Rene-NASA-Mooned-America

Space Navigation / Chap. 7 p. 60
The internal computer performs a series of rather complex calculations on the changing
frequency of the transmissions from that satellite. It then draws mathematical LOPs, finds
the intersection, and displays or prints your position, velocity, and much more. The accuracy
to a ground station can be about 50 meters (yards) and to ships at sea 200 yards. However it
wasn't until late in 1971 that this type of accuracy was achieved. 1
The one thing all three of these systems have in common is that the lines of position are
all drawn on the surface of the Earth, which drastically reduces the number of possible
positions. Even if you are in an airplane or submarine, your position is, relatively speaking,
on the Earth's surface. A surface is further divided into land and sea areas which are all
additional reference points when we are trying for a fix. The Earth also has a magnetic field
that tells us north from south, as well as celestial bodies that appear to rotate from east to
west as the day progresses.
Our celestial navigation by sextant depends upon our ability to "shoot" (measure angle
of elevation from the horizon) certain of the brighter navigational stars whose geographical
positions are easily determined. The navigator picks them out through familiarity with the
various constellations, which, though the stars do move, change shape so slowly that a
lifetime could pass before any change could be detected by so crude an instrument as even
the best sextant in the world.
With a sextant you can shoot a particular star and then correct the angle for various
mechanical and observational errors. What you really want is the angular distance of the star
from your zenith. But since the horizon is 90° from your zenith, you can subtract your
measured angle and determine the distance of that star's zenith from yours. From this you
can get an LOP just like we did in drawing # 1. Repetition of this process, using other stars,
will develop a fix as shown in drawing # 3.
Now let's turn to navigating in space. The only thing that the stars in any constellation
have in common is that they all share the same general direction from Earth. They have little
else in common except that they are all a part of our galaxy. Although each star itself is in
very rapid motion in relation to our Sun and the rest of the stars in that particular
configuration we call a constellation, they are so distant from our Earth that they seem to be
stationary. Were this not true, the "fixed" stars of constellations would become unrecognizable
in a short period of time. We know from historical records that they stay the same.
Michael Collins said, "The basic idea behind the Apollo guidance and navigation system
was simple enough. It all began with the stars, whose position in inertial space was well
known and unchanging.... They are so far away, of course, that they appear the same whether
one is on earth or a mere lunar distance away." 2
While preparing for the Moon landings he claimed that navigation was his personal hair
shirt. He goes on to say, "I had made several trips to Massachusetts Institute of Technology
near Boston, and had tried my level best to suffer through a couple of weeks of "simple"
explanations of the system by their experts, but I always came away shaking my head." 3
Perhaps he felt he was being told nonsense something like, "The framus wittigates on
the thrum rod activating the holcroid. Once it dizzies you are halfway home." Over the
NASA MOONED AMERICA! / Rene