Sun-synchronous orbit
A near-polar orbit tilted so that the spacecraft passes over any given point on Earth at the same local solar time on every pass.
Constant local time means constant lighting: shadows fall the same way in every image of the same place, week after week. That is what makes two pictures taken months apart genuinely comparable, and it is why Earth-observation satellites live here almost by default. The orbit is not free - it is maintained by exploiting the bulge of the Earth to precess the orbital plane about one degree per day, which constrains altitude and inclination together. Pick the altitude and you have largely picked the inclination.
Sun-synchronous orbit accounts for 36 of the 350 missions we track, behind low Earth orbit (144) and polar orbit (47), and well ahead of geostationary transfer orbit (23). It is also the destination of SpaceX's Transporter rideshare line, which is why a single sun-synchronous launch can put dozens of unrelated Earth-observation satellites into the same lighting conditions on the same day.
- 2026-03-30 Falcon 9 Block 5 | Transporter 16 (Dedicated SSO Rideshare) Launch Successful
- 2026-07-07 Falcon 9 Block 5 | Transporter 17 (Dedicated SSO Rideshare) Launch Successful
- 2026-04-23 Electron | Kakushin Rising (JAXA Rideshare) Launch Successful
Polar orbit. Every sun-synchronous orbit is near-polar, but the reverse is not true: a polar orbit simply crosses near both poles, with no constraint tying it to local solar time. The distinction matters when reading a launch manifest, because the two are often used interchangeably in press material and they are not the same product.