Aeronautics Industry Aeronautics Industry    FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Weight Growth          Aeronautics Industry Forum Index -> Aeronautics Industry View previous topic :: View next topic   Author Message John Stoffel Guest Posted: Wed May 30, 2007 6:32 pm    Post subject: Weight Growth I found it interesting, though maybe not totally surprising, to read in a recent AvLeak that the Capsule was something like 3,000 lbs over weight targets, and that the booster was near it's maximum thrust as well, which was leading to all sorta of tricks and changes to cut the capsule weight down. One was to re-do the entire interstage (sorry, don't have the article near me to put down the right terms...) thrust structure which holds the OMS and solar panels and other equipment in an effort to reduce weight. To me, it sounded like they were doing a piss-poor job of initial estimation, and hadn't budgetted for any growth outside their control. Which seems ludicrious since the Apollo program had exactly the same problems and von Braun quietly upped the numbers of the apollo launchers to address this exact issue. Is the problem today that they're talking too closely to each other early on? Or that they're believing each other too much and not padding the initial numbers enough? Basically, were the capsule people saying "Yeah, we can do it all with a mass budget of 10,000lbs max" and the launcher people said "Yeah, we can give you 10,000lbs max" and they both started AT 10,000 (number grabbed out of thin air)? Should the launcher people had said "Sure you want 10,000 max, we'll build for 15,000 since we know you'll go over." Or "Sure you'll get 10,000 no problem. Quickly guys, let's plan for 15,000 but not tell anyone..." Or how do you budget properly for weight growth? I read about jet engines for the A380 and B787 which are supposed to be comming in around 80,000lbs each, but that GE/Rolls/Pratt have actually run them at 86,000 already, even though they'll be rated lower. How hard would it be to just build in a margin and hope to never use it? Or is the design so damm tight, and the perception of "If we don't use every last pound of thrust available to launch every last ounce of mass we can use, we're wasting money?" I dunno... I just don't have a good feeling about CEV and Ares I at all. John Back to top   Ads Advertising Sponsor Henry Spencer Guest Posted: Thu May 31, 2007 6:09 am    Post subject: Re: Weight Growth In article <87r6oyz8jz.fsf@stoffel.org>, John Stoffel <john@stoffel.org> wrote: Quote: Which seems ludicrious since the Apollo program had exactly the same problems and von Braun quietly upped the numbers of the apollo launchers to address this exact issue. And even so, it came out pretty marginal -- a lot of sweat got expended on LM weight reduction just to achieve a system that could do fairly tightly constrained missions. Apollo margins typically were so tight at launch that they were technically negative -- it was usually necessary to violate at least one official flight rule slightly just to achieve lunar orbit. (They progressively eased up after that, as contingencies that might have required extra fuel etc. didn't happen and the unused contingency reserves accumulated.) Quote: Is the problem today that they're talking too closely to each other early on? Or that they're believing each other too much and not padding the initial numbers enough? I think part of the problem is the latter: on Apollo, it worked in NASA's favor that the Huntsville people had a low opinion of the Houston people and simply didn't believe pronouncements that "this is positively the last weight increase". Also, the NASA centers then had a lot more autonomy. Huntsville in particular really was an independent empire, which told outsiders as little as it could and listened to Headquarters only when it felt like it. So there was more room for a cautious von Braun to quietly slip a large fudge factor into the payload mass. I suspect that's a lot harder now, because in the name of being one big happy efficient family, the centers are being forced to work much more closely with each other. More subtly, though, von Braun was working with systems that were fully under his control and were being designed from scratch, so he *could* just dial up the size as required, within very broad limits. A large part of the problem here is that NASA drank ATK's "simple safe soon" Kool-Aid, and bought into a rather marginal launcher concept which made some optimistic assumptions and didn't have much leeway for trouble. (Which is not to say that said concept, stupid though it always was, couldn't have been made to work. But it would have taken just the right sort of leadership, as opposed to management -- a combination of solid authority over the entire project, iron-fisted "you WILL make this approach work within your weight budget" discipline, and the technical savvy needed to help one subsystem after another find ways around insoluble-looking weight problems. The real masters of weight discipline, like Ed Heinemann, considered von Braun rather sloppy about it.) Quote: How hard would it be to just build in a margin and hope to never use it? Or is the design so damm tight, and the perception of "If we don't use every last pound of thrust available to launch every last ounce of mass we can use, we're wasting money?" There's certainly a large element of that in the traditional spaceflight culture exemplified by JSC and MSFC. Quote: I dunno... I just don't have a good feeling about CEV and Ares I at all. Join the club... -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | henry@spsystems.net Back to top   Ads Advertising Sponsor mmaker@my-deja.com Guest Posted: Thu May 31, 2007 3:45 pm    Post subject: Re: Weight Growth On May 30, 3:32 pm, John Stoffel <j...@stoffel.org> wrote: Quote: How hard would it be to just build in a margin and hope to never use it? Or is the design so damm tight, and the perception of "If we don't use every last pound of thrust available to launch every last ounce of mass we can use, we're wasting money?" I suspect a large part of the problem is that the first stage design performance is pretty much fixed by the choice of the 'shuttle derived' SRB. Start trying to improve that and pretty soon no-one will be able to call it 'shuttle derived' anymore while keeping a straight face; even today it's debatable. That means the only parts they can improve are the second stage and CEV/SM, and the second stage also has some similar constraints (it's based on shuttle ET tooling, isn't it?). Mark Back to top   Ads Advertising Sponsor Jeff Findley Guest Posted: Tue Jun 05, 2007 12:07 am    Post subject: Re: Weight Growth <mmaker@my-deja.com> wrote in message news:1180611911.094494.165150@g4g2000hsf.googlegroups.com... Quote: On May 30, 3:32 pm, John Stoffel <j...@stoffel.org> wrote: How hard would it be to just build in a margin and hope to never use it? Or is the design so damm tight, and the perception of "If we don't use every last pound of thrust available to launch every last ounce of mass we can use, we're wasting money?" I suspect a large part of the problem is that the first stage design performance is pretty much fixed by the choice of the 'shuttle derived' SRB. Start trying to improve that and pretty soon no-one will be able to call it 'shuttle derived' anymore while keeping a straight face; even today it's debatable. That means the only parts they can improve are the second stage and CEV/SM, and the second stage also has some similar constraints (it's based on shuttle ET tooling, isn't it?). They've already "improved" the SRB in the design by adding another SRB segment to the stack. Also, the thrust curve (thrust versus time plot) for Ares I will need to be different, which means a slightly different grain cross section. And then there are the changes needed to put a payload (second stage) on top versus attaching to the ET on the side. And then there is the need for a roll control package during SRB firing (the SRB can vector its thrust, but with one SRB, that doesn't give you roll control). Is that still "shuttle derived"? Jeff -- "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety" - B. Franklin, Bartlett's Familiar Quotations (1919) Back to top   Ads Advertising Sponsor Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         Aeronautics Industry Forum Index -> Aeronautics Industry All times are GMT Page 1 of 1   Jump to: Select a forum Aeronautics Industry----------------Aeronautics Industry  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum 222 Attacks blocked Powered by phpBB © 2001, 2005 phpBB Group