Sun-synchronous orbit (SSO)

A sun-synchronous orbit (SSO) is a near-polar low Earth orbit tuned so the satellite passes over every location at the same local solar time on each visit.

This keeps lighting consistent, which is essential for Earth-observation and weather satellites that compare images taken days or years apart.

The trick exploits Earth's equatorial bulge, which slowly rotates the orbital plane by about one degree a day so it tracks the Sun.

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Related terms

LEO — Low Earth orbit (LEO) is the region of space from about 160 to 2,000 km above Earth's surface, where satellites circle the planet in roughly 90 minutes.
Orbital inclination — Orbital inclination is the angle between a satellite's orbital plane and Earth's equator, measured in degrees.
RAAN & the ascending node — The ascending node is where a satellite crosses the equator heading north; RAAN (right ascension of the ascending node) is the angle that fixes that crossing point in space.

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