Uwe wrote in an answer that

The possible payload of Saturn V was carefully planed for the whole mission, but the difference of the payloads of the missions Apollo 11 and 17 was less than 3000 kg.

To me, that feels backwards: Why would you build a huge rocket, with a lead time approaching years, to the exact payload specifications that you thought you would need for the mission? Would it not be better to build as powerful an Up Goer as you reasonably could, then bring along as much payload as you could given what it could carry to wherever you were going, in order to get as much as possible useful work done for the money spent?

Or put differently, to what extent did Apollo payload mass drive the capability of the Saturn family of rockets; as opposed to the extent to which the capability of the Saturn family of rockets limited Apollo payload mass?

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    $\begingroup$ Von Braun was quoted once (Cannot find the source, read it years ago) that he hid some of the capacity knowing that Apollo would get too heavy. $\endgroup$ – geoffc Feb 24 '17 at 20:22
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    $\begingroup$ I think that to some extent, that is what actually happened. Saturn V was at the limit of what could be built and flown within the Kennedy time frame. That drove the selection of mission mode (one mode would have involved two Saturn launches for one lunar mission). Direct ascent would have been simpler, but involved landing the entire mass of the spacecraft on the Moon that was going to fly back to Earth - too much for Saturn to carry. Counter-intuitively, bringing along a separate lander actually reduced the overall mass to LEO to what Saturn could manage. 1/2 $\endgroup$ – Anthony X Feb 25 '17 at 2:14
  • $\begingroup$ See this Wikipedia article for an overview of some of the mission modes and engineering trade-offs. 2/2 $\endgroup$ – Anthony X Feb 25 '17 at 2:17
  • $\begingroup$ The Saturn family had to use the rocket engines developed for this mission. A larger Saturn version using 10 or 20 engines for the first stage would have been possible. But I doubt that such a large rocket would have been large enough for a direct lunar landing without any rendezvous maneuver in earth or moon orbit. A direct lunar landing needed even larger engines, but engines with so much thrust were not available. The development of such gigantic rocket engines would require some extra years. $\endgroup$ – Uwe Feb 27 '17 at 20:24
  • $\begingroup$ @Uwe The Saturn C-8 design, with 8 F-1 on the first stage, massing 60% more than Saturn V, would have been sufficient for a direct-ascent lunar mission. Certainly it would have taken longer than Saturn V, but it required no new engines or major technological advancements over the V. en.m.wikipedia.org/wiki/Saturn_C-8 $\endgroup$ – Russell Borogove Mar 7 '17 at 21:27

Both: The capability of the Saturn V set the maximum weight of the Apollo spacecraft, and the development of Apollo forced some changes to the Saturn.

Originally, the plan was to develop a large semi-modular family of rockets under the Saturn moniker, at one point ranging from the C-1 for LEO medium-lift (which evolved into the Saturn I) to the 4800-ton C-8 for lunar direct ascent. At the same time, the Apollo program was conceived as a general purpose LEO and lunar spacecraft, with the Apollo CSM being the final lunar-ascent-and-earth-return stage in a direct ascent mission mode.

When Kennedy set the end-of-decade goal for lunar landing in his May 1961 address to Congress, waiting for the massive C-8 became unacceptable, so the choice of mission mode came down to the Earth orbit rendezvous (EOR), with two C-4 launches to either assemble or fuel the complete lunar spacecraft, or lunar orbit rendezvous (LOR), using a single C-4 launch with a small lunar lander. In the end, LOR was selected as the fastest and cheapest plan. The C-4 design used 4 F-1 engines on the first stage, 4 J-2 on the second stage, and the single J-2, S-IVB as the third stage.

Before LOR was chosen, the Apollo CSM design had already stabilized to some extent, which is why the engine on the service module is so large: it was intended for lift-off from the moon.

By the end of 1961, it appeared the C-4 would not be big enough for the single-launch LOR mission, so the C-5 was developed. This configuration originally had only 4 engines on the first stage, but NASA's Director of Launch Vehicles, Milton Rosen, pushed for the fifth engine. According to Stages To Saturn:

Adding the extra power plant really did not call for extensive design changes; this was Rosen's most convincing argument. Marshall [Space Flight Center] engineers had drawn up the first stage to mount the original four engines at the ends of two heavy crossbeams at the base of the rocket. The innate conservatism of the von Braun design team was fortunate here, because the crossbeams were much heavier than required. Their inherent strength meant no real problems in mounting the fifth powerplant at the junction of the crossbeams, and the Saturn thus gained the added thrust to handle the increasingly heavy payloads of the later Apollo missions. "Conservative design," Rosen declared, "saved Apollo."

At second glance, MSFC people themselves found no good reason not to add the extra engine, especially with the payload creeping upward all the time. "I had an awfully uneasy feeling, you know," von Braun remembered; "every time we talked to the Houston people, the damn LEM had gotten heavier again."

NASA announced plans to build the C-5 at the beginning of 1962, and by early 1963 it was confirmed as the launcher choice for Apollo and renamed Saturn V.

Late in the project, Grumman had real trouble with weight overruns on the lunar module. With the somewhat over-built CSM, the total weight of the spacecraft ran up against the payload limits of the Saturn V, and multiple "campaigns" of weight-stripping engineering effort had to be made to reach the final landing weight goals. As late as Apollo 10, the LM was still a couple hundred pounds overweight, in fact.

So early on, the spacecraft drove the launcher payload capability, forcing the 5th engine to be added, and late in the program, the launcher payload limits drove the spacecraft design.

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    $\begingroup$ When you talk of the spacecraft in the final paragraph, you're referring to the CSM/LM combination, correct? $\endgroup$ – user Mar 8 '17 at 17:50
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    $\begingroup$ Yes. The CSM also underwent weight reduction efforts in the Block I -> Block II revisions after the January '67 Apollo 1 fire, but seems to have been more or less frozen before the LM. $\endgroup$ – Russell Borogove Mar 8 '17 at 19:07

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