Date: Fri, 2 Dec 1988 02:35-EST From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #16 Contents: Bob Munck Re: Solar Dynamic Power Alan Raskin Astronomy Programs a la Jean Meeus Norman C. Kluksdahl Private space operations Paul Dietz Distributed Injection Ballistic Launcher Henry Spencer Re: Distributed Injection Ballistic Launcher Marc Ringuette Ion Propulsion + Lightweight solar power ------------------------------------------------------------ Date: Mon, 21 Nov 88 16:27:55 EST From: Bob Munck To: space-tech@cs.cmu.edu Subject: RE: Solar Dynamic Power > ... inject the > hydrogen into the chamber through a set of nozzles that set up a matrix > of meshing vortices. On the central axis of each vortex is a small exit > nozzle. Each vortex is a micro tornado; it spins so fast that the heavy > atoms of the nuclear fuel are centrifugally separated from the hydrogen. > Only hydrogen is able to make it to the inside of the vortex where it > can escape through the exit nozzle. ... My gosh! It's my old Science Project, the Hilsch Vortex Tube. I won a bunch of blue ribbons with it as a high school soph, in 1960. Idea was taken from a Scientific American Amateur Scientist article of about that vintage. The HVT had an inlet for compressed air (from an old refrigerator compressor, natch) and outlets at right angles from the center of the cycloid-shaped chamber (cold) and from its outside diameter (hot). The theory was that slower molecules moved to the center and faster ones to the outside. I got -20C and +70C from the two outlets. It seems to me that the thermal effect of the HVT would tend to counter the desired effect of molecular weight. Weight should probably dominate, but I'm not positive of it. Your description implies that the nuclear version has been tried. With what results? -- Bob Munck ------------------------------ Date: Mon, 21 Nov 88 14:28 PDT From: Alan Raskin Subject: Astronomy Programs a la Jean Meeus To: space-tech@cs.cmu.edu If anyone is interested, I have written programs for calculating planetary positions, lunar phases, general eclipse information, and the configuration of the main satellites of Jupiter using the data and formulae in Jean Meeus' book. The programs are in Fortran and include *all* of the terms in the various expansions, and are therefore very accurate. I also have a much less accurate program in C for calculating the configuration of Saturn's main satellites. I would be willing to upload the programs from my PC in text mode; I can also upload the source and/or binary programs in ARC format (assuming you are on a VAX so that I can use the VMSDUMP format to send binaries; the entie package is about 250K). -Alan Raskin (raskin@max.acs.washington.edu) ------------------------------ Here's a message from sci.space, in case you haven't seen it. I told the guy about our satellite ideas, and asked him to let me know what response he gets. Maybe we can contribute some ideas. I've also been writing back and forth with Chuck Brunow, who's hot on a Spaceplane project. Personally, I would still emphasize satellites or more exotic ideas over trying another shuttle. -- Marc From: kluksdah@enuxha.eas.asu.edu (Norman C. Kluksdahl) Subject: private space operations Date: 21 Nov 88 03:01:43 GMT I am flabergasted. Only a short while ago, there was some discussion, including a few hearty `count me ins', on the subject of a privately run, homebuilt-style launch system. And now... nothing. Not one peep. Is it any wonder, then, why the USSR is orbiting MIR and launching Buran an nearly a hundred payloads annually, including automated docking for re- supply of their space station, while the US's program languishes for lack of support? Why is it that so many of us complain vociferously about the lack of progress in establishing a true space effort, and yet are unwilling to back their fancy words with a serious commitment. I've heard the excuses hundreds of times before, relating to hundreds of subjects. They range from the 'it's not possible' to `the government won't let us' to 'what can one person do'. Frankly, those willing to criticize quickly disgust me. We have at our fingertips a vast resource of technically skilled people, who also seem to believe strongly in some dream of the final frontier. Or must the talent remain unused and criminally wasted? Let me kick up a suggestion. First, will all of you who are willing to DO SOMETHING e-mail me a response. I need to know how serious people are. Second, consider this. It was stated that something like 60 man-years would be sufficient to develop a private space vehicle. How can a group of dedicated people achieve such a goal? What treaties/regulations lie in the way? Can a corporation (non-profit or otherwise) be formed for the purpose of achieving this goal? Could this corporation be sustained by contributions of materials/manual labor? How about if a share in the corporation be given for each dollar worth of contributed money or material or work? I implore all of you to think seriously about this issue. Since our future in space rests in the hands of Congress, the GAO, and our executive branch, it is likely NASA will be fighting major battles for survival, let alone vigorous expansion. Is there a way we can make a difference, or must the space enthusiasts of this hemisphere be forced to learn Russian or French? N. Kluksdahl ..ncar!noao!asuvax!enuxha!kluksdah disclaimer: this message in no way reflects the opinions or policies of any official agency of the state of Arizona. ------------------------------ Date: Wed, 30 Nov 88 17:23:07 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Distributed Injection Ballistic Launcher I just read an interesting article: "The Distributed Injection Ballistic Launcher" H. Gilreath et. al., JHU APL Technical Digest 9(3), 1988, pp. 299-309. In a conventional gun, pressurized gas is injected once, and expands as the projectile travels down the barrel. As a result, acceleration drops off. The initial pressure is limited by the strength of the projectile and/or the barrel. Ideally, a gun should maintain constant pressure on the projectile. The DIL (approximately) does this by injecting gas behind the projectile from the sides at points along the barrel. This is a fairly old idea; the German V-3 guns in WWII used it (although they were never made operational). Just as a mass driver can be thought of as a linear electric motor, a DIL can be thought of as a linear internal combustion engine. Discrete injection of gas behind a flat-based projectile doesn't work very well. Instead, Gilreath et. al. propose to make the projectile boat-tailed -- that is, make its base be a long cone -- and inject the gas against the boat-tail as the projectile passes. If the boat-tail is sufficiently pointy (small boat-tail angle theta) then the axial velocity the gas must attain is reduced (by a factor of tan(theta)), and the system can operate efficiently even if the projectile is travelling much faster than the speed of sound in the gas. The limit the authors give is about 15 km/sec. The authors say (but do not justify) the mass penalties associated with launching directly to orbital velocities would be very great, due to the need for thermal protection. They suggest using the DIL as a first stage. They do say, however, that "complex electronics packages ... can easily tolerate accelerations of tens of thousands of g." That they say this isn't surprising, since JHU APL developed the first gun launched proximity fuse during WWII, and it tolerated 20,000 g, even though it contained five vacuum tubes. The article has an interesting picture of an extended-barrel 16" gun (conventional, not a DIL) that was operated in Barbados in the 1960s and early 70s. It could launch atmospheric diagnostic probes at 1.6 km/sec, with apogees up to 100 km (at a launch cost of few dollars per kilogram). The gun was used to launch scramjet test vehicles; they failed at launch, but theoretically they could have had a range of up to 3700 km with apogee at up to 1000 km. There is a picture of one test vehicle. It had a mass of 100 kg and burned 3 kg of triethyl aluminum (it is not clear if this vehicle had the stated range). It was designed to withstand accelerations up to 10,000 g, but suffered structural damage to its fins and skin in the test firing. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Fri, 2 Dec 88 00:36:18 EST From: attcan!utzoo!henry@uunet.UU.NET To: space-tech@cs.cmu.edu Subject: Re: Distributed Injection Ballistic Launcher > ... "complex electronics packages > ... can easily tolerate accelerations of tens of thousands of g." > That they say this isn't surprising, since JHU APL developed the first > gun launched proximity fuse during WWII, and it tolerated 20,000 g, > even though it contained five vacuum tubes. Said packages do have to be specially built, though. The vacuum tubes for the proximity fuzes (a "fuse" is an electrical safety device) were quite unorthodox designs. They were placed on the axis of the shell to minimize centrifugal force, and the tube elements were made of the thinnest practical wire to get maximum benefit from the square-cube law. The tube envelopes, needless to say, were metal. I'm trying to recall a piece I saw some years ago on the electronics in the Copperhead laser-guided shell. My dim recollection is that they used ring-shaped circuit boards around a central core, supported the boards at both core and outer edge, and otherwise just used careful mil-spec circuit construction. > The article has an interesting picture of an extended-barrel 16" gun > (conventional, not a DIL) that was operated in Barbados in the 1960s > and early 70s. It could launch atmospheric diagnostic probes at 1.6 > km/sec, with apogees up to 100 km... Ah yes, HARP. (High Altitude Research Project.) A joint US-Canada project. The gun was two battleship barrels end-to-end. One hears occasional mutterings that work along those lines may have been continued for a while, on a smaller scale in secret. HARP used fairly straightforward methods: an extra-long barrel, smoothbore (it was actually 16.5 inches when they bored out the rifling, I think) with fin-stabilized projectiles, and subcaliber projectiles (that is, projectiles rather smaller than the gun bore, padded out to full diameter with a light-alloy jacket that falls off on departure from the barrel). These techniques are all standard, on a less ambitious level, for modern tank guns (although smoothbore guns weren't in HARP's day). "Distributed Injection Ballistic Launcher", indeed. :-) It's a booster cannon. (I think we can claim that Heinlein's name for it has priority, by about 40 years.) Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Fri, 2 Dec 1988 02:10-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Ion Propulsion + Lightweight solar power I'm still working on bits and pieces of my conception of a good space probe which can motor around the Earth-Moon system and maybe farther. My current best plan has ion propulsion and lightweight solar power. I'm encouraged about these - here is some of what I found out from the library down the hall. It's mostly old news, though - some 1966, some 1981. I give references at the end. Any more up-to-date info is appreciated. Ion Propulsion -------------- There has been a lot of work done on ion propulsion, and NASA said in 1981 (in the Finke book) that ion propulsion is mature and ready to do real missions, now. They had been looking towards a mission to Halley's comet. NASA's Lewis Research Center has working mercury ion-bombardment thrusters that have been tested for up to 4000 hours, and really work. They think along the lines of 2 ton vehicles, so it may not be possible to get a small ion propulsion unit off the shelf. However, I bet a small unit could be designed and built as a small college project, given the thorough debugging NASA has done. This is encouraging enough that for the time being I'll assume that the problem of turning electric power into thrust is solved, and turn to the power question. Lightweight Solar Power ----------------------- Solar cells are getting better, but we can't expect huge improvements in power per kilogram here. Almost certainly the way to go is a high-temperature system using a solar collector, generator, and radiator. I'll deal with each of these in turn. 1. Collector ------------ Use a mirror. With lightweight mirrors, however, accuracy is a problem. In the Szego book, p. 900, is a NASA Langley paper on mirrors. They use - one-piece mirrors of aluminum or nickel (weights .5 to 1 lb/ft/ft, very accurate, but only 25-100 sq.ft. in area) - cone-and-column concentrator, based on reflection + Fresnel. Not great. - whirling membrane paraboloid mirrors of .0005-inch aluminized plastic (Lightweight, but give concentrations of only 200 because they aren't perfect parabolas. Maybe spinning isn't the best way.) - inflatable-rigidized mirrors. They were going to test them, as of '66. 2. Generator ------------ I mentioned solar dynamic power earlier, and boilers based on mercury or alkali metals have been developed at NASA Lewis. There are some tricky problems with these, which are only partially solved. A very interesting alternative is Thermionic Energy Conversion. Either method operates best at high temperature. Thermionic Energy Conversion (TEC) ---------------------------------- The idea: heat up an electrode until electrons are moving so fast that some of them can jump across a potential gap. Make sure the other electrode isn't as hot, so they don't jump back. Use this to drive an electrical load. It looks like a winner. No moving parts, turns a temperature difference directly into electricity, doesn't use up any material, works at high temperatures for good power-to-weight. The research was mostly done at NASA Lewis. A 1981 article in the Horton book cited these figures: input power densities of up to 100 Wt/cm/cm (Wt = watts total) output power densities 10-40 We/cm/cm (We = watts electrical) operating temperatures 1300-1900K input 900-1500K output 500-1000K differential gives 10-40 We/cm/cm Note that the power densities are in watts per unit area, rather than watts per kilogram. I have figures for solar flux level in outer space of 0.1 to 0.15 W/cm/cm, so an input flux of 100 Wt/cm/cm is about 700-1000 times that of ambient sunlight. Another 1966 paper from the Szego book, from JPL, has a TEC working at 24 W/cm/cm, weighing 260g, producing 48W at 2000K emitter temperature. Pretty good power densities for that early stage. An article by Shimada and Ewell of JPL, in the Horton book, suggests lower-density TEC's which radiate themselves. Densities are 100w/kg for the TEC's only, not really good enough. 3. Radiator ----------- The radiator could potentially be the heaviest part of the system. However, the higher the temperature, the more energy you can radiate, which is just fine for a TEC or solar dynamic system. The basic radiator has fins; the heat is conducted by fluid flow or a heat pipe. There's an interesting alternative, though - spray hot droplets of liquid from an emitter to a collector. You can get really big surface areas that way, for a given mass of radiator. In the Horton book is a paper by Knapp of Astro Research which outlines the spraying-droplets idea, which was just an idea at the time (1981). They projected really high dissipation-per-kilogram figures - 2 to 12 kW/kg - but such a system had never been built. It's promising but risky - I wonder how it turned out. Getting that kind of improvement in heat dissipation would be incredibly useful. What Next? ---------- I wonder if any of these are ripe for an experiment we could do? Ion propulsion + flexible mirror + TEC would make a pretty flashy low-acceleration probe. References ---------- Finke, Electric Propulsion and its Application to Space Missions, AIAA, 1981 Horton, ed., Spacecraft Radiative Transfer and Temperature Control, AIAA, 1981 Szego & Taylor, Space Power Systems Engineering, AIAA, 1966 Cheers! ----------------------------------------------------------------------------- | Marc Ringuette | mnr@cs.cmu.edu | "Silly rabbit, Trix are for kids! | | CMU Computer Science | 412-268-3728(w) | -- watch this space for other | | Pittsburgh, PA 15213 | 412-681-5408(h) | quotes from great literature | ----------------------------------------------------------------------------- ------------------------------ End of Space-tech Digest #16 *******************