This question appears in Mumbai University > Satellite Communication and Network subject

Marks: 6 M

Year: May 2015

A sun-synchronous orbit (SSO, and also called a heliosynchronous orbit) is a geocentric orbit that combines altitude and inclination in such a way that the satellite passes over any given point of the planet's surface at the same local solar time.

A sun-synchronous orbit during different seasons

In a sun-synchronous orbit the satellite crosses the same spot on the earth at the same local time each day, so that the same area of the earth can be viewed under approximately the same lighting conditions each day. So, the orbital cycle in a sun-synchronous orbit can be defined as a path taken by the satellite so that it passes over a certain part of the surface at exactly the same time every time with the same lighting conditions.

A sun-synchronous orbit is inclined slightly to the west of the North Pole. By definition, an orbital pass from south to north is referred to as an ascending pass, and from north to south as a descending pass.

This can make communication and various forms of data collection very convenient. For example, a satellite in a sun-synchronous orbit could measure the air quality of Ottawa at noon.

In a dawn-to-dusk type of sun-synchronous orbit, the satellite trails the Earth's shadow. When the sun shines on one side of the Earth, it casts a shadow on the opposite side of the Earth. (This shadow is night-time.) Because the satellite never moves into this shadow, the sun's light is always on it (sort of like perpetual daytime). Since the satellite is close to the shadow, the part of the Earth the satellite is directly above is always at sunset or sunrise. That is why this kind of orbit is called a dawn-dusk orbit. This allows the satellite to always have its solar panels in the sun.

Generally, sun-synchronous orbits are medium or low orbits.