A geosynchronous orbit is a path around a planet or moon with a period identical to its rotation. Satellites in this orbit maintain a ground track of a single point on Earth’s surface. Telecommunications satellites maintain a Clarke orbit at an altitude of 22,236 miles. Satellites drift out of this orbit due to various factors, so they are equipped with thrusters to keep them in orbit. Supersynchronous and subsynchronous orbits are used for satellite disposal and position changes, respectively. Syncom 3 was the first satellite in geostationary orbit.
A geosynchronous orbit is a curved gravitational path around a planet or moon with a period of time identical to that planet or moon’s rotation. Specifically, the orbital period is considered to coincide with the sidereal day, the time it takes for a planet or moon to make one complete rotation. In the case of Earth, this is approximately 23 hours and 56 minutes. Usually, geosynchronous orbit refers to the synchronized rotation of an object around the Earth, commonly a satellite or spacecraft.
Any object with a geosynchronous orbit maintains a ground track of a single point on the Earth’s surface. A ground track is the location on the surface of the Earth below the satellite. This dot follows going around the world in the form of a figure eight, returning to the exact same place every day.
Telecommunications satellites, as well as other types of satellites, maintain a geosynchronous orbit known as a Clarke orbit. This is essentially a stationary orbit located at an altitude of 22,236 miles (35,786 km) above sea level. An object in Clarke’s orbit would always appear to maintain the same position above the planet. This concept was proposed by author Arthur C. Clarke specifically for communications satellites, as a way to ensure relative stability of point-to-point communications. All satellites orbiting at this altitude are part of the Clarke Belt.
A challenge in keeping objects in geosynchronous orbits is the fact that satellites drift out of this orbit. Factors such as solar winds, radiation pressure, and the effects of the gravitational fields of the Moon, the Sun, and the Earth itself can cause drift. To compensate for this effect, the satellites are equipped with thrusters that keep the object in orbit. This process is known as station holding.
There are some additional geosynchronous orbits outside the Clarke Belt to address position changes and satellite disposal. Supersynchronous orbit, located above normal geosynchronous orbit, is used to store or dispose of satellites or spacecraft that reach their operational end. Also known as a graveyard orbit, it is designed to limit the possibility of collisions with usable vehicles and maintains a directional westward path. Similarly, subsynchronous orbit falls below geosynchronous orbit and is generally used for objects that undergo changes in position. These objects maintain an east directional path.
The first satellite to be placed in geostationary orbit was Syncom 3, launched aboard a Delta D launch vehicle on August 19, 1964 from Cape Canaveral. It was used to broadcast the 1964 Summer Olympics from Tokyo to the United States. By the early 21st century, thousands of satellites from 50 countries had been launched into orbit, although only a few hundred are operational at any given time.
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