What Exactly is a Satellite?

According to its most basic definition, a satellite is anything that orbits something else. Satellites, other than moons, function in a variety of capacities from weather reporting to communications and from GPS data to solar monitoring. A communications satellite functions as a relay between points, for example, between a ship at sea and the port at which it docks or with weather stations. These satellites can have any number of orbit types such as geosynchronous, where the satellite is positioned to stay above a point on Earth at all times, or a Molniya orbit, which has an inclination of 63.4 degrees and is highly elliptical. Most of Earth's satellites have an LEO orbital type; LEO stands for Low Earth Orbit and has an altitude of up to thirteen hundred miles. All of the space shuttle missions have been in low Earth orbit, and the International Space Station is located in a low Earth Orbit.

Satellites are also used in remote sensing data recovery efforts by a multitude of government and private institutions. The idea of remote sensing has its roots in the early days of photography, when cameras were attached to the bottoms of balloons, and images were taken of the Earth from afar. The same idea has been placed in the space industry and satellite field of science with weather satellites.

Weather satellites give forecasters and meteorologists the ability to see the interactions of fronts, air masses and temperatures, to more accurately forecast the coming weather. The satellites can observe the planet without any obstructions or interference and can view much larger areas with better accuracy than ground based systems such as radar. The information can be compiled into massive databases that can then be extrapolated and formulated into forecasts and predictions about longer term weather conditions as well as climate changes. Weather satellites will be in one of two commonly used orbits; geosynchronous or polar orbits. Polar orbits use a low altitude orbit and the satellite will see or look at the same portion of Earth every twelve hours.

Scientific research is a primary use of satellites; by all standards and definitions the Hubble Space Telescope is in fact a satellite. Space weather is monitored closely, using a multitude of satellites and sensors in orbit around the Earth. The long range communications needed to control the Mars rovers and robots need to be transmitted via a satellite in order for information and orders to be received by NASA and by the machines. Satellites also function to give geologists and oceanographers information on the slight and miniature movements of the Earth's tectonic plates and climatologists the exact sea level and water temperatures.

The most well known application of satellites is for GPS locators in cell phones, cars, airplanes, military vehicles and merchant marine vessels. These satellites are in a higher Earth orbit and are always geosynchronous. At least four satellites must be visible to have the most accurate readings from the GOS receiver, and therefore GPS would not work with any other orbit such as a highly elliptical orbit. Elliptical orbiting satellites are the norm of any orbiting object; all orbits are elliptical in nature due to the effects of gravity. Basically, the satellite is closer to the orbited body at some point in its orbit than others. GPS systems were first used by governments until their recent introduction into the commercial market.