Date: Wed, 20 Sep 1989 14:04-EDT From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #34 Contents: Paul Dietz Mars Mission plans Henry Spencer fuel for getting around on Mars Jonathan Leech Space Adaptation Syndrome Peter Scott Re: Mars missions Paul Dietz Spinning up tethered spacecraft Marc Ringuette Re: Spinning up tethers, lightweight mirrors Tom Neff Re: Spinning up tethers, lightweight mirrors Paul Dietz Homemade liquid fueled rockets David Birnbaum Re: Homemade liquid fueled rockets Stephen Hathorne Re: Homemade liquid fueled rockets Korak MacArthur Re: Homemade liquid fueled rockets Ollie Eisman Re: Homemade liquid fueled rockets Paul Dietz Re: Homemade liquid fueled rockets Paul Dietz Hybrid Rockets ------------------------------------------------------------ Date: Fri, 15 Sep 89 13:35:54 EDT From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Mars missions Here is some information from the 1986 NASA Mars Conference on possible mission plans... (1) Conjunction Class Missions The most traditional type. It is relatively low energy, with a long stay time. Outbound 270 Stay 530 Return 209 ------------------- Total 1009 days (2) Opposition Class Missions Very high energy, much shorter trip time, but also shorter stay time. Outbound 254 Stay 20 Return 245 ------------------- Total 519 days An inbound swing-by of Venus reduces the energy requirements of this class of missions, and increases the stay time, at the cost of a slight increase in trip time: Outbound 267 Stay 60 Return 366 ------------------- Total 693 days (3) Low Thrust Transfer Missions These employ low thrust electric rockets or solar sails. They include a coasting portion during the middle of the trip when no thrust is applied. Earth Spiral 52 Outbound 510 Mars Spiral 39 Stay 100 Mar Spiral 23 Return 229 Earth Spiral 16 ------------------- Total 969 Not all of this time need be taken by the crew; the crew could board after the vehicle has spiralled above the van Allen belts. I do not know what acceleration these numbers imply; an ultra low mass solar sail could probably do better. The inbound spiral at Earth could be avoided by parking the vehicle in HEO and returning the crew via OTV. (4) VISIT (Cycler) Orbits The next two concepts use "spaceports" in solar orbit as stepping stones to/from Mars. The VISIT-1 orbit is a 1.25 year orbit that swings close to Earth once every five years while approaching Mars once every 3.75 years. The VISIT-2 orbit is a 1.5 year orbit that approaches Earth once every three years while approaching Mars once every 7.5 years. The orbits would have to be retuned once every 20 years or so, and do not exploit planetary swing-by. (5) Escalator (Cycler) Orbits Unlike VISIT orbits, these orbits (due to Buzz Aldrin) use planetary swingby to rephase the cycler orbit. Basically, it is a more elliptical orbit that passes by the Earth once an orbit and Mars twice an orbit. At Earth, a wingby redirects it on to the next Mars encounter. The orbit's period is about 2 years. It would require a bit of nudging at times, for a total of about 2 km/s over 15 years. The orbit is high energy. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ From: henry@utzoo.uucp To: cs.cmu.edu!space-tech@cs.toronto.edu Subject: fuel for getting around on Mars Date: Fri, 15 Sep 89 13:36:28 EDT > How do they get around once they're finally on Mars? CO/O2 rockets seem > feasible, and all the raw materials are readily available. H2/O2 is better, > of course, but possibly the raw materials are harder to get (and the finished > materials are harder to handle). There was a paper in JBIS a little while ago about this exact topic. CO/O2 performance is pretty crummy, but it has the advantage that the materials are available everywhere on Mars (CO2 from the atmosphere). If there is any source of hydrogen -- notably permafrost, which is *probably* widespread on Mars -- then CH4/O2 is miles ahead on performance and not much harder to make. You probably would not want to bother with liquid hydrogen -- it is too hard to store and too bulky for the performance boost it gives. Another topic of interest, which came up in sci.space (I think) a while ago, is surface propulsion. Titanium will burn in CO2, and it's quite a common metal. (It's hard to extract it with sufficient purity for structural use -- its mechanical properties are spectacularly sensitive to impurities -- but for fuel that's not an issue.) Picture the Mars buggy chugging across the landscape, belching black smoke (Ti+CO2->TiO2+C) and stopping occasionally to shovel the ash out of the firebox... :-) Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Fri, 15 Sep 89 15:43:45 EDT From: Jonathan Leech To: space-tech@cs.cmu.edu Subject: Space Adaptation Syndrome Re the discussion about artificial gravity, here's a tangentially (sic) related reference: in Nature V340 (31 Aug 1989), pg. 681, "Space Sickness on Earth": "Sir: We report here the surprising aftereffects of prolonged centrifuge runs in which we, the three scientist-astronauts on board the D-1 Spacelab mission, have participated. We think we can simulate the space adaptation syndrome..." To summarize, they found that after several hours of centrifuging at 3G, they felt SAS-like effects upon returning to 1G, and suggest this provides a good way of studying SAS. This is a letter, not an article, so details are sparse. Jon Leech (leech@cs.unc.edu) __@/ ------------------------------ Date: Fri, 15 Sep 89 17:50:29 PST From: Peter Scott Subject: Re: Mars missions To: space-tech@cs.cmu.edu X-VMS-Mail-To: EXOS%"space-tech@cs.cmu.edu" Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU writes: >marsh@linus.MITRE.ORG (Ralph Marshall) writes: >> ...Winch the two pods into the center of the cable >> so that they form a solid mass. The thing is going to be whipping around >> at an amazing speed, but if you put the astronauts in a non-rotating >> ball at the center for the duration of the thrust you should be able >> to withstand it. > >I don't think your idea is practical. The structural strength of the >capsules would have to be very high. This conflicts with the the strong >desire not to drastically increase any weight requirement. One of the >reasons that a spinning system at 1 g can be considered is that the capsules >will be strong enough to withstand atmospheric pressure and probably a >multi-gee launch anyway. But withstanding more than maybe 5g would require >stronger, heavier structure, and the cost would rise. Yeah, but it's a great way to make cheese ;-) Never mind the capsules, what would the tensile load on the cables get to just before the capsules joined? Now, this discussion has sparked off an interesting thought: is there a structure that would take a circular mylar sheet, and in combination with rapid rotation and some kind of constant linear acceleration, allow the structure to form a paraboloid, which happens when rotating liquids on earth? My mechanical aptitude is somewhat rusty. I know that hanging cables form catenaries, so presumably a spinning sheet would form the surface of rotation of a catenary, but there again, isn't there some nifty secondary mirror shape that could be used to make the image come out right (of course, this is an idea for constructing giant space telescopes)? I believe that telescopes have been constructed on Earth from rotating vats of mercury. Unfortunately they are only good within a few degrees of the zenith. Out in space, you could create your own acceleration in any direction. Peter Scott (pjs@grouch.jpl.nasa.gov) ------------------------------ Date: Sat, 16 Sep 89 07:18:39 EDT From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Spinning up tethered spacecraft It was suggested that the way to spin up a tethered mars spacecraft is with rockets. There is a way to reduce the amount of reaction mass you use. Extend the tether out to (say) a radius of ten kilometers. Fire rockets to accelerate the ends to 10 m/s. Now, with a winch at the center, reel the tether in. Conservation of momentum will spin up the structure. The reeled-in part of the tether need not be very strong, since the forces are initially small. You could do even better with counterrotating structures -- no reaction mass would be needed at all, and they could be made to precess against one another. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 19 Sep 1989 14:06-EDT From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Re: Spinning up tethers, lightweight mirrors Paul Dietz writes: > It was suggested that the way to spin up a tethered mars spacecraft > is with rockets. There is a way to reduce the amount of reaction mass > you use. > > Extend the tether out to (say) a radius of ten kilometers. Fire rockets > to accelerate the ends to 10 m/s. Now, with a winch at the center, > reel the tether in. Conservation of momentum will spin up the structure. > The reeled-in part of the tether need not be very strong, since the > forces are initially small. Good idea, Paul. I should mention that this method doesn't change the total energy to be put into the system; it just replaces rocket energy with the electricity you need to crank the capsules up the cable as it's spinning. However, if you want to shift the balance from rockets to electric power, this is a way to do it. I'm still not convinced one way or the other on the exact best form of a rotating structure. I'm definitely convinced that cables are better than a fixed structure for any large diameters (which are probably necessary for strength and dizziness reasons). I'm not so sure how to accomplish off-axis accelerations: my triangle idea is one way that seems to hold up under a little analysis; maybe just very small accelerations at the axis of a single-cable system would be adequate; or if the mission requires only a small number of course corrections, perhaps de-spinning the system would avoid the problems of oscillations in the system. Let me know if you think I've missed something. ============== Peter Scott writes: > Now, this discussion has sparked off an interesting thought: is there > a structure that would take a circular mylar sheet, and in combination > with rapid rotation and some kind of constant linear acceleration, > allow the structure to form a paraboloid, which happens when rotating > liquids on earth? This is worth some investigating. I recall seeing a NASA Lewis paper on this idea, which studied a simple rotating plastic sheet; unfortunately I can't remember their exact assumptions. The kind of paraboloid they were producing from a perfect parabola by enough that they were limited to about a 100x magnification of sunlight. For reference, I think in order to have a high-temperature thermionic system, we want something like 700x sunlight at 1 a.u. from the sun. There might be other ways to firm up a plastic film in the correct shape. Perhaps a combination of spinning forces and guy lines. Or how about making the mirror as a mylar bag full of gas? This is just my idea, and may not work out at all, but gas pressure is another tool that might help us produce the precise shape we want. We don't need THAT much improvement in order to get a good enough shape to focus sunlight. ---------------------------------------------------------------------------- | Marc Ringuette | mnr@cs.cmu.edu | Never lick a gift | | Carnegie Mellon Comp. Sci. | 412-268-3728(w) | horse in the mouth. | | Pittsburgh, PA 15213 | 412-681-5408(h) | | ---------------------------------------------------------------------------- ------------------------------ From: tneff%bfmny0@uunet.UU.NET (Tom Neff) Date: Tue, 19 Sep 89 16:50:04 EDT X-Mailer: Mail User's Shell (6.5.6 6/30/89) To: SPACE-TECH Mailing List Subject: Re: Spinning up tethers, lightweight mirrors I would point out that if a midcourse correction is applied along the rotational plane of a tethered system, the physics are simpler. So if you have a gyroscopic way of turning the rotational plane before applying thrust, you can probably navigate without despin. One advantage of a rigid tower over a flexible tether is that you could despin by transferring rotational energy to a momentum "log" at the hub, and then respin by braking it. This conserves energy. I can't think of how to do this offhand with a flexible tether although someone else is probably cleverer and has a way. -- 'UNIX should be used :: Tom Neff or as an adjective.' -- AT&T :: ...uunet!bfmny0!tneff (UUCP only) ------------------------------ Date: Tue, 19 Sep 89 13:50:43 EDT From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Homemade liquid fueled rockets The Mars ship discussion seems to have stopped, so here's another topic. How hard is it to make a liquid-fueled rocket motor at home? I assume a small group of motivated amateurs with modest funds. I assume the rocket is pressure fed. A related topic: How small can one make a rocket motor? What are the scaling laws at work? Smaller is clearly safer (less fuel, smaller explosions), as well as having lower materials costs. Would a liquid fueled rocket < 1 pound in weight qualify as a model rocket? Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 19 Sep 89 12:42:37 MDT From: To: space-tech@cs.cmu.edu Subject: Homemade liquid fueled rockets This is something that I'm interested in as well. Are there any plans available for construction of a small liquid fueled motor? I would assume you could use parts from a hardware store, but some items (nozzle, for example) would require the use a machine shop. Also, what good fuels could one use? For obvious reasons, cryogenic fuels are difficult to purchase and handle. A friend of mine created a self-accelerating ram-jet using a hydrocarbon fuel (perhaps an alcohol or a heavier hydrocarbon) with air as the oxidant. David Birnbaum | "It shouldn't suprise anyone when the Networking, Computer Center | net messes up; the suprise is that New Mexico State University | the damn thing works at all!" Find me at: dbirnbau@nmsu.edu | Please do "make clean" on /dev/earth ------------------------------ Date: Tue, 19 Sep 89 15:37:10 -0400 (EDT) From: Stephen Hathorne To: dbirnbau@nmsu.edu, space-tech@cs.cmu.edu Subject: Re: Homemade liquid fueled rockets I am not sure, but I think it is illegal to make liquid fueled model rockets.. does anyone know about this... also what about a 5 lb propane tank from the hardware store... does anyone know the math for pressure and thrust that you would achieve stephen hathorne sh2v@andrew.cmu.edu =============================================================================== the question is: why can't I have a space shuttle of my own....? ------------------------------ Date: Tue, 19 Sep 89 16:35 EDT From: Subject: liquid fuel rockets To: space-tech@cs.cmu.edu X-Original-To: space-tech@cs.cmu.edu, K_MACARTHUR I think they would be great to tinker with, but the feds don't. It seems that "model rockets" (unlicensed,amusement only devices) can't have any metal on them officially. I think to make even aluminum casing rockets, you would have to apply and receive special permits and other red tape garbage. At least in the US. Maybe they're worried about the home made bazookas showing up at airports. (doesn't make a diff, remember the rifle hole in that small plane a while back?) One way to loophole your way around is with composites and plastics. Cost would be higher, and you still might be visited by the men in dark glasses. B( At UNH, we had a Physics club that sent up a couple of cardboard rockets with the larger, F engines. Had to notify the nearest airbase (Pease) before we fired because it went over 1000 feet. Sigh. Korac MacArthur ------------------------------ Date: Wed, 20 Sep 89 00:04:43 MDT From: SEDS-UNM To: dbirnbau@nmsu.edu, sh2v+@andrew.cmu.edu, space-tech@cs.cmu.edu Subject: Re: Homemade liquid fueled rockets When we build our space-tech rocket, let's launch at White Sands! Seriously, didn't a group from MIT build a small liquid-fuel rocket and send it up from WSMR? Ollie Eisman SEDS-UNM ------------------------------ Date: Wed, 20 Sep 89 09:35:27 EDT From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: liquid fuel rockets > I think they would be great to tinker with, but the feds don't. It > seems that "model rockets" (unlicensed,amusement only devices) can't > have any metal on them officially. In a slightly different context, Dani Eder mentioned that it saves paperwork to call your vehicle a model *airplane*. Those can have metal. I wonder what the altitude/speed limitations are for model airplanes? Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Wed, 20 Sep 89 09:22:50 EDT From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Hybrid rockets You know about the hybrid rocket AMROC is making -- solid rubber fuel with liquid oxygen oxidizer. Given that liquid oxidizers are a bit difficult for amateurs to handle, I was wondering if this could be reversed -- build a hybrid rocket with a solid oxidizer and liquid fuel. I'm thinking of some nitrate compound for the oxidizer. Say, lithium nitrate. If it is too mechanically weak, one could increase its strength making a composite with small glass fibers. Use gasoline as a fuel. I don't know how well this would work, but the exhaust would be a pretty red color from the lithium. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ End of Space-tech Digest #34 *******************