posted 07-22-2011 02:52 AM               

And how long the second stage burns really is (mostly) irrelevant. The S-II burned that long because it was of low thrust. When an engine went out the other engines simply burned longer (Can't remember the mission, AS-504?). Less thrust in later stages is good only if you are trying to limit the acceleration you submit your payload to. But I'll concede your point and pull 2 of the center H-1 engines off my second stage S-IB, and just burn the remaining six longer.

I do concur that the H-1 nozzles were not vacuum optimized, they are some altitude above sea level optimized. But I counter with this--so what? If they get the job done who cares? Constructing the S-IB itself from 9 separate tanks and 8 separate engines wasn't horribly efficient, but it got the job done.

posted 07-22-2011 07:31 AM               

However run time is an issue with hydrocarbon engines because petroleum distillates like RP-1 when combusted produce contaminates which clog up injectors. RP1 also has a high freeze point.

posted 07-22-2011 08:25 AM               

"The combination of hydrogen and oxygen for propellants made the moon shot feasible," he declared. "Its use in upper stages results in a significant increase in performance over the propellant combinations of oxygen and kerosene then in use in first-stage boosters.

posted 07-22-2011 07:56 PM               

Also, the S-IB was designed to launch a payload to 100 n mi. Skylab was put into a higher orbit because the supremely excess payload capacity of the Saturn V used to deliver it. Higher orbit meant less atmospheric decay meant longer unboosted orbital lifetime. So correspondingly, the CSM's which were sent there had lighter propellant loads in order to reach it (They also required less propellant as they were not doing a TEI burn). The CSM still had far more propellant than was necessary for the Skylab missions as they were used to re-boost Skylab prior to departure.

With regards to LH2 and LOX being higher performance, I concur, however, a Ferrari is higher performance than a Volkswagen. But if I already own a Volkswagen and I need a loaf of bread, I am pretty sure I would take the Volkswagen to the grocery store and buy a loaf of bread and save myself $100,000 dollars.

I still think the S-IB would do the job. The Russians use Kerosene and LOX in the R-7 that they have been launching the Soyuz with for 40 years without any problems.

And strange as I understood it, it was more desirable to stage at lower velocities rather than higher.

On edit: The S-I was designed to get the S-IV aloft. The S-I was upgraded to the S-IB to get the S-IVB aloft. While the second stage weight increased from 12,000 lbm in the S-IV to 21,000 lbm in the S-IVB. The S-IB stage had it mass reduced by 20,000 lbm and its thrust increased from 1,500,000 lbf to 1,600,000 lbf.

posted 07-22-2011 09:41 PM               

quote:

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Originally posted by David Hinners:
I can't find the reference, but I have read somewhere that an H-1 was static fired for over 8 minutes during testing.

Also, the S-IB was designed to launch a payload to 100 n mi.

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posted 07-22-2011 10:53 PM               

The 155s firing time was how long was necessary to complete the stage mission not the other way around. I am certain they didn't compromise mission safety if they burned 156s. If you want man rate them for 8 minutes you put them in the test stand and burn em for eight minutes, tear the engine down and take a look. Pretty sure that's easier than figuring out how to explosively deform hemispherical LH2 tank ends or handle the center engine pogo or hand form and apply each piece of insulation for the chemically milled tank walls. Certainly cheaper than building the Seal Beach facility to do all this work in anyway.