Subject: Space-tech Digest #150 Contents: SSI Mailing List (1 msg) silanes as rocket fuels? (1 msg) Zephyr paper available (1 msg) Misc rocket fuels & systems (12 msgs) ------------------------------------------------------------ Date: Thu, 27 May 93 16:24:26 EDT From: u2n25@link.com (Mitchell James) To: space-tech@cs.cmu.edu Subject: SSI Mailing List Cc: ssi_mail-request@link.com I am creating a network mailing list for the Space Studies Institute for members and non-members. The purpose of this list is to facilitate communications between SSI members on topics of interest. If you would like to subscribe to receive mail please send your email and ground mail name and address to ssi_mail-request@link.com Mitchell James mjames@link.com ------------------------------ 27 May 1993 Date: Fri, 28 May 93 09:15:45 -0400 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: anyone ever used silanes as rocket fuels? Has anyone on this list ever heard if anyone has used a silane as a rocket fuel? The oxidation of silicon releases more energy per mass of reactants than the oxidation of carbon, and silicon dioxide is stable at higher temperature. Indeed, the specific energy of silane + oxygen is higher than that of hydrogen + oxygen (although the rocket performance is likely worse, due to condensation in the exhaust). Silanes are rather explosive and pyrophoric, but perhaps they would make good fuels for ET manufacture, as they are more dense than hydrogen and liquify at higher temperature. Disilane (Si2H6) boils at -14.5 C; trisilane at 52.9 C. All have slightly positive energy of formation. Paul ------------------------------ To: space-tech@CS.CMU.EDU Subject: Zephyr paper available, more forthcoming Date: Mon, 31 May 93 21:36:03 PDT From: George William Herbert I'm back from Case for Mars V, and as I've presented the Zephyr paper it's text will be available for FTP access at ocf.berkeley.edu in pub/Space/Zephyr (along with the postscript for the four illustrations). I will probably type in a version of the other paper I presented orally only, on mars environment space suits, sometime. Case was pretty interesting. I'll run down some of the technical discussions in a post to sci.space which I'll also mail out here (if nobody objects), but let me recover from the drive first. 8-) -george william herbert Retro Aerospace ------------------------------ Date: Fri, 4 Jun 93 11:21:02 -0400 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: once again on pressure fed engines with LOX I was thinking some more about this (not in the context of Bruce Dunn's P2, but rather Sea Dragon or some large booster with a high enough flight rate and low enough structural cost that fuel cost is significant.) Two problems arose with the idea: embrittlement of steel and higher pressurant requirements at low temperature. I'm not convinced the second is a problem. Amroc uses hot helium to pressurize their hybrid rocket, so I am not sure the rate of heat transfer from LOX to the gas is necessarily unmanagable. It should become less important in larger boosters. So, what about the steel? I think there is a simple solution here. Line the inside of the steel tank with a solid material with a much lower thermal conductivity than steel. Then, if the steel's outer surface is maintained at room temperature, most of the temperature drop will occur in the inner liner, not in the metal. Are there suitable materials? Yes -- the thermal conductivities of nylon or teflon are more than 300 times lower than that of plain carbon steel. These are solid materials, so they will withstand high pressure, and are cheap and fairly low in density (nylon more so). Insulation with a fraction of the mass of the steel would keep the temperature drop in the steel to less than 10 C. Some heating of the steel may be necessary to avoid the thermal resistance of the steel/air boundary layer. Alternately, the LOX tank could be placed inside a room temperature hydrocarbon tank, exploiting the higher heat transfer rate across the liquid/metal interface. For a sea-launched booster, contact with water would provide the thermal input. How much heat gets through the plastic? A 2 cm layer of teflon conducts 12 W m^-2 K^-1. For a 300 K difference, this is about 3.6 kW/m^2, enough to boil about 35 grams of oxygen per second per m^2. The time to boil off a 10 meter tank would be about 15 minutes. The time goes up as one goes to larger tanks (not only by the square cube law, but because the teflon could be made thicker as well, so the time to boil off would go as R^2; alternately, the mass of the plastic could be made proportionally smaller for a larger tank). I neglect here the thermal resistance of the LOX/plastic boundary, which may be significant (if film boiling occurs, say). I am not sure what the ideal material would be. It would have to be not too brittle at LOX temperature, and have a low density x thermal conductivity product. Nylon's figure of merit is better than teflon's, but it may not be compatible with LOX. It would be desirable to use a material that is compatible with hot oxygen, so that fairly high temperature gas could be used as a pressurant. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Fri, 4 Jun 93 13:13:43 -0400 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: correction I said: > The time to boil off a 10 meter tank would be about 15 minutes. This is obviously wrong; the correct answer is about 1 day. Paul ------------------------------ To: uunet!cs.rochester.edu!dietz@uunet.UU.NET Cc: space-tech@cs.cmu.edu, gwh@lurnix.COM Subject: Re: once again on pressure fed engines with LOX Date: Fri, 04 Jun 93 10:56:47 -0700 From: gwh@lurnix.COM Nylon is a poor choice. Nylon burns, rather well in fact. I prefer insulation materials that don't introduce failure modes in my rockets. Other than that, you're generally right. The reason I rejected that approach was that if you get a localized insulation failure (crack, whatever) you get a pressure vessel failure due to brittle fracture. Which means that the insulation quality is as important as the steel quality and the weld quality, which means it has to be as well known and as well tested... Presuming an easy to produce and perfect insulation material, it works. If you can't get that, and my looking around didn't find any that were up to my standards, then it's risky. [Trust me, though, if my Nitric Acid/Zinc rocket flies I'll drop money into research on LOX insulation materials 8-) ] -george william herbert Retro Aerospace ------------------------------ Date: Fri, 4 Jun 93 18:55:30 -0400 From: dietz@cs.rochester.edu To: gwh@lurnix.lurnix.com Subject: Re: once again on pressure fed engines with LOX Cc: space-tech@cs.cmu.edu Frankly, I'd think putting in insulation is going to be easier than playing with nitric acid. The insulation should be easily installed, near perfect, and testable. It should likely be some kind of fluoropolymer that is compatible with oxygen. Teflon is one possibility, but there are some other thermoplastic fluoropolymers that may be more easily worked with (FEP? PCTFE? teflon-PFA?). PCTFE, at least, is rated for use with liquid oxygen, and I believe FEP and teflon-PFA are more easily former than teflon itself. Here's one possible way to install it. Attach glass or metal fibers to the inner wall of the tank. Melt the polymer and pour onto the tank wall, rotating as you go. The top of the plastic layer should be fiber-free. It shouldn't be too hard to test; observe the outside of the tank with a thermal imager while holding the interior at low temperature. One would work up to high pressure and low temperature in stages. Defects can be repaired by localized heating. Small cracks in the insulation are not necessarily disastrous. Small enough defects would just depress the outside temperature slightly. The maximum defect area would be on the order of the square of the thickness of the steel wall divided by the ratio of thermal conductivities. Comments? Paul ------------------------------ To: uunet!cs.rochester.edu!dietz@uunet.UU.NET Cc: gwh@lurnix.COM, space-tech@cs.cmu.edu Subject: Re: once again on pressure fed engines with LOX Date: Fri, 04 Jun 93 16:35:42 -0700 From: gwh@lurnix.COM Paul writes: >Frankly, I'd think putting in insulation is going to be easier than >playing with nitric acid. Why? With Inhibited NA, I'm not showing any problems with it at all. The Cryo handling precautions and the Acid handling precautions balance out about equally. The tank doesn't need any protection from the acid (it self-protects by forming a flouride layer, as does everything else in contact...). If it spills, it's more of a mess, but I can live with that. >Here's one possible way to install it. Attach glass or metal fibers >to the inner wall of the tank. Melt the polymer and pour onto the >tank wall, rotating as you go. The top of the plastic layer should be >fiber-free. In theory this results in good results. In practice, it is a very large scale industrial process with numerious potential problems... 8-) >It shouldn't be too hard to test; observe the outside of the tank >with a thermal imager while holding the interior at low temperature. >One would work up to high pressure and low temperature in stages. >Defects can be repaired by localized heating. And if the insulation cracks only under additional flight stresses? >Small cracks in the insulation are not necessarily disastrous. >Small enough defects would just depress the outside temperature >slightly. The maximum defect area would be on the order >of the square of the thickness of the steel wall divided by >the ratio of thermal conductivities. I'll look at this and see if I can do a more detailed analysis. I still am leery about breaking things this way. -george ------------------------------ Date: Fri, 11 Jun 93 09:43 PDT To: space-tech@cs.cmu.edu Subject: Materials for LOX tanks From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) There has been an ongoing discussion about the possibility of insulating materials for steel LOX tanks which would allow the steel to be operated above the temperature at which it becomes brittle. In actual fact, there is no strong reason to make LOX tanks out of steel. Aluminum will do quite nicely - remember that aluminum is used for the Shuttle external tank containing LOX and LH2, and that this tank is a pressure vessel in its own right. The highest strength steel which has been widely used for pressure vessels in the aerospace field seems to be D6Ac, from the Ladish steel company. It can be heat treated to a variety of combinations of strengths and toughnesses. When used for the casings of the Shuttle SRBs, it is treated to a yield strength of 1340 MPa. It has a density of approximately 7.8. For use with LOX, there are a number of aluminum alloys which have yield strengths of around 400 MPa at LOX temperatures, and adequate toughness. Aluminum density is approximately 2.7. The lower density makes up for the lower strength, and aluminum tanks are no heavier than steel tanks. The only problems arise from tank wall thickness, which are nearly 3 times thicker for an aluminum tank. For large tanks at high pressures, wall thickness can be several centimeters. Thick walls probably will lead to welding difficulties during fabrication. I presume that thick sections can be welded by forming the sections to have a double V-groove at the joint, and using multipass welding, but I also presume that this is likely to be expensive. Clarifications from someone more familiar with welding technology would be appreciated (George ?). One alternative would be to use a cluster of narrow diameter LOX tanks instead of a single thick walled cylinder. Another alternative would be to build large tanks in layers out of welded thinner material, like an onion. -- Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ To: Bruce Dunn Cc: space-tech@cs.cmu.edu, gwh@lurnix.COM Subject: Re: Materials for LOX tanks Date: Fri, 11 Jun 93 11:05:18 -0700 From: gwh@lurnix.COM Bruce Dunn writes: > There has been an ongoing discussion about the possibility of >insulating materials for steel LOX tanks which would allow the steel to be >operated above the temperature at which it becomes brittle. In actual fact, >there is no strong reason to make LOX tanks out of steel. Aluminum will do >quite nicely - remember that aluminum is used for the Shuttle external tank >containing LOX and LH2, and that this tank is a pressure vessel in its own >right. Yes and no; the pressure inside (30 psi?) is primarily to stiffen the tank, not as a pressure-feed system. Aluminum structures will probably cost 5 times what steel ones will for the same pressure and volume. Why do I care? Well... I'm looking at vehicles where this will add 50% or more to base hardware and assembly price, and I don't like that sort of ineffeciencies. It turns out to be better to use lower Isp propellants and (significantly) increase the GLOW than to switch materials away from steel. And yes, I've done detail design comparasons for a nominal vehicle, down to the weld specification level ( 8-) across the potential list of oxidizers and tank materials. Big stupid steel wins out on final vehicle cost, if you can keep guidance electronics costs down. Quick order of magnitude numbers... T-1 (690 MPa, 100ksi yield) steel tanks run about $1.25-1.50/lb; Aluminum seems to run $5.50-6.00/lb. Both these are including full assembly, welding, inspection, and test of the tank. Aluminum tanks end up about 20% lighter, so the actual differential is more like 3:1 rather than 4:1, but it's still significant. The change in overall vehicle mass ratios usually improves it another chunk, but I never got two vehicles with less than twice the tank cost for aluminum using the best assumptions I used. Which drove the final vehicle cost up about 35%. > [discusses D6ac and aluminum tanks] > Thick walls probably will lead to welding difficulties during >fabrication. I presume that thick sections can be welded by forming the >sections to have a double V-groove at the joint, and using multipass welding, >but I also presume that this is likely to be expensive. Clarifications from >someone more familiar with welding technology would be appreciated (George >?). Yes; or with the most modern welding technology you can actually weld up to 100ksi steel in one pass up to a foot thick or so. Aluminum welding technology for thick plates is not as well developed, but could likely be done using similar processes. The "old faithful" method of multipass double sided groove welding (alluded to above) works fine with both Steel and Aluminum, though it's not very cheap. -george william herbert Retro Aerospace ------------------------------ Date: Fri, 11 Jun 1993 13:26:36 MST From: "Richard Schroeppel" To: space-tech@cs.cmu.edu Subject: Re: Materials for LOX tanks Query: Is is worth fishing the tank out of the ocean & selling the scrap? Rich Schroeppel rcs@cs.arizona.edu ------------------------------ Date: Fri, 11 Jun 93 13:40 PDT To: space-tech@cs.cmu.edu Subject: LOX tanks From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) George Herbert writes: regarding the Shuttle ET as a pressure vessel > > Yes and no; the pressure inside (30 psi?) is primarily to stiffen the > tank, not as a pressure-feed system. Aluminum structures will probably > cost 5 times what steel ones will for the same pressure and volume. The tank isn't a pressure vessel from the point of view of being the sole source of propellant pressure. However, the pressurization is needed not just for tank stiffening, but to prevent pump cavitation. In effect, you can regard the tank as a pressure feed system for the pump inlets. References I have seen suggest that the tank mass is dominated by the pressure requirements, and that a safety factor of 1.25 has been used in the design of pressure loads. Wall stress in this huge tank is thus perhaps of the same order of magnitude as would be involved in a smaller diameter pressure fed system employing LOX. > Quick order of magnitude numbers... T-1 (690 MPa, 100ksi yield) steel > tanks run about $1.25-1.50/lb; Aluminum seems to run $5.50-6.00/lb. > Both these are including full assembly, welding, inspection, and test > of the tank. Thanks for including these very useful numbers, George. Any idea about the fabricated cost of D6Ac steel? Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ To: space-tech@cs.cmu.edu, gwh@lurnix.COM Subject: Re: Materials for LOX tanks Date: Fri, 11 Jun 93 15:05:50 -0700 From: gwh@lurnix.COM Richard Schroeppel: >Query: Is is worth fishing the tank out of the ocean & selling the scrap? T-1 is worth about $0.50/lb new. After having been shaken up and such, probably a lot less. Maybe $0.25, probably less. Compared to the effort to design the tanks to float and finding and recovering them, probably it's not worth it. Someone's welcome to work numbers on it and prove me wrong, though 8-) Bruce Dunn: > The tank isn't a pressure vessel from the point of view of being the >sole source of propellant pressure. However, the pressurization is needed >not just for tank stiffening, but to prevent pump cavitation. In effect, you >can regard the tank as a pressure feed system for the pump inlets. >References I have seen suggest that the tank mass is dominated by the >pressure requirements, and that a safety factor of 1.25 has been used in the >design of pressure loads. Wall stress in this huge tank is thus perhaps of >The same order of magnitude as would be involved in a smaller diameter >pressure fed system employing LOX. Looking at the internal structure of the tank, all the primary reinforcing is longitudional, not circumfrential. This fits with what I'd heard, which was that the primary loads were the SSME thrust paths and problems making it stiff, not strong, enough not to be a problem. Someone with a copy of the plans (dammit, I need these sometime...) is welcome to correct this if I'm wrong. And yes, you're right about cavitation being an additional reason to pressurize the feed lines. >> Quick order of magnitude numbers... T-1 (690 MPa, 100ksi yield) steel >> tanks run about $1.25-1.50/lb; Aluminum seems to run $5.50-6.00/lb. >> Both these are including full assembly, welding, inspection, and test >> of the tank. >Thanks for including these very useful numbers, George. Any idea >about the fabricated cost of D6Ac steel? No idea. Nobody around here can fabricate D6Ac. 8-) There are two or three shops i can find that can weld the stuff, but when I said "Ten foot diameter hundred foot long pressure vessel" they said "gah?". -george william herbert Retro Aerospace ------------------------------ Date: Mon, 14 Jun 93 18:26:11 -0700 From: gwh@lurnix.COM (George William Herbert) To: space-tech@cs.cmu.edu Cc: gwh@lurnix.COM Subject: Gary Hudson's on the Net! Self_Organization: Retro Aerospace, (510) 849-4853 Work_Organization: Lurnix, (510) 849-4478 x229 fax (510) 849-0409 Gary Hudson has a bix account, and started talking to me about the LOX / Steel tank insulation problem 8-) -george ------------------------------ Date: 14-JUN-1993 21:37:29.52 From: "Gordon D. Pusch (708)252-3843" Subject: FYI: pump-fed engine article To: SPACE-TECH@BITNET.CC.CMU.EDU Noticed the following article on a small *piston-pump-fed* rocket engine. Not of much personal interest to me, but perhaps of interest to others in this group (i.e., this is as much summary as you're going to get 8-). (The journal is worth checking out, if only for the way-cool ultra- high-speed laser-illuminated photos of a shaped-charge explosion :-T) Gordon D. Pusch ======================================================================== ``A New Rocket Propulsion System for Small Spacecraft'' [apparently by:] John C. Whitehead, (D.G. Swink and H.G. Toews?) [article does not list actual author] Energy and Technology Review, pp13--25 (UC/LLNL, Mar-1993, publ.no.: UCRL-52000-93-3) avail.from: NTIS, US DoC, 5285 Port Royal Rd., Springfield VA 22161; Price codes: printed, A03; fiche, A01 (author-note states: ``for further information, contact John C. Whitehead (510)423-4847''; I'm sure at least one or two of you will take him at his word... :-) Blurb: A new liquid rocket propulsion system, which won a 1992 R&D-100 award, features miniature pumps that can turn on and off and can change speed within a millisecond to meet a wide range of thrust requirements. Abstract: Our unique rocket engine design uses piston pumps to deliver fuel from lightweight tanks to rocket thrusters. Fuel is stored at low pressure, so fuel tanks can be lightweight --- as little as one-fifth the weight of previous tanks. With this reduction in weight, spacecreft designers can increase the payload or reduce launch costs. ------------------------------ End of Space-tech Digest #150 *******************