Low Earth Orbit

LEO (Low Earth Orbit) satellite communication systems is a recent development of systems for mobile satellite communications that now exist, such as Inmarsat, AMSC. Mobile Satellite systems (satellites for mobile communications) are in operation today use satellite traveling 36,000 kilometers on the surface of the Earth and have STP 24-hour time. With a career that coincides with the equatorial zone, from a point on the Earth, the satellite appears as if the movement Geostationary Earth Orbit (GEO).

In December 1990, Motorola filed an application with the FCC for the purposes of constructing,

launching, and operating a LEO global mobile satellite system known as Iridium. This was the hot

button that sparked the world into a frenzy. Iridium was a concept of launching a series of 66

satellites

The concept of the LEO arrangement is shown. In this particular case, the satellites

are traversing the earth's surface at a height of 400+ nautical miles above the earth, in a polar orbit.

In the polar orbit, the satellite moves around the earth's poles and passes over any specific point

along its path very quickly. The satellites move at approximately 7,400 meters per second in

different orbits. Therefore, as one target site moves out of view, a new one comes into view at

approximately the same time. A handoff will take place between the individual satellites (using the

Ka band).

A variety of different types of satellite use the LEO orbit levels. These include different types and applications including:

-Communications satellites - some communications satellites including the Iridium phone system use LEO.

-Earth monitoring satellites use LEO as they are able to see the surface of the Earth more clearly as they are not so far away. They are also able to traverse the surface of the Earth.

-The International Space Station is in an LEO that varies between 320 km (199 miles) and 400 km (249 miles) above the Earth's surface. It can often be seen from the Earth's surface with the naked eye.

Space debris in LEO

Apart from the general congestion experienced in Low Earth Orbit, the situation is made much worse by the general level of space debris that exists.

There is a real and growing risk of collision and major damage - any collisions themselves are likely to create further space debris.

The US Joint Space Operations Center currently tracks over 8 500 objects that have dimensions larger than 10 centimetres. However debris with smaller dimensions can also cause significant damage and could render a satellite unserviceable after a collision.