Sun-Synchronous Orbit
A near-polar low Earth orbit where the satellite passes over any given point on Earth at the same local solar time on every pass.
Explanation
Sun-synchronous orbits (SSO) take advantage of Earth's equatorial bulge to create a controlled nodal precession — roughly one degree per day, matching Earth's orbit around the Sun. This keeps the angle between the orbital plane and the Sun nearly constant throughout the year. The effect is achieved by selecting a specific combination of altitude and inclination — typically between 600 and 800 kilometers at around 98 degrees inclination. The result is that a satellite in SSO crosses the equator at the same local time on every orbit, which provides consistent illumination conditions for imaging. This makes SSO the workhorse orbit for Earth observation, reconnaissance, and environmental monitoring. Landsat, Sentinel-2, and most commercial remote-sensing constellations operate in sun-synchronous orbits because repeatable lighting simplifies change detection, crop health analysis, and mapping.
Why It Matters
Consistent solar illumination is the single most important requirement for optical remote sensing. Without SSO, comparing satellite images taken days apart would be complicated by shifting shadows and changing Sun angles. SSO enabled the modern Earth-observation industry.
Concept Map
How Sun-Synchronous Orbit connects to other glossary terms:
Frequently Asked Questions
Why is SSO also called polar orbit?
SSO is a specific type of polar orbit. All SSOs are polar or near-polar, but not all polar orbits are sun-synchronous.
What happens to SSO over decades?
The orbit slowly drifts if uncorrected. Satellites with propulsion can perform small station-keeping maneuvers to maintain the sun-synchronous condition.
Sources
Last updated: July 1, 2026