was felxibility of apollo design

Derek Lyons ) wrote:

(Henry Spencer) wrote:

In article ,
Derek Lyons wrote:

There is nothing modular about the Apollo spacecraft. The CSM is a
matched pair always and forever.
Wasn't there some non-trivial thoughts about a light-weight mini-SM for
use with Earth-orbit missions like Skylab?

There was. But substituting a SM late in the game isn't the same as
designing a modular system.

And likewise, designing a modular system which ends up only existing in
one version isn't the same as designing a non-modular system.

...you note the modularity is defined as 'being able to
leave bits not needed behind', something the Apollo spacecraft is
decidedly not able to do. Whether it's the super-heavy J mission SM,
or the ultra lightweight CRV SM, the CM is wedded always and forever
to a SM.

Note that Owen Maynard, who Kieran was quoting, was there, and you
weren't.

Note that Kieran isn't quoting him, he's giving his impression of
Maynard's reminiscences.

I have to admit a big mea culpa he my posting was definitely in the
category of doing my best to recall one of Owen's many splendid
anecdotes. If only Owen were still with us, I'd call him up and
get a clarification, but I can't anymmore :-(

(About Owen' reminisces:
He was one amazing raconteur, you could tell that he had
told some of these over and over again, over the years, to as many
people as were willing to listen. He had the sense that he'd been part
of something of tremendously, historically significant, and he was
frequently consumed by the need to "pass the torch" (he would occasionally
cite that line from In Flanders Fields, one of his favorite Candian poems,
when he got into this mode) of the experiences he'd had during those

years, to the next generation of space engineers. Comparing notes
with others who'd had the pleasure over the years to hear "The Stories"
from Owen (as his family affectionately refer to them), it seems to me
that the details hadn't drifted in the re-telling; so, as reminisces
go, I think they're pretty reliable. If anything, it's *my* recollection
of The Stories that are probably the most suspect :-)

Note that Henry also spent some time with Owen, and got to hear some
of this as well...and *his* memory I trust implicitly :-) :-)

Hint: think of what the M stands for in CM, SM, LM.

Hint: Lacking formal naming terminology, names mean little. Gemini
also had 'modules', but wasn't modular either.

The context in which I remember Owen talking about these things, was
as part of a years-long discussion we had about spacecraft systems
engineering (he was the guy in charge of the systems engineering
branch of the Apollo spacecraft program office from the mid-1960s
on, and had been in a systems-engineering role at the very start of
Apollo; from 1962-65 he was away from the overall systems engineering
job, as he got the Lunar Excursion Module design and procurement
on the rails). In that contact, I think he looked at Modularity from
a Functional perspective (Owen was a great one for capitalizing
important nouns in his write-ups, for emphasis :-).

Remember the
historical context: STG was still at the beginning of Project Mercury
(Owen moved over to the post-Mercury design group shortly after
participating in the Mercury-Atlas-1 failure investigation), before
Alan Sheppard had flown, and the engineers there were dealing with a
pretty hypothetical situation: "what if we're given the job to continue
with spaceflight after Mercury, what should the USA do, and what sort of
vehicles should be specified to do that?" They didn't *know* what the
next mission would be, they could only try designing a bunch of hopefully-
attractive mission concepts, and hope that the government would agree
to fund at least one of them. Given a small design team with a limited
budget, I think that it wouldn't have been feasible to do a completely
new from-scratch design for each mission (space station, Moon fly-by,
Moon landing, Mars landing); I think the modular design was a tool to
allow a lot of design details to be re-used from one concept to the next.

Given that, I'm certain that Owen and the others looked at this from a
Functional perspective, listing functions that needed to be carried out
by and within each mission, and then allocating these to various equipment
items. The Modular approach would allow certain groups of functions to
be incorporated into common pieces of equipment (e.g., the CM would be
fairly similar from one mission to the next), while other functions would
be allocated to equipment items that were expected to be quite different
from one mission to the next (e.g., the SM for one type of mission could
be quite different from the SM for another type of mission).

Note that the Modular concept was, for the time, relatively new and
controversial. Owen definitely mentioned that on Mercury they'd had a
hard time squeezing all the necessary functions into the single capsule,
based on what he believed was a fallacious requirement to make all the
avionics accessible to the crew, in-flight. The Apollo concept was partly
meant to show-case an improved way of packaging equipment, based on the
assumptin that overall system reliability would be higher if some of
the avionics (plus things like propellant tanks, etc.) was placed
on the outside of the manned capsule. At about the same time Jim Chamberlin
(a good friend of Owen's, from back when Jim was the chief engineer on the
Avro Arrow, and Owen was working as a subsystem engineer under him)
was pushing for Gemini, which also incorporated this concept (I suspect that
this good idea may well have been Chamberlin's).

Straying from Owen's stories, to my interpretation now:
This design group didn't know if there'd be any post-Mercury mission, or
if there'd be a single post-Mercury mission, or if there'd be *many*
post-Mercury missions. The Modular concept enveloped all of these
possibilities. If the competition with the Russians, and other political
factors, had led to the many-mission scenario, then the modularity would
had to have been adapted to the style that Derek alluded to: a set of
actual modules that would have to be built in a way that would allow
mixing and matching for the different missions. In the event, there was
really only one post-Mercury mission for this design team (Chamberlin's Gemini
team was a different group), and so while the *conceptual design* had
the seeds of strong-definition modularity built into it, by the time the
preliminary and detailed designs were being done much of this was
discarded (due to the incredible time-pressure, anyhting that wasn't
absolutely needed for the Apollo mission was deliberately pruned out).
What remained was the system-architecture concept of functions parsed into
different equipment modules, but by then the Apollo CM wasn't required to
support a Space Station or Mars mission, and so any functions associated
with that, and any interfaces associated with the SM for those missions,
would have been dropped.

I think you can see more than a hint of this thinking when it came time
to think about post-Apollo missions; Skylab and Apollo-Soyuz were, in
this context, exercises in designing back in some of the Apollo
strong modularity that had been dropped in the early 1960s.

- Kieran A. Carroll