Reading through several old reports, I have come across studies conducted by MSFC on improved Saturn V designs with greater payload capacity, and with uprated engines. As a result of increasing launch vehicle propellant masses, the first stage 'MS-IC' engines had to produce more thrust to lift the upper stages efficiently. Rocketdyne's F-1 would have continued on as UF-1 and F-1A variants.

Marshall reports from 1965 make reference to the F-1 qualification engine, which was rate down at a peak sea level thrust of 1,522,000 pounds force. The UF-1 ('Uprated F-1') was intended to serve as an interim model that would generate higher thrust levels but not require intensive redevelopment required for substantial boosting. As such, the UF-1 would settle at a thrust of 1,650,000 pounds force. The F-1A would make further improvements not including completely new component design to achieve 1,800,000 pounds force.

The UF-1 is the model that interests me, because there isn't much writing on it elsewhere. MSFC researchers intended to increase its thrust, but also stated that the standard 1,522k F-1 thrust was limited by the horsepower of its '35 inch turbopump.' To update to 1,650k the UF-1 would feature a new 30 inch turbine and improved pump inducers to support it, and also a strengthened gas generator operating at a lower lox/fuel ratio. The 30 inch turbine would then limit the thrust because of its critical turbine speed. However, the F-1A would surpass this with the same 30 inch model by adding new, increased diameter impellers (as well as larger gas generators and exhaust manifolds).

But here's where it gets interesting: I have also been reading 'Stages to Saturn' by Roger E. Bilstein, in which the author writes of a test run of an early completed thrust chamber at Edwards AFB. On April 6th 1961, 'the thrust of the prototype chamber peaked at 7,295,000 newtons (1,640,000 pounds).' If originally developed to be limited to 1,522k pounds force by turbine horsepower constraints, how could this engine generate so much more thrust without the 1965-listed improvements to the turbine and GG?

This reminds me of various other articles listing F-1 thrusts beyond 1,522k pounds throughout Saturn V operation: from 1,530k on Apollo 11 to 1,565k on Apollo 15 and 1,580k on Skylab. But 1640k?

So here are the questions: - How did the old turbine allow for 1,640klbf thrust? - Would chamber pressure or specific impulse be increased? - Could Saturn V have been propelled with this thrust level?

I want to know if 1,640k could be sustained...

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    $\begingroup$ Was the 1961 thrust chamber test using the final pump design? $\endgroup$ Dec 17, 2016 at 15:07
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    $\begingroup$ No idea unfortunately, the book doesn't specify other than calling it a pre-production 'prototype thrust chamber.' Whatever they did to it seems to have worked pretty well! But do you think this could have been used for actual launches, and could it have had an effect on the engine's efficiency? $\endgroup$ Dec 17, 2016 at 21:22

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My explanation for this is in theory, since I haven't found yet a source that confirms what the reason is.

In that book the author writes that was a test run. Also other sources in internet says that it was a static firing testing. It doesn't explain how successful that test was. It doesn't mean that the F-1 engine ran for about 176.9 seconds which is the burning time of F-1 engine in S-IC first stage of Saturn V launch (168 seconds after liftoff + 8.9 seconds before liftoff). Maybe F-1 engine was capable of reaching 1640k pounds but there was no guarantee that it would resist for 177 seconds or even less.

At the time that F-1 engine was certified to be operational it had a thrust of 1500k pounds. This was the level of thrust where engineers proved that the engine was within acceptable parameters, it was 100% of its nominal value (further info about this you find here). I am suggesting that the F-1 engine with the technology of 1961 was capable of operating at 109%-110%, but it would last for only a few seconds. Static firing test are very short compared to burning time in a mission. Until now info for that test doesn't clarify what happened next, if the engine was damaged, if yes how much it was and if it could be operational or tested again. F-1 engines in those years were prototypes. Many tests and experiments were done at that time. But this was their first test, so doesn't exclude the possibility that the real purpose of static firing short test was just for the level of thrust and not trying to make the engine reliable.

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    $\begingroup$ That seems fair enough. The F-1 was riddled with combustion instability problems early in development, and with this being one such prototype it may have met that fate. Or in the case of a static firing, a quick shutdown may have prevented destruction but could have left the engine damaged. Thank you for picking up on the possibility of engine failure. That one skipped past me! $\endgroup$ Dec 23, 2016 at 21:15

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