Orbits of Satellites

Jered B. / Physics 338 / 19 May 1997
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A satellite is a device which resides in space, intended for observation, research, or communication that is in orbit around the earth. In order for it do a specific job it requires a certain orbit.

Different Types of Satellite Orbits

Most satellites are placed into orbit by multistage booster rockets that are released after the fuel is consumed. Once the satellite is about two hundred miles from the earth's surface it is free from the earth's drag on it. Some orbits are circular while others are elliptical, or oval shaped. Satellites that have an elliptical orbit, have both an apogee and a perigee. An apogee is the satellites farthest point from the center of the earth. The perigee is when it is closest to the earth's center. The altitude of the orbit decides on the period of time it takes to complete one orbit, this is called the orbital period. In order for the satellite to remain in orbit, the satellite needs to maintain a constant velocity while the earth's pull of gravity keeps it in orbit. The velocity helps the satellite to try to escape the atmosphere but the earth's gravity holds it in orbit.

Satellites that have low altitude orbits are a couple hundred miles above the earth's surface. The satellites are in the earth's atmosphere, but in the highest level and can orbit the earth in ninety minutes. The satellite can be very large with this type of orbit and less propulsion is needed. There is little air resistance against them but they only stay in orbit for a short time, about a couple of weeks to a month.

An orbit that takes about twenty-four hours to revolve around the earth is called a geosynchronous orbit or a high altitude orbit. It is about 22,282 miles from the earth's surface and stays in the same spot over the earth at all times, because it is moving at the same speed as the earth. A satellite in this orbit moves in the same direction as the earth along the equator. While moving along the equator line, the satellite moves slightly up and down along the line forming a sort of figure eight. For a satellite to be put into this type of orbit a very powerful launch vehicle is needed.

Another type of orbit that is similar to the geosynchronous orbit is the geostationary orbit. A satellite in the geostationary orbit circles the earth at the same altitude as the geosynchronous orbit, at 22,282 miles but orbits directly over the equator with out moving up or down. To get a satellite to maintain this orbit is very difficult and often impossible. Both the geosynchronous and the geostationary orbits are good for communication, broadcasting, and weather satellites.

A third type of orbit is the sun-synchronous orbit or the polar orbit. It passes over the North and South poles. Its "orbit requires one entire earth year to make a full revolution about the sun. As observed from the position of the sun, the satellite orbit plane remains in the same apparent orientation throughout the year" (Parker 42). In a day a satellite in this orbit makes about fifteen revolutions and a good use for it is reconnaissance satellites.

Placing a Satellite in Orbit

"In order for a satellite to be orbited, it must be propelled at a velocity that imparts enough energy to keep it in that orbit with out the application of additional force. If the orbit is low, the resistance of the outer most atmosphere will cause the satellite to lose orbital speed and reenter the atmosphere" (Encyclopedia America 288). Once a satellites velocity decreases it will start to fall from orbit and the gravitational force of the earth pulls it down into a dense part of the atmosphere. Eventually the satellite is pulled down far enough into the atmosphere. When this happens the satellite rapidly compresses the air in front of it. This causes the air to become so hot, that all or most of the satellite will burn up.


For a satellite the type of orbit and the amount of velocity are two key roles in order for a satellite to do its job. The type of orbit the satellite takes depends upon the job it has to do. The velocity plays a key role in a satellites orbit, in that the speed that the satellite is going will decide if it will remain in orbit.


Parker, Sybil P. "Satellite" McGraw Hill Encyclopedia of Science and

Technology. New York: McGraw Hill Inc., 1992. Volume 16, pgs. 41-


Satellite, Artificial. Encyclopedia America International Edition. Danbury:

Grolier Incorporated, 1994. Volume 24, pgs. 286-290.

Satellite, Artificial. The World Book Encyclopedia. Chicago: World Book Inc., 1995. Volume 1, pgs. 150-150c.

Space Satellites. New book of Popular Science. Danbury: Grolier Incorporated, 1994. Volume 1, pgs. 304-305.

VanDoren, Charles. "Satellite" Science and Technology Illustrated.

Chicago: Encyclopedia Britannica, 1984. Volume 23, pgs. 2830-2831