How do satellites remain in their orbital plane, even as the Earth rotates around the sun?
Turns out that this process, called precession, is similar to the gyroscopic forces which act on a spinning bike wheel.
A sun-synchronous orbit (also called a heliosynchronous orbit) is an orbit around Earth with the right combination of altitude and inclination such that the Earth’s oblateness causes it’s orbital plane to precess once a year.
The end result is that the satellite will always cross the equator at roughly the same local time during each orbit, which means the lighting conditions are similar from one orbit to the next. This is essential for making the consistent measurements required for climate analysis.
This scene shows the precession of a polar orbiting satellite over the course of a year. The satellite’s orbital plane is indicated by the red torus and the Earth’s polar axis by the cyan line.