Equinoctial Coordinate Type

The Equinoctial coordinate type uses the center of the Earth as the origin and the plane of the satellite's orbit as the reference plane.

The equinoctial coordinate type is not available if a Fixed coordinate system is selected.

The advantage of this element set is that singularities are limited to retrograde equatorial orbits, parabolic/hyperbolic orbits and collision orbits. The Keplerian element (right ascension of ascending node) is undefined when the inclination is 0 and is numerically unstable for an inclination near 0. As the inclination approaches zero, the line of nodes becomes indeterminate. The Keplerian element (argument of perigee) becomes singular when the eccentricity is zero. As eccentricity approaches zero, the line of apsides becomes indeterminate. The Air Force Satellite Control Network (AFSCN) typically solves for the equinoctial elements during the orbit estimation process.

Equinoctial coordinate type elements

Option	Description
Orbit Size	Semimajor Axis (default) - Half the length of the major axis of the orbital ellipse. Mean Motion- The average angular rate of the satellite based on 2 body motion.
h/k/p/q	h / k collectively describe the shape of the satellite's orbit and the position of perigee. p/q collectively describe the orientation of the satellite's orbit plane: where , where posigrade formulation indicates +1 and retrograde formulation indicates -1.
Mean Longitude	Specifies a satellite's position within its orbit at epoch and equals the sum of the classical Right Ascension of the Ascending Node, Argument of Perigee, and Mean Anomaly. Longitude is:
Formulation	Retrograde, which has its singularity at an inclination of 0 deg. Posigrade, which has its singularity at an inclination of 180 deg.