What are the Parts of a Satellite?

There are many kinds of satellites and many ways of building a satellite. Most satellites have similar parts, however. These parts include (1) radios to talk to people on earth; (2) rockets to move the satellite in space; (3) batteries to supply energy; and (4) computers to control the satellite. Some satellites also have cameras to take pictures from space.

Here is a picture of a typical communications satellite, which is made of many different parts.

• Antennas and transceivers send and receive radio signals to and from the Earth or another satellite;
• Rocket motors move the satellite in space;
• Fuel tanks store the fuel for the rocket;
• Solar panels use solar cells to turn the sun's energy into electricity;
• Batteries store the electricity generated by the solar panels; and.
• On-board processors provide the “brain” of the satellite and tell the satellite to do what humans want it to do.

In order for a satellite to work effectively, several different subsystems must work together:

A propulsion system is used to move the satellite in space. The propulsion system consists of a large rocket motor that is used to move the satellite into the desired location, as well as smaller thruster rockets that keep the satellite at that location. These motors are powered by electric or chemical fuel. Thrusters are needed because various natural forces cause satellites in orbit to drift out of position. These forces include the pressure of the solar wind, the effects of the Earth's and moon's gravity, and variations in the Earth's magnetic field.

An attitude control system keeps the satellite pointed towards the desired location on the Earth. If a satellite is not pointed in the right direction, or moves out of position, communications will be interrupted. Because a satellite is weightless in space, it is very susceptible to external forces of the Sun and Earth that will cause the satellite to move. There are two ways to control a satellite's attitude. First, the satellite can be spun up or down (usually between 30 and 300 rotations per minute, or “rpm”) around its axis which provides stability and keeps the satellite pointing in the right direction. These satellites are cylindrical in shape and often referred to as “spinners.”

The second method of controlling a satellite's attitude is by using a “momentum wheel”, which is a solid metallic disk driven by an electric motor. By spinning the disk, the stability of the satellite is maintained. Satellites using momentum disks are often called “three-axis stabilized” satellites.

The power system generates electricity from solar cells placed on panels outside of the satellite. On “spinner” satellites, the solar cells cover the outside of the satellite. On “three-axis stabilized” satellites, the solar panels extend out like wings from the satellite. The solar cells convert solar energy to electricity that is then stored in batteries inside the satellite and is used to power the electronics on board the satellite.

The communications system consists of antennas used to transmit and receive radio signals to and from the Earth, as well as electronic devices to strengthen or “amplify” these signals. These electronic devices are called “transponders.” They are called transponders because, in addition to amplifying radio signals, they also change the frequency of the radio signal.

A thermal control system is necessary to keep the electronics on board the satellite cool enough to work properly. Without thermal control, electronics would overheat and cease to work. The thermal control system releases unnecessary heat into space, so that it will not interfere with satellite operations.

A telemetry and command system consists of antennas and computers on board that satellite that allow people on the Earth to tell the station what to do and to monitor the health of the satellite. A satellite sends information about its operations, called “telemetry”, back to the Earth. Based on this information, operators send commands to the satellite.