Mean anomaly is a satellite's position along its orbit expressed as a uniform angle: the fraction of the period elapsed since perigee, times 360°. It advances at a constant rate even though the satellite itself speeds up and slows down — the clean timekeeping variable of orbital mechanics.
Understanding Mean Anomaly
The propagation pipeline
Every position you see on a tracking globe traces the same path: take the TLE's mean anomaly at epoch, add mean motion times elapsed time, solve Kepler's equation for eccentric anomaly, convert to true anomaly, then combine with the orbit's size, shape and orientation elements to get coordinates. SGP4 wraps this skeleton with perturbation corrections — drag, oblateness, lunisolar effects — but uniform-advancing mean anomaly remains the engine at its core.
Phasing constellations by mean anomaly
Constellation designers space satellites within a plane by assigning them evenly separated mean anomalies — eight satellites 45° of M apart share one orbit like beads on a rotating ring. Walker constellation notation extends this with a phasing offset between adjacent planes, so the whole shell interleaves: mean anomaly is the coordinate in which that choreography is written.