As I understand it we circled the earth gaining speed and used a figure 8 thru space to gravity shoot around the moon into a stable orbit.
(Note that, in all that follows, the formulae for orbital calculations were written by Johannes Kepler ~400 years ago, and the equations for rocket thrust were created by Konstantin Tsiolkovsky ~100 years ago. They work and they are not terribly difficult to use. The astronauts trained to work them with pencil & paper, which is all that Kepler and Tsiolkovsky had.)
The launch puts the spacecraft it a circular orbit of Earth at ~35,560 feet-per-second. With the nose pointed forward in its direction of orbit, the S-IVB (third stage of the Saturn V) then fires its rocket to increase the orbital speed by ~10,000 ft/sec. This changes the circular orbit at an altitude of ~100 miles to an elliptical orbit with a perigee of ~100 miles and an apogee somewhere out near the Moon. If the Moon wasn't there, the spacecraft would follow its ellipse out to ~240,000 miles and return (the Soviet Zond 4 spacecraft did this). When aimed towards the Moon, spacecraft gets to a point where it is attracted more by the Moon's gravity than the Earth's. Thus its course transitions from an elliptical orbit of the Earth that is anti-clockwise (when seen from above the north) to a
clockwise elliptical orbit around the Moon. However, this new orbit has an aposelene towards the Earth and as it climbs up from its periselene, it crosses the boundary where the Earth's gravity dominates and and then starts falling towards the Earth. This is what gives it its distinctive "figure-8" shape:
Here's part of the question, and I hope I can find the words to ask it correctly.
We leave Earth's orbit at what speed?
~35,500 feet-per-second
Traveling directly toward the moon? or at a trajectory that will allow the craft to meet with it 240 thou miles later as it will have traveled in space?
The latter, since the apogee is on the opposite side of the Earth from the perigee, which is where the ~5 minute translunar injection burn (TLI) took place.
(assuming it is the latter, why is the moon always visible as if straight ahead?
It isn't. They show it that way in the movies because it looks cool and the audience expects it (like showing stars in the background even though they would not be visible with sunlit objects in the foreground).
constant adjustments are not economical, so assuming minimal adjustments for course.
Very little course adjustments were necessary. The TLI burn would get them in the speed ballpark. While the spacecraft was coasting its trajectory was measured and adjustments were made using the RCS. Typically, these adjustments were on the order of only a few feet-per-second.
(3 days? - How far has the moon traveled thru space?)
Geometry problem: The Moon orbits Earth at an average radius of ~240,000 miles and takes ~27 days to complete a 360° orbit. How far will it travel in 3 days. Show your work.
Incidentally, the 3-day flight time was peculiar to the "figure-8" orbit described and shown above. It was not used for unmanned science probes. The first Soviet moon probe (Luna-3) took only 23 hours to reach the Moon in 1959, and the ESA's Smart-1 probe took months to get there using an ion engine in the 1990s. However, the 3-day trajectory is the only orbit that will swing your spacecraft around the Moon and send it back towards Earth with no extra rocket burns needed. This "Free-Return Trajectory" was considered the safest for manned missions and was used by the Soviet Zond missions (which were unmanned tests of craft intended for manned missions) and the first four Apollo lunar missions. Apollo 13 was the first mission to deviate from the FRT. After they stabilized the spacecraft following the Service Module explosion, their first order of business was to use the Lunar Module's engine to put them back on a Free-Return Trajectory.
Does all of this make sense?
Yes
OR point me in the direction for this info?
Bob Braeunig's Apollo PagesApollo by NumbersEncyclopedia AstronauticaThanks
Sure!
How much energy or joule or whatever does it require to alter course?
That depends on how much mass you're moving. Is the LM still attached? How much fuel (i.e. mass) is still in your tanks? Again, this is just stuff that you can plug into the Tsiolkovsky equation.
considering the lateral RCS Thruster are tiny?
It doesn't matter if they're small. In space all thrust counts, and it add up. Apollo 11 landed ~ 3 miles past its aim-point because the tunnel between it and the Command Module wasn't completely depressurized when they undocked. This extra little puff of air affected the LMs orbit and it wasn't caught until they were well into their powered descent. Fortunately they were more concerned with landing safely than landing accurately.
Do they blow Air or is it a fuel like a rocket?
They are hypergolic rockets that provide ~100lbs of thrust each.
How fast is the craft traveling as it reaches the moon...
I don't have the exact numbers handy, but a quick calculation shows that they were going at ~7,500 ft/sec as they rounded the Moon.
...and is it simply gravity itself that puts it into orbit?
No, to convert the elliptical orbit to circular, they had to burn their engine with the rocket facing the direction of travel to slow down by ~3,000 ft/sec. This put them in a roughly circular 2-hour orbit at an altitude of ~60 miles.
Hope this helps.
(Edit: Dang, ninja'd!)
