SATELLITE Introduction Satellites on the basis of nature are of two types: natural and artificial. Natural satellites are those which have been found in nature itself while artificial satellites are the man-made satellites that have been placed into orbit for radio, television and much other electronic communication. The first artificial satellite was “Sputnik 1”. Soviet Union launched it in 1957. After this, several thousands of satellites have been launched into the Earth’s orbit. Among then few are currently operating while other obit the earth as space debris. Satellites are also further of different types on the basis of its functions and uses. Like common types are military satellite and civilian Earth observation Satellite, communication satellite, weather satellites and research satellites. Spacecrafts in orbits are also a type of satellite. Different satellites orbit differently on the basis of the purpose of their use. Some of them are low Earth orbit, polar orbit and geo-stationary orbits. Satellites are generally controlled by computers. History of artificial satellites Soviet Union launched the world’s first artificial satellite named Sputnik 1 on October4, 1957. It helped in identifying the density of the atmospheric layers. It could measure the orbital changes and give data on radio signals distribution in the ionosphere. Sputnik 2 was launched again in the same year on November3. It carried the first living passenger, a dog named “Laika”. The cold-war of so-called Space Race arose among different nations. In July29, 1955 U.S. announced to launch its first satellite by the beginning of spring in 1958. Soviets on July 31st announced to launch a satellite by the end of 1957. U.S. launched its first satellite named as Explorer 1 on January 31 in 1958. International Space Station is the largest satellite which is currently orbiting the Earth. Space Surveillance Network (SNN) currently tracks more than 8,000 man-made orbiting objects out of 26,000 space objects. The rest of the space objects have re-entered Earth’s atmosphere and disintegrated. Space objects now orbiting earth weigh several tons to few pounds. Only seven percentages of them are operational satellite. The remaining others function as a space debris. Non-Military Satellite services Non military services are of three basic types. Fixed satellite services are the types which handle hundreds of billions of voice data and videos across all countries and continents or on earth’s surface. Mobile satellites systems connect remote regions ship, vehicles, aircrafts and peoples to another part of the world. It also serves as a navigation system. Scientific Research Satellites provides the world with various types of information relating basically to meteorology, radio, marine science, earth science and atmospheric research. Different types of satellites Killer satellites are armed which are designed to take out enemy warheads or satellites. They may contain particle weapons, kinetic weapons. Energy weapons, missiles, etc. Astronomy satellites are used for observing planets and galaxies. Biosatellites are those satellites that can carry living bodies for scientific research and experiments. Communication satellites are useful to telecommunication through different radio signals. Miniaturized satellites are small in sizes and weigh less. Navigational satellites use radio signals to enable the mobile users on the ground to navigate their desired location. Reconnaissance satellites are communication or Earth observation satellites. Earth observation satellites are sued for study of earth like meteorology, map making etc. Space stations are designed for human beings to live in outer space world while in research or experiments. Tether satellites are the satellites that are connected by tether, a thin cable. Weather satellites are used in studying Earth’s weather and climate. Satellite Modules A satellite module consists of different subsystems. Structural subsystem prevents the satellite from extreme temperature change and controls the satellite’s spin function. The telemetry subsystem is another module that transmits data to earth and receive earth control station commands. Power subsystem supplies the power to the satellite when the satellite faces the earth’s shadow. It consists of solar panels and backup batteries. The thermal control subsystem protects electronic equipments from being damaged due to extreme temperatures. The altitude and orbit controlled subsystem has a small rocket thruster which positions the satellite in correct orbits. Communication Pay load is the second major module of satellite. It is made up of transponders which are capable of receiving radio signals from earth station, amplifying received signals and directing the output signals to the proper download link antennas. After the mission completes, satellite should be de-orbited which rarely happens. Instead, they are left in their current orbit or moved to a graveyard orbit. However missiles from earth have been able to destroy the satellites. Russia, U.S. and China showed this capability of destruction of satellites after completion of mission. For instance weather satellite was destroyed in 2007 by Chinese Military. The technologies of satellite have made the world easy to transmit and receive the information. It also has been successful to transmit information about the outer world to earth. Thus, invention of such technology has been a great step in the field of science and technology.