Inclined orbit

A satellite is said to occupy an inclined orbit around the Earth if the orbit exhibits an angle other than zero degrees with the equatorial plane. This angle is called the orbit's inclination.

Special case: geosynchronous inclined orbit

A geostationary orbit occurs when an object (satellite) is placed approximately 37,000 km (22,300 miles) above the Earth's equator with the characteristic that, from a fixed observation point on the Earth's surface, it appears motionless. A satellite is in an inclined orbit when its orbital plane is tipped some number of degrees from the horizontal defined by the equator. In the case of an inclined geosynchronous orbit, although the satellite remains geosynchronous (that is, completing one orbit around the earth every 24 hours), it is no longer geostationary. From a fixed observation point on Earth, it would appear to trace out a figure-eight with lobes oriented north-southward once every twenty-four hours.

A geostationary orbit is not stable. It takes regular manoeuvers to actively control it. The majority of the fuel spent for this purpose is to counteract the gravitational forces of Sun and Moon which mainly increase the inclination over time. At the end of the satellite's lifetime, when fuel approaches depletion, satellite operators may decide on omitting inclination manoeuvres and only control eccentricity. This could prolong the life-time of the satellite as it needs less fuel. On the other hand the satellite can only be used by ground antennae capable of following abovementioned north-south movement. Before the fuel comes to an end, satellites shall be moved to a graveyard orbit to keep the geostationary altitude free for subsequent missions.

NASA maintains a Java based real-time display of most commercial satellites which can be helpful in visualizing the various orbits.

ee also

* List of orbits

External links

*http://science.nasa.gov/RealTime/jtrack/3d/