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Assuming the engine is recovered on a platform at sea similar to SpaceX, could it be refurbished and reflown at a low cost? Would the coking, corrosion, and other problems be any worse than that in Merlin 1? Could they deal with them in the 60s and 70s? Have any detailed studies been done?

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  • $\begingroup$ Are you assuming that flight ready F-1s exist now, or are asking if this could have been done back in the 70s, or what? $\endgroup$ May 9, 2023 at 16:05
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    $\begingroup$ @OrganicMarble the latter $\endgroup$ May 9, 2023 at 16:07
  • $\begingroup$ Thanks for asking this question. I've been wondering for a while about really big, non-LH2 pump-fed's being reused. $\endgroup$ May 10, 2023 at 6:14

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I found a definitive statement from one of the engine designers, Robert Biggs:

The only reason this was a non-reusable engine was it was non-recoverable. If we could have recovered it after a flight, it would have [been] reusable.

Remembering the Giants, Chapter 1

During testing, one engine was started 20 times, another 34 times.

enter image description here

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    $\begingroup$ Did they have to do a lot of cleaning? $\endgroup$ May 10, 2023 at 16:35
  • $\begingroup$ @Abdullah It is not discussed in the paper. $\endgroup$ May 10, 2023 at 17:31
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    $\begingroup$ @Abdullah After a test, the F-1 engines were cleaned with the solvent trichloroethylene to remove coke deposites. A lot of the solvent polluted the soil below the test stands $\endgroup$
    – Uwe
    May 11, 2023 at 7:39
  • $\begingroup$ @Uwe how much cost and time? $\endgroup$ May 11, 2023 at 8:21
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    $\begingroup$ @Abdullah you mean like the 2913 seconds that were spread over 34 tests? No. $\endgroup$ May 11, 2023 at 14:01
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According to Henry Spencer on this yarchive.net posting:

almost any regeneratively-cooled liquid rocket engine is reusable, even if it was built for expendable vehicles. The design requirement for the F-1 was 20 starts and 2250s of firing; as part of the test program, six of them accumulated over 5000s each.

That design requirement would allow for 15 full-length Saturn V first-stage burns. Between-flight cleanup might be more difficult and expensive than the Merlin since it wasn't designed specifically for reuse, and the engines are individually much larger and thus more expensive to handle, but it would have been feasible.

I can't find a reference now, but there was a proposal for a Saturn V derived booster to have the four outer engines of the first stage drop off partway through the first-stage burn to reduce weight once enough fuel had burned off. Those could have been parachute-recovered, refurbished, and reused.

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    $\begingroup$ And now I'm imagining the glorious alternate universe where F-1s were being reused. What a world that would be! $\endgroup$ May 9, 2023 at 20:21
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    $\begingroup$ You mention the stage-and-a-half Saturn: you are (probably) looking for the Saturn V-B. A similar system was also proposed to reuse RS-25's on SLS, back when it was still being conceptualised. $\endgroup$ May 9, 2023 at 22:54
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    $\begingroup$ Literally anything is reusable in some sense. Far fewer things are economically reusable. $\endgroup$
    – fectin
    May 10, 2023 at 2:21
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    $\begingroup$ @fectin as Asimov said, it's hard to put the mushroom cloud back in the shiny uranium sphere. $\endgroup$ May 11, 2023 at 0:12
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    $\begingroup$ @OrganicMarble give it a few million years and you can mine the volatiles again... Perhaps not the same volatiles, but still.... $\endgroup$
    – Moo
    May 11, 2023 at 1:33
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fectin has it- Physically reusable, practically, not worth it.

Physically, the metals involved were pretty much kept within their operating limits, and the bearings might also be within their lifetimes (or overhaul-able).

Practically, the assembly was not intended for long life, streamlined field ops, and TCO (total cost of ownership). The Apollo unspoken motto was “waste anything but time”, and anything that did not help the mandated schedule was de facto hurting the schedule, and was to be cut.

In particular, fuel was wasted. This was the Sixties, peak US light oil had not happened yet, and the Arab nations were still getting their footing after World War II/decolonization. Therefore the petro-fuel was (in the grand scheme of things) cheap, and treated no better than monopoly money. This was also a first-stage engine, so the payload penalty of less-than-perfect efficiency was tolerable if not desirable.

The wasted fuel (partial combustion) kept the engine cool, but left carbon deposits on surfaces. If you think scrubbing the grill is annoying, try scrubbing an assembly of multiple, giant garbage disposals and a giant fireplace. There’s a reason chimney sweep was a profession. A limited amount of deposit thickness is insulating, and tolerable if not perhaps beneficial. So running an engine test of limited duration produces tolerable carbon ‘fouling’, if understood and controlled. A long engine run, however, implies an engine teardown and scrubbing, since the consequences would be staggering.

Nowadays, we have higher-temp alloys, and tighter tolerances on the kerosene. Engines can now run more efficiently, leaving less soot and gunk. Not so in 1967.

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    $\begingroup$ Has the specification of RP-1 changed since 1967? $\endgroup$ May 10, 2023 at 17:52
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    $\begingroup$ I don't disbelieve most of this answer, but it'd be better with references $\endgroup$
    – Erin Anne
    May 10, 2023 at 18:58
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    $\begingroup$ @RussellBorogove, it would be more interesting to know if the actual formulation of RP-1 has changed. RP-1 doesn't call for a specific combination of ingredients; rather, it places limits on what's allowed to be present. $\endgroup$
    – Mark
    May 10, 2023 at 23:56
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    $\begingroup$ Worse, the added mass of the recovery related systems would have meant smaller payload and/or lower orbital altitude, thus changing the mission profile to where probably a single launch solution to the moon would not have been possible. Which is why some F9 and FH missions don't recover, and have the recovery hardware removed. $\endgroup$
    – jwenting
    May 11, 2023 at 7:57

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