What is a satellite?
A satellite is any object that orbits something else, as, for example, the Earth orbits the sun. There are hundreds of satellites in operation. They are used for diverse purposes such as weather forecasting, television signal, amateur radio and internet communications and the Global Positioning System. They are also used to look outward at the solar system for research and data gathering purposes.
In a communications context, a satellite is a specialized wireless receiver/transmitter that is launched by a rocket and placed in orbit around the Earth.
The Soviet Union launched the first manmade satellite in 1957. Sputnik I was about the size of a basketball and transmitted a simple Morse code signal over and over. In contrast, modern satellites can receive and retransmit thousands of signals simultaneously, from simple digital data to complex television programming.
How do satellites work?
Satellites are typically launched into orbit using a rocket. They are positioned at different heights and travel different tracks around the Earth at different speeds. Once in orbit, the Earth’s gravitational pull keeps the satellite from following a path straight out into space.
These devices usually have an antenna that lets them send and receive data. They also have a power source, typically a battery or solar power panels. Other equipment on a satellite depends on its purpose. They may have cameras, telescopes and sensors. The International Space Station is a complex satellite with living and working quarters for its inhabitants along with equipment for research.
The exact way a satellite works also depends on its purpose. One may collect images and other data from the solar system and transmit it back to Earth. Communication satellites capture signals sent from the Earth, increase their strength and retransmit them to receiving stations on Earth. Satellites are critical when transmitting television, radio, voice and data signals across virtually any distance.
Satellites do have transmission delays based on the distance a signal travels in its round-trip from Earth to the satellite and back to Earth. These transmission delays, also called propagation delays, are only a fraction of a second, but they can cause quality issues. Advances in technology have reduced these delays.
Why are satellites important?
Satellites serve a range of important purposes, including the following:
Earth surveillance and research. Satellites can view large parts of the Earth. This enables them to gather data and video signals quickly, typically faster than equipment at ground level. This information is used in various ways, including weather, climate and military applications.
Space data collection and research. Satellites also facilitate space exploration. Specialized systems, such as the Hubble Space Telescope, capture images of the solar system and celestial phenomena faster and more clearly than ground-based telescopes. They are not restricted by the Earth’s atmosphere, which reduces the level of image clarity.
Communications. Satellites extend the reach of ground-based communications systems that typically connect with a line-of-sight signal or wireline media such as copper or fiber optic cables. They also eliminate signal blockage by fixed objects on the ground, such as mountains and tall buildings.
What are the three satellite orbit types?
There are three types of communications satellite systems. They are categorized according to the type of orbit they follow.
Geostationary orbit
A geostationary satellite orbits the Earth over the equator, approximately 22,000 miles up. At that altitude, one complete trip around the Earth relative to the sun takes 24 hours. These satellites remain over the same spot on the Earth’s surface at all times. A geostationary satellite stays fixed in the sky from any point on the Earth’s surface from which it can be seen. Weather satellites are usually of this type.
A geostationary satellite can “see” approximately 40% of the Earth’s surface. Three such satellites, spaced at equal intervals — 120 angular degrees apart — can provide coverage of the entire inhabited world. A dish antenna aimed at the spot in the sky where the satellite is can access a satellite internet connection.
Low Earth orbit
A low Earth orbit (LEO) satellite system uses a large fleet of satellites, each in a circular orbit at a constant altitude of a few hundred miles. The orbits take the satellites over, or nearly over, the geographic poles. Each revolution takes from 90 minutes to a few hours. The fleet is arranged in such a way that at least one satellite is on a line of sight from any point on the Earth’s surface at any time.
The entire system operates in a manner similar to the way a cellular telephone functions. The main difference is that the transponders, or wireless receiver/transmitters, are moving rather than fixed, and are in space rather than on the Earth.
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