This equation computes the period of a satellite's retrograde orbit around the Earth in minutes based on the input of the change in longitude of the ascending node, `DeltaL`.

Notes

The Orbit Period, P, is equal to the time during which the Earth rotates through two successive intersections of the satellite track with equator, in other words the satellite passing two successive longitudes of the ascending node.

Orbits which move westward are referred to as retrograde orbits and for retrograde orbits we measure the change in longitude on successive orbits as positive to the West.

The definition of period does not apply for polar orbits.  A prograde or direct orbit has inclination i < `90^o`. A retrograde orbit has inclination i > `90^o`.  And a polar orbit has inclination i = `90^o`.