There was a lot of talk going back and forth about fuel usage, etc. during and after the Apollo missions that I followed closely I learned a lot. As
everyone should know, every celestial body has an "escape velocity"
"In the case of the earth, the escape velocity is 11.2kps/6.9mps; the moon, 2.4kps/1.5mps; Mars, 5kps/3.1mps; and Jupiter, 59.6kps/37mps."
Lets talk about thrust:
The first stage of the Saturn V had five engines. At launch, each engine produced about 1,500,000 pounds (or 6,670,000 newtons, the SI unit of force)
of thrust. The five engines therefore produced about 7,500,000 pounds or about 33.4 million newtons.
As the rocket rose through the atmosphere, its thrust actually increased to almost nine million pounds due to the decreasing pressure of the
surrounding air. I remember watching it and noticed as the air got thinner, the flames turned into a giant 'ball'. At the same time, it got much
lighter as it furiously burned its propellants. This caused the rocket's acceleration to increase to where it could have damaged its structure or the
Apollo spacecraft on top. To keep acceleration under 4 "G's", the center or "inboard" engine was shut down about 26 seconds before the other four.
The Apollo crafts spent 8 days total in space, 4 days to get there (don't forget, they are simply coasting and don't need to fire the engine on the
service module other than for course corrections. The reason for coarse corrections are due to 'out-gassing' from various components in the complete
vacuum of space pushing it around (I work with vacuum systems in the semiconductor industry and all the bolts in the vacuum chambers are 'vented' that
is, they have a hole drill through to the bottom to prevent out-gassing thus taking days to reach the necessary vacuum. We wear gloves in the
clean-rooms as a single fingerprint will outgas! There was never a problem about IF the Lunar module had enough fuel as it used it ONLY in takeoff
from the moon, not landing! The only concern was it HAD TO FIRE or they would have been marooned on the moon. (Nixon had already prepared a speech in
case that happened!)
when the lunar accent stage linked up with the command module after going to the surface, it was jettisoned and as the service module with the 3
astronauts and several hundred pounds of lunar rocks swung around the moon, they fired the command module engine to achieve 2.4 kilometers per second
to 'escape' from the pull of the moon. during the coast back the command module reached 22,435 mph! That is why the reentry angle was so important, if
it headed right for the earth it would slam into the atmosphere and be destroyed, if it hit the edge, it would 'skip' off the atmosphere and travel
back into space, it came in and out to slowly bring it to a safe speed where it would be pulled into the earths gravity, falling until the drogue
chutes slowed it down, then the main chutes opened for a water landing.
edit on 17-4-2014 by wulff because: (no reason given)