How Do Satellites Work?

Kayleen M. / Physics 336 #18 / 17 April 1997
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Satellites perform many functions. In order to carry out these functions, satellites use different subsystems. Basic Subsystems are groups of devices that help the instruments aboard a satellite work together and keep the satellite operating properly.


The communications subsystem of a satellite is essential to the function of all satellites. There are many different components used in spaceborne communications subsystems including: special antennas, receivers, and transmitters. All components must be highly reliable and low weight. Most satellites are fitted with beacons or transponders, which help with easy ground tracking. Global receive and transmit horns receive and transmit signals over wide areas on earth. Many satellites and ground stations have radio dishes that transmit and receive signals to communicate. The curved dishes reflect outgoing signals from the central horn and also reflect signals in incoming beams. Transmitting antennas transmit pictures at different frequencies and varying coverage. They also receive command signals from earth. A satellites ability to receive signals is also necessary in order to trigger the return of data or to correct a malfunction if possible.

Command and Data

Command and data subsystems are also extremely important to the functions of satellites. The command and data handling subsystems consist of computers that gather and process data from aboard a satellite. These computers then execute commands from the earth to the satellite.

The process of making physical measurements from a distance is called telemetry. The inputs of a satellites telemetric are received by any one of the satellites many sensors. The outputs are the "encoded information" that the satellite transmits to ground receivers for storage and later analysis (Urdway 289). Encoding is the transfer of output in a useful manner to earth. The communication of this data is key to the jobs of many satellites.

Power Supply

The power supply of a satellite is essential to all satellite functions. A satellite could not function at all without a power source. "The task of a satellites power supply subsystem is to accept the original power in whatever form it comes, condition it properly, and then relay it to the necessary on-board equipment" (Urdway 288). The power supply subsystem generates, stores, and distributes a satellites electrical power. The amount of electrical power required ranges, depending on the instrumentation and communications load on a satellite. It also depends on the lifetime of a satellite. There are many different types of power that may be used for a satellites power supply subsystem. Power can be supplied by short-lived fuel cells or batteries, by longlived solar cells, or by radioisotope devices.

Solar cells are very common in satellite power subsystems. They take solar energy available in space and convert it directly to electrical energy. Solar cells are often used with chemical batteries, which provide energy when the satellite is in the shadow of the earth. Solar cells are reliable and are usually used on scientific and applications satellites. Although, they are heavy, expensive, and take up a large volume. Fuel cells take fuel and oxidize it to produce power. The comparison of weight to the energy provided makes fuel cells less attractive, but they are often used in short satellite missions. Turbogenerators produce power from the heat of the sun or of nuclear reactions. Thermionic generators produce power from sunlight. In both of these, radioisotopes or small reactors produce heat. This is then converted into electricity. Radioisotope devices have been used, but are still in the developmental stages.


The functions of a satellite are carried out by different subsystems. The power supply subsystem of a satellite is the basis for all satellites functions. From the power source, satellites can communicate and receive and send data to and from earth. These subsystems together perform the functions that make satellites work.

Reference Section

Beatty, Kelly. "Galileo: An Image Gallery." Sky and Telescope. November 1996: cover.

Charyk, Joseph V., and Metzger, Sidney. "Satellite, Artificial." Groliers Multimedia

Encyclopedia. CDROM. Grolier Publishing, 1995.

"Nasa Communicates With Lost Satellite." New York Times. February 1996: A15.

Urdway, Frederick I. "Satellites, Artificial." Encyclopedia Americana: International

Edition. New York: Grolier Inc, 1996.