Subject: Space-tech Digest #111 Contents: Re: P2 Launcher (17 msgs) ------------------------------------------------------------ Date: Sun, 29 Mar 92 21:53:21 -0500 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Re: P2 Launcher (long) Very interesting! Some comments... Your use of high nickel steel: aren't some high-nickel steels immune to embrittlement at low temperature? In particular, stainless steel is a standard material for terrestrial cryogenic equipment. Pressurization: would it be possible to pressurize the peroxide tank using a gas generator, directly exhausting decomposed peroxide into the tank? Granted, this would be kind of hot, but perhaps that could be controlled somehow, say by mixing the exhaust from the gas generator with an inert gas. Pressurizing a peroxide tank with hydrogen sounds risky, as decomposition of the peroxide will fill the head space with oxygen. Some sort of continuous prelaunch purge system might be needed (with nitrogen, perhaps, or maybe a catalytic combustor to react the oxygen to form water). Another idea is to include a gas that inhibits combustion, like a halon. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Mon, 30 Mar 92 10:39:26 -0500 From: dietz@cs.rochester.edu To: Bruce_Dunn@mindlink.bc.ca Subject: Re: P2 Launcher (long) Cc: space-tech@cs.cmu.edu Bruce Dunn said: > 100% hydrogen peroxide is a relatively stable material, with decomposition > rates of about 1% per year. Is this assuming the peroxide is free of contaminants? I understand that all commercial hydrogen peroxide is contaminated to some extent, and stabilizers must be added to reduce the decomposition rate. Also, tanks must be passive for use with peroxide. In particular, iron catalyzes decomposition, so the interior of the steel tank would have to be coated somehow. > refining peroxide to 100% is a relatively simple process involving > distillation. I understand to concentrate 90%-->100% peroxide the standard technique is fractional crystallization. > it is impossible to get bulk hydrogen peroxide to detonate This is contradicted by the industrial chemistry encyclopedia I consulted. It was said that a booster charge is need for detonation of the concentrated stuff. Here are some prices: Grade Cost (FOB producer cents/kg, 1980) 30%, reagent grade 51 in drums 35% 57 " 35% 40 tank cars 50% 56 " 70% 79 " Assuming a factor of 2 increase in price since, the cost of 70% H2O2 today is $.72/lb, or about $1/lb for 100% (ignoring the cost of the further processing). This is about a factor of 20-40 times more expensive than LOX of equal oxidizing power. > [ UDMH and N2O4 has an alternative fuel ] What about hydrocarbon/N2O4? I like the idea of using the same module in the first and second stage, but maybe you can vary the fuel composition. The first stage could propane mixed with heavier hydrocarbons (butane, perhaps); the second could use propane with dissolved methane (at 900 psia, propane dissolves considerable methane). This could complicate metering, granted. Does hydrogen dissolve in propane? Paul F. Dietz dietz@cs.rochester.edu ------------------------------ From: henry@zoo.toronto.edu Date: Mon, 30 Mar 92 11:41:13 EST To: space-tech@cs.cmu.edu Subject: Re: P2 Launcher (long) >...Each individual first stage booster is used and >recovered two times, then is converted into a second stage and is expended. >This semi-reusable system achieves multiple re-use of hardware, while >minimizing the need to design for long component lifetimes. Actually, I think you may have the worst of both worlds here: a requirement to recover and refurbish large rocket stages whose life is too short to really cover the extra costs incurred. People have argued that re-use of the shuttle SRB hardware gives NASA no benefit except public relations, since recovery/refurbishment costs appear to equal or exceed the cost of buying the SRBs as throwaways in larger numbers. Have you looked into this aspect? More comments later when I have a chance to read further. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Mon, 30 Mar 92 13:48:31 EST From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: P2 Launcher (long) Sender: mnr@DAISY.LEARNING.CS.CMU.EDU Bravo! A whole new proposal, using room temp fuel. The only thing which jumps out at me is the safety of the H2 pressurizing gas. I would like to see figures on the vapor pressure vs temp, and what constitutes an explosive mixture. Actually maybe a cayalyst could be in the chamber to safely combine any spare O2 while it was still in a sub-combustible ratio. Seems to me that's what happens in closed "cold fusion" experiments, and what could be better than using cold fusion technology in a launch vehicle? Still, if this were practical I suppose NASA would have done it in the shuttle instead of scrubbing a launch everythime there's a tiny leak. Wouldn't they? ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Mon, 30 Mar 92 13:51:00 EST From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: P2 Launcher (long) Sender: mnr@DAISY.LEARNING.CS.CMU.EDU Before someone tells me, yes, I know that you don't want a catalyst which would decompose the peroxide, but the gasses are the problem, so the liquid should not be in contact with the catalyst. ------------------------------ Date: Mon, 30 Mar 92 14:01:37 -0800 From: George William Herbert To: space-tech@cs.cmu.edu Subject: Re: P2 Launcher (long) Offhand, does anyone know if Peroxide/hybrid engines have been tested? 8-) A few comments about the P2: 1. The use of Hydrazine/Tetroxide anywhere in the vehicle more or less means you have to treat the whole thing as dangerous that way. You might investegate using something less hazardous. 2. I didn't and still don't like the ultra-high-strength-steels 8-) About 100ksi yield strength (55% of the Maraging steel Bruce wants to use) is as high as cheap easy to fabricate and inspect steels go. The Maraging described as "easy to fabricate and weld" is relative to say building Diamond Fiber rope. Compared to lower strength steels, overall build costs for the steel are roughly x6-10 as high for the same rocket (taking smaller overall vehicle due to smaller tankage fraction into account). Or so said my numbers when I cranked them for the BDHB. Since my steel costs were about 10% of vehicle cost, I figured it was economically not worth it 8-) Bigger, Dumber, Cheaper! These are the cries of the BDB crowd 8-) -george william herbert gwh@lurnix.com gwh@ocf.berkeley.edu ------------------------------ Date: Mon, 30 Mar 92 18:08:22 -0500 From: dietz@cs.rochester.edu To: gwh@ocf.Berkeley.EDU Subject: Re: P2 Launcher (long) Cc: space-tech@cs.cmu.edu GWH asked if peroxide hybrid rockets had been built. Yes! Peroxide polybutadiene and peroxide polyethylene rockets have been used in military drones. I don't have more specific information, however. So, how expensive is nitrogen tetroxide, guys? Paul ------------------------------ Date: Mon, 30 Mar 92 17:56:39 EST 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: P2 Launcher >Before someone tells me, yes, I know that you don't want a catalyst >which would decompose the peroxide, but the gasses are the problem, >so the liquid should not be in contact with the catalyst. Possible problem: catalysts tend to heat up, as a function of the net energy release of the reaction they assist, the amount of material reacted per unit time, and several other factors. (That's why cars with catalytic converters are not supposed to be parked in tall dry grass while at operating temperature.) If it gets hot enough, the surface of the catalyst may cause ignition of the remaining material. The Shuttle probably leaks enough that this would be a concern. (Note: the Shuttle invariably leaks both hydrogen and oxygen before launch. While the safety limit is way below explosive mix, that still likely represents an impressive total amount. The limit may be set where it is because an unusually high leak rate could be a symptom of a problem that could become serious later, and there may be some concern about the characteristics of the exhaust flames in a hydrogen or oxygen- enriched ambient atmosphere.) It has been implied that hydrazine monopropellant thrusters such as those on Galileo and the Voyagers are fired simply by passing the fuel over a catalyst, with no other heating, spark, etc. required. (Can anyone confirm this?) I think platinum black (and possibly metallic platinum mesh) can do this for a proper mix of hydrogen and oxygen. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ From: henry@zoo.toronto.edu Date: Mon, 30 Mar 92 20:54:03 EST To: space-tech@cs.cmu.edu Subject: Re: P2 Launcher >It has been implied that hydrazine monopropellant thrusters such as those >on Galileo and the Voyagers are fired simply by passing the fuel over a >catalyst, with no other heating, spark, etc. required. (Can anyone confirm >this?) ... Hydrazine monopropellant thrusters do indeed just run the fuel through a catalyst bed. The design of good catalysts is non-trivial; for one thing, they typically deteriorate with use, due to mechanical loss of fine particles into the exhaust, poisoning by impurities in the fuel, and channel formation. The usual hydrazine catalyst is iridium metal on porous ceramic pellets. Galileo's thrusters are bipropellant, by the way. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Mon, 30 Mar 92 13:54:29 EST From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: P2 Launcher (long) Sender: mnr@DAISY.LEARNING.CS.CMU.EDU > Pressurizing a peroxide tank with hydrogen sounds risky, as > decomposition of the peroxide will fill the head space with oxygen. > Some sort of continuous prelaunch purge system might be needed (with > nitrogen, perhaps, or maybe a catalytic combustor to react the oxygen > to form water). Another idea is to include a gas that inhibits > combustion, like a halon. See my followup to my own catalyst thoughts. With all the efforts going into getting things like haylon out of use, I think helium is better both politically and practically, since it haylon is heavy. ------------------------------ Date: Mon, 30 Mar 92 23:35:01 -0500 From: dietz@cs.rochester.edu To: Bruce_Dunn@mindlink.bc.ca Subject: Re: P2 Launcher Cc: space-tech@cs.cmu.edu I was looking at some crude numbers for various oxidizers. N2O4/hydrocarbon looks almost as dense as peroxide/hydrocarbon, but has higher energy. However, to really figure out the relative performance I'd need a code for computing the equilbrium concentrations of various species in the expanding gases. Where can I find tables of the free energies of the various species or, better yet, a full-blown code? If you want density, you can go with nitric acid (1.5 g/cc) or RFNA (1.55-1.6 g/cc), used with either hydrocarbons or denser organic fuels like aniline. Paul ------------------------------ Date: Tue, 31 Mar 92 08:17:47 CST From: ssi!lfa@uunet.UU.NET (Louis F. Adornato) To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: Re: P2 Launcher Nice work! Could you mail me a list of your references? I'd like to add my voice to those who caution against UDMH and Nitric Acid for the third stage; the operational costs of dealing with these agents could come to dominate the whole system. Is there a vacuum capable solid that could be used? Is 18Ni(250) the same stuff that's used in making nuclear devices? There's been some mention in the news of tracing magaging steel in Iraq. Those reports made it sound like the stuff was fabulously expensive - how much is it in volume? How difficult is it to X-ray? One benefit that you've missed - by using essentially the same design for the first and second stages (even disregarding the recovery/refurb savings, if any), you've reduced the development costs, and significantly dropped the part count and the number of on-hand spares the launch center will need. Furthermore, by combining two low volume production lines into one, you've got a much better chance of crossing the threshold into the "mass production" volume, and getting some _real_ savings on the engines. If you're really interested in recovering second stages (which would kill the volume production argument), then in the section on enhancements: >The velocity and range achieved by the second stage normally make this >impossible. However, the following scenario may bear investigation: >1) The engine of the second stage booster is shut off before all propellant is >burned, and the third stage is separated. >2) The second stage (at this point in free-fall in a vacuum) re-orients >itself, pointing roughly back along its ascent trajectory. >3) The second stage re-ignites, kills its forward velocity, and gains enough >velocity to travel ballistically back to the prime recovery area. >4) The falling second stage is recovered by parachute. Add: 2.5) Settling rockets (possibly using the same mountings as the separation rockets for first stage operations) are fired, returning the pressurization gas to the "top" of the tanks. Lou Adornato | The secretary (and the rest of the company) Supercomputer Systems, Inc | have disavowed any knowledge of my actions. Eau Claire, WI | Engineers create jobs. Manned space uunet!ssi!lfa or lfa@ssi.com | exploration creates engineers. ------------------------------ Date: Tue, 31 Mar 1992 12:46:04 -0500 (EST) From: PLATT@WCSUB.CTSTATEU.EDU Subject: Re: P2 Launcher (long) To: mnr@DAISY.LEARNING.CS.CMU.EDU X-Vmsmail-To: SMTP%"mnr@DAISY.LEARNING.CS.CMU.EDU" With this talk of using Hydrogen Peroxide in a launch system, does anyone know of any details about either the fractional crystalization or distillation methods to purify H2O2? -Don Platt ------------------------------ Date: Tue, 31 Mar 1992 09:22:04 -0500 (EST) From: Ted_Anderson@transarc.com To: space-tech@cs.cmu.edu, Bruce Dunn Subject: Re: P2 Launcher (long) There was a very interesting article on using peroxide as a rocket propellant in JBIS in July 1990. It has been a while since I read it but I recall that using 100% H2O2 was fraught with difficulties and dangers. Surely you should check out this paper and perhaps do a citation search on its references to get more recent work on peroxide. Here is the reference: David Andrews, "Advantages of Hydrogen Peroxide and a Rocket Oxidant", Journal of the British Interplanetary Society, vol 43, number 7, page 319-328, July 1990. Interestingly they refer to this stuff as HTP (High Test Peroxide). Does anyone else get the feeling that soon (or perhaps already) they will be able to build a Black Brant rocket from a tinker toy kit in their sleep with both hands tied behind their backs? (Yes, the latest issue us another BB retrospective.) Ted Anderson ------------------------------ From: henry@zoo.toronto.edu Date: Tue, 31 Mar 92 11:31:28 EST To: space-tech@cs.cmu.edu Subject: Re: P2 Launcher (long) >... I think helium is >better both politically and practically, since it haylon is heavy. Helium is light but storage for it is heavy. Compressed-gas tanks need very strong walls. The P2 proposal mentions storing it as liquid, but I'm unaware of any rocket that does that; liquid helium has a very low boiling point and very small specific heat and latent heat (translation: it boils really easily), and isn't all that dense in the first place. The Saturns kept it as a pressurized gas, with some improvement in density by putting the helium tanks inside cryogenic propellant tanks. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ From: henry@zoo.toronto.edu Date: Tue, 31 Mar 92 11:25:11 EST To: dietz@cs.rochester.edu Cc: Bruce_Dunn@mindlink.bc.ca Subject: Re: P2 Launcher Cc: space-tech@cs.cmu.edu >... I'd need a code for computing the >equilbrium concentrations of various species in the expanding >gases... Static data you should be able to get, but don't get your hopes too high otherwise. *Nobody knows* reaction rates and such under those conditions; they're almost impossible to measure. You can calculate for "shifting flow" (reaction rates assumed infinite) or "frozen flow" (reaction rates assumed zero), and assuming shifting flow to the throat and frozen flow after that is said to give good results in many cases, but the data needed to do a realistic calculation simply isn't to be had. Normal design practice is to do the best you can with calculations and fudge factors, and then build it and see. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Tue, 31 Mar 92 12:09 PST To: space-tech@cs.cmu.edu Subject: P2 Technical Issues From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) Thank you everone for the comments. Henry Spencer writes: > Actually, I think you may have the worst of both worlds here: a > requirement > to recover and refurbish large rocket stages whose life is too short to > really cover the extra costs incurred. People have argued that re-use of > the shuttle SRB hardware gives NASA no benefit except public relations, > since recovery/refurbishment costs appear to equal or exceed the cost of > buying the SRBs as throwaways in larger numbers. Have you looked into > this aspect? A very valid point. I have considered it, but without any real cost information so far, can't defend this aspect of the concept other than by some handwaving. I am aware that the SRB reuse is marginal in economic terms. However, I suggest that it is much simpler to refill a liquid fueled booster than to recycle SRB parts. If it proves cheaper to simply throw away the hardware than recycle it, then so be it. Presumably there is good data on how many man hours and how much permanent equipment is needed to get an SRB back to port after recovery (maybe this could be extracted from some NASA budget). This data could be applied to give a preliminary estimate of getting the P2 booster back to where it can be inspected, refurbished, tested, and ready for reuse. If recovery and refurbishment costs more than to weld together a new set of tanks and buy the needed components, then recycling clearly is not worth the trouble. I suspect that the issue of reuse would depend on launch rate. It is easier to pay for recovery ships and refurbishment facilities that are used once a week than for those which are used 6 times a year. The launch performance would rise slightly ( 1.1 %) to LEO and the booster cost would be lower if parachutes were not used. I can't offhand however think of anything else about the booster which could be made cheaper or lighter if it were assumed to be expended (suggestions are of course welcome). Ted Anderson writes: > There was a very interesting article on using peroxide as a rocket > propellant in JBIS in July 1990. It has been a while since I read it > but I recall that using 100% H2O2 was fraught with difficulties and > dangers. Surely you should check out this paper and perhaps do a > citation search on its references to get more recent work on peroxide. > Here is the reference: > David Andrews, "Advantages of Hydrogen Peroxide and a Rocket > Oxidant", Journal of the British Interplanetary Society, vol > 43, number 7, page 319-328, July 1990. In actual fact I went through this article last week. Consistent with the title of the article, Andrews, who worked with peroxide/hydrocarbon engines in England, was very positive about how safe peroxide was. The peroxide that they were using was "High Test Peroxide" which contains 1 mole water per 3 moles peroxide. He did not have any direct experience with higher strengths, but other references have suggested that if anything 100% peroxide is more stable than poorer grades. It is not apparently the peroxide which gives the trouble, but impurities dissolved in it. He takes a jab at Sutton ("Rocket Propulsion Elements") suggesting that Sutton overemphasizes the dangers of peroxide as an oxidizer because Sutton's information on instability relied on reports of problems with impure peroxide produced in Germany during the war. davidsen@crdos1.crd.ge.com writes: > The only thing which jumps out at me is the safety of the H2 > pressurizing gas. I would like to see figures on the vapor pressure vs > temp, and what constitutes an explosive mixture. Paul Deitz writes: > One problem I have with the hydrogen pressurization system is that the > peroxide will be slowly decomposing. This will naturally put some > oxygen gas into the tank. Hydrogen/oxygen is flammable over a wide > range of concentrations, so the tank may have to be purged with inert > gas (nitrogen, say) before launch. Perhaps use of a combustion > inhibiting gas, like a halon, could be beneficial. I did not mention it in the posting, but I have been making the assumption that the ullage space above the peroxide would be cleared of oxygen by inert gas flushing with nitrogen or argon, prior to pressurizing with hydrogen. The only figure that I have for the decomposition of good quality hydrogen peroxide in reasonable surroundings is "about 1% per year". At 1% per year, the 460 tons of hydrogen peroxide in a P2 booster would generate about 17 cubic meters of oxygen per hour. For comparison, the ullage space above the peroxide is about 16 cubic meters. Clearly, after any time sitting on the pad the ullage space will be 100% oxygen. I think that this could be dealt with by leaving the tank vented on the pad, and arranging a high volume inert gas flush just before pressurization. This could perhaps be done by injecting liquid nitrogen into the peroxide (it will float), and allowing the boil-off gas to exhaust. The vapor pressure of hydrogen peroxide at room temperature is 2 mm Hg, or about 1/400 atmosphere. Mainly to avoid thermal initiation of peroxide decomposition, I am proposing to use only room temperature pressurization gas. I don't know of any tables for the explosive limits of peroxide vapor in hydrogen, but my gut feeling is that the level of peroxide is far too low to cause a problem. In contrast, I think that oxygen from decomposition is worth worrying about. Incidentally, Huzel and Huang ("Design of Liquid Propellant Rocket Engines") mention something to the effect that hydrazine decomposition products (containing among other things considerably hydrogen) have in preliminary experiments been shown to be feasible for pressurizing "storable oxidizers". (the exact wording escapes me, and I don't have the reference handy). Paul Deitz writes (by E-mail): > Does hydrogen dissolve in propane? I certainly hope not! Does anyone have any information on this? Henry Spencer writes: > Helium is light but storage for it is heavy. Compressed-gas tanks need > very strong walls. The P2 proposal mentions storing it as liquid, but > I'm unaware of any rocket that does that; liquid helium has a very low > boiling point and very small specific heat and latent heat (translation: > it boils really easily), and isn't all that dense in the first place. > The Saturns kept it as a pressurized gas, with some improvement in > density by putting the helium tanks inside cryogenic propellant tanks. Storage for compressed gas is indeed very heavy, and takes all the fun out of trying to develop a gas pressurized propellant flow system. For pump fed rockets, pressurized storage is feasible as the tanks only need a couple of atmospheres of pressure. To avoid the huge mass involved in storing pressurized gas, I propose to store the material as a liquid, then pump it to high pressure and vaporize it as needed. The storage tank requirements then become essentially negligible. The P2 booster uses a little less than 3 tons of hydrogen for pressurization. Tankage fractions for liquid hydrogen are about 15% for upper stage work, indicating a tank mass of perhaps 450 kg. Double this for an awkward shaped tank and adding 100 kg of foam insulation gives a conservative tank of 1 ton mass. If built correctly, loss rates for such a container could probably be held to a few percent a day. A comparison of hydrogen vs. helium or nitrogen for pressurization shows that to pressurize one P2 stage (of the three used) requires: Gas MW Liquid Density Tons needed Liquid Volume needed (m^3) Hydrogen 2 0.0708 2.89 40.88 Helium 4 0.122 5.79 47.45 Nitrogen 28 0.808 40.52 50.15 George Herbert writes: > The use of Hydrazine/Tetroxide anywhere in the vehicle more or less > means you have to treat the whole thing as dangerous that way. > You might investegate using something less hazardous. Louis Adornato writes: > I'd like to add my voice to those who caution against UDMH and Nitric > Acid for the third stage; the operational costs of dealing with these > agents could come to dominate the whole system. Is there a vacuum > capable solid that could be used? It is for exactly this reason that large lower stages of the vehicle are designed to used propane and peroxide. The only hydrazine on the lower stages is for the turbines of the hydraulic power supply system for thrust vector control. Hydrazine is used, as this is the baseline system used on the SRB. Personally, I would be happy to see this source of hydrazine eliminated and the system replaced by peroxide powered turbines. The use of hydrazine/N2O4 in the upper stage is a compromise designed to eliminate the need to design a new engine (or at least modify an existing one). Using a solid stage would compromize performance, as would using a pressure fed upper stage. The payload mass is more strongly dependant on the mass fraction of the upper stage than on that of the lower stages. With a clean sheet of paper, I would prefer a pump-fed upper stage burning propane and peroxide for propellant commonality. An alternative with lower development costs would be to use a LOX/RP-1 upper stage, although this would add a cryogenic propellant to the vehicle. The hazards of large hydrazine/nitrogen tetroxide boosters are well known. A Titan in a silo had a punctured tank some years ago which sent a deadly orange cloud over the surrounding neighborhood (I presume this was the N2O4). After the February 1990 destruction of an Ariane 44L at 1 minute 41 seconds after liftoff, Spaceflight (Vol 32, p 138) reported that "Debris from the Ariane 4 rained down into the Atlantic. Launch personnel and local residents were advised to stay indoors in case toxic fumes from the explosion were blown back to shore." I would not want to be the one who had to write an environmental impact statement which would have to consider the threat to the residents of Florida if 1000 or so tons of N2O4 were involved in a pad accident. Although it deserves respect in handling, peroxide is not all that toxic. Actually, the thing that worries me about the propane/peroxide combination is the propane. A tank rupture while a P2 booster is being pressurized would release about 60 tons of propane. If not ignited by the rupture, this would rapidly vaporize and form a ground hugging flammable cloud which I would not want to encounter. In most cases, I belive however that the propane would be dispersed to non-flammable limits before leaving the pad security area. I expect that this sort of problem is well studied and can be dealt with. Certainly, large quantities of propane are routinely transported by road and rail through cities and if this practice if not totally safe at least appears to be reasonably accepted. If propane is unacceptable for safety reasons, RP-1 or an equivalent would work nearly as well, although it brings its own problems in that it will stay at the site and under some circumstance can give an unholy explosion with spilled peroxide (see "Ignition" by J.D. Clark). George Herbert writes: > I didn't and still don't like the ultra-high-strength-steels 8-) > About 100ksi yield strength (55% of the Maraging steel Bruce wants to use) > is as high as cheap easy to fabricate and inspect steels go. > The Maraging described as "easy to fabricate and weld" is relative to > say building Diamond Fiber rope. Compared to lower strength steels, > overall build costs for the steel are roughly x6-10 as high for the > same rocket (taking smaller overall vehicle due to smaller tankage fraction > into account). Or so said my numbers when I cranked them for the BDHB. > Since my steel costs were about 10% of vehicle cost, I figured it was > economically not worth it 8-) > Bigger, Dumber, Cheaper! These are the cries of the BDB crowd 8-) Point well taken. The P2 design is however somewhat different than the Big Dumb Hybrid Booster in that the "engine" is not scalable. Thrust is limited (unless pressure is increased). Thus there is a limit to the total amount of mass which can be lifted with the two engines, and losses due to heavier construction cannot be regained by simply making the booster bigger. Assuming the use of steel at 100,000 psi yield (689 MPa by my conversion) cuts the calculated payload from 50.852 tons to 40.440 tons, a loss of 10.41 tons (and no, I don't really believe in the number of significant figures I am quoting). The basic question for the P2 design then becomes: Is it worth the extra costs of using a high strength steel to gain an additional 10 tons of payload to orbit. I suspect that the answer is yes, but currently have no numbers whatsoever to back it up. If you can help me on this George, I would greatly appreciate it. I can provide you with details of tanks sizes - if you can estimate constructions costs we could see what the trade-off actually is. Paul Deitz writes (by E-mail): > 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. -- Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ End of Space-tech Digest #111 *******************