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Types of Satellites and Their Uses

Many types of satellites are in constant orbit around the Earth. Some space satellites travel deeper into the solar system to orbit other planets and bodies, including the sun. Each has a specific job, whether it's as a storm-tracker, communications station or as part of our nation's military surveillance operations.

Any object that orbits another is technically a satellite. Natural satellites include the moon, as it orbits Earth, along with comets and so-called space junk. Artificial satellites are those that are man-made and provide useful information for everyday use and scientific advancement.

Different Types of Satellites

Each type of satellite has a specific purpose, which means it also carries different equipment according to use. General classifications include:

communications
military
navigational
scientific
weather.

Among these groups, some applications overlap from government and business to civilian use.

Communications satellites are vital to our everyday lives. They're responsible for beaming signals around the world for a host of correspondence devices, including:

computers
fax machines
pagers
telephones
television.

They may act singly, accepting radio waves from ground-based systems. They can also coordinate as a constellation in a low orbit, passing those signals along to other high-orbit satellites before they reach the ground. Communications satellites may also carry transponders that keep those bouncing signals from distorting before they reach their final destination.

Military satellites provide a number of services to the government and private sector. They do act as spy satellites and perform reconnaissance missions within their orbits. These satellites can also:

observe land and sea transport movements
offer navigational assistance
provide top-secret communications on secure channels
track weather.

Navigational satellites have been around for many years. They provide location data to ships and planes. Vehicles now incorporate global positioning systems (GPS) and even individuals can carry handheld systems to avoid getting lost. These satellites work as a platform of networks that send and receive radio signals. By using a series of distance calculations from various satellites, the source is quickly identified.

Scientific, or research, satellites operate in several different ways. They may focus on the Earth or can be catapulted into space to study the universe. Many contain telescopes in hopes of making far-reaching new discoveries. Others, equipped with cameras, provide important information on what lies below the Earth's surface. These satellites don't just orbit the Earth; many of them are assigned to follow the sun or other planetary systems.

Scientific satellites' uses are numerous and include:

crop studies
freshwater depletion tracking
locating pollution sources.

Weather satellites relay real-time information to meteorologists and databases around the world. They provide instant information that individuals can access through most means of communications. These satellites are capable of assessing atmospheric conditions and can collect information through infrared or standard cameras. Weather satellites are also vital in following the paths of storms, including hurricanes and cyclones.

Scientists rely on weather satellites to study existing patterns and compare changes. In order to collect the widest range of data, these satellites travel in various orbits, but the greatest value to scientific research are those that track in the same spot each day.

In the highest orbits, some satellites can view up to 50 percent of the Earth's surface. That makes them valuable in search and rescue as well; they're equipped to detect transponder distress signals.

Types of Satellites and Their Orbits

In order to do their jobs, different types of satellites launch into orbit at varying altitudes. The basic altitude levels are:

Low Earth Orbit (LEO): up to 1,240 miles.
Medium Earth Orbit (MEO): up to 22, 240 miles.
Highly Elliptical Orbit (HEO): characterized by a low-altitude perigee and an extremely high-altitude apogee
Geosynchronous Orbit (GEO): approximately 22,300 miles.

Within that framework, satellite orbits sometimes make reference to more specific paths:

Geostationary orbit is similar to geosynchronous orbiting, but satellites track directly above the equator. The majority of communications devices are geostationary satellites, and they remain fixed on one spot with a 24-hour rotation.
Low Earth orbits contain numerous satellites that move at lightning speeds. These typically circle the earth every 90 minutes. Generally used in military surveillance operations, they can track vehicles at close range and provide detailed information in real time. Their lifespan is short, however, compared to stationary satellites.
Molniya (geosynchronous) orbits follow the rotation of the Earth. Satellites in this range follow a 24-hour pattern, often in a high-elliptical, or egg-shaped, track. Some communications satellites take this longitudinal set path, moving at top speed when out of range and slowing when they can receive signals.
Sun-synchronous orbits, or polar orbits, place satellites in a fixed path based on the sun's location. Many weather satellites follow this orbit, circling the Earth several times a day to provide accurate forecasting and storm tracking data.

Countries that Launch Satellites

The Soviet Union launched the first satellite into space in 1957. Sputnik I prompted other countries to join in the race for newer and better technologies. Today, several countries continue efforts to place and keep devices in orbit. Agencies, including NASA and the European Space Agency, from around the world also work in cooperation to gain greater knowledge.

Currently, the leading countries with known satellites in operation include:

Australia
Canada
China
France
India
Israel
Japan
Soviet Union
United Kingdom
United States.

Others countries with the capabilities of launching different types of satellites exist, but they have yet to be successful. Some use the launching facilities of other countries to place their own satellites in orbit.

Resources

Library.thinkquest.org (n.d.) Satellites. Retrieved January 23, 2008, from the Oracle Education Foundation ThinkQuest Web site: http://library.thinkquest.org/J0112188/satellites.htm.

Oberright, John E. (2004). "Satellite, Artificial." Retrieved January 23, 2008, from the World Book Online Reference Center/World Book, Inc. Web site: http://www.worldbookonline.com/wb/Article?id=ar492220.

Satellites.spaces.im.org (n.d.).Weather Satellites. Retrieved January 23, 2008, from the Satellites Web site: http://www.satellites.spacesim.org/english/engineer/
copy/weather/index.html.

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