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Geosynchronous and Geostationary Orbits

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Geosynchronous Orbit

  • geosynchronous orbit (GSO) is an orbit around the Earth with an orbital period of one sidereal day, matching the Earth's sidereal rotation period (approximately 23 hours 56 minutes and 4 seconds). In other words we can say that Orbital speed of the satellite in geosynchronous orbit is same as the rotational speed of the Earth(23 hours 56 minutes and 4 seconds ). The synchronization of rotation and orbital period means that, for an observer on Earth's surface, an object in geosynchronous orbit returns to exactly the same position in the sky after a period of one sidereal day.
  • Key features:
    1. Orbital speed of satellite is same as earth’s rotational speed i.e, one sideral day which is 23 hours 56 minutes and 4 seconds.
    2. The geosynchronous orbital plane have an inclination with the equatorial plane means they are not in equatorial plane.
    3. It looks oscillating for a observer from the earth.
    4. Used for monitoring weather, communications and surveillance.
    5. There are infinite number of Geosynchronous Orbit. 

Geostationary Orbit

 

  • A geostationary equatorial orbit (GEO) is a circular geosynchronous orbit in the plane of the Earth's equator.
  • Key features: 
    1. Orbital speed of the satellite in geostationary orbit is same as the rotational speed of the Earth(One Sideral day i.e., 23 hours 56 minutes and 4 seconds ). Hence In geostationary orbit satellite remains in the same position i.e it seems to be at fixed spot for a observer from ground. Hence it is advantageous to use such satellite for direct broadcast, radio broadcasting, data relay, navigation and signal intelligence.
    2. A satellite in such an orbit is at an altitude of approximately 35,786 km (22,236 mi) above mean sea level.
    3. It lies in the equatorial plane means they have zero inclination with equatorial plane.
    4. Eccentricity of geostationary orbits are zero means they are circular and not elliptical
    5. There is ONLY one geostationary orbit.
    6. These satellites placed in geostationary orbit have trouble monitoring activities near the poles

Difference between Geosynchronous and Geostationary satellite

  • Key difference between Geosynchronous and Geostationary orbit is geostationary orbit lies on the same plane as the equator while the geosynchronous satellites has a different inclination from the equatorial plane.

Semi-synchronous orbit

  • A semi-synchronous orbit has an orbital period of ½ sidereal day (i.e., 11 hours and 58 minutes). Relative to Earth's surface, it has twice this period and hence appears to go around Earth once every day. Example orbits of the satellites in the Global Positioning System. These orbits are close to zero in eccentricity, meaning they are near-circular. semi-synchronous orbits are approximately 20,200 kilometers above the surface.

Sun Synchronous Orbit

  • These orbits are used for satellites that need a constant amount of sunlight. Satellites that take pictures of the Earth would work best with bright sunlight, while satellites that measure longwave radiation would work best in complete darkness.

  • Sun-synchronous orbit (SSO, also called a heliosynchronous orbit) is a nearly polar orbit around Earth (also called geocentric orbit) in which the satellite passes over any given point of the planet's surface at the same local mean solar time. Such an orbit can place a satellite in constant sunlight and is useful for imaging, spy, and weather satellites.

     


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