Ye Olde Rocket Forum - View Single Post - BT-80 based Saturn V/ "Saturn I-F"

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Ok... back to the drawing board...

Interesting topic of conversation over on the nasaspaceflight.com/forums came up about "what if Apollo had continued..." In part of the discussion, it came to replacing Saturn IB's "cluster's last stand" first stage powered by eight H-1 engines with "something else".

At one point the 260 inch monolithic SRM being developed and tested by Aerojet was proposed, but the thing was SO massively heavy it was going to require an ENTIRELY new integration and stacking design at KSC to make it work, and that wasn't in the cards. As it was, only the half-length motor was ever built and test fired before the project was canceled.

The subject came up about LIQUID replacements for the S-IB stage... interestingly enough they'd been proposed but of course never developed, due to the fact that, being a first stage, weight and ISP inefficiencies don't hurt performance anywhere NEAR as much as they do on upper stages, where weight and ISP is critical to performance. S-IB was actually somewhat of a weight savings over the earlier Saturn I first stage it replaced, though of course the basics of the design in using multiple tanks clustered together could NEVER be as efficient as a monolithic fuel tank and monolithic oxidizer tank, even separate bulkhead tanks like the Saturn V S-IC stage used. But, you have to save about 11 pounds of weight on the first stage to increase payload by 1 pound, unlike on upper stages where it's much closer to 1 pound weight saved equals 1 pound of extra payload (this is especially true of escape stages leaving earth for the moon or elsewhere). SO it was judged not worth the expense to develop a replacement.

Now, in an alternate universe, which the thread presupposed, where shuttle was deemed 'a bridge too far' and was rejected in 1972 instead of being approved and all Saturn hardware and capabilities ultimately scrapped, the opposite decision is taken to "build upon what we have" (much like the Russians did incidentally) and so a program was initiated to evolve Saturn into something more affordable and sustainable-- cheaper to build, cheaper to integrate, and cheaper to fly. Obviously in this paradigm, you have to streamline production and reduce programs where possible-- engine programs, stage programs, etc all soak up funds and make the overall program more expensive, so being able to eliminate the H-1 engine, and the S-IB first stage would have been highly desirable. Replicating it's performance and capabilities (and actually improving upon them) would have been nice side-benefits, especially if it could be done with the existing F-1/F-1A engines and structures similar to that in use on the S-IC Saturn V first stage, and using the existing S-IVB stage, which would surely have switched to the J-2S engine at that time.

Now, Improvements to Saturn V had been proposed including using up to FOUR strap-on liquid rocket booster pods (LRB's) to supplement the Saturn V first stage thrust. There were similar proposals using SRB's of various type and designs (from 120 inch SRB's from Titan III, to 156 inch "notional" SRM's (which eventually became the SRB's I suppose) to even mammoth 260 inch monolithic SRM's by Aerojet). Basically ALL the proposals for Saturn V boosters ignored or glossed over various important constraints on the KSC infrastructure, such as the fact that the acoustics (noise) from the ignition and liftoff of THIRTEEN F-1 engines AT ONCE from a Saturn V (5 F-1's) with FOUR LRB's (2 F-1's EACH) would have broken every window in the eastern half of the state of Florida...

Now, there were proposals to use this dual F-1 booster as a first stage replacement. Someone pointed out on the NSF thread that this wasn't particularly feasible-- the thrust from TWO F-1's was ENTIRELY too much for a Saturn IB type vehicle (unless it was ONLY launching massive payloads instead of crews, which would have required a BIG redesign of the S-IVB most likely). The EIGHT H-1 engines of the S-IB first stage produced 205,000 lbs thrust each (in their last upgrade) for a total of 1,640,000 lbs, a little more than the 1.5 million pound thrust of the stock F-1. Two F-1's on the first stage of a Saturn IB type vehicle would produce around 3 million pounds of thrust, about DOUBLE the Saturn IB first stage! Talk about "blink and you miss it!" The gee loads on a crew would have been unedurable! A single F-1A would have produced 1.7 million pounds thrust at liftoff and would have been a suitable replacement for the cluster of H-1's. Assuming you desired to keep the initial liftoff thrust/weight about the same, and simplified the control of the vehicle at the same time, using a standard F-1 on the first stage augmented by a PAIR of H-1's mounted on either side in the outboard positions (to provide roll control and augment thrust) would have increased the liftoff thrust substantially (to nearly 2 million pounds) allowing for heavier payloads without overaccelerating the stack (would probably have required shutdown of the outer 2 H-1's before burnout, just as the inner four H-1's shut down early on S-IB and the central F-1 shut down early on S-IC.) Weight savings by switching to monolithic tanks on the stage similar to S-IC and powering the stack by a single F-1/F-1A and implementing a pair of roll-control verniers or other methods would have probably been preferable, ESPECIALLY for a crew launch vehicle! In addition, this S-IB stage replacement could have produced a SINGLE F-1/F-1A booster for use with Saturn V-- a pair of which would have provided SEVEN F-1's thrusting at liftoff-- surely all the "boost" a Saturn V would ever have needed!

SO-- the "Saturn I-F", which I've faithfully copied from the EXISTING NASA STUDIES OF THE TIME, is basically over-powered and unrealistic. A SINGLE F-1 booster is MUCH more likely, ESPECIALLY if using the substantially higher-thrust F-1A engine! Such a booster would have had a realistic (if perhaps unaffordable or unnecessary, if no large payloads needing it were funded) performance for a booster for Saturn V, if needed, and would have had double duty as a crew launch vehicle first stage.

Such a single F-1/A first stage/S-IVB second stage crew launcher would basically have given NASA the safety benefits touted for the Ares I "Stick" crew launcher (two stage launcher, single engine on each stage) without the problematic issues such as motor buzz and the impossibility of shutting down an errant SRM first stage, and trying to do an abort off an exploding SRB "unzipped" by range safety in the event of an abort, which would have filled the sky with burning chunks of APCP. A single F-1/A booster would have had the same benefits of a single engine on the first stage, coupled with a single engine on the second stage, with one staging event, and the added benefit of being able to simply turn off the F-1 in the event of an abort.

SO, back to the drawing board... I'll have to replace the twin F-1 first stage on the "1-F" with a single F-1 version... no problem as I can build a twin of it for a pair of LRB's for the BT-80 Saturn V (which would have had NINE F-1's thrusting at liftoff, STILL too much IMHO, but if you deleted the center engine on the S-IC itself and capped it off, you'd have had a more manageable EIGHT F-1's with the twin-F-1 boosters on either side... (which would likely be more efficient anyway as it would allow the S-IC to burn longer with the same fuel load, with only 4 F-1's guzzling the fuel instead of 5...)

Later! OL JR