Subject: Space-tech Digest #147 Contents: High density fuels (zinc, MDNA, etc) (19 msgs) ------------------------------------------------------------ Date: Fri, 26 Feb 93 17:26:52 -0500 From: dietz@cs.rochester.edu To: gwh@lurnix.lurnix.com, space-tech@cs.cmu.edu Subject: Molten zinc as a rocket fuel Some additional comments on the zinc idea... Zinc melts at 420 C. There are two eutectics with magnesium: one (49/51 Mg/Zn) melts at 340 C; the other (about 4/96 Mg/Zn) melts at around 370 (?) C. The latter is probably the better of the two, as it is denser. There is also a Zn/Mg/Al eutectic with a slightly lower melting point. Can one build a pressurized steel tank at this temperature? It appears so. D-6a ultrahigh strength steel retains most of its strength at these temperatures: Temperature (C) Yield Strength (MPa) 260 1295 315 1256 370 1167 425 1096 480 976 540 832 595 396 (This is for D-6a normalized at 900 C, oil quenched from 845 C and tempered 30 C above the indicated temperature.) This shows that D-6a steel tanks would be ok for molten zinc or zinc/magnesium mixtures, but not for, say, molten aluminum or magnesium. What's the sea-level Isp of zinc/peroxide? 200 seconds? What's the optimal mixture ratio for optimal expansion from (say) 1000 psia? Zinc's Achilles heel may be pollution: the EPA may class zinc as a toxic heavy metal. Magnesium, on the other hand, is abundant in seawater. Paul ------------------------------ Date: Fri, 26 Feb 1993 16:28:09 MST From: "Richard Schroeppel" To: space-tech@cs.cmu.edu Subject: Zinc toxic? > Zinc's Achilles heel may be pollution: the EPA may class zinc as a toxic heavy metal. Magnesium, on the other hand, is abundant in seawater. Zinc is an essential trace element. ZnO is a standard sunblock. Zn metal is used to coat roofing nails (to prevent corrosion), and it's an ingredient in pennies. Is it really toxic? Rich Schroeppel rcs@cs.arizona.edu ------------------------------ Date: Fri, 26 Feb 93 19:10:56 -0500 From: dietz@cs.rochester.edu To: rcs@cs.arizona.edu, space-tech@cs.cmu.edu Subject: Re: Zinc toxic? Rich Schroeppel asks if zinc is toxic. No, not very; it is the second most abundant transition metal in the human body, after iron. However, this hasn't stopped the EPA from trying to regulate it. They recently issued for public comment some regulations for metals, including zinc. Someone pointed out that their proposed limits for human intake of the element were actually less than the US RDA, and that, under the proposed regulations, zinc supplement pills would be classified as hazardous waste (that is, you could eat them, but you could not legally throw them in the trash.) The proposed regulations were withdrawn. The point of this is that there would be a political risk to using zinc as a fuel. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ To: uunet!cs.rochester.edu!dietz@uunet.UU.NET Cc: gwh@lurnix.COM, space-tech@cs.cmu.edu Subject: Re: metal fuels for hybrids Date: Fri, 26 Feb 93 12:30:32 -0800 From: gwh@lurnix.COM High Grade, Paul? Why would I need High Grade zinc? 8-) Cheaper grades will do just fine for what I have in mind. -george ------------------------------ From: henry@zoo.toronto.edu Date: Sat, 27 Feb 93 01:22:34 EST To: Richard Schroeppel Cc: space-tech@cs.cmu.edu Subject: Re: Zinc toxic? >> Zinc's Achilles heel may be pollution: the EPA may class zinc as a >> toxic heavy metal. Magnesium, on the other hand, is abundant in >> seawater. > >...it's an ingredient in pennies. Is it really toxic? Everything is toxic in sufficient quantity. It is possible to die from drinking too much water, although you really have to apply yourself. Contrariwise, many toxic materials are necessary to the body in small quantities. Cobalt is a heavy metal and fairly toxic, but it is also an essential part of the chemical structure of vitamin B-12 and vitally necessary (in very small quantities) to your body. The real questions are whether zinc is dangerous enough to (a) present significant handling hazards [no], (b) be subject to regulation [not at the moment], or (c) be subject to public hysteria [not yet...]. Oh yes, another real question is whether the form involved is different enough to change the rules. For example, plutonium oxide is not overly toxic when eaten but is lethal when inhaled as fine dust. Zinc oxide in large quantities as fine atmospheric dust is not quite the same problem as sunblock cream or roofing-nail coatings. Incidentally, one should not assume that presence in (e.g.) seawater rules out government regulation or public hysteria. Sometimes it's even for good reason. (Most of the toxins and carcinogens in your diet are natural compounds; if you eat peanut butter, worrying about trace quantities of Alar on apples is pretty ludicrous...) Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Sat, 27 Feb 93 00:05 PST To: space-tech@cs.cmu.edu Subject: Zinc From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) Finally there may be some justification for an otherwise inexplicable blunder in one of Robert Heinlein's early books. In "Rocketship Galileo", he pictured an atomic rocket with using zinc as a reaction mass. This made no sense, as even the then-current textbook would have made it plain that what was needed would be something like hydrogen. Clearly, he could see a bright future for zinc however. I am a bit surprised by the use of zinc. A graph that I have of the head of combusion of various metals indicates that zinc is outperformed by: Li Be C Na Mg Al Si P S Ca Ti V Cr Mn Fe Ga Sr Y Zr Many of these are of course not practical as fuels for one reason or another. -- Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ Date: Sat, 27 Feb 93 07:31:11 -0500 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Zinc Bruce Dunn said: > I am a bit surprised by the use of zinc. Well, it does have a lousy heat of combustion, but in a rocket first stage or strapon that is discarded after delivering a delta-V of < the exhaust velocity of that stage, the figure of merit for a propellant in a pressure-fed rocket is something like density * exhaust velocity. Very naively, doubling the molecular weight of the reactants while keeping bond energies constant will double the density but cut the exhaust velocity only 40%. Stoichiometric zinc/peroxide has about 2.5x the density of propane/peroxide, yet its specific energy is 60% of that of P/P. Even if much of that energy is wasted because of nonstoichiometry and condensation of zinc oxide, the density advantage is considerable. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sun, 28 Feb 93 21:54:28 -0500 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Dense propellants? Out of curiosity, I computed the density * sqrt(specific energy) of a number of stoichiometric metal/peroxide combinations (specific energy computed naively by computing the heat of combustion to oxides and water vapor at 298 C). Al and Be come in slightly below zinc; carbon is considerably worse. Zirconium is a bit better than zinc. The winners among the elements I looked at, however, were uranium and thorium! The Isp of these combinations would no doubt be dreadfully low, of course, and the cost would be much higher. (Not to mention the environmental impact.) Some of the heavier rare earths are close. A misch-metal hybrid? At the least, it might be interesting to make the inner surface of the fuel of a hybrid or solid rocket be enriched in heavy elements, to increase the total useful impulse delivered by an engine of a given volume by modulating the exhaust velocity to increase with time. Alternately, perhaps one could build a tripropellent engine, in which a dense but mostly inert metal is injected early in the flight, to reduce the early consumption of the less dense propellants, and thus reduce the burnout mass of the stage. Zinc would be nice there; a shame lead is too toxic. Paul ------------------------------ Date: Sun, 28 Feb 93 23:20 PST To: space-tech@cs.cmu.edu Subject: Dense Propellants From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) > Paul Dietz writes: > Alternately, perhaps one could build a tripropellent engine, in which > a dense but mostly inert metal is injected early in the flight, to > reduce the early consumption of the less dense propellants, and thus > reduce the burnout mass of the stage. Zinc would be nice there; > a shame lead is too toxic. From "Ignition" by J.D. Clark Soon after the end of the war, then, several organizations set out confidently to design - and fire - hybrid rockets, and fell flat on their corporate faces. The experience of GE (in 1952, on Project Hermes) was typical. Their intention was to use a polyethylene fuel grain, with hydrogen peroxide as the oxidizer. And when they fired their rocket, the results were worse than depressing - they were disasterous. Combustion was extremely poor, with a measured C* to make an engineer weep. And when they tried to throttle their motor, the oxidizer-fuel ratio varied madly and was never anywhere the optimum for performance. (This is hardly surprising, since the oxidizer consumption depends on the rate at which it is injected, while the fuel consumption depends on the area of the fuel grain exposed.) And tinkering with the injector and the exact shape of the fuel grain did very little good. The engineers had been guilty of a sin to which engineers are prone - starting their engineering before doing their research. For it had become devastatingly clear thet nobody knew how a solid fuel burned. Did it evaporate, and then burn in the vapor phase? Or was a solid-state reaction involved? Or what? There were lots of questions, and very few answers, and hybrid work languished for some years. Only the Navy, and NOTS, kept at it, trying to learn some of the answers. The revival started in 1959 when Lockheed, with an Army contract, started hybrid work.... ... more important, in the long run, was some of the work at UTC, who had a Navy contract to investigate the basic mechanism of hybrid combusion. (This of course should have been done at least ten years earlier, and before a lot of money had been sunk into hybrid work. But it's always easier to get money for engineering than for fundamental reasearch. Don't ask me why). ...They learned that the oxidizer reacts with the fuel only in the vapor phase, and that the rate was controlled by diffusion, while the rate of regression (consumption) of the fuel depended largely upon heat transfer from the hot reacting gases. (This of course was not strictly true when the fuel grain contained oxidizer of its own). They learned that proper injector design could keep the regression rate uniform across the whole grain surface, but that the mixing of the fuel vapor and the oxidizer was so slow that addiitional mixing volume downstream of the grain was usually necessary to get reasonable combustion efficiency. This extra volume did much to reduce the density advantage claimed for the hybrid systems. But they learned how to build a hybrid motor that would work with reasonably efficiency. All sorts of efforts were being made, during the late 50s, to increase propellant densities, and I was responsible (not purposely, but from being taken seriously when I didn't want to be) for one of the strangest. Phil Pomerantz, of BuWeps, wanted me to try dimethyl mercury (Hg(CH3)2) as a fuel. I suggested that it might be somewhat toxic and a bit dangerous to synthesize and handle, but he assured me that it was (a) very easy to put together , and (b) as harmless as mother's milk. I was dubious, but told him that I'd see what I could do. I looked the stuff up, and discovered that, indeed, the synthesis was easy, but that it was extremely toxic, and a long way from harmless... Phil wanted density. Well, dimethyl mercury was dense, all right - d=3.07 - but it would be burned with RFNA, and at a reasonable mixture ratio the total propellant density would be about 2.1 or 2.2 (the density of the acid-UDMH system is about 1.2). That didn't seem too impressive, and I decided to apply the reducto ad absurdum method. Why not use the densest known substance which is liquid at room temperature - mercury itself? Just squirt it into the chamber of a motor burning, say, acid-UDMH. It would evaporate into a monatomic gas (with a low Cp which would help performance), and would go out the nozzle with the combustion products. That technique should give Phil all the density he wanted! Charmed by the delightful nuttiness of the idea, I reached for the calculator. [material on paper design of a monopropellant motor with mercury injection - system looked good for an air to air missile] I solemly and formally wrote the whole thing up, complete with graphs, labeled it - dead pan - the "Ultra High Density Propellant Concept" and sent it off to the Bureau. I expected to see it bounce back in a week, with a "Who do you think you're kidding?" letter attached. It didn't. Phil bought it. He directed us, forthwith, to verify the calculations experimentally, and NARTS, horified, was stuck with the job of firing a mercury-spewing motor in the middle of Morris County, New Jersey. ...So a scrubber had to built, a long pipe-like affair down which the motor would be fired, and fitted with water sprays, filters, and assorted devices to condense and collect the mercury in the exhaust before it could get out into the atmosphere. ... At NOTS, Dean Couch and D.G. Nyberg took over the job, and by March 1960 had completed their experiments. They used a 250 pound thrust RFNA-UDMH motor, and injected mercury through a tap in the chamber wall. And the thing did work. They used up to 31 volume percent of mercury in their runs, and found that at 20 percent they got a 40 percent increase in density impulse.... Technically, the sytstem was a complete success. Practically - that was something else again. Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ To: Bruce Dunn Cc: space-tech@cs.cmu.edu, gwh@soda.berkeley.edu Subject: Re: Dense Propellants Date: Mon, 01 Mar 1993 01:08:36 -0800 From: George William Herbert ...Good story to post, Bruce. I'm not insane enough to be interested in Mercury. IMHO Zinc gives good enough performance and cost and is probably as safe for the environment as Aluminum is, or more. -george ------------------------------ Date: Mon, 1 Mar 93 19:42:37 -0500 From: dietz@cs.rochester.edu To: henry@zoo.toronto.edu, rcs@cs.arizona.edu Subject: Re: Zinc toxic? Cc: space-tech@cs.cmu.edu Henry wrote: > Incidentally, one should not assume that presence in (e.g.) seawater > rules out government regulation or public hysteria. (this was in reference to magnesium, I believe) Hysteria can never be entirely avoided, but magnesium really is plentiful in seawater -- it's the fifth most common element there (after hydrogen, oxygen, chlorine and sodium), and makes up .1% of seawater by weight. In fact, seawater is commercially mined as a source of magnesium. Magnesium oxide is the primary ingredient in some commercial antacids, so I can't be too toxic. paul ------------------------------ Date: Tue, 2 Mar 93 19:51:31 -0500 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: MDNA? I came across a reference to something called "maximum density nitric acid" (MDNA), which contains 52% NO2. Can someone tell me the vapor pressure and density of this stuff at 300 K, and can it be inhibited like RFNA (20% NO2)? Paul ------------------------------ Date: Tue, 2 Mar 93 18:14 PST To: space-tech@cs.cmu.edu Subject: MDNA From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) Paul Dietz writes: > I came across a reference to something called "maximum density > nitric acid" (MDNA), which contains 52% NO2. Can someone tell > me the vapor pressure and density of this stuff at 300 K, and > can it be inhibited like RFNA (20% NO2)? Gordon and Lee (previously quoted on metallized propellants) have one calculation in their paper referring to "MDFNA", equal to Maximum Density Fuming Nitric Acid. They give the following reference for its properties: Mason, D.M., Petker, I. and Vango, D.K. Viscosity and density of the nitric acid-nitrogen dioxide-water system" J. Phys. Chem. 59: 511 (1955) If you can get this, I suspect that it may have answers to your question on vapor pressure. You must distinguish two types of vapor pressure. One is the pressure immediately measurable when you pop the acid into a sealed container. The other is the "decomposition pressure" which is what the container eventually reaches. The acid-N2O4-water system is unstable, and through a very complex series of reactions evolves oxygen. Left long enough, the reaction will stop only when the partial pressure of oxygen over the acid reaches a level high enough to shut the reaction down. There are only certain proportions of acid-N2O4-water whose chemistry generates "decomposition pressures" which are reasonable. Anhydrous WFNA acid is particularly bad, with a decomposition pressure of about 70 atmospheres. Clark (in "Ignition") mentions MDNA only in passing: "The only other sort of acid worth mentioning is "Maximum Density Nitric Acid". This was proposed by Aerojet for applications in which density is all-important and freezing point requirements are not too strict. It contains 44 percent N2O4, and has a density of 1.63" I presume that MDNA could be inhibited - Clark goes into a lot of detail about the corrosion problems caused by uninhibited acid, and I suspect that if MDNA could not be inhibited by HF, that he would have mentioned the fact as a black mark against it. Once IRFNA had been developed, I don't think that anyone would serious propose using a corrosive acid even if its density were high. Note Paul that Clark and your reference don't agree on the percentage of N2O4 (or NO2) in the maximum density acid. -- Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ Date: Thu, 4 Mar 93 11:07:19 -0500 From: dietz@cs.rochester.edu To: Bruce_Dunn@mindlink.bc.ca, space-tech@cs.cmu.edu Subject: Re: MDNA About MDNA... I looked up the J. Phys. Chem. article. At 0 C, the density maximum is indeed around 44% NO2, at about 1.67 g/cc. The viscosity is also quite high, more than 3 times that of 100% nitric acid. The maximum solubility of NO2 in nitric acid at 0 C is 52%, which is perhaps where that number came from. I don't see how a N2O4-nitric acid system could decompose. If *water* were present, then, yes, it could react to make nitric acid and oxygen. Nitric oxide (in WFNA) has a positive energy of formation, unlike NO2, so it is not surprising that WFNA has a high decomposition pressure. BTW, if one wants a dense oxidizer, with so-so performance, perhaps one should dissolve a nitrate salt in nitric acid. The metal adds nothing to the energy, so Isp is down, but density is up. Many nitrate salts are cheaply available as fertilizer. Perhaps potassium nitrate would be a good choice? Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Fri, 5 Mar 93 06:41:33 -0500 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: nitrate salts (was MDNA) Potassium nitrate is quite soluble in conc. nitric acid (roughly 50/50 by weight at 25 C). Most of nitrates are not nearly so soluble in the acid, however. Another oxidizer suggests itself: molten nitrate salts. Potassium and sodium nitrates melt in the low 300 C's; lithium nitrate melts at 254 C. Binary and ternary eutectics of alkali metal nitrates exist with even lower melting points (as low as 120 C in one case, I believe). A sodium/potassium nitrate eutectic has been seriously proposed as a heat transfer and storage fluid for solar thermal receivers ("power towers"). Although their performance is lower than nitric acid, these salts are a bit more dense, and should be much safer to transport and handle than an acid. Paul ------------------------------ Date: Fri, 5 Mar 93 14:56:49 -0500 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Yet more on nitrates... Out of curiosity, I looked up some mixtures of various nitrate salts. There are some surprisingly low melting point eutectics: Cations Proportions (weight %) Melting point (C) of anhydrous salts NH4 100 169 Ca/K 51/49 142 Ca/NH4 29/71 111 K/Li 60/40 170 K/Mg 42/58 178 71/29 195 K/NH4 14/86 157 K/Na 50/50 220 Li/NH4 27/63 90 Li/Na 55/45 196 Mg/Na 51/49 135 NH4/Na 79/21 121 Ca/K/Li 15/62/23 117 Ca/K/Mg 41/53/6 137 Ca/Li/Na 30/30/40 170 Ca/NH4/Na 18/69/13 107.5 K/Li/Na 120 K/Mg/Na 130 K/NH4/Na 12.5/66.5/21 118.5 (It would be interesting to see data on lithium/ammonium/whatever ternary nitrate eutectics, but I haven't seen any.) The melts with ammonium nitrate are particularly interesting, as they require much less fuel, and produce more gas vs. metal oxides. AN starts decomposing around 200 C (depending on purity), making nitrous oxide. It also becomes subject to detonation if heated, especially if mixed with a reduced material (as at the Texas City disaster, for example). However, a eutectic, like the lithium nitrate mix, would serve not only to reduce the temperature at which the material is liquid, but also make the mixture more oxidizing, which should reduce its propensity to explode. The melting point of some of these salts (AN, for example) can be reduced by adding water. AN also dissolves in ammonia. That's more dangerous, as the ammonia is a fuel; a solution of AN in anhydrous ammonia has been proposed as a monopropellant ("Diver's solution"), but I think it may be too unstable. What says "Ignition", Bruce? Paul ------------------------------ Date: Fri, 5 Mar 1993 13:32:04 MST From: "Richard Schroeppel" To: space-tech@cs.cmu.edu Subject: High density oxidizers & fuels. Has anyone looked into oxidizers based halogens, such as Cl2, Br2, Cl2O, etc.? These have various different liquid densities & boiling points to work with. Br2 is even a liquid at room temperature. Perhaps include dissolved I2 to increase molecular weight. Periodic charts sometimes identify 4 elements as liquids: Br & Hg are unequivocal; sometimes Ga & Cs are also marked. Rich Schroeppel rcs@cs.arizona.edu ------------------------------ Date: Fri, 5 Mar 93 16:33:15 -0500 From: dietz@cs.rochester.edu To: rcs@cs.arizona.edu, space-tech@cs.cmu.edu Subject: Re: High density oxidizers & fuels. People sure have looked at halogens and halogenated compounds. I was ignoring them, because of their toxicity, cost and environmental effects (bromine being even worse on ozone than chlorine). Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sat, 6 Mar 93 08:36 PST To: space-tech@cs.cmu.edu Subject: Yet more on nitrates... From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) > Paul Dietz writes: > The melting point of some of these salts (AN, for example) can be > reduced by adding water. AN also dissolves in ammonia. That's more > dangerous, as the ammonia is a fuel; a solution of AN in anhydrous > ammonia has been proposed as a monopropellant ("Diver's solution"), > but I think it may be too unstable. What says "Ignition", Bruce? From "Ignition", by J.D. Clark: [in Germany] In 1937-38 a good deal of work was attempted with solutions of N2O or NH4NO3 in ammonia. (The latter mixture, under the name of Driver's solutions, had been known for many years.) The only result of these experiments was a depressing series of explosions and demolished motors. And at Peenemunde, A Dr. Wahrmke tried dissolving alcohol in 80% H2O2 and then firing that in a motor. It detonated, and killed him. [the moral of the story, when you read Clark, is that monopropellants only differ from liquid explosives to a subtle degree. If you use the wrong mixture of oxidizer and oxidizable material, when you ignite it in a motor, the reaction may travel upstream from the injector, through the propellent feed line, and touch off the main propellant tank] More from Clark: Some years later, in the late 1950s, Commercial Solvents ... devised a series of monopropellants which were rather similar to the hydrazine mixtures, except that they were based on methyl amine, to which was added ammonium nitrate or hydrazine nitrate or methylammonium nitrate, or lithium nitrate. Thee were safe enough, but their energy and performance were low. [then there was a conceptual discovery] .. almost any amine, and not just extremely stable ones like pyridine, could be made into a monopropellant, if its nitrate salt were made first and then dissolved in the acid. And God only knows how many amines there are! ... We had a lot of pyridine around the place, and for some unknown reason, a tank of liquified trimethylamine. Plus of course, unlimited nitric acid, so things went fast. [they named the pyridine nitrate/acid mix "Penelope" and tried to fire it. Normal ignition methods did not work] Bert Abramson, who was in charge of the test work, then took an acetylene torch and heated the motor red hot, and opened the prop valve. This time he got ignition, and some half hearted operation for a few seconds. Inspired to further effort, he crammed about a yard of lithium wire into the chamber, and pushed the button. Penelope sprayed into the chamber, collected in a puddle in the bottom, and ***then*** reacted with the wire. The nozzle couldn't cope with all the gas produced, the chamber pressure rose exponentially, and the reaction changed to a high order detonation which demolished the motor, propogated through the fuel line to the propellant tank, detonated the propellant ***there*** (fortunately there were only a few pounds in the tank) and wrecked just about everything in the test cell. Penelope should have been named Xantippe. She also scared everybody to death - particularly Abramson. [they then got systematic, made a number of new salts, and tested their stability before attempting to fire them] Joe Pisani phoned me from RMI one day late in 1958, asking me if I'd do a thermal stability run on a sample of propargyl nitrate. ....[disaster omitted]... I got on the phone. "Joe? You know that suff you sent me to test for thermal stability? Well, first, it hasn't got any. Second, you owe me a new bomb, a new Wianco pickup, a new stirrer, and maybe a few more things I'll think of later. And third (crescendo and fortissimo) you'll have a couple of flunkies up here within fifteen minutes to clean up the (-bleep-) mess or I'll be down there with a rusty hacksaw blade" I specified the anatomical use to which the saw blade would be put. [after some years of work, the best monopropellants that Clark came up with was an acid solution of "1,4 diaza, 1,4 dimethyl, bicyclo 2,2,2, octane dinitrate", which he called "Cavea" as it had a symmetrical closed cage structure, or an acid solution of a methyl derivative called Cavea B] Cavea B was the winner, and seemed to be the ideal monopropellant. And by the end of the year it had been fired successflly, by NARTS, GE, Wyandotte, and Hughes Tool, with JPL soon fo follow. It performed very well in a motor, yielding 94 or so percent of the theoretical impulse with a compartitively small chamber. Combustion was remarkably smooth - better than that with the Original Cavea. [when working with monopropellants, it is customary to bend the propellant line in an overlapping loop, called a detonation trap. If the reaction tries to propogate up the propellant line, the detonation cuts off the propellant flow above the detonation, at the point the tube overlaps itself] But detonation traps aren't always the complete answer. We discovered that then, in the summer of 1960, we tried to fire a 10,000 pound trust Cavea B motor....Well, through a combination of this and that, the motor blew on startup. We never discovered whether or not the traps worked - we couldn't find enough fragments to find out. The fragments from the injector just short-circuited the traps, smashed into the tank, and set off the 200 pounds of propellant in that. (Each pound of propellant had more available energy than two pounds of TNT). I never saw such a mess. The walls of the test cell, two feet of concrete - went out, and the roof came in. The motor itself - a heavy workhorse job of solid copper - went about 600 feet down range. And a six-foot square of armor plate sailed into the woods, cutting off a few trees a the root, smashing a granite boulder, bounding into the air and slicing off a few few treetops, and finally coming to rest some 1400 feet from where it started. The woods looked as though a stampeding herd of wild elephants had been through it. As may be imagined, this incident tended to give monopropellants something of a bad name. Even if you could fire them safely - and we soon saw what had gone wrong with the ignition process - how could you use them in the field? Here you have a rocket set up on the launching stand, under battlefield conditions; and what happens if it gets hit by a piece of shrapnel? ... And as for the future of the high-energy monopropellants: I'm afraid that it's in the past. We all worked for years trying to reconcile properties which we finally and sadly concluded were irreconcilable - high energy and stability. For all our efforts, no high energy monoprop has made the grade to operational status. Cavea B almost made it, but "almost" is not success. But it was a dammed good try! -- Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ End of Space-tech Digest #147 *******************