gandalf@pro-canaveral.cts.com (Ken Hollis) (11/15/90)
Greetings and Salutations: I don't always catch reply's to messages, so if I miss something you wish for me to see, just send it & I will try to answer. Now in particular: >From: brettvs@blake.u.washington.edu (Brett Vansteenwyk) >Subject: New Shuttle Engines > >Not long ago it was noted that the first of Endeavour's engines had >arrived at KSC. Some mention was made that these engines were "new and >improved". The "New & Improved" was mostly the new Block II engine controller, going from an Honeywell old fighter (F-100? Super Saber?) jet fire control computer (can you believe discrete components, plated wire memory...) To a REAL MC68000 micro (space hardened, of course...). Other changes are from the HPFD (High Pressure Fuel Duct) changing from Titanium to Inconel (This had already been implemented) and other misc changes (nothing major). >[1].Are these new engines useable in the older shuttles? It would seem Yes, these engines are LRU's (Line Replaceable Units) >[2].Are these engines part of a more "mature" system? Currently Pratt & Whitney is working on a second generation HPFTP (High Pressure Fuel Turbopump) and HPOTP (High Pressure Oxidizer Turbopump). These are also LRU's, but P&W has integrated advances in manufacturing techniques, for example less welding. >[3].(Slight rehash from [2]). While the SSME's have not been a >particular safety problem (in hindsight, at least relative to the >SRB's), their turnaround launch to launch has been a nightmare for >costs--so much of each engine needs to be rebuilt. Oh? About the only thing that has to be "worked on" is the HPOTP. Other than that, they are really not that much different than the rest of the shuttle for turnaround. > This seems to stem >from the fact that this design pushed the envelope for efficiency and >thrust to weight ratio. This engine has been in use for almost 10 >years, and it would seem that it could be classified as a "mature" >system by now--a learning curve with subsequent reduction in >refurbishment costs as well as a more reliable engine. Is there >evidence to indicate that this has happened? Yes, it has happened, and they are still learning new things every day. This is part of the reason for the new P&W HPOTP & HPFTP. Please remember that it takes YEARS to qualify anything for NASA on the shuttle. Changes are made gradually so that you don't screw anything up by fixing one small problem to create a BIG new problem. . . . >[4].Whenever I see any discussion about new launcher development, I >never, or almost never see any suggestion to using the SSME's, nor do I >see any indication of an engine derived from SSME technology. The >tendency is to discuss systems originating 25 or even 30 years back. I >am assuming that the SSME was the most recent major engine development. >Has all the time and talent spent to make the SSME work been wasted on >what is now considered an evolutionary dead-end? While it may seem >disconcerting, it seems where the evidence is pointing. > The SSME is made for a MAN RATED rocket. Redundancy, double checks, etc. It was also created as a singe stage to orbit rocket, able to work both at sea level & in the vacuum of space. When the unmanned rocket motors are designed, they don't need all of the safeguards, and they are designed to operate only within a certain part of the atmosphere (the section they are active for) not the whole way. The SSME's are EXPENSIVE, not to be used on expendables (But if you were riding that roman candle, wouldn't you be rest assured that the gov't bought the BEST low bid equipment they could... ;->). >[5].If not the evolutionary dead-end as postulated in [4], could there be >an SSME derivative for an expendable launcher, or a restartable version >for purposes similar to the Saturn 3rd stage system? Indeed, you find Rocketdyne using the experience gained from the SSME's to design cheap engines for the expendables (By the way, Rocketdyne makes MOST of the engines for the expendables anyway...). > Just some random thoughts. > --Brett Van Steenwyk Just some random answers..... Ken Hollis ProLine: gandalf@pro-canaveral Internet: gandalf@pro-canaveral.cts.com UUCP: crash!pro-canaveral!gandalf
henry@zoo.toronto.edu (Henry Spencer) (11/16/90)
In article <5667@crash.cts.com> gandalf@pro-canaveral.cts.com (Ken Hollis) writes: >The SSME is made for a MAN RATED rocket. Redundancy, double checks, etc... >... When the unmanned rocket motors are designed, >they don't need all of the safeguards... Uh, let us not forget that most of the major "unmanned" rocket motors designed in the US are, or have been at one time, man-rated. Atlas and Titan have both launched manned spacecraft, Delta uses Atlas-derived engines, and the Saturns were man-rated from the start. None of them had anywhere near the hideous engine cost and complexity problems of the SSMEs. This is an excuse, not a reason. Lest anyone claim that reusability makes the difference, note that all regeneratively-cooled liquid engines are reusable in principle, and some of them are cleared for far longer use without maintenance than the SSMEs. The RL-10 in the Centaur is cleared for something like seven firings with a total burn time of over an hour... on a single mission, no maintenance. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry
gandalf@pro-canaveral.cts.com (Ken Hollis) (11/17/90)
Greetings and Salutations: >From: henry@zoo.toronto.edu (Henry Spencer) >Subject: Re: New Shuttle Engines >In article <10948@milton.u.washington.edu> >brettvs@blake.u.washington.edu (Brett > Vansteenwyk) writes: >>Not long ago it was noted that the first of Endeavour's engines had arrived >>at KSC. Some mention was made that these engines were "new and improved". >Don't read too much into this. There has been no major design change, just >a bunch of small incremental improvements. The Main Engine Controller is a major upgrade for the engine, with completely new programming & components. >>[5].If not the evolutionary dead-end as postulated in [4], could there be >>an SSME derivative for an expendable launcher... >The definitive Shuttle C proposal wanted to use life-expired shuttle engines >in an expendable launcher. The Hughes/Boeing Jarvis proposal also used >expendable SSMEs, after they tried very hard to come up with a viable >scheme for reviving the F-1 and J-2 and couldn't make it work. The SSME >is just too expensive to be a good expendable engine, though. -- >"I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology >"Not to worry." | henry@zoo.toronto.edu utzoo!henry Rocketdyne has been discussing the engines for the new generation ELV's (Expendable Launch Vehicles) and basically said that they would be a scaled down, less costly version of the SSME's. Ken Hollis ProLine: gandalf@pro-canaveral Internet: gandalf@pro-canaveral.cts.com UUCP: crash!pro-canaveral!gandalf
henry@zoo.toronto.edu (Henry Spencer) (11/18/90)
In article <5687@crash.cts.com> gandalf@pro-canaveral.cts.com (Ken Hollis) writes: >>Don't read too much into this. There has been no major design change, just >>a bunch of small incremental improvements. > >The Main Engine Controller is a major upgrade for the engine, with completely >new programming & components. If I'm not mistaken, though, its external behavior is more or less identical. Given that the MEC isn't a problem area of the engine, I think it fair to class this as an incremental improvement. >>The SSME is just too expensive to be a good expendable engine, though. > >Rocketdyne has been discussing the engines for the new generation ELV's >(Expendable Launch Vehicles) and basically said that they would be a scaled >down, less costly version of the SSME's. It depends on which new-generation expendable you are talking about. The more sensible ALS people definitely would run miles to avoid using SSMEs or any derivative thereof. It also depends on who you are talking to. Rocketdyne clearly has an interest in seeing that an SSME derivative -- built by Rocketdyne -- is used, as opposed to a new design done by competitive procurement. Considering how badly Rocketdyne's SSME has failed to meet its promises, one might suspect that the next big engine contract would go to someone else. Rocketdyne is not an unbiased source. I've seen a number of new-generation expendable proposals, and (ignoring the explicit shuttle derivatives), Jarvis is the only one I can recall that specified use of SSME derivatives. Nobody who thinks he can afford to (a) develop a new engine, (b) live without liquid hydrogen, or (c) live with clustered RL-10s wants anything to do with the SSME. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry
gandalf@pro-canaveral.cts.com (Ken Hollis) (11/23/90)
Greetings and Salutations: >From: henry@zoo.toronto.edu (Henry Spencer) >Subject: Re: New Shuttle Engines >People have explored more devious schemes, like variable-length nozzles, >but no real use has been made of them yet. The MX Missile uses a 2 piece extendible, variable length nozzle. >>... If this is a heavy constraint, why light >>the SSMEs at sea level at all ... > >One very important practical reason is that the #1 time for engine trouble >is at ignition. Lighting the SSMEs on the pad means that the more benign >kinds of engine failures simply cause a pad abort. There may also have been You also would have a center of gravity that would be way off since this is an asymmetrical launch vehicle. (In another article...) >>The Main Engine Controller is a major upgrade for the engine, with completely >>new programming & components. > >If I'm not mistaken, though, its external behavior is more or less identical. Increased memory & CPU speed allows more parameter monitoring at a faster speed. This could be critical for shutting the SSME down faster if needed. >Given that the MEC isn't a problem area of the engine, I think it fair to >class this as an incremental improvement. Some other improvements (You be the judge on incremental or not...) Pratt & Whitney Turbopumps : Longer life expectancy between changeouts, beefier & heavier. Large throat MCC (Main Combustion Chamber) >competitive procurement. Considering how badly Rocketdyne's SSME has >failed to meet its promises, one might suspect that the next big engine >"Not to worry." | henry@zoo.toronto.edu utzoo!henry At least give them credit for getting the performance requirements to 109% of design. While I will agree that the maintenance was not as expected, the design was pretty ambitious. >From: brettvs@blake.u.washington.edu (Brett Vansteenwyk) >Subject: Re: New Shuttle Engines >My impression was (especially from reading Feynman's book) that the SSMEs were >virtually rebuilt after each launch--the component parts going into a system >of inspection and repair such that when a given engine was rebuilt, many >of the pieces in the new build came from other engines that were also in the >rebuild process at the time--the original engine's parts by and large would... > --Brett Van Steenwyk I now see what you are referring to. Currently about the only thing that is removed each flight for inspection is the HPOTP (High Pressure Oxidizer Turbopump). However parts from one engine are removed (whether they failed or are needed on another engine) and used in other places. Each part has a serial number, and they are all interchangeable. But for the most part SSME's do not have a lot of part swapping. Ken Hollis ProLine: gandalf@pro-canaveral Internet: gandalf@pro-canaveral.cts.com UUCP: crash!pro-canaveral!gandalf
henry@zoo.toronto.edu (Henry Spencer) (11/23/90)
In article <5817@crash.cts.com> gandalf@pro-canaveral.cts.com (Ken Hollis) writes: >>People have explored more devious schemes, like variable-length nozzles, >>but no real use has been made of them yet. > >The MX Missile uses a 2 piece extendible, variable length nozzle. No, sorry, its nozzle telescopes for compact stowage -- this is also done in sub-launched ballistic missiles, which are *very* cramped, and in the shuttle's IUS upper stage -- but it extends to full length before ignition and stays that way. It is *not* variable length while the engine is firing, which is the issue. >Some other improvements (You be the judge on incremental or not...) > >Pratt & Whitney Turbopumps : Longer life expectancy between changeouts, >beefier & heavier. Very true... except that these are *not* incorporated in Endeavour's engines. The P&W turbopumps, at the moment, are a prototyping exercise only. There is no commitment to *ever* use them as flight hardware. If NASA *does* switch from the Rocketdyne pumps to the P&W ones, then yes, I would agree that this is more than an incremental improvement. "If". >Large throat MCC (Main Combustion Chamber) Recent progress on this is essentially zero. And again, there is *no* commitment to ever use it for flight hardware; it is being treated as a technology experiment only, and a low-priority one at that. NASA has been criticized for this attitude. No change so far. >>... Considering how badly Rocketdyne's SSME has >>failed to meet its promises... > >At least give them credit for getting the performance requirements to 109% of >design... Sorry, I don't give credit for a capability that is not being used because of fears that it is unsafe. They don't run the SSMEs at 109% any more. -- "I'm not sure it's possible | Henry Spencer at U of Toronto Zoology to explain how X works." | henry@zoo.toronto.edu utzoo!henry