As I understand it, 6 numbers are needed to completely specify elliptical motion of satellites. This is so that we can constrain the exact shape and position of the object moving in this elliptical path. Conceptually,
The semi-major axis number constrains the size of the ellipse.
The semi-minor axis number (thus, by calculation eccentricity) constrains the roundness of the ellipse.
The inclination contrains the tilt of the orbit, or how much it is tilting from the equator plane.
The longitude of the ascending node constains the swivel amount of the orbit, or how much the earth needs to be rotated to fit the orbital path of this satellite.
The argument of periapsis?
I am not sure why this constrain is needed? Since the ellipse is already constrained in shape and roundness by [1] and [2], and its inclination/swivel is already constrained by [3] and [4], isn't this enough to completely constrain the position of the perigree of this orbit?
If not, can anyone please help explain how might we for example manipulate the pedigree (closest point to the earth) after [1], [2], [3], [4] is already fixed?
Thank you!
The argument of periapsis describes the orientation of the major axis of the elliptical orbit in the plane determined by the ellipse. It is the angle measured between the vector along the major axis and the ascending node vector.