The semi-major axis of an orbit flown at a mean motion, in kilometres, by
Kepler's third law, the mean motion in revolutions a day as the Elements
give it. Unlike the apsides, which SGP4 reads off a record it
initialises from a whole set, this needs the one number, so a change in
mean altitude between two sets can be told from their mean motions alone:
the un-Kozai correction it leaves out moves the axis by a few kilometres
at most, and a change in it by a part in a thousand.
The semi-major axis of an orbit flown at a mean motion, in kilometres, by Kepler's third law, the mean motion in revolutions a day as the Elements give it. Unlike the apsides, which SGP4 reads off a record it initialises from a whole set, this needs the one number, so a change in mean altitude between two sets can be told from their mean motions alone: the un-Kozai correction it leaves out moves the axis by a few kilometres at most, and a change in it by a part in a thousand.