Re: Weight Growth
- From: henry@xxxxxxxxxxxxx (Henry Spencer)
- Date: Thu, 31 May 2007 02:09:41 GMT
In article <87r6oyz8jz.fsf@xxxxxxxxxxx>,
John Stoffel <john@xxxxxxxxxxx> wrote:
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.)
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.)
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.
I dunno... I just don't have a good feeling about CEV and Ares I at all.
Join the club...
--
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mail to henry at zoo.utoronto.ca instead. | henry@xxxxxxxxxxxxx
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- From: John Stoffel
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