Subject: Space-tech Digest #160 Contents: Alternative oxidizers for pressure fed rockets (3 msgs) isp program available for anonymous ftp (3 msgs) P2 technical issues (2 msgs) ------------------------------------------------------------ Date: Tue, 20 Jul 93 23:29:28 -0400 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Alternative oxidizers for pressure fed rockets I was playing with the ISP program Bruce sent me (it will be available for anonymous ftp as soon as I can figure out how to load MS DOS files through a sparcstation), and compared some alternate oxidizers to peroxide for use with RP-1. Burning with RP-1 at a chamber pressure of 1000 psia and nozzle exit pressure of 14.7 psia, the maximum Isp and corresponding propellant bulk density for the oxidizers was: Oxidizer Isp (SL) Bulk Density ---------------------------------------------------------------------- nitric acid 263 sec 1.31 g/cc 100% hydrogen peroxide 278 1.31 chlorine trifluoride 258 1.39 perchloryl fluoride (ClO3F) 283 1.22 (1.38) perchloric acid 274 1.44 Cl2O7 285 1.42 ---------------------------------------------------------------------- Some of these oxidizers are very unpleasant. Chlorine trifluoride, for example, causes asphalt to burn on contact, and has a low boiling point (and its lack of oxygen makes it perform poorly with a carbonaceous fuel like RP-1). Perchloric acid is very corrosive and somewhat unstable. Cl2O7, an oily liquid with a boiling point of 82 C and a density of 1.82 g/cc, can explode when heated and decomposes slowly at room temperature (but otherwise its high Isp and density seem attractive for pressure-fed rockets). Perchloryl fluoride is the most stable of the bunch. Indeed, this gas has been proposed for use in high voltage transformers, as it is noncorrosive (at least when dry) and resists electrostatic breakdown. Unlike some other fluorine/chlorine compounds, it does not etch glass, even when the glass is heated to near the softening temperature. Its boiling point is -46.8 C, but it can be liquified under pressure at room temperature (1.392 g/cc at 25 C). At its boiling point at 1 bar, its density is 1.66 g/cc, giving a denser mixture (1.38 g/cc) than peroxide/RP-1. There are steels that have adequate toughness at the boiling point (HY 130, for example), and the absolute temperature is not so much lower (225 K) that helium requirements would be greatly increased. The drawbacks of perchloryl fluoride would be: possible ozone depletion potential, higher combustion temperature, and cost (unlike peroxide, there is no very large terrestrial market, and its manufacture involves electrolysis of perchloric acid dissolved in anhydrous hydrogen fluoride). Perhaps it would be useful in an upper stage. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 20 Jul 93 21:43 PDT To: space-tech@cs.cmu.edu Subject: Alternate oxidizers for pressure fed rockets From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) Regarding alternate oxidizers Paul Dietz writes: > Perchloryl fluoride is the most stable of the bunch. Indeed, this gas > has been proposed for use in high voltage transformers, as it is > noncorrosive (at least when dry) and resists electrostatic breakdown. > Unlike some other fluorine/chlorine compounds, it does not etch glass, > even when the glass is heated to near the softening temperature. > Clark, in his book "Ignition" says that "PF" was much admired by the people who had to do actual motor testing, as it was so benign a compound that the worst thing that you could do to hurt yourself would be to drop a cylinder of it on your foot (but don't breath the exhaust). Paul mentions ClF3 as a oxidizer, and notes that it performs poorly with a carbon containing fuel. The drill then is to use a mix of ClF3 and PF, which if I remember are miscible. Even better is a mixture of ClF5 and PF, particularly with a fuel rich in hydrogen such as propane. The ultimate in performance for upper stage work is to get rid of the carbons and burn N2H4 burned ClF5, or even better with N2F4 (dinitrogen tetrafluoride, often called tetrafluorohydrazine). These oxidizers all deserve respect. Clark relates an incident where a steel cylinder was pre-chilled before being filled with ClF3 (if I remember correctly). The steel was brittle, and the cylinder cracked, dumping its load of oxidizer on the floor where it promptly ate through a considerable amount of concrete. Clark mentions that nitric acid and kerosene, while appearing attractive because of cost, is a difficult mixture to get ignited and is plagued by combustion problems unless a lot of work has been put into chamber and injector development. A lot of work was put into trying to find additives to get kerosene to burn nicely with nitric acid. The best bet was to add some form of hydrazine to the kerosene. I think a couple of early missile systems used kerosene/hydrazine mixes with nitric acid. However, the hydrazine performed so much better than the kerosene that people lost interest in kerosene, and simply went to various hydrazine mixtures (formulated to have low freezing points for military purposes). While the fluorine containing oxidizers give good performance, the combustion temperature is frightfully high, requiring good cooling systems for the injectors, chamber and throat. -- Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ Date: Wed, 21 Jul 93 14:26:28 -0400 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: perchloryl fluoride I wrote: > its manufacture involves electrolysis of perchloric acid dissolved in > anhydrous hydrogen fluoride) This is incorrect: it involves electrolysis of sodium perchlorate in anhydrous HF. A good thing, as perchloric acid is much more expensive and not available in bulk. One can estimate the cost of the stuff by the cost of the feedstocks. Sodium perchlorate for blasting cost $.41/kg in 1979, which would be roughly $.40/lb today. Hydrogen fluoride costs about $1/lb, I think. Electricity for electrolysis, amortization of the plant and operation cost would increase the cost of PF above that of the feedstocks, but it looks like it could be made for not too much more than peroxide. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ To: dietz@cs.rochester.edu Cc: space-tech@cs.cmu.edu, gwh@soda.berkeley.edu Subject: Re: Alternative oxidizers for pressure fed rockets Date: Tue, 20 Jul 1993 21:57:50 -0700 From: George William Herbert I also recieved a copy of the program, and will by week's end have it at a nearby FTP site and probably at ftp.isunet.edu as well... 8-) -george ------------------------------ Date: Wed, 21 Jul 93 13:40:26 -0400 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: isp program available for anonymous ftp Look in the directory pub/isp on cayuga.cs.rochester.edu. The files are copied directly without changes from the MS DOS diskette, so their carriage return/linefeeds look strange under UNIX. Paul ------------------------------ Date: Wed, 28 Jul 93 22:23:10 -0400 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Fun and games with the Isp program I've been playing a bit with the AF Isp program Bruce sent me (remember, it is available by anonymous ftp in /u/ftp/pub/isp on cayuga.cs.rochester.edu). Lots of fun. Here are some interesting things I found. All of the following are for optimal expansion (shifting) to 14.7 psia. Hybrid rockets with peroxide... there are many possibilities here. One of the more interesting is peroxide/magnesium hydride. MgH2 is a fairly unreactive powder that is stable in dry air. It is made by heating magnesium to several hundred C and cooling it 1 bar of hydrogen (I think some small amount of nickel speeds up the reaction, but it not strictly necessary). MgH2 has a density of 1.45, about the same as peroxide. Isp is good (ratio of 1.5 MgH2 to 1 H2O2): Chamber Pressure Isp (opt) ------------------------------------------ 200 (psia) 228 seconds 300 244 400 254 500 261 750 274 1000 283 Magnesium is more expensive than hydrocarbon fuels, but less expensive than hydrazine-based fuels. Commodity Mg sold for $1.43/lb as of 1991; I don't know what the recent price behavior is but I have heard that Russian exports are driving down the price of many metals, including perhaps magnesium. (George, do you have a more recent number?) Even better performance can be obtained from peroxide + MgH2 + polyethylene. At a ratio of .44 H2O2 + .48 MgH2 + .08 PE (density 1.38): Chamber pressure Isp (opt) ---------------------------------------- 200 234 300 250 400 260 500 268 750 280 1000 288 Even better Isp can be obtained using the strong reducing agent lithium aluminum hydride. This reagent is expensive, however, and use in rocketry would probably require a dedicated production plant to supply the necessary volume. LiAlH4 is made by reaction of lithium hydride with aluminum chloride. It has been studied before for use in peroxide hybrids, back in the 1960s. At a mixture ratio of .48 peroxide to .52 LiAlH4 (bulk density 1.11): Chamber pressure Isp (opt) ---------------------------------------- 200 248 300 265 400 276 500 284 750 298 1000 307 George was discussing magnesium/nitric acid as a fuel. The Isp on this is not high. Interestingly, both the Isp and bulk density are increased (from 1.55 to 1.81-1.84) by adding teflon to the mix. Chamber Pressure Isp (with teflon) Isp (w.o.) ---------------------------------------------------------- 200 186 177 250 193 184 300 199 189 350 203 193 400 207 197 500 214 203 750 224 212 1000 225 219 Teflon helps because magnesium fluoride has a high heat of formation (-268.5 kcal/mole at 25 C), and because the C-F bond in teflon is not terribly strong (heat of formation is -97.6 kcal/mole, where the formula = CF2). Even without the oxidizer, Isp at 1000 psia is surprisingly high. Composition Isp Bulk Density ------------------------------------------------------------- .34 Mg, .66 teflon 181 2.08 .2 Mg, .42 teflon, .38 polyethylene 196 1.38 .42 MgH2, .58 teflon 201 1.85 Teflon's density suggests alloying it with a lighter plastic, say polyethylene, until its density is the same as peroxide (1.4422), then forming a monopropellant with a suspension of the particles in the oxidizer. (The question here is can the particles be made small enough to burn efficiently without being so small as to react while in suspension, or sustain detonation.) The ratio is 62% PTFE, 38% PE, to 314% peroxide, for an Isp of 268 seconds at 1000 psia. A similar scheme with 56% aluminum and 44% PE yields better Isps (again, in peroxide). Pressure Isp ------------------------------ 200 230 300 246 400 255 500 262 1000 283 This is several seconds higher than peroxide/RP-1 (278 at 1000 psia). One would want to make PE/aluminum pellets containing very small flakes of aluminum powder, so they could burn effectively while in the motor. A long motor would be better, to give the plastic more time to evaporate. Paul ------------------------------ Date: Fri, 6 Aug 93 23:01:17 -0400 From: dietz@cs.rochester.edu To: Bruce_Dunn@mindlink.bc.ca, space-tech@cs.cmu.edu Subject: Re: P2 Technical Issues Bruce Dunn wrote (some time ago) on the subject of LOX for P2, and materials for the pressurized tank: > > You're using a high nickel steel. Aren't there high nickel steels > > that do not suffer from embrittlement at low temperature? I know > > stainless steel is used for terrestrial LOX tanks. > I just dug up some information on stainless steels for cryogenic use, > and the yield strength of these materials is dismal. Compared with > George's cheap steel at 689 MPa and maraging steel at 1700 MPa, > cryogenic grade stainless steels have a yield point of 150 to 200 MPa > at room temperature. At liquid oxygen temperature the ultimate > tensile strength gets quite high (1200 to 1500 MPa) but the yield > point is still poor (maximum of about 650 for some alloys). Trying to > employ the cryogenic strength of the steel would require that the > whole tank be insulated so that no part of the wall warms up. Even > assuming that this could be done, the resulting tank mass would take > away any advantage for liquid oxygen as an oxidizer. I think Bruce overlooked something here. Austentic stainless steels are indeed the steels rated down to near absolute zero, and they aren't very good. But down to LOX temperature, there is another possibility: ferritic 9% nickel steel (ASTM A553). Steel of this kind is used in LNG tankers, and maintain adequate toughness down to the boiling point of liquid nitrogen. The ASTM standard for this steel specifies a minimum yield stress of 80 ksi (550 MPa), I believe at room temperature. This steel has a fracture toughness at 77 K comparable to the fracture toughness at room temperature of some of the ultrahigh strength steels Bruce is considering. Bruce mentioned the problem of keeping the tank cold. A way to help do this is to wrap the tank in fibers. We've been discussing (off line) use of fiberglass and other fibers for reinforcing cylindrical tanks. These composites typically have thermal conductivity much lower than that of steel (kevlar in particular has a very low thermal conductivity), so most of the temperature drop from the tank to the outside will be in the composite, not the metal. This also requires a composite with good properties at low temperature, but I believe some exist. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sat, 7 Aug 93 19:45:00 -0400 From: dietz@cs.rochester.edu To: Bruce_Dunn@mindlink.bc.ca, dietz@cs.rochester.edu, space-tech@cs.cmu.edu Subject: Re: P2 Technical Issues I wrote: > nitrogen. The ASTM standard for this steel specifies a minimum yield > stress of 80 ksi (550 MPa), I believe at room temperature. This steel > has a fracture toughness at 77 K comparable to the fracture toughness > at room temperature of some of the ultrahigh strength steels Bruce is > considering. In more detail... "class 8" 9% nickel steel has a yield strength of 90 ksi at room temperature and 135 ksi at 77 K. Its Charpy V-notch impact energy is 25 ft-lb at 77 K, vs. 14 ft-lb for D6a at room temperature. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ End of Space-tech Digest #160 *******************