What is SSO?
A Sun-Synchronous Orbit (SSO) is a nearly polar orbit configured so that the orbital plane precesses at the same rate as Earth revolves around the Sun — approximately 1° per day eastward. The result: the satellite always crosses the equator at the same local solar time on every pass. At ~700 km, a typical SSO satellite has an inclination of about 98°, slightly retrograde relative to Earth's rotation.
Why consistent lighting matters
For Earth observation and remote sensing satellites, consistent solar illumination is critical. A camera passing over the Amazon at noon every day produces images with identical sun angles, making multi-temporal analysis — detecting deforestation, crop health changes, or disaster impact — far more accurate than images taken at random times with varying shadows and reflectance.
Dawn-dusk vs. noon-midnight SSO
Two popular variants exist. Dawn-dusk SSO orbits ride along Earth's terminator (the day-night boundary), keeping the satellite in near-continuous sunlight — ideal for power-hungry optical or radar payloads and for maximising solar panel charging. Noon-midnight SSO maximises sun angle for optical sensors. Major Earth observation constellations — ESA Sentinel series, Landsat, Planet Labs, ICEYE SAR satellites — operate in SSO.
Altitude and coverage
SSO altitudes typically range from 500 to 900 km. At 700 km, a satellite completes 14 orbits per day and revisits any given latitude approximately once every 1–3 days depending on swath width. The polar inclination means full global coverage including polar regions, unlike GEO satellites.