What is Satellite Communication?
A communications satellite is a specialized wireless receiver or transmitter receiving radio waves from one location and transmitting them to another (also known as a “bent pipe”) that is launched by a rocket and placed in orbit around the earth. Today, there are hundreds of commercial satellites in operation around the world. Those satellites are used for such diverse purposes as wide-area network communications, weather forecasting, television broadcasting, amateur radio communications, Internet access and the Global Positioning System.
Satellites have many important uses, not just communications. Most modern weather reports rely on satellite information. Global Positioning systems work because of a linked set of satellites. Scientific studies of our planet, the atmosphere and the universe all rely on satellites.
ORBITS
There are three areas for satellite orbits:
- GEO: Geostationary Earth Orbit
- MEO: Medium Earth Orbit
- LEO: Low Earth Orbit
GEO satellites orbit the earth directly over the equator, approximately 35 400 km (22 000 miles) up. At that altitude, one complete trip (orbit) around the earth takes 24 hours. Thus, the satellite remains over the same spot on the surface of the earth (geo) at all times, and stays fixed in the sky (stationary) from any point on the surface from which it can be "seen."
MEO is defined simply as the area between LEO and GEO. The primary satellite systems there are the GPS (Global Positioning System) satellite constellations.
LEO is between 200 and 1400 km above the earth. Satellites in LEO rapidly circle the earth and are typically in range of one location for only 90 minutes. Their main advantage is how close they are, providing shorter delays for faster communications. However, for consistent communications they require a constellation of satellites so that communications can be maintained as one satellite moves out of range and another moves within range of the ground station. LEO satellites are less expensive to build, typically less powerful, and have a shorter average life span.
A satellite is something that orbits, or goes around a larger something, like the Earth or another planet. Some satellites are natural, like the moon, which is a natural satellite of the Earth. Other satellites are made by scientists and technologists to go around the Earth and do certain jobs.
Some satellites send and receive television signals. The signal is sent from a station on the Earth's surface. The satellite receives the signal and rebroadcasts it to other places on the Earth. With the right number of satellites in space, one television program can be seen all over the world.
Some satellites send and receive telephone, fax, and computer communications. Satellites make it possible to communicate by telephone, fax, or computer with anyone in the world.
Other satellites observe the world's weather, feeding weather information into computer programs that help scientists know what the weather will be.
Still other satellites take very accurate pictures of the Earth's surface, sending back images that tell scientists about changes that are going on around the world and about crops, water, and other resources.
The satellite HS 376, built by Hughes Space and Communications Company. The HS 376 is used mostly for broadcast television and cable television.
The satellite HS 601 which is also built by Hughes Space and Communications Company. The HS 601 is used for many purposes, including direct broadcast TV. Direct broadcast TV is a new system of receiving television using a very small satellite dish. The television signal is relayed by an HS 601 satellite. The HS 601 also relays telephone, fax, and computer communications.
