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Given the lack of clarity about weight of CM, SM and LEM while designing Saturn V, how and who calculated the thrust required from first stage of launch vehicle (Saturn V), for moon landing? were the weights of CM,SM and LM assumed?

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Chariots For Apollo is an excellent resource for this.

The initial numbers followed from a large number of feasibility studies, dating back to the late 1950s. These feasibility studies gave rough numbers on various parameters. Those numbers evolved continuously as they learned more about (manned) spaceflight. At some point decisions had to be taken to take program (and NASA in particular) forward:

It has become increasingly apparent that a preliminary program for manned lunar landings should be formulated. This is necessary ... to provide a proper justification for Apollo, and to place Apollo schedules and technical plans on a firmer foundation.

There were a number of decision points that roughly fixed design parameters, although not in hard numbers.

At this point, only very rough design parameters were set. The F1 wasn't ready, so while they had target performance numbers, they were not fixed. Same for the J2 engines for the upper stages. And this meant that the weight budgets were also not fixed, etc. With the contracts awarded started a back-and-forth game to make everything fit that would last till the very end.

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Apollo was just like any large program/project; the mass of the vehicles and resource usage changed from initial design through the end of the program.

Even ignoring the addition of the moon buggies in the later missions, over the the years as they moved from initial design, interim design, construction, testing and flight these numbers changed. There may have even been changes based on the lessons learned in the early flights. Every time something changed, everything was recalculated to see if the mission was still possible, and what changes it would make the mission profile.

Initially they would have made sure that the rocket would have more than enough capability even taking into account growth in mass. The vehicle designers would have been under pressure to keep that growth to a minimum.

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  • $\begingroup$ Agree that there would have been changes in designs of CM, SM & LEM etc. & consequently their weight, but we need to have an approximate estimate of "Payload" for a rocket engine to be designed. E.g. the "F1" was designed to meet the needs expressed by US AF, in 1951-53. It had a load figure to begin with. I was wondering if there was any such figure while designing the Saturn v first stage (deciding on the number & type of engines to be used). Or perhaps, they first decided to use 5# of F1, & then the effective thrust dictated the wt. limits for LM, SM & LEM. Ur comment pls. $\endgroup$
    – Niranjan
    Jul 1, 2022 at 15:07
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    $\begingroup$ First test firing of F-1 components was done in 1957, first test of a full engine was done 1959. So in 1960 and 1961 the thrust to be expected from a F-1 should be known very precisely. $\endgroup$
    – Uwe
    Jul 4, 2022 at 1:20

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