't move at all the less you have to move. The most you have to move is pi*2*sin(TiltOfMoon)*2000/28 miles/day. If the tilt is 4 degrees this comes out to 31 miles/day or about 1 MPH, 10 degrees would be about 3 MPH. Anyone know the tilt of the moon offhand? This could be a really nice way to go. You can explore the area near your base. I really don't think it will be hard to average 5 MPH or more. -- Vince ------------------------------ Date: Wed, 21 Mar 90 19:16:22 EST From: Gord Deinstadt To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: Powering a Lunar Bobcat Mr. Ott asked: >Some mention has been made of running the lunar bobcat on solar power. >What are the advantages of solar power over radioisotope power in this case? >Which has a higher power per lb. launched from Earth? My guess is that you could manage about 100 grams/sq metre for lunar solar cells (thin-film type). This yields on the order of 100 watts/sq metre, or 1 kilowatt/kilogram. I don't know the numbers for radioistope thermal generators, but they are considerably worse. An RTG needs a radiator plus shielding, both of which are relatively massy. Space probe designers use solar cells whenever possible, falling back on RTGs when the probe is going to the outer solar system. >How do the systems compare with regards to reliability? Solar cells are damaged by radiation, and consequently have a limited lifetime on the lunar surface. The lifetime is measured in years, though, and the damage shows up as a gradual degradation rather than a sudden failure. I believe amorphous and polycrystalline solar cells are more resistant to radiation than single-crystal types, because in a sense they are already damaged; their efficiency starts out lower. Both solar cells and RTGs have a serious problem when used on the Moon; dust! Every moving vehicle is going to stir up dust, and that is going to coat any nearby solar cells or RTG radiators. For the RTG, we can just wipe off the radiator every once in a while. For solar cells, we have to worry about scratching the surface. The obvious solution is to put a hard coating on the solar cells (say, diamond film) but this is unlikely to have the optical properties we need for best efficiency. If we want to use solar cells (which I believe we do, based on power density), we may have to locate them in a suburb far away from the dust of the lunar base. And we'll still have to worry about dust thrown up high by rockets taking off and landing; maybe the only way to escape this is to build a hard-surface pad. Or employ a lot of robots wiping solar panels. Now they're stupid, shivering robots doing menial labour! :-) -- Gord Deinstadt gdeinstadt@geovision.UUCP ------------------------------ Date: 21 Mar 90 18:53:00 EST From: GORDON D PUSCH -PHYSICS Subject: Lunar Polar Solar Power (was: South for the Winter) To: space-tech From: Vincent.Cate@SAM.CS.CMU.EDU > This reminds me of another idea I had: Another option is to spend 6 > months at the pole and then run around near the pole to stay in the > sunlight the other 6 months. How big a circle you have to make depends > on which part of the year it is - the closer to the six months where > you don't move at all the less you have to move. The most you have to > move is pi*2*sin(TiltOfMoon)*2000/28 miles/day. If the tilt is 4 > degrees this comes out to 31 miles/day or about 1 MPH, 10 degrees would > be about 3 MPH. Anyone know the tilt of the moon offhand? My encyclopaedia gives the inclination of the plane of the moon's orbit wrt the ecliptic as varying from 4.98deg to 5.3deg, with its axis inclined at 6.67 to its orbital plane. The inclination of the plane varies because solar tidal effects cause its semimajor axis and line of nodes to precess w/ periods of 18.6 and 8.85 yrs, resp. As it happens, the moon's pole is only 1.58deg away from the pole of the ecliptic, precessing about it with a period of about 18.67 yrs. In other words, the moon doesn't really *have* seasons. Put another way, its artic circle is only about 60km from its pole. It follows that the simplest way for ``Polar base'' to obtain power for the entire Lunation is to space, say, three solar power stations about the pole, with 60 klick cables back to Polar base. Then two of the three are in sunlight at any given time. The disadvantage of this is that you triple your capital investment in power stations (less, in the limit of a large number of power stations, since each one can be smaller; roughly half of them are in the sun at any given time. Also, you add the cost of the cables. Alternatively, a mast about 661m tall is in sunlight all year round, unless I've dropped a decimal point or goofed on the trig. (the exact formula in TeX notation is: h = { R {\sin}^{2}(\alpha) } \over { 1 + \sqrt{ 1 + {\sin}^{2}(\alpha) } } or h \simeq { R {\sin}^{2}(\alpha) } \over 2 [[by small angle approx.]] Here \alpha is the lunar axial inclination (1.58deg) and R is the Lunar radius (1738km).) Does building a 700 meter mast out of indigenous Lunar materials in six months seem unreasonable to anyone? :-) Gordon D. Pusch < PuschGD @ vtcc1.BITnet > Physics Dept., VPI&SU < PuschGD @ vtcc1.cc.vt.edu > Blacksburg VA 24061 ------------------------------ End of Space-tech Digest #56 *******************