I had never heard of a sun-synchronous orbit before. Intuitively it shouldn't work; if you're orbiting the earth in a plane perpendicular to the sun now, then in three months' time you'd expect to have moved round and the sun to be in that plane.

However, it turns out that the orbital plane can be made to precess by means of interaction with the earth's equatorial bulge: https://en.wikipedia.org/wiki/Sun-synchronous_orbit#Orbital_...