A sun-synchronous orbit, also known as a helio-synchronous orbit, is one thatlies in a plane that maintains a fixed angle with respect to the Earth–sun direction. Thus, the orbital plane has a fixed orientation with respect to the Earth–sun direction and the angle between the orbital plane and the Earth–sun line remains constant throughout the year, as shown in Figure.
As a result of this property, sun-synchronous orbits ensure that:
- The satellite passes over a given location on Earth every time at the same local solar time,thereby guaranteeing almost the same illumination conditions, varying only with seasons.
- The satellite ensures coverage of the whole surface of the Earth, being quasi-polar in nature.
Satellites in sun-synchronous orbits are particularly suited to applicationslike passive remote sensing, meteorological, military reconnaissance and atmosphericstudies