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From: (Henry Spencer)
Subject: Saturn stage numbers (was Re: 6xAtlasIII+(2RS68+ET)+DeltaIV=...)
Date: Wed, 4 Aug 1999 13:57:31 GMT

In article <>, Tom  <> wrote:
>> - how much did loaded CM + loaded LM + S-III weigh ?
>SIVB. There was no SIII. (Don't know why).

Complex history.  There was lots of early confusion about Saturn upper
stages -- the original development program was only doing the first stage,
the S-I, in anticipation of being able to use existing missiles as upper
stages.  When things settled down in favor of new LOX/LH2 upper stages...

The idea was to start with a relatively small stage which could use an
existing engine (the RL10, already in the works for Centaur).  Then bigger
LOX/LH2 stages, using a new engine, would be added *between* that one and
the S-I.  The S-I itself would be progressively upgraded, and eventually
re-engined with one or two F-1s.

(I should add that the terminology for versions and stages was terribly
confused, and I am oversimplifying somewhat in the interests of clarity.)

The plan envisioned an eventual maximum configuration with a total of five
stages; the fifth, the S-V, would be a slightly modified Centaur.  So the
first new stage would be the S-IV.  Hence the Saturn I:  S-I plus S-IV.
(In principle, a three-stage Saturn I configuration with an S-V could have
been built, but the Saturn I was overtaken by events and never carried any
"real" payloads, so there was no point in messing around with a stage that
didn't need any real development.)

Under the original plan, the next step would have been a Saturn II with an
improved S-I (the S-IB), an S-III, and the existing S-IV and S-V.  But at
around this time, the race to the Moon got started in earnest, and NASA
started being interested in more rapid and drastic evolution of the
Saturn.  Plans to improve and re-engine the S-I got steadily more
ambitious, the S-III got bypassed in favor of building the S-II first, and
the S-II itself got bigger and bigger to match the growing S-I.  Finally
it became clear that the S-IV was too small to be a good third stage for
such a configuration, so NASA contracted with Douglas (the S-IV builder)
for an enlarged and re-engined S-IV variant.

The original S-IB was built, and it plus the enlarged S-IV (the S-IVB)
became the Saturn IB.  (There was almost a Saturn II, a Saturn IB with an
S-V on top, for big unmanned planetary missions, but it was cancelled.)

What had started out as a simplification of the S-I by replacing the eight
H-1s with an F-1, and had progressed to a modest upgrade using an F-1 and
four H-1s, and then to a slightly less modest upgrade using two F-1s,
mutated under the stress of the Moon race to have three, and then four,
and then *five* F-1s:  the S-IC.

The S-II got bigger and bigger to match.

The S-III quietly disappeared from planning, although conceivably it might
one day have reappeared, as a larger third stage -- the S-IVB was smaller
than optimum as a Saturn V third stage, and there was talk of eventually
building a full-diameter (same diameter as the S-IC and S-II) third stage,
perhaps with nuclear engines.  (It would probably have been preceded by a
nuclear S-IV, sometimes called the S-IVN.)

The S-IVB really was pretty much just an enlarged S-IV, apart from the
change of engine.

Centaur never did fly as the S-V.
The good old days                   |  Henry Spencer
weren't.                            |      (aka

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