Orbital period is the time a satellite takes to complete one revolution — about 90 minutes in low Earth orbit, 12 hours for navigation constellations, and 23 h 56 m at geostationary altitude. Period depends only on the orbit's size, not the satellite's mass.
Understanding Orbital Period
The period ladder
Reading altitude from period becomes second nature: ISS-class orbits tick just over 90 minutes and deliver ~15.5 orbits a day; Sun-synchronous imagers near 700 km run ~99 minutes; GPS-class semi-synchronous orbits complete two revolutions per sidereal day; and the one-sidereal-day geostationary period closes the ladder. Special rungs exist — the 12-hour Molniya orbit shares GNSS's period but spends it utterly differently, dwelling over one hemisphere.
Resonance and repeat cycles
When a period divides evenly into Earth's rotation, the ground track repeats: a satellite at exactly 15 orbits per day retraces its path daily. Designers tune periods a shade off resonance to make tracks march steadily in longitude, building repeat cycles of N days that guarantee a sensor revisits every point on a fixed schedule — the backbone of systematic Earth observation.