Satellite Communication

 I. Introduction

An artificial satellite is a manufactured object that continuously orbits the Earth or some other body in space. Most artificial satellites orbit the Earth. People use them to study the universe, help forecast weather, transfer telephone calls over the oceans, assist in the navigation of ships and aircraft, monitor crops and other resources, and support military activities.

Artificial satellites also have orbited the moon, the sun, asteroids, and the planets Venus, Mars, and Jupiter. Such satellites mainly gather information about the bodies they orbit.

Piloted spacecraft in orbit, such as space capsules, space shuttle orbiters, and space stations, are also considered artificial satellites. Artificial satellites differ from natural satellites, natural objects that orbit a planet. Earth\'s moon is a natural satellite.

The Soviet Union launched the first artificial satellite, Sputnik 1, in 1957. Since then, the United States and about 40 other countries have developed, launched, and operated satellites. Today, about 3,000 useful satellites and 6,000 pieces of space junk are orbiting Earth.

II. The early birds of the satellite story

  

The first artificial satellite, Sputnik 1 was launched by the Soviet Union on

4 October 1957. Sputnik 1 helped to identify the density of high atmospheric layers through measurement of its orbital change and provided data on radio-signal distribution in the ionosphere. The success ofSputnik ignited the so-called Space Race within the Cold War.

Sputnik 2 was launched on November 3, 1957 and carried the first living passenger into orbit, a dog named Laika.

Explorer 1 became the United States\' first satellite on January 31, 1958.

In June 1961, three-and-a-half years after the launch of Sputnik 1, the Air Force used resources of the United States Space Surveillance Network to catalog 115 Earth-orbiting satellites.

The largest artificial satellite currently orbiting the Earth is the International Space Station.

III. Types of Satellite

1. Killer Satellites are satellites that are armed and designed to take out enemy warheads, satellites and other space assets. They may have particle weapons, energy weapons, kinetic weapons, nuclear and/or conventional missiles and/or a combination of these weapons. Anti-satellite weapons (ASATs) are space weapons designed to incapacitate or destroy satellites for strategic military purposes. Currently, only the 

1. USA, the former USSR and the People\'s Republic of China are known to have developed these weapons.
2. Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects.
3. Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation.
4. Communication satellites are satellites stationed in space for the purpose of telecommunications. Modern communication satellites typically use geosynchronous orbits, Molniya orbits or Low Earth orbits (polar and non-polar Earth orbits). For fixed (point-to-point) services, communication satellites provide a microwave radio relay technology complementary to that of submarine communication cables. They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, and for TV and radio broadcasting, for which application of other technologies, such as cable, is impractical or impossible.
5. Miniaturized satellites are satellites of unusually low weights and small sizes. New classifications are used to categorize these satellites: minisatellite (500–200 kg), microsatellite (below 200 kg), nanosatellite (below 10 kg).
6. Navigational satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few metres in real time.
7. Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications. Little is known about the full power of these satellites, as governments who operate them usually keep information pertaining to their reconnaissance satellites classified.
8. Earth observation satellites are satellites intended for non-military uses such as environmental monitoring, meteorology, map making etc.
9. Space stations are man-made structures that are designed for human beings to live in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities — instead, other vehicles are used as transport to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.
10. Tether satellites are satellites which are connected to another satellite by a thin cable called a tether.
11. Weather satellites are primarily used to monitor Earth\'s weather and climate. 

IV. Communication Satellite

A communications satellite (comsat) is an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbits, other elliptical orbits and Low (polar and non-polar) Earth orbits.

For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that of submarine communication cables. They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, and for TV and radio broadcasting, for which application of other technologies, such as cable, is impractical or impossible.