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The idea of a geosynchronous satellite for communication purposes was first published in 1928 by Herman Potočnik . The geostationary Orbit was first popularised by Science Fiction author Arthur C. Clarke in 1945 as a useful orbit for communications satellites. As a result this is sometimes referred to as the Clarke orbit. Similarly, the '''Clarke Belt''' is the part of space approximately 35,786 km above Mean Sea Level in the plane of the equator where near-geostationary orbits may be achieved. Geostationary orbits are useful because they cause a satellite to appear stationary with respect to a fixed point on the rotating Earth. As a result, an Antenna can point in a fixed direction and maintain a link with the satellite. The satellite orbits in the direction of the Earth's rotation, at an Altitude of approximately 35,786 Km (22,240 Statute Miles) above ground. This altitude is significant because it produces an Orbital Period equal to the Earth's period of Rotation , known as the Sidereal Day . USE IN ARTIFICIAL SATELLITES Geostationary orbits can only be achieved very close to the ring 35,786 km directly above the equator. In practice this means that all geostationary satellites have to exist on this ring, which poses problems for satellites needing to be decommissioned at the end of their service life (for example when they run out of thruster fuel). Such satelites will either continue to be used in Inclined Orbit s (where the orbital track appears to follow a figure-of-eight loop centred on the Equator) or be raised to a "graveyard" Disposal Orbit . A Geostationary Transfer Orbit is used to move a satellite from Low Earth Orbit (LEO) into a geostationary orbit. A worldwide network of operational geostationary satellites are used by meteorological satellites to provide visible, as well as infrared images of Earth's surface and atmosphere. These satellite systems include:
Most commercial Communications Satellite s and television satellites operate in geostationary orbits. (Russian television satellites have used Elliptical Molniya and Tundra orbits due to the high latitudes of the receiving audience.) A Statite , a hypothetical satellite that uses a Solar Sail to modify its orbit, could theoretically hold itself in a "geostationary" orbit with different altitude and/or inclination from the "traditional" equatorial geostationary orbit. However, this would rely on using the solar wind at high altitude outside the Earth's magnetosphere. DERIVATION OF GEOSTATIONARY ALTITUDE In any circular orbit, a satellite is neither plunging towards the earth nor flying away from it. Therefore, the inward and outward Force s on the satellite must equal each another (by Newton's First Law of motion). To calculate the geostationary orbit altitude, one begins with this equivalence and factors in the orbital period of one day. : By Newton's Second Law of motion, we can replace the forces with the Mass of the object multiplied by the Acceleration felt by the object due to that force: : We note that the mass of the satellite, , appears on both sides -- geostationary orbit is independent of the mass of the satellite. So calculating the altitude simplifies into calculating the point where the magnitudes of the Centrifugal Acceleration derived from orbital motion and the Centripetal Acceleration provided by Earth's gravity are equal. The Centrifugal Acceleration 's magnitude is: | ||
| :<math>a G | rac{M_e \cdot G}{r^2}</math> |
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