Pat Flannery wrote:
Ed Kyle wrote:

The S-IB stage wasn't as heavy as it looked. It actually compares
well with the Zenit 3 first stage - which can be considered a modern
equivalent in that it uses the same propellants and delivers about the
same total impulse. S-IB had a propellent mass ratio of about 0.907.
The Zenit first stage propellent ratio is about 0.909.


Yeah, but look at the actual physical size of the two stages:
S-1B was 6.52 m. in diameter by 24.48 m. long, and weighed in at 448,648
kg. fully fueled.
Zenit's first stage is 3.90 m. in diameter by 32.90 m. long and weighs
in at 354,300 kg. fully fueled.

True, Zenit's first stage weighs 21-22% less, both fueled and
empty, than S-IB did, but Saturn's multi-tankage layout itself is
not necessarily the dominant reason why. One important
reason is that Zenit's RD-171 main engine is seriously more
fuel efficient than Saturn's H-1 engines. RD-171 has a
311/337 sec sea-level/vacuum specific impulse, 14-19% better
than H-1's 262/296 sec. ISP. Another reason is that Saturn IB
was designed to haul more payload. A Saturn IB could put
15.6 tonnes into a 50 degree 200 km orbit, about 14% more
than Zenit.

As I recall - but don't trust me on this completely - the cluster
tankage only added something like 10% to the S-IB dry mass
versus an ideal single diameter tank design. Of course,
first stage dry mass is quite a bit less important than upper
stage dry mass for total vehicle performance.

As for size, S-IB was shorter and fatter than Zenit, which isn't
much of a big deal. The Saturn stage could be hauled on a
relatively simple trailer pulled by a standard cab-over semi-tractor.
Zenit uses a slick erector system. NASA never bothered to
develop such a setup - Saturns were erected with a gantry bridge
crane augmented by a mobile ground crane - but there is no
reason that a Saturn erector could not have been developed if
needed.

It is interesting, BTW, to note that RD-171 weighs 8.8 tonnes
dry while Saturn's eight H-1 engines taken together only
weighed about 7.2 tonnes.

Although using the Jupiter and Redstone tankage tooling made for a
quick
way to make a large rocket stage (the S-1B stage consisted of a large
diameter central LOX tank based on the Jupiter tooling, surrounded by a
total of eight smaller diameter tanks based on the Redstone tooling,
four of which held LOX and four kerosene) without much new tooling
needed, it wasn't a very efficient design from an internal volume vs.
overall size viewpoint due to the empty spaces between the clustered tanks.
For a really clunky design, compare the R-7 Semyorka to Atlas for size
and weight.
Both the stage and a half Atlas D (such as used to launch Mercury) and
central core and four strap-ons R-7-8A91 (such as used for Sputnik 3)
could carry about the same payload into orbit. Atlas D weighed in at
120,000 kg. fully fueled and the R-7-8A91 at 269,973 kg. fully fueled.
Hoorah for balloon tankage.

R-7 may not have matched the Atlas mass ratio, but it is hard to argue
with its results. R-7 (still the world's busiest launcher) has now
flown
about 1,150 more times than the stage-and-a-half Atlas (retired in
2004)
did!

- Ed Kyle