Satellite Orbits and Kepler's Laws

Artificial satellites follow the same Keplerian laws as planets. The choice of orbit—its altitude, shape, and inclination—depends on the satellite's mission, and each choice reflects the physics described by Kepler and Newton.

Low Earth Orbit (LEO)

Altitude: roughly 200–2,000 km above Earth's surface. Orbital period: about 90 minutes to 2 hours (Third Law). Used by the International Space Station, Earth observation satellites, and many communication satellite constellations (e.g., Starlink). The orbit is nearly circular (low eccentricity).

Geostationary Orbit (GEO)

Altitude: approximately 35,786 km. Orbital period: exactly 24 hours, matching Earth's rotation. A satellite in GEO appears to hover over the same spot on the equator. Using Kepler's Third Law with Earth's mass, you can calculate this altitude precisely. GEO is used by weather satellites, communication satellites, and some military assets.

Molniya Orbit

A highly elliptical orbit (First Law) with a period of about 12 hours. The satellite spends most of its time near apogee (farthest point) over the northern hemisphere, thanks to Kepler's Second Law—it moves slowly when far from Earth. Russia developed this orbit type to provide coverage at high latitudes where geostationary satellites are low on the horizon.

Sun-Synchronous Orbit

A polar LEO orbit whose plane precesses (rotates) at exactly the rate needed to stay aligned with the Sun. This is caused by Earth's equatorial bulge—an orbital perturbation that is deliberately exploited for consistent lighting conditions in satellite imagery.