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#21
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Pat Flannery wrote:
Derek Lyons wrote: Nonsense. If you allow for testing/tweaking time in your manufacturing schedule and budget, it doesn't matter if you are making 10 motors or 10,000. Do you think you are going to have more man hours in five big motors and their plumbing or thirty medium sized ones? More man hours mean more possibility for mistakes. All of our manned moon landings (Apollos 11, 12, 14, 15, 16, 17) used the same number of F-1 motors as the number of NK-15's used in one N-1 first stage. If you have forever to make them, you can take time on each of the motors and check it out... No, you simply have multiple checkout and assembly pipelines running in parallel. but the 14 N-1's the soviets had finished or in construction meant they needed 420 motors for the first stages, and an additional 112 modified NK-15s for the second stages. That's 532 motors total, and that is a _lot_ to build and inspect. Not particularly. During WWII air craft engine manufacturers routinely turned out 10-12 motors a day from a single factory. The Russians knew about assembly lines Pat. One thing that indicates the degree of confidence that the Soviets had in the N-1 was that they wanted a dozen successful unmanned launches before they were going to put a crew on it. Right. As compared to every US manned booster, with the exception of the Saturn V and the Shuttle, which had that many or more. Don't confuse prudence with a lack of confidence. D. -- Touch-twice life. Eat. Drink. Laugh. -Resolved: To be more temperate in my postings. Oct 5th, 2004 JDL |
#22
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Am Tue, 21 Dec 2004 14:55:14 -0600 schrieb "Pat Flannery":
But assuming that the motors have an equal potential for catastrophic failure, the more motors you put on the vehicle, the more likely it is that one will catastrophically fail. Because of its large size, the F-1 probably had a greater potential for catastrophic failure than a NK-15, like the N-1's first stage used, but to get equal reliability in the overall booster stage, the NK-15 would have to be _six times_ as reliable as a F-1 in this respect...and I don't think that that was the case. [...other conclusions snipped...] I agree totally. And I see a very parallel development in computer technology that is the business of many writers here. See RAID systems: You can increase their reliability by using redundant amounts of hard disks for building arrays that have the capability to survive single or sometimes even multi disk failures. E.g. a raid-5 array of three disks survives the crash of one disk. But with increasing numbers of disks the probability of single failures itself increases (multiplies by number of used disks), too. So, at some point, increasing numbers of disks in hard disk arrays begins to reduce over-all reliability of the total array. That is a known fact - and btw: one main factor for that decrease in overall reliability is the increased complexity of "plumbing". (:-) The parallels are obvious. And so is the actual trend of using as few as possible disks for getting the necessary storage capacity. cu, ZiLi aka HKZL (Heinrich Zinndorf-Linker) -- "Abusus non tollit usum" - Latin: Abuse is no argument against proper use. mailto: http://zili.de |
#23
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Let see...
- Kerosene engines - Small maneuvering engines - Something to calculate the orbital maneuvers And so on. Personally, I think that technologies probably already existed in the 1930's, and perharps even before it. By the 1940's, nuclear engines probably is much prefered than kerosene engines, just like in Herge's "Objectif Lune" (which I suspect was done with help from outside sources, it's just too detailed for a comic book). Though it should be noted that there were ancient batteries and ancient clocwork type devices already existed thousands of years ago, so it could have happened thousands of years ago. |
#25
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Kevin Willoughby wrote:
In article , says... Nonsense. If you allow for testing/tweaking time in your manufacturing schedule and budget, it doesn't matter if you are making 10 motors or 10,000. To a first approximation, yes. When you start looking at the details, should you spent $1,000,000 in R&D expenses to save $500 per motor? If you are building 100 motors, then obviously not. If you are building 10,000 motors, then obviously so. Certainly. But we weren't talking about saving money, but about producing motors, especially large ones, in significant quantities on a schedule. However Pat dismissed even the possibility of such a program for the N-1 out of hand, which is incorrect and what I was adressing. (Pat and I were also discussing tweaking/tuning in the name of building safe, reliable motors. Cost is somewhat less of an issue in that instance.) D. -- Touch-twice life. Eat. Drink. Laugh. -Resolved: To be more temperate in my postings. Oct 5th, 2004 JDL |
#26
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Derek Lyons wrote:
Certainly. But we weren't talking about saving money, but about producing motors, especially large ones, in significant quantities on a schedule. However Pat dismissed even the possibility of such a program for the N-1 out of hand, which is incorrect and what I was adressing. I didn't say it was impossible to do, just that is was going to be damn hard to do, and that it would be difficult to give each motor a decent check-out before shipping it off the the launch site. I don't know haw many man-hours went into each motor's construction, but it was a fairly sophisticated design that had a better ISP than the F-1, and it sounds like a lot of floor space and people would be needed to build them in the numbers needed for large-scale use of the rocket. The original plan was for variants of the N-1 using its stages in various configurations were going to become the standard Soviet medium and heavy lift rocket systems- there was even a ICBM variant proposed: http://www.astronautix.com/lvs/n11gr.htm (Pat and I were also discussing tweaking/tuning in the name of building safe, reliable motors. Cost is somewhat less of an issue in that instance.) I'd be more concerned about the production rate than the cost per motor. Pat |
#27
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In article ,
Pat Flannery wrote: Manufacturing problems can easily happen when you have a very small, limited production run, which means that your need for "strenuous tests" is likely higher with a small run as compared to a very large run, where repeatability in the manufacturing processes has already been achieved. In the perfect world, yes...but in the real world every one of those motors is going to be at least a bit different from its sisters due to it's complexity, and when you are dealing with hundreds of them turned out in a fairly short period of time, at least one is going to be different in a fatal way. I missed this in Jeff's post - I was distracted and not reading closely, unfortunately. In any event Pat's point is well-taken, especially given the Soviet production standards of the day. Jeff states "where repeatability in the manufacturing process has already been achieved." Personally, I think it's a big and unwarranted assumption to state or even imply that a large production run indicates that repeatability has been achieved. A large production run, in and of itself, means nothing. If your qualification testing program is valid, and ONLY IF, you can presume the various widgets you're manufacturing are fungible (rather than frangible, as the N-1 engines turned out to be . . . ;-) Otherwise you're just turning out mass quantities of stuff with no guarantees that s/n 1 is at all similar to s/n 50 or 500. You need strict control of your manufacturing process, from beginning to end, in order to ensure that those units are in fact similar enough to count on behaving similarly. It gets back to the age-old design engineering debate: do you qualify for flight by test? (e.g., hotfire each engine, etc) or by analysis (e.g., very limited testing combined with documentation demonstrating repeatability and consistency in manufacturing?) Obviously, for the state of the Soviet art at the time, the N-1's designers picked the wrong approach for the entire vehicle. -- Herb Schaltegger, B.S., J.D. "Wow! This is like saying when engineers get involved, harmonic oscillations tear apart bridges." ~Hop David http://www.angryherb.net |
#28
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Herb Schaltegger wrote:
If your qualification testing program is valid, and ONLY IF, you can presume the various widgets you're manufacturing are fungible (rather than frangible, as the N-1 engines turned out to be . . . ;-) There was only three motor malfunctions that could be possibly attributed to a fault in the motor itself- on the first flight, a motor developed a high frequency oscillation from bits of metal that got into the turbopump, and this caused it to rip free from its propellant plumbing. On the second flight, one of the motors ingested a temperature sensor, bolt, or piece of welding slag (stories vary) from inside the Lox tank and exploded, damaging the other motors in its vicinity and causing the KORD system to shut all the motors down. On the fourth flight what went wrong depends on who's telling the story- from the engine builder's viewpoint what went wrong was that a too rapid shutdown of the center six motors caused a water-hammer effect to rupture their plumbing. From the rocket designer's viewpoint another turbopump had exploded in one of the center six motors (Turbopump overspeed due to propellant cut-off?). Otherwise you're just turning out mass quantities of stuff with no guarantees that s/n 1 is at all similar to s/n 50 or 500. And when you need 30 motors per first stage of each individual N-1 rocket, you are turning out large numbers of motors that you can't be sure of until the first launch is attempted and then you get a few successful launches under your belt. How would you like to be looking at a room with a hundred or so NK-15 motors sitting in it, and be trying to figure out if the turbopumps have an inherent problem in their design, or if simply sticking filter screens on the propellant feed lines will fix the problem? You'd better hope the latter will be the case, as if it is a design problem on the motor you're going to have to explain to the Kremlin that all those motors are going to need major modifications or be simply scrapped....and you may find yourself living in a tiny Siberian yurt made out of a scrapped NK-15 motor. The motor was made by the Kuznetsov Design Bureau BTW....the design bureau had plenty of experience in building gas turbine motors for aircraft, but had almost no experience with liquid-fueled rocket motors when the N-1 got dropped into its lap. So that was another thing that the design of the N-1 had going in its favor. You need strict control of your manufacturing process, from beginning to end, in order to ensure that those units are in fact similar enough to count on behaving similarly. It gets back to the age-old design engineering debate: do you qualify for flight by test? (e.g., hotfire each engine, etc) or by analysis (e.g., very limited testing combined with documentation demonstrating repeatability and consistency in manufacturing?) Obviously, for the state of the Soviet art at the time, the N-1's designers picked the wrong approach for the entire vehicle. That pretty well sums it up; as one of the designers said about it: "How do you explain to your government that you have a rocket that weighs more than a Saturn V, develops more thrust than a Saturn V, and yet can carry far less to the Moon than a Saturn V?" I imagine that after each of the four failures, that became a little harder to do. Pat |
#29
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Pat Flannery wrote:
And when you need 30 motors per first stage of each individual N-1 rocket, you are turning out large numbers of motors that you can't be sure of until the first launch is attempted and then you get a few successful launches under your belt. sigh Pat... You keep repeating this as fact, and it is not. It is possible, nay fairly straightforward, to produce a large number of motors *and* to be sure of their performance. That the Russians screwed it up by making the wrong choices doesn't change this. How would you like to be looking at a room with a hundred or so NK-15 motors sitting in it, and be trying to figure out if the turbopumps have an inherent problem in their design, or if simply sticking filter screens on the propellant feed lines will fix the problem? Problems easily resolved with a proper design, qualification, and production process. That the Russians chose not to follow this well trodden path is no indication that the job is impossible. D. -- Touch-twice life. Eat. Drink. Laugh. -Resolved: To be more temperate in my postings. Oct 5th, 2004 JDL |
#30
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Pat Flannery wrote:
I didn't say it was impossible to do, just that is was going to be damn hard to do, and that it would be difficult to give each motor a decent check-out before shipping it off the the launch site. It's not difficult at all. It's a straightforward matter to schedule your production start early enough and to provide enough test stands. (Pat and I were also discussing tweaking/tuning in the name of building safe, reliable motors. Cost is somewhat less of an issue in that instance.) I'd be more concerned about the production rate than the cost per motor. Again, not an issue. Start your production early enough with one line, then 'twin' it (I.E. move experienced workers from the first line to the second, then filling both with less experienced). Repeat as needed. (Or start a bunch of lines at once and be prepared to scrap a lot of early motors.) It's all about proper management and having enough resources, and the Russians chose (for various reasons) not to apply themselves to the task. D. -- Touch-twice life. Eat. Drink. Laugh. -Resolved: To be more temperate in my postings. Oct 5th, 2004 JDL |
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