Orbital Period
The time a satellite takes to complete one full revolution around its primary body.
Explanation
Orbital period is determined by Kepler's third law: the square of the period is proportional to the cube of the semi-major axis. For Earth orbits, the period of a circular orbit is about 90 minutes at 400 km altitude (typical LEO), about 12 hours for a semi-synchronous orbit (like GPS at 20,200 km), and 24 hours for geosynchronous orbit (35,786 km). Period is also affected by orbital eccentricity — a satellite in an elliptical orbit moves faster at perigee and slower at apogee, but the mean period still follows Kepler's law. Period is a fundamental parameter for mission planning: it determines how often a satellite passes over a given point, how frequently it enters eclipse, and how ground tracks evolve over time. For Earth observation, period directly affects revisit time.
Why It Matters
Orbital period governs the timing of everything a satellite does — communication passes, imaging opportunities, eclipse duration, and orbital maintenance scheduling.
Concept Map
How Orbital Period connects to other glossary terms:
Frequently Asked Questions
How is orbital period calculated?
For a circular orbit around Earth, period = 2π × sqrt(a³/μ), where a is the orbital radius and μ is Earth's gravitational parameter (398,600 km³/s²).
Do all satellites at the same altitude have the same period?
Nearly, for circular orbits. Eccentricity slightly affects the mean period, and perturbations from Earth's J2 effect cause small variations.
Sources
Last updated: July 1, 2026