Launching and Retrieving Satellites

Matthew D. / Physics #338 / 15 April 1997
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[ Launching ]
[ Falling From Orbit ][ Re-entry of a Satellite ]
Physics play a major role in the launching and retrieving of satellites. The launching and retrieving of a satellite are the most important part of a functioning satellite. Satellites are launched in many different ways including the use of space shuttles and rockets. There are many different ways of using the earth around you making it easier to launch a satellite, for instance the use of equatorial and polar orbits. The forces found in these orbits are also used for the re-entry of a satellite. Launching and retrieving of satellites depends on many factors which make it useful in the atmosphere.

Launching a Satellite

There are a variety of ways a satellite can be launched into orbit, mainly two. Space shuttles carry some satellites into space, but most satellites are launched by rockets that fall into the ocean after their fuel is spent. Many satellites require minor adjustments of their orbit before they begin to form their function. Built-in rockets called thrusters - some as small as a mechanical pencil - make these adjustments. Once a satellite is placed into orbit, it can remain there for a long period of time without further adjustments. Many satellites, when launched, are projected into the earth's atmosphere much like a space shuttle launched by NASA, except satellites are launched mainly for the use of scientists.

To take advantage of the speed of the earth's rotation, satellites are normally launched in a easterly direction. When they are launched into polar orbits, which means to move in a direction from the North Pole to the South Pole, their booster thrust must provide the whole orbital velocity. Polar orbits have certain advantages. In time, because the earth is rotating beneath it, the satellite will pass over its entire surface. In addition, as in an equatorial orbit, the movement of direction from east to west or vice versa. The satellite can be observed once in each revolution by a single tracking station, in this case at one of the poles. Polar and equatorial orbits help a satellite into orbit, using the earth's motion to give the satellite a extra "boost" into the atmosphere.

Falling From Orbit

Without any plan of re-entry, a satellite has forces acting on it , causing it to return to earth on its own. A satellite remains in orbit until its velocity decreases and the gravitational force pulls it down into the relatively dense part of the atmosphere. A satellite slows down due to the friction of air particles in the upper atmosphere and the gentle pressure of the sun's energy. When the gravitational force pulls the satellite down far enough, the air in front of it becomes so hot that most or all of the satellite burns up. There is not always a definite chance a satellite will make it back to the earth's surface in its entirety. It cannot with-stand the pressure of the earth's atmospheric pressure during movement through the orbit.

Re-entry of a Satellite

There are many elements which need to work for a satellite to return successfully. When re-entering, "the satellite tends to lose velocity faster and faster, because, as its apogee shortens, its ellipse loses more and more of its eccentricity, approaching a circular orbit and passing through perigee" (Jackson 202). Apogee is the point in the orbit of the moon or of a artificial satellite where it is farthest from the earth. Perigee is the exact opposite, it is the point nearest the earth. When the ellipse finally degenerates into a circle, the atmosphere is dragging continuously on the satellite. The perigee height becomes the apogee height, and the two switch back and forth as the satellite spirals in through the atmosphere.

" The satellite that broke free from the shuttle Columbia is to plunge back to the earth's atmosphere as in expected to burn up completely and not hit the ground. The fiery re-entry will be bright because of the 12 mile long tether dangling from the half- ton satellite" (NY Times C5).

The launching and retrieving of satellites involves many aspects of physics. These include the use of the earth itself and its motion as well as the atmosphere surrounding it. As stated, a satellite does not have to be launched or retrieved manually but can use the natural elements to provide us with the information we are looking for.


Jackson, Joseph. Pictoral Guide to the Planets. New York: Cromwell Company, 1973.

Oberright, John E. "Satellites, Artificial." World Book Encyclopedia. CD-ROM.

Chicago: World, 1995.

"Satellite On Wire to Plunge Tonight." NY Times. 19 March 1996: Pg. C5.