📘 Definition
Mean motion is the average angular velocity of a satellite, expressed in revolutions per day in TLE format. The ISS has a mean motion of approximately 15.5, meaning it orbits Earth about 15.5 times per day (roughly every 93 minutes). A GEO satellite has a mean motion of approximately 1.0 (one orbit per day). Mean motion can be converted to orbital period and semi-major axis, making it a compact way to encode orbital size. Formula: period (minutes) = 1440 / mean motion.
15.5 rev/day
ISS
1.0 rev/day
GEO
2.0 rev/day
GPS
1440 / n (minutes)
Period Formula