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Space Forum / Shuttle / August 2005Transverse Turbopump
Rick Nelson wrote: > ... We have 100% > reliable rocket engines using the transverse turbopump technology that > the Russians invented in the late 80's.. Can you provide a pointer to transverse turbopumps? I googled "transverse turbopump" and nothing came up. Thanks. Tom Clarke > Rick Nelson wrote: >> ... We have 100% [quoted text clipped - 4 lines] > > I googled "transverse turbopump" and nothing came up. If he's talking about the RD-17x/RD-180 family, that's a staged-combustion, oxidizer-rich turbopump design with a single preburner and both propellant pumps on a single shaft. I think the RD-17x four-nozzle engine has two turbopump assemblies, the RD-180 has one. The single-shaft arrangement appears to be preferred Russian design and they have an apparent monopoly on oxidizer-rich engine design. It's not easy to tell, but it appears the turbopump assembly is parallel to the combustion chamber and nozzle. The hot gas duct does a 180 degree bend at the top into the main combustion chamber. For comparison, the SSME has a pair of fuel-rich preburners driving separate fuel and oxidizer turbopumps, in a kind of 'tee' assembly. The proposed COBRA engine would have a single preburner driving separate turbopumps in a 'wye' configuration right on top of the injector assembly. Clear yet? (Didn't think so...) --Damon >> Rick Nelson wrote: >>> ... We have 100% [quoted text clipped - 29 lines] > > --Damon Don't oxidizer-rich pumps tend to erode fairly rapidly? If so, wouldn't that exclude them from consideration for reusable systems? And do Russian multi-nozzle designs run at lower chamber pressures, making them a little easier to maintain? If both of these answers are yes, wouldn't a combination of the COBRA turbopump and Russian nozzle layout be very cheap and reliable--though maybe a little heavy? > Don't oxidizer-rich pumps tend to erode fairly rapidly? If so, > wouldn't that exclude them from consideration for reusable systems? > And do Russian multi-nozzle designs run at lower chamber pressures, > making them a little easier to maintain? If both of these answers are > yes, wouldn't a combination of the COBRA turbopump and Russian nozzle > layout be very cheap and reliable--though maybe a little heavy? Apparently not, if materials are chosen carefully and temperatures kept reasonably low. The Russians have gotten very good at oxidizer-rich engines, especially hydrocarbon/LOX engines. Kistler wants to use first-generation Russian engines on their reusable rocket and Aerojet has certified their reusability. (Staged combustion engines using hypergolic propellants, another Russian specialty, are another question.) I gather that one reason a multi-chamber design was chosen was that they had combustion instability problems that were easier to solve by keeping the size down. Also, it's handy to have two or more steerable nozzles on a stage--eliminates steering/roll control thrusters. I don't see any obvious problems with current Russian design practice, though additional testing and certification may be needed for engines that will be reused. Keep in mind that the SSME is a cryogenic engine that runs fuel-rich and thus can run hotter, and is an exercise in getting high Isp at all altitudes. Despite being staged combustion engines, the technologies are considerably different in details. COBRA would use the improved SSME turbopumps, but they are not designed for oxidizer-rich operation. The Russians also have perfected the milled-wall combustion chamber and nozzle, which technology NASA wanted to transfer to the SSME to lower cost. COBRA was to be a test bed for building an improved and cheaper SSME, and might eventually fly on Shuttle-derived vehicles. --Damon >> Don't oxidizer-rich pumps tend to erode fairly rapidly? If so, >> wouldn't that exclude them from consideration for reusable systems? [quoted text clipped - 35 lines] > > --Damon That's a lot of interesting stuff. You mentioned several areas where the Russians had perfected this area or that. In your opinion, what area does the US (or maybe even other countries) have the inside track on? I would think nozzle design would be one, as well as maybe throttlability. The SSME's have an incredibly wide power band. > That's a lot of interesting stuff. You mentioned several areas where > the Russians had perfected this area or that. In your opinion, what > area does the US (or maybe even other countries) have the inside track > on? I would think nozzle design would be one, as well as maybe > throttlability. The SSME's have an incredibly wide power band. I'm not aware that the SSMEs have a "wide power band", at least not for operational flight (deep throttling has been demonstrated in ground testing); the only other large US engine I know of that uses throttling is the RS-68 (60% - 100%). The SSME's thrust has been increased appreciably, so that effectively has increased the throttling range (as long as we don't count the 'panic' setting). The Russian RD-180 used on the Atlas V also is throttleable, down to 47%. To make a broad generalisation, the US has considerable expertise with large and small cryogenic engines, and large and medium solid fuel motors that Russia lacks--but not from having tried apparently. They did develop and fly a SSME equivalent, but not really on an operational basis, and a small cryo engine is only just beginning to be used. Russia has a virtual monopoly on oxidizer rich staged combustion engines, and milled wall nozzles, among other things. And there are many more examples of these engines than US engines in the latter's specialty. Indeed, Russia's liquid engine expertise in the latter 60's and early 70's was very remarkable, and almost unknown and unrecognized in the West. The US focused on Shuttle and SSME, and no large liquid fuel engines were developed for about 30 years until the RS-68 for Delta IV. And note that Atlas V went with a Russian engine. Existing rockets were augmented with medium and large solid fuel motors, rather than developing new large liquid engines or using the F-1 developed for the Saturn V. Overall, I'd give the advantage to the Russians for taking a cost- effective approach to liquid fuel rocket propulsion. It's not a clear or pretty picture, however. Much of this has to do with the lack of really heavy payloads; real-world payloads did get larger, but only at a rate that could be accomodated with modifications and uprating of existing rockets. In the end, Saturn V, N-1 and Energia became dead ends and it could be said that after the Moon race, US rocketry sort of stagnated for decades, although we're benefiting now from the Energia's propulsion developments. That's my take on the situation; opinions may vary, wildly. --Damon > I'm not aware that the SSMEs have a "wide power band", at least not for > operational flight (deep throttling has been demonstrated in ground > testing); 104% down to 65% and back up to 104% is fairly wide and is pretty much the baseline throttling range through max-q, isn't it?  Signature"Fame may be fleeting but obscurity is forever." ~Anonymous "I believe as little as possible and know as much as I can." ~Todd Stuart Phillips <www.angryherb.net> >> I'm not aware that the SSMEs have a "wide power band", at least not for >> operational flight (deep throttling has been demonstrated in ground >> testing); > > 104% down to 65% and back up to 104% is fairly wide and is pretty much > the baseline throttling range through max-q, isn't it? I must have a different definition of 'wide'. Rocketdyne was able to take it down below 25% I think; below that ran into turbopump instability problems and there probably wasn't any point in going that low most of the time. Aside from SSME, RD-180, and RS-68, how many other large engines can be throttled? Prior to the SSME, were any large engines throttled in actual practice? Closest I can think of was the single-chamber engine used on the X-15. --Damon > Aside from SSME, RD-180, and RS-68, how many other large > engines can be throttled? Prior to the SSME, were any large > engines throttled in actual practice? Closest I can think of > was the single-chamber engine used on the X-15. The lunar module descent engine, of course. Paul >>> I'm not aware that the SSMEs have a "wide power band", at least not for >>> operational flight (deep throttling has been demonstrated in ground [quoted text clipped - 12 lines] > engines throttled in actual practice? Closest I can think of > was the single-chamber engine used on the X-15. I guess I was considering 65% to 108% a wide power band, considering there are few motors with equivalent capabilities. You named the only ones I know of, but there are likely some others. I can't imagine one going down to 25%. That's pretty remarkable given how sensitive these things are to internal flow disruptions (cavitation, etc...). Its seems possible that component erosion actually goes up when the power gets that low as laminar flow breaks down in some of the internals. If thta's true, then throttling could be a limiting factor in reusability. > I guess I was considering 65% to 108% a wide power band, considering > there are few motors with equivalent capabilities. You named the [quoted text clipped - 5 lines] > the internals. If thta's true, then throttling could be a limiting > factor in reusability. Rocketdyne's testing of the SSME at very low power levels ran into 'chugging' issues; I think the thrust must have been surging due to some internal flow problem. I neglected to save the online articles detailing extended testing of the SSME, to my frequent regret. I am reminded that the J-2S was tested down to extremely low power levels, but it's not clear that the turbopumps were actually running in this 'idle' mode. This engine, a highly modified 'tapoff cycle' version of the J-2 used on the Saturn launch vehicles, never flew in space but had considerable test stand time. It has been frequently mentioned as an upper stage engine for SDV and was in turn modified into the RS-2200. Note throttling down to 20%. http://www.astronautix.com/engines/rs2200.htm I have no real idea what lower power levels do to engine components; I would have expected lower wear rates, but... The SSME's throat did have appreciable wear rates and a thicker nickel alloy layer was applied to that area (throat diameter has since been increased as well). The turbopumps were completely replaced by Pratt and Whitney's design for a variety of reasons. Since the SSME is the only engine we have that actually gets reused, that's about the only benchmark we have and it's just for one type of engine and propellant combination. I think it's clear that an engine with a normally rated lifetime of minutes, does not readily compared to a modern turbojet engine with lifetimes in the thousands of hours. That's due to extreme difference in power levels, but also the fact that rocket engines are seldom recovered for reuse and so aren't rated or designed to reliably operate for hours or many flights. In fact, rocket engines do get tested a lot on the ground, which indicates to me that extended life is just a matter of design. --Damon > That's a lot of interesting stuff. You mentioned several areas where > the Russians had perfected this area or that. In your opinion, what > area does the US (or maybe even other countries) have the inside track > on? I would think nozzle design would be one, as well as maybe > throttlability. The SSME's have an incredibly wide power band. http://www.astronautix.com/engines/rd0120.htm This summary of the Energia's SSME-equivalent covers some interesting points. --Damon |
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