Sun Synchronous Orbit UPSC

Sun Synchronous Orbit

• Sun-synchronous orbit or a heliosynchronous orbit very important because of its particular importance to satellites intended for remote sensing and military applications. 
• A sun-synchronous orbit is one that lies in a plane that maintains a fixed angle with respect to the Earth-sun direction. 
• In other words, it combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. 
• We can say that the orbital plane in such a case has a fixed orientation with respect to the Earth-sun direction and the angle between the orbital plane and the Earth-sun line remains.

Features of Sun Synchronous Orbits:

1. The satellite passes over a given location on Earth every time at the same local solar time. Thus, it guarantees the same illumination condition, which varies only with seasons. 
2. The orbit is Quasi-polar in nature and so ensures coverage of the whole surface of the Earth. 
3. Every time a sun-synchronous satellite completes one revolution around the earth, it traverses a thin strip on the surface of the Earth. During the next revolution, it traverses another strip.

Advantages of Sun Synchronous Orbit :

• The satellites in this orbit can help in monitoring activities near the poles unlike other satellites.
• The orbit is designed in such a way that angle between orbital plane and sun remains constant resulting into consistent lighting conditions.
• Low altitude of this orbit allows good ground resolution.
• The Sun synchronous orbiting satellites cover entire globe on regular basis and provides repetitive coverage on periodic basis. Satellite passes over all places on earth having same latitude twice in each orbit at the same local suntime.
• It offers easy active measurements with the help of Radar or using Lidar.

Disadvantages of Sun Synchronous Orbit :

• The satellite launched in this orbit can not view a particular spot on the Earth's surface continuously. This is done by geosynchronous orbiting satellite.
• Sun synchronous orbiting satellite passes over polar parts on every orbital period which is 2 times a day where as geosynchronous orbiting satellite orbital period is approx. 24 hours. Hence Geosynchronous satellite can view a particular spot on the Earth's surface continuously.
• For weather forecasting the use of polar orbiting satellite data is limited unlike Geosynchronous orbiting satellite.