Special Case: Geosynchronous Inclined Orbit
A geostationary orbit occurs when an object (satellite) is placed approximately 37,000 km (23,000 mi) 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 small ellipse as the gravitational effects of other stellar bodies (Sun & Moon) exhibit influence over the satellite, as the effect accumulates over time the trace becomes an analemma with lobes oriented north-southward. The satellite traces the same analemma once each sidereal day.
A geostationary orbit is not stable. It takes regular manoeuvres to actively counteract the above gravitational forces. The majority of the fuel of the satellite, typically hydrazine is spent for this purpose. Otherwise, the satellite experiences a change in the inclination over time. At the end of the satellite's lifetime, when fuel approaches depletion, satellite operators may decide to omit these expensive manoeuvres to correct inclination and only control eccentricity. This prolongs the life-time of the satellite as it consumes less fuel over time, but the satellite can then only be used by ground antennae capable of following the north-south movement, Satellite Tracking earth stations. Before the fuel comes to an end, satellites can 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.
Read more about this topic: Inclined Orbit
Famous quotes containing the words special, inclined and/or orbit:
“A successful woman preacher was once asked what special obstacles have you met as a woman in the ministry? Not one, she answered, except the lack of a ministers wife.”
—Anna Garlin Spencer (18511931)
“It is always dangerous to generalise, but the American people, while infinitely generous, are a hard and strong race and, but for the few cemeteries I have seen, I am inclined to think they never die.”
—Margot Asquith (18641945)
“The human spirit is itself the most wonderful fairy tale that can possibly be. What a magnificent world lies enclosed within our bosoms! No solar orbit hems it in, the inexhaustible wealth of the total visible creation is outweighed by its riches!”
—E.T.A.W. (Ernst Theodor Amadeus Wilhelm)