Artificial satellites are placed in different orbits according to their mission objectives. Two important orbits used in space technology are geosynchronous orbit and sun-synchronous orbit. A geosynchronous orbit is useful for continuous coverage of a region, while a sun-synchronous orbit is useful for repeated Earth observation under similar lighting conditions.
Geosynchronous Orbit
A geosynchronous orbit is an Earth-centred orbit in which a satellite takes about 24 hours to complete one revolution around the Earth. Thus, its orbital period matches the Earth’s rotation period. It is usually placed at an altitude of about 35,786 km.
If a geosynchronous satellite has zero inclination and circular orbit, it becomes a geostationary satellite and appears fixed over one point on the equator.
Applications of geosynchronous/geostationary satellites:
- Communication: They support television broadcasting, telecommunication, internet services and satellite phones.
- Weather monitoring: Satellites like INSAT-3D, INSAT-3DR and INSAT-3DS provide continuous weather observation over India.
- Disaster warning: They help in cyclone tracking, flood alerts and disaster communication.
- Navigation support: Some regional navigation systems use geosynchronous/geostationary satellites.
- Strategic communication: Defence and emergency networks use them for wide-area communication.
The INSAT system is one of the largest domestic communication satellite systems in the Asia-Pacific region, with operational communication satellites placed in geostationary orbit. It supports telecommunications, TV broadcasting, weather forecasting, disaster warning and search-and-rescue services.
Sun-Synchronous Orbit
A sun-synchronous orbit (SSO) is a near-polar orbit in which the satellite passes over a given place on Earth at nearly the same local solar time during each visit. It is generally a low Earth orbit, often around 600–900 km altitude.
This orbit allows satellites to capture images under similar sunlight conditions. Therefore, scientists can compare images taken on different days more accurately.
Applications of sun-synchronous satellites:
- Remote sensing: They help monitor land, water, forests, agriculture and urban areas.
- Cartography: Satellites such as Cartosat series support mapping and planning.
- Agriculture: They help assess crop area, crop health and drought conditions.
- Disaster management: They provide data for floods, landslides, forest fires and cyclones.
- Environment monitoring: They track glaciers, forests, wetlands, coastal zones and pollution.
- Security and surveillance: High-resolution imaging supports border management and strategic assessment.
ISRO states that Earth observation satellite data supports agriculture, water resources, urban planning, rural development, mineral prospecting, environment, forestry, ocean resources and disaster management.
Difference in Applications
The difference in applications comes from their orbital behaviour:
- Geosynchronous satellites stay linked to the same region, so they suit communication and continuous weather monitoring.
- Sun-synchronous satellites revisit places with similar lighting, so they suit imaging, mapping and resource monitoring.
- Geosynchronous orbit gives wider coverage but lower image resolution due to high altitude.
- Sun-synchronous orbit gives better spatial resolution but covers a region only during periodic passes.
Conclusion
Thus, geosynchronous and sun-synchronous orbits serve different but complementary purposes. Geosynchronous satellites strengthen communication, broadcasting and weather services, while sun-synchronous satellites support remote sensing, mapping, disaster management and environmental monitoring. Together, they make space technology useful for governance, economy, security and sustainable development.
