What is orbital period?
Orbital period is the time a satellite takes to complete one full revolution around Earth. It is determined entirely by orbital altitude (or more precisely, semi-major axis) through Kepler's third law: T² ∝ a³, where T is the period and a is the semi-major axis of the orbit. Higher altitude means longer period. At geostationary altitude (35,786 km), the orbital period exactly equals Earth's sidereal rotation period (23h 56m 4s), making the satellite appear stationary relative to the ground.
Period and coverage geometry
For LEO satellites, the short orbital period (95 minutes at 550 km) means rapid motion across the sky relative to any ground point. A single Starlink satellite at 550 km completes approximately 15.5 orbits per day. Each pass over a given ground location lasts only 5–10 minutes before the satellite drops below the horizon, which is why global broadband coverage requires thousands of satellites in coordinated constellations. By contrast, a single MEO GPS satellite at 12-hour period can serve a much larger swath of ground with fewer satellites.
Resonant orbits
Some missions exploit resonant orbits where the orbital period is a simple fraction of Earth's rotation period, causing the satellite to overfly the same ground tracks on a regular schedule. The Galileo navigation constellation uses a near-resonant period of 14.07 hours, producing a 10-day ground track repeat cycle that provides geometrically uniform coverage. Remote sensing constellations are often designed with specific repeat cycles (e.g., Sentinel-2 at 10-day exact repeat) to enable consistent multi-temporal image comparisons.