Geosynchronous orbit

A geosynchronous orbit is a satellite orbit with an orbital period of the earth which corresponds to the rotational period ( sidereal day). The semi-major axis of the web is still 42157 km.

A geosynchronous satellite is theoretically in each cycle always above the same spot on the Earth's surface. Therefore perturbations fall due to the fact that the gravitational field of the earth is not rotationally symmetric, geosynchronous orbits so striking.

Uses geosynchronous satellites are communications, remote sensing and military surveillance. While geostationary satellites remain above a point on the equator, can be personalized with a system consisting of a few major geosynchronous satellite orbit inclination and regions at high latitudes cover without interruption.

Orbit classes

Inclined orbit

Geosynchronous orbits have inclination angles of 0 ° ( geostationary ) over 90 ° (polar path ) to 180 ° ( contrariness to the Earth's rotation ) and hot inclined geosynchronous orbit, geosynchronous orbit inclined English ( IGSO ).

Inclined orbits with low orbital inclination are used under the name of former inclined orbit geostationary communications satellites to extend their life at almost depleted fuel reserves. Since then, however, varies its position in the sky, such satellites can be received only with professional antennas with antenna tracking.

High Elliptical Orbits large inclination are called Tundra orbits.

The Quasi - Zenith Satellite System ( QZSS ) are a system of three satellites, which was planned for the improvement of GPS reception in Japan. Satellites on a 45 ° angled rail with an eccentricity of 0.09 and a Perigäumswinkel (argument of perigee ) of 270 °, eight hours almost vertically above the island.

Geostationary orbit

The special case of a circular orbit, the orbital inclination is zero and is oriented in the direction of east is, geostationary. The web speed is always 3,075 meters per second ( 11,070 km / h ), the orbital radius 42,157 km, which corresponds to a distance of about 35,786 km above the earth's surface.

From the Earth viewed from a geostationary satellite in the sky seems to stand still, as the observer on Earth at the same angular speed as the satellite. Therefore, this current path is commonly used for television and satellite communication. The antennas on the ground are firmly aligned to a certain point, and each satellite always covers the same area of ​​the world.

Formulas

To keep a body of mass with angular speed on a circular path with the radius, a centripetal force is the strength

Necessary. In a circular orbit around a planet gravity is approximately the only acting force. In the distance - from the center of the planet, starting - they can use the formula

Be calculated. This means the gravitation constant and the mass of the planet.

Since gravity so the only force that keeps the body on the circular path, its value must correspond to the centripetal force. Thus:

It is calculated by inserting:

Solving for yields:

The angular frequency is derived from the orbital period as:

Inserting into the formula for yields:

This formula now determines the radius of the geostationary orbit a center of mass from the center of the observed planets starting.

The removal of the web from the surface of the planet - for example the height of a geostationary satellite over the earth's surface - to be obtained, the radius must be subtracted from the result. Thus we have:

Where the radius of the planet referred to.

If the planet has a moon (eg moon) with known orbital data, and the third law of Kepler can alternatively

Apply to satellite and geostationary satellite.

In the example of a terrestrial satellite, the orbit data of the Moon can be used ( orbital period TMond ≈ 655 h, semi-major axis of the lunar orbit rMond ≈ 384000 km, Tsat = 24 h). Solving for the orbital radius of the geostationary satellite, which is the orbital radius of the circular path due to the same, becomes:

The height above the surface of the planet Earth here, is again obtained by subtracting the radius of the planet.

History

In the 1928 published book The problem of navigation of the space - the rocket motor by Herman Potočnik we find the first publication of the idea of a geostationary satellite.

In 1945 suggested the science fiction writer Arthur C. Clarke to position satellites in geostationary orbit. With three satellites in each case offset by 120 °, a radio communication would be possible worldwide. He assumed that within the next 25 years, satellites could be positioned there. With Syncom 2 in geosynchronous Syncom 3 and in the geostationary orbit, his idea was realized in 1963 and 1964 after about 19 ​​years.

The picture on the right shows the diagram in which Clarke presented his ideas in the magazine Wireless World to the public for the first time.