posted 07-08-2014 07:37 PM
The NASA Technical Reports Server used to have a series of LEM Mass Property Reports, dating back to July 1963. (They haven't been re-added since the NTRS was down in early May 2013.)
There are numerous discussions regarding the impact of the LM's weight. Early on, Grumman formulated growth factors:
This included things like the additional propellant, increases to the propellant tanks to hold the additional propellant, and increases to the landing legs.
- All items carried from separation to touchdown (staged) must be multiplied by the Descent Growth Factor 2.824.
- All items carried from Separation to Burnout (unstaged) [i.e., back to lunar orbit] must be multiplied by the Round Trip Growth Factor 6.682.
- To obtain the affect of items carried from lift-off to burnout in the Ascent Stage multiply the item by the Ascent Growth Factor 2.366.
- The penalty for lunar liftoff capability differs from the Round Trip Growth Factor. The lunar lift-off payload is only carried
from the lunar surface to Burnout, however, the Descent stage must carry an increase in propellant to land the Ascent stage propellant required to carry the lunar payload. The lunar lift-off capability factor is 4.285.
At one point, NASA decided to increase the theoretical size of the astronauts from 65 to 75 percentile men (which added 13.2 pounds). I seem to recall reading somewhere (although apparently not in the Mass Properties Reports) that they were considering reducing rations to a lower calorie count, again to shave weight.
As noted above, the weight of the LM also influenced the size of the Saturn V. Stages to Saturn takes a slightly different look at it:
To get one more kilogram of payload, the laws of orbital mechanics required that 14 kilograms be cut from the S-IC; or four to five kilograms from the S-II; but only one from the S-IVB. As noted in the Mass Properties Reports, consideration to the size of the astronauts was given.
As to the choice of lunar orbit rendezvous, there were several advantages. As noted in another post, less spacecraft mass was required. This implies that a single Saturn V, rather than some newer and larger booster (or multiple Saturn Vs), was sufficient to launch the lunar mission.
Developing a newer, larger booster would have taken additional time, making it unlikely to land a man on the moon before the end of the decade.
A direct ascent would have required landing a rocket approximately the size of an Atlas on the lunar surface. It took a small army to launch an Atlas, but launching from the lunar surface would have to be done by only the crew, with little to no access to the booster during the countdown.
It would have been much more challenging to land such a large vehicle on the lunar surface. Additionally, most studies had the astronauts in their couches -- attempting to land this large spacecraft on their backs, with no direct viewing the landing area.
You can read more about LOR in Enchanted Rendezvous: John C. Houbolt and the Genesis of the Lunar-Orbit Rendezvous Concept [direct link to 1.3M PDF].