Communication: How Satellites Work

This article explains the different types of artificial satellites, how they remain in orbit, and what they are used for once there.

A satellite is any body that orbits a planet. Our moon is an example of a natural satellite. In the following article, we will discuss man-made, or artificial, satellites.

There are two main types of satellites: polar orbiting (revolving north to south, crossing over the poles) and geostationary (revolving above the equator at a speed that matches that of the earth's rotation). Satellites have many uses, including navigation, military surveillance, search-and-rescue, scientific study, communication, and weather forecasting, among others. Its intended use determines what type of orbit is used. For example, search-and-rescue and navigational satellites are generally polar orbiting, while the satellites used by weather services like the Weather Channel are geostationary.

In order for a satellite to function, it first has to get into space. Satellites are launched either with rockets, or carried by a Space Shuttle. Once the satellite has reached the desired distance from Earth (usually approximately 23,000 miles above the earth), it must revolve at a specific speed; too fast or too slow, and the satellite may fall back to Earth, or continue out into space because of the intense speed needed to escape Earth's gravitational pull. This ideal speed is known as orbital velocity. The closer the satellite is to Earth, the faster it must travel to remain in the proper orbit.

Once a satellite is in place, how does it work? All artificial satellites have the same basic components:

- the body, or bus, which is usually made mostly of metal;

- a power source, such as solar or nuclear, which powers rechargeable batteries;

- computers to control the various systems;

- a radio system and antenna, which allows the crew back on Earth to communicate with the satellite; and

- an attitude control system, or ACS, which keeps the satellite pointing in the right direction.

Depending upon the intended function, other specialized components are added. Weather satellites may contain cameras and forecasting equipment. Communication satellites, such as those used by telephone and television services, contain transponders, which receive signals, convert and amplify them, and send them back to Earth on a different frequency. Scientific satellites may contain science equipment and/or powerful telescopes. Military satellites may even contain missile detection or radar scanning equipment.

The first artificial satellite, Sputnik, was launched by the Soviet Union on October 4, 1957. It was fairly simple by today's standards. Intended chiefly to be used for scientific research purposes, it contained a battery, nitrogen gas, a radio transmitter, and a thermometer. Four antennas were attached to the outside of the metal ball bus, which was 23 inches wide and weighed 184 pounds.

Though most satellites contain rechargeable batteries, they don't last forever. Once the batteries die, the satellites are unable to receive or transmit any more signals. There are thousands of dead satellites that continue to revolve around the earth. These satellites, along with other debris such as discarded rocket boosters, are collectively known as "space junk." Sometimes, this debris is pulled toward the earth due to the planet's gravitational pull; in most cases, it burns up in the atmosphere before ever reaching the ground.

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