WI: balloon tanks used in S-1/S-1B and Saturn upper stages?

After reading "Atlas: the ultimate weapon", "Stages to Saturn", "Apollo: the
definitive sourcebook", and a lot of online stuff, including posts here,
it's apparent that the pressure-stabilized tanks of the Atlas and Centaur
were very effective at reducing stage mass and manufacturing times in a
relatively straightforward way - provided one can get past the part about
keeping them inflated. What if the idea had played a larger role in the
early space age, specifically Apollo?

The Atlas/Centaur apparently suffered few if any of the tank manufacturing
nightmares, rework and collossal expenses to reach weight objectives
encountered by those forced to remove weight from rigid, self-stabilized
rockets. Of course, Convair did have troubles with the rocket, but the
design choice paid off in a missle that met it's range objectives, could be
produced in quantity and later reached orbit simply by flying the
appropriate trajectory and otherwise operating normally - no SWIP, SCRAPE or
other costly rework was required. The balloon-tank Centaur is still used
today and it's inherently light weight is key to it's high performance.

So what if the four propellant tanks in the S-1 and S-1B had been replaced
with pressure-stabilized tanks? These containers were non-structural. Why
bother lightening only four of nine containers, and in a first stage, you
ask? Well, the MSFC people didn't like balloon tanks - what if they could
have been persuaded to try this? Doesn't seem like a big risk, what with the
LOX tanks carrying the load. The payoffs would have been an immediate
performance increase and actual experience to support going for it on the
giant upper stages. Von Braun certainly made a number of decisions said to
have astonished his own people at the time - agreeing to use cryo upper
stages on Saturn before any had ever flown successfully and supporting LOR,
to name two. Why not use balloon tanks in the first Saturn to see if proper
German rocket men can make good use of that crazy idea? Why not assume that
success would have had some previously unknown fathers in Huntsville?

There's no way guys like George Mueller, Werhner Von Braun and Kurt Debus
would ever have agreed to put 4 million pounds of main stage propellant in a
metal balloon and light five F-1s under it. The notion of stacking an entire
moon rocket atop a foundation of air would have been seen as completely
crazy. Speculating about an Atlas-like S-IC is a waste of time. But the
greatest benefit of the balloon design seems to be in low-density cryogenic
upper stages, not the high-density first stage. And once you've decided to
put some of the Mercury Seven atop Atlases....

The S-II was an immense and complex rigid stage and it's truly remarkable
that NAA was able to deliver Apollo 8's at only 88,500 lbs, and Apollo 13's
at an astonishing 78,000 lbs (lighter than Apollo 7's S-1B first stage). But
all concerned seem to have gone through hell to achieve these weights, it
was done late and cost far too much. And there's no way it could have flown
without the benefit of pressurization, anyway - there's just not enough
metal there to deal with such forces unaided. Indeed, its said *all* Saturns
relied on tank pressure during flight for structural stability. So they
relied on the concept, but refused to take advantage of it's full benefits.

Here, too, it's a bit much to imagine Dr. VB and the boys going for the full
Monty on a million-lb stage. But imagine how it could have been if the S-II
had been a balloon stage with enough self-support to allow unpressurized
empty handling. I can't find figures on the weight of the S-II's tanks, but
we could speculate that such a stage might have weighed 60,000 lbs. As
important as weight is time - going with balloon tanks could have saved a
lot of it. The hydrogen tank's huge wall could have been made of sheet metal
and stringers, not sections machined from billets. Stainless steel is a lot
easier to weld than the aluminum alloy NAA chose for the S-II, and they
struggled with welding. Since time equals money, faster completion would
have saved funds. A lighter second stage could have achieved higher velocity
at burn out and reduced the burn time for the third stage to make parking
orbit, thus allowing a heavier payload to be pushed into TLI.

The S-IVB was where the benefits really could have been reaped - every pound
saved goes directly to the payload. This stage weighed 10% of the total
flight weight (S-V) and wasn't lightened by even 5% during the program. This
LH2 tank could have been made faster, too. Building a big Centaur would have
made a lot of sense. Speculating that models produced for both S-V and S-IB
would have weighed 10,000 lbs less is not unreasonable. Apollo could have
used extra weight, either in the familiar spacecraft delivered quicker, but
heavier, or delivered late but with more capabilities.

This kind of weight, money and time relief would have changed a lot of
things. Tom Kelly wrote that stopping the LM's weight growth busted the
schedule and budget. With a ton or so shed from the S-1B, 10,000 lbs freed
up from the S-IVB, and LM allowed to get fat but stay on schedule, the plan
to have an Earth orbit test of the CSM with the LM - flown on a single
S-1B - could have happened. A lighter S-V, delivered sooner, would've
changed a lot of other things.

J

On Sat, 7 Oct 2006 20:48:52 -0700, "Mr Jim"
wrote:

After reading "Atlas: the ultimate weapon", "Stages to Saturn", "Apollo: the
definitive sourcebook", and a lot of online stuff, including posts here,
it's apparent that the pressure-stabilized tanks of the Atlas and Centaur
were very effective at reducing stage mass and manufacturing times in a
relatively straightforward way - provided one can get past the part about
keeping them inflated. What if the idea had played a larger role in the
early space age, specifically Apollo?

[Insert engineering nightmare of a Saturn-V built along these lines]

OM
--
]=====================================[
] OMBlog - http://www.io.com/~o_m/omworld [
] Let's face it: Sometimes you *need* [
] an obnoxious opinion in your day! [
]=====================================[

OM wrote:
On Sat, 7 Oct 2006 20:48:52 -0700, "Mr Jim"
wrote:

After reading "Atlas: the ultimate weapon", "Stages to Saturn", "Apollo: the
definitive sourcebook", and a lot of online stuff, including posts here,
it's apparent that the pressure-stabilized tanks of the Atlas and Centaur
were very effective at reducing stage mass and manufacturing times in a
relatively straightforward way - provided one can get past the part about
keeping them inflated. What if the idea had played a larger role in the
early space age, specifically Apollo?

[Insert engineering nightmare of a Saturn-V built along these lines]

OM
--
]=====================================[
] OMBlog - http://www.io.com/~o_m/omworld [
] Let's face it: Sometimes you *need* [
] an obnoxious opinion in your day! [
]=====================================[

I second the OM comment, (It would have been a nigtmare to construct,
and maintain prior to launch). The problems would be to many in number,
to organize design/construction groups, (and make the deadlines put out
by NASA).

Carl
P.S.
Not that the atlas should be put down for having used these method, (It
is the main reason for it being dropped as a Dyna-Soar Booster early
on). They could have reinforced it but, the project would have become
to compl. to man rate fast enough. The Atlas family has been a great
player in World Space History.