Post by JorP on Oct 23, 2002 9:43:06 GMT -5
What is a Satellite?
A satellite is any smaller object traveling around a larger object. By this definition, the Moon is a satellite to the Earth and the Earth is a satellite to the Sun. However, for this reference, a satellite is a human-made spacecraft placed in space to orbit another body. These spacecraft can be crewed, such as the Space Shuttle, or uncrewed, such as NASA's Hubble Space Telescope. They can be sent into space with the intention that they will not be recovered, or they can be designed to be recovered or repaired by Space Shuttle crews.
Satellites may be either active or passive. Passive satellites contain no radio transmitters or other energy signals, but rather only reflect signals beamed at them from Earth. Active satellites collect data and emit radio signals that transmit the information down to Earth.
Satellites are designed to serve one of three general purposes: space science, applications, or communications. Space science satellites carry instruments to study the Sun, measure magnetic fields or to examine the universe in the different energy wavelengths of the electromagnetic spectrum, including gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves. Application satellites survey the Earth's resources and supply weather photographs and other information to forecasters. Communication satellites relay telephone calls and television signals, transmit scientific information from other satellites down to Earth, and relay voice communications between the astronauts orbiting on the Space Shuttle and mission controllers on Earth.
Communications Satellites
Communications Satellites have been around since 1958. A communications satellite is a spacecraft that orbits the Earth and relays messages, radio, telephone and television signals. Stations on the ground, called earth stations, transmit signals to the satellite, which then relays the signal to other earth stations. As a newer form of communications, communications satellites are very useful in bringing the people in the world together. Communications between people that used to take days or even months, now take only minutes or seconds using satellites.
First Satellites
The first satellite to relay messages from one Earth Station to another was SCORE (Signal Communicating by Orbiting Relay Equipment) launched December 18, 1958. These early satellites, because they were visible from both sides of the Atlantic Ocean simultaneous for only a short time could provide only a period of five hours a day for communications.
In 1960 the United States launched the Echo satellite, a metallic balloon that reflected signals. Later satellites, such as Telestar and Relay, included electronic relay equipment called transponders. Syncom II, the first satellite to be placed in a synchronous orbit, was launched in 1963. The first commercial communications satellites were launched in 1965.
Relaying of Signals
This relaying of signals from one Earth Station to another is done through the satellite's transponder. Most communications satellites have more than one transponder and antenna so that they can relay several users of radio waves or signals at the same time.
Launch of Communication Satellites
Communications satellites are launched by rockets or carried into space by the Space Shuttle. Once in space, small engines on the satellites guide the satellite into orbit and help keep them there. Most communications satellites are placed in orbit at an altitude of 22,300 miles above the Earth. This is known as a geostationary or synchronous orbit. This allows the satellite to orbit the Earth at the same speed as the rotation of the Earth. As a result, the satellite appears to be stationary above the same location on Earth.
Satellite Broadcast Range
Broadcasts from a satellite in synchronous orbit can cover only about one third of the Earth's surface. To send signals anywhere in the world, three communications satellites in geostationary orbit are needed.
Communication
Communications satellites will be used to link all the regions and people of the world. This is a giant step from the early uses of communication satellites. "What at the beginning of the decade, was no more than a concept in the minds of a few engineers had, by the end, become a fully commercial system providing global communication system" (Fishlock 23). This global system will consist of many satellites, positioned in geostationary orbit, providing high bandwidth capacity, interconnect many highly specialized Earth Stations operating in more than thirty countries. This network, already in progress by consortiums headed by Motorola (Iridium) will provide the framework and capability for anyone in the world to communicate with anyone else, regardless of location.
A satellite is any smaller object traveling around a larger object. By this definition, the Moon is a satellite to the Earth and the Earth is a satellite to the Sun. However, for this reference, a satellite is a human-made spacecraft placed in space to orbit another body. These spacecraft can be crewed, such as the Space Shuttle, or uncrewed, such as NASA's Hubble Space Telescope. They can be sent into space with the intention that they will not be recovered, or they can be designed to be recovered or repaired by Space Shuttle crews.
Satellites may be either active or passive. Passive satellites contain no radio transmitters or other energy signals, but rather only reflect signals beamed at them from Earth. Active satellites collect data and emit radio signals that transmit the information down to Earth.
Satellites are designed to serve one of three general purposes: space science, applications, or communications. Space science satellites carry instruments to study the Sun, measure magnetic fields or to examine the universe in the different energy wavelengths of the electromagnetic spectrum, including gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves. Application satellites survey the Earth's resources and supply weather photographs and other information to forecasters. Communication satellites relay telephone calls and television signals, transmit scientific information from other satellites down to Earth, and relay voice communications between the astronauts orbiting on the Space Shuttle and mission controllers on Earth.
Communications Satellites
Communications Satellites have been around since 1958. A communications satellite is a spacecraft that orbits the Earth and relays messages, radio, telephone and television signals. Stations on the ground, called earth stations, transmit signals to the satellite, which then relays the signal to other earth stations. As a newer form of communications, communications satellites are very useful in bringing the people in the world together. Communications between people that used to take days or even months, now take only minutes or seconds using satellites.
First Satellites
The first satellite to relay messages from one Earth Station to another was SCORE (Signal Communicating by Orbiting Relay Equipment) launched December 18, 1958. These early satellites, because they were visible from both sides of the Atlantic Ocean simultaneous for only a short time could provide only a period of five hours a day for communications.
In 1960 the United States launched the Echo satellite, a metallic balloon that reflected signals. Later satellites, such as Telestar and Relay, included electronic relay equipment called transponders. Syncom II, the first satellite to be placed in a synchronous orbit, was launched in 1963. The first commercial communications satellites were launched in 1965.
Relaying of Signals
This relaying of signals from one Earth Station to another is done through the satellite's transponder. Most communications satellites have more than one transponder and antenna so that they can relay several users of radio waves or signals at the same time.
Launch of Communication Satellites
Communications satellites are launched by rockets or carried into space by the Space Shuttle. Once in space, small engines on the satellites guide the satellite into orbit and help keep them there. Most communications satellites are placed in orbit at an altitude of 22,300 miles above the Earth. This is known as a geostationary or synchronous orbit. This allows the satellite to orbit the Earth at the same speed as the rotation of the Earth. As a result, the satellite appears to be stationary above the same location on Earth.
Satellite Broadcast Range
Broadcasts from a satellite in synchronous orbit can cover only about one third of the Earth's surface. To send signals anywhere in the world, three communications satellites in geostationary orbit are needed.
Communication
Communications satellites will be used to link all the regions and people of the world. This is a giant step from the early uses of communication satellites. "What at the beginning of the decade, was no more than a concept in the minds of a few engineers had, by the end, become a fully commercial system providing global communication system" (Fishlock 23). This global system will consist of many satellites, positioned in geostationary orbit, providing high bandwidth capacity, interconnect many highly specialized Earth Stations operating in more than thirty countries. This network, already in progress by consortiums headed by Motorola (Iridium) will provide the framework and capability for anyone in the world to communicate with anyone else, regardless of location.