Sun-synchronous orbits are designed to ensure what about ground track timing?

• A. They pass over a given region at roughly the same local solar time.
• B. They maintain constant altitude above sea level.
• C. They remain fixed relative to the stars.
• D. They cross the equator every orbit.

Answer: (A)

The main idea is that a sun-synchronous orbit is arranged so a satellite crosses over the same region at roughly the same local solar time on each pass. This happens because the orbital plane is designed to precess westward at a fixed rate due to Earth's equatorial bulge, and the altitude and inclination are chosen so that this nodal regression matches the apparent daily motion of the Sun. As Earth orbits the Sun, the Sun’s direction relative to the Earth changes; aligning the orbital plane so that its orientation to the Sun stays nearly constant keeps the ground track timing (the local solar time of crossings) the same from pass to pass. This yields consistent lighting conditions for imaging, which is why sun-synchronous orbits are favored for Earth-observation missions. The altitude stays roughly constant as a practical matter, but that alone doesn’t guarantee the same local solar time; the key is the deliberate, Sun-synchronous precession of the orbital plane.