Date: Fri, 22 Sep 1989 10:23-EDT From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #35 Contents: John DuBois Re: Hybrid rockets Mike Bird Re: Hybrid rockets Paul Dietz Re: Hybrid rockets Henry Spencer Re: Homemade liquid fueled rockets Paul Dietz Re: Homemade liquid fueled rockets Korac MacArthur fuels for rockets Henry Spencer Re: fuels for rockets Roger Arnold Re: fuels for rockets Tero Siili Re: fuels for rockets John Roberts Re: Lightweight mirrors Roger Arnold Re: Lightweight mirrors ------------------------------------------------------------ Date: Wed, 20 Sep 89 12:37:38 -0700 From: spcecdt@ucscb.UCSC.EDU (Space Cadet) To: space-tech@cs.cmu.edu Subject: Re: Hybrid rockets Liquid oxidizers needn't be cryogenic. How about hydrogen peroxide? Granted, it has dangers of its own, but it seems to be popular for low-budget rockets. Polybutadiene/H2O2 would probably have fair performance. An H2O2 monopropellant system might be simpler, but with poorer performance. John DuBois ------------------------------ Date: Thu Sep 21 09:17:34 1989 CDT From: Mike Bird To: space-tech@cs.cmu.edu Subject: Re: Hybrid rockets In reference to H2O2 rockets, My fraternity (an Electrical Engineering frat) once made an H2O2 rocket-powered car. The U of Mn Institute of Technology sponsors 'E-Week' every spring. Once of the festivities is a non-internal combustion powered car race. One year, we built an H2O2 powered car. When the E-Week people saw it, they changed the rules from a simple race to one which included steering through some pylons and stopping within a certain distance. Anyway, my point is that H2O2 is an easy rocket to make, but difficult stuff to control. The motor was heavily eroded (corroded?) by the one and only time we fired it (we wanted to see what it could have done if it had been allowed in the race). Also, the specific thrust, while fine for what we needed, whould have been lousy for lift. This all happened in 1974-75. (o.k. The exhaust went out for 30 feet, and the two members on the go-kart frame on which it was mounted damn near were shaken to pieces.) I have no data on the beast, but I could always ask my frat if anyone was interested. -- Mike Bird - B. Dalton, Bookseller UUCP: ...umn-cs!bungia!kksys!clavdivs!bird Helen Bird - Hummingbird Tailors Domain: bird@kksys.clavdivs.MN.ORG You can't call ME 'Books'! All opinions void where prohibited by law! ------------------------------ Date: Thu, 21 Sep 89 21:47:26 EDT From: dietz@cs.rochester.edu To: bird@clavdivs.MN.ORG Cc: space-tech@cs.cmu.edu Subject: Hybrid rockets > Anyway, my point is that H2O2 is an easy rocket to make, but difficult stuff > to control. The motor was heavily eroded (corroded?) by the one and only > time we fired it (we wanted to see what it could have done if it had been > allowed in the race). Also, the specific thrust, while fine for what we > needed, whould have been lousy for lift. Sounds like you solved the problem of getting the peroxide into the combustion chamber (I assume it was pressure-fed?). The erosion, I bet, was caused by the hot steam + oxygen. What material was the nozzle made of? You could get around erosion to some extent by taking up the original suggestion of a peroxide hybrid rocket. This would boost the Isp (I recall an Isp of > 250 s for peroxide + (CH2)n), and you could perhaps tailor the flow rate so the exhaust is not oxidizing. Why should a peroxide monopropellant rocket be hard to control, I wonder? Can't you just throttle the fuel flow into the catalyst bed? I wonder if it would be possible to make a hybrid rocket in which the fuel is wood (!). Maybe the chinese will, to go with their oak heat shields. For an amateur, it would be a readily available, strong, easily formed material. Lower Isp than rubber, I suppose. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ From: henry@utzoo.uucp To: uunet!cs.rochester.edu!dietz@cs.toronto.edu Cc: cs.cmu.edu!space-tech@cs.toronto.edu Subject: Re: Homemade liquid fueled rockets Date: Thu, 21 Sep 89 15:10:28 EDT > How hard is it to make a liquid-fueled rocket motor at home? Not especially difficult. Read a good historical account of the VfR (the German Rocket Society, pioneers of liquid-fuelled rocketry in the early thirties -- people like Willy Ley and Wernher von Braun). They had rockets flying reliably to heights of several kilometers after a few years. These were hobbyists on miniscule budgets in the middle of the Depression, not professionals with government support (that came later). The problems are legal, not technical. Building the thing is no problem; flying it is another story. Especially since one can confidently expect the first few attempts to end in explosions. The word is not "make" but "develop", and development includes failures. The VfR had the advantage of operating before rules and regulations for such things were drawn up. > ... Would a liquid fueled rocket < 1 pound > in weight qualify as a model rocket? No. One of the restrictions on model rockets, as I recall, is that you are not allowed to make your own engines. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Thu, 21 Sep 89 17:33:30 EDT From: dietz@cs.rochester.edu To: henry@zoo.toronto.edu Subject: Homemade liquid fueled rockets >> How hard is it to make a liquid-fueled rocket motor at home? >Not especially difficult. Read a good historical account of the VfR (the >German Rocket Society, pioneers of liquid-fuelled rocketry in the early >thirties -- people like Willy Ley and Wernher von Braun). They had rockets >flying reliably to heights of several kilometers after a few years. We have some advantages over these pioneers. Lots of literature is available. Data acquisition and control should be much easier with modern microcomputers and microsensors (weren't the AMROC tests run from a Macintosh?). And, we can simulate at least some aspects of engine behavior on computer (I am not naive enough to think such simulations are more than a guide to what will happen to the real thing). >The problems are legal, not technical. Building the thing is no problem; >flying it is another story. Especially since one can confidently expect >the first few attempts to end in explosions. The word is not "make" but >"develop", and development includes failures. The VfR had the advantage >of operating before rules and regulations for such things were drawn up. Yes, "develop". Hopefully, at least some of the engine explosions would occur on the test stand, not in the air. I was thinking the first step would be small engines, burning maybe a few ounces of propellant for a few seconds -- the liquid or hybrid equivalent of model rocket engines. Would ground tests violate fire codes? Surely not if performed at a remote location. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Wed, 20 Sep 89 17:06 EDT From: Subject: fuels for rockets To: space-tech@cs.cmu.edu X-Original-To: space-tech@cs.cmu.edu, K_MACARTHUR Solid rocket fuel has its uses, but control is not one of its strong points. Hybrid solid/liquid has merit. How about hypergolic fuels? Both components are relatively inert until mixed, and are controled easily. I don't think previous hypergolic fuels were cryogenic, either. I wonder what policy is about buying them as well. Store them on opposite sides of your garage, though. Question: To minimize rocket power needed, would a ramjet powered craft launched atop a rocket stage have enough speed to make low orbit before it ran out of thin air to use? I bet an SR-71 pilot could speculate an answer. Not that ramjets are cheap at the moment, either, but they have no major moving parts and no O-rings. Just ramblings.... Korac MacArthur K_MACART@UNHH.BITNET ------------------------------ From: henry@utzoo.uucp To: cs.cmu.edu!space-tech@cs.toronto.edu Subject: Re: fuels for rockets Date: Thu, 21 Sep 89 15:10:26 EDT > ... How about hypergolic fuels? Both > components are relatively inert until mixed, and are controled easily... Uh, whether they are relatively inert depends a whole lot on what they are. The standard hypergolic combination -- hydrazine (or minor variants thereon) and nitrogen tetroxide -- is truly vile. Hydrazine is corrosive, volatile, flammable, prone to spontaneous decomposition, poisonous, dangerous by skin contact, and carcinogenic. Nitrogen tetroxide is merely corrosive, volatile, and poisonous. I'm not aware of *any* oxidizer that can be said to be "relatively inert". With care, you can get fairly safe fuels, but all powerful oxidizers are dangerous. > Question: To minimize rocket power needed, would a ramjet powered > craft launched atop a rocket stage have enough speed to make low orbit before > it ran out of thin air to use?... Fundamentally impossible: its orbit must pass through the point where thrust was last applied, and either that's in the atmosphere (in which case reentry will be prompt) or not (in which case the last thrust cannot be a ramjet). That's a quibble, though, as almost everyone assumes a final push from a rocket to circularize the orbit. The really hard part is building a ramjet that will operate up to Mach 25 or so, and building a vehicle that can stand the atmospheric heating implied by flying in air at those speeds. (Rockets avoid most of this by doing most of their accelerating at still higher altitude.) What you're talking about here is a scaled-down NASP. That's, uh, a challenging project. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ From: telesoft!roger@ucsd.edu (Roger Arnold @prodigal) Date: Thu, 21 Sep 89 23:26:58 PDT To: space-tech@cs.cmu.edu Subject: Re: fuels for rockets > > ... How about hypergolic fuels? Both > > components are relatively inert until mixed, and are controled easily... > > Uh, whether they are relatively inert depends a whole lot on what they are. > The standard hypergolic combination -- hydrazine (or minor variants thereon) > and nitrogen tetroxide -- is truly vile. Hydrazine is corrosive, volatile, > flammable, prone to spontaneous decomposition, poisonous, dangerous by skin > contact, and carcinogenic. Nitrogen tetroxide is merely corrosive, volatile, > and poisonous. Quite true. Probably the most practical fuel combination for an amateur-built liquid rocket would be hydrogen peroxide and anhydrous amonia. They're not without hazard, but they're a lot safer than nitrogen tetroxide and hydrazine, and reasonably easy to come by. I don't believe the combination of hydrogen peroxide and amonia is hypergolic, but H2O2 decomposes exothermically into steam and oxygen when pumped over a catalyst. Amonia can be kept as a liquid at room temperature under tolerable pressure, but will vaporize nicely on the downstream side of a pressure reduction valve. Having gaseous fuel and oxidizer means that you don't have to worry much about fancy injector design. The exhaust is clean--just steam and nitrogen--and relatively cool, as rocket exhaust goes. H2O2 is a low energy oxidizer, compared to straight O2, or even nitrogen tetroxide. Yet because of the low molecular weight of the exhaust, specific impulse is respectable. I seem to recall something like 250 seconds? Amonia as a fuel has one additional advantage: it's excellent for cooling the combustion chamber. It has high thermal conductivity, for one thing. But more importantly, it can't coke the cooling tubes, as most hydrocarbon fuels do, because it has no carbon. That means that the engine can be made reusable. Correct me if I'm wrong, Henry, but I seem to recall hearing that H2O2 and H3N were used in the early X15 rocket engines. Or maybe it was H2O2 and methanol? That's another fairly benign choice. Later X15 models used a more powerful engine, with liquid oxygen as the oxidizer, I think. - Roger Arnold ucsd!telesoft!roger ------------------------------ Date: Thu, 21 Sep 89 11:57 EET From: Tero Siili Subject: RE: fuels for rockets To: space-tech@cs.cmu.edu X-Vms-To: IN%"space-tech@cs.cmu.edu" > Question: To minimize rocket power needed, would a ramjet powered >craft launched atop a rocket stage have enough speed to make low orbit before >it ran out of thin air to use? I bet an SR-71 pilot could speculate an >answer. Not that ramjets are cheap at the moment, either, but they have >no major moving parts and no O-rings. If I have not misunderstood, this is exactly what is being developed using lots of funds in projects such as NASP, HOTOL and Saenger. The aim is, however, to use horizontal, not vertical takeoff. The advantage in using air as long as possible is, that in a LOX/LH2 combination the LOX may constitute up to almost 90 % of mass (this is not accurate in practice, as the mixing ratios in rockets such as SSME:s are not stochiometric). Using atmospheric oxygen one saves mass. In HOTOL a dual propulsion system is used: LOX/LH2 rocket to accelerate to craft to 1-2 Mach, then ramjet and when atmosphere gets too thin, LOX/LH2 rocket again up to LEO. Tero Siili siili@csc.fi ------------------------------ Date: Thu, 21 Sep 89 20:00:41 EDT 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: Re: Lightweight mirrors >From: Marc.Ringuette@daisy.learning.cs.cmu.edu >Subject: Re: Spinning up tethers, lightweight mirrors >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. I haven't worked out the math on this recently (very difficult), but I remember that I used to wonder whether a slack rope on earth would assume the form of a parabola. I eventually found out that it does not (I *think* the shape it forms is a hyperbola). I imagine that this would also be the case with a "slack disk". It is possible, however, that it could be made close enough to a parabola to be useful. (As an analogy, a Newtonian telescope mirror can be spherical if it has a high enough f ratio (f/10, I think, for a 4" mirror), and still be close enough to a parabolic form to be usable. This is important because it is much easier to grind a spherical mirror than a parabolic mirror.) >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. Any large, thin-walled inflated object in space will eventually lose enough of its gas through meteorite punctures and/or diffusion that it will lose its shape. (I assume that's what happened to the Echo satellites, if they didn't burn up first.) To assemble a really large reflecting surface in space, it *might* be practical to inflate a pre-formed balloon, then spray the back of the surface with a stiffening agent. A passive or active support structure could possibly be added behind the surface. Precision would seem to be limited only by the degree of control available. (How about a 100' open-frame telescope at L5? :-) John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ From: telesoft!roger@ucsd.edu (Roger Arnold @prodigal) Date: Thu, 21 Sep 89 23:21:21 PDT To: space-tech@cs.cmu.edu Subject: solar concentrating mirrors >I haven't worked out the math on this recently (very difficult), but I remember >that I used to wonder whether a slack rope on earth would assume the form of >a parabola. I eventually found out that it does not (I *think* the shape it >forms is a hyperbola). .. It's a catenary. Not quite the same thing. > .. I imagine that this would also be the case with a >"slack disk". [..] Not really. Because you're dealing with a two dimensional surface, the final shape can be determined, within limits, by the shape you start out with. Witness the fancy advertising baloons that are becoming popular. Getting a parabola is no problem, in principle. >>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. [..] > >Any large, thin-walled inflated object in space will eventually lose enough >of its gas through meteorite punctures and/or diffusion that it will lose its >shape. [..] To assemble a really large reflecting surface in space, it >*might* be practical to inflate a pre-formed balloon, then spray the back of >the surface with a stiffening agent. A passive or active support structure >could possibly be added behind the surface. Precision would seem to be limited >only by the degree of control available. (How about a 100' open-frame telescope >at L5? :-) > John Roberts > roberts@cmr.ncsl.nist.gov If you can make really light metal films in space, a'la Drexler's solar sail material, then light pressure alone is quite sufficient to inflate them. Of course, if you can make that sort of material, you wouldn't need big solar concentrators to power high impulse engines. You'd use solar sails, instead. - Roger Arnold ucsd!telesoft!roger ------------------------------ End of Space-tech Digest #35 *******************