The Anatomy of a Satellite


Satellites have 6 basic parts:
1.  Satellite housing-  The shape of the housing (outside container) of the satellite depends upon the
     system employed to keep the satellite within the orbit at a stabalized altitude.  If the satellite has a
     three-axis stabilization system, its housing will be rectangular with solar panels protruding from two
     opposite sides.  If the satellite has a spin stabilization system, the housing will be cylindrical.  The
     solar cells will be mounted on the surface of the cylinder.  The antenna will be connected on the body
     by a rotating bearing to keep it pointed in a fixed direction.
2.  Power System-  Satellites must have a continuous source of electrical power.  The two most common
     power sources are high performance batteries and solar cells.  Solar cells are lightweight, resilient, and
     their efficiencies have been improving over the years.  There is one large problem with solar panels.
     Twice a year geosynchronous orbit will go into a series of eclipses where the sun is screened by the
     earth.  To solve this problem, batteries are used as supplemental on-board energy sources.
3.  Antenna System- has two jobs:
    a.  Receive and transmit telecommunications signals
    b.  Provide tracking, telemetry, and command functions which maintain the satellite's operation in
4.  Command and Control System-  The "brain" of the satellite.  It monitors the satellite to ensure
     that all vital operating parameters are working.  It receives the data from the earth station, interprets
     the commands, and relays the processed information to earth.
5.  Station keeping-  To ensure that the satellite stays in its orbit, this system employs the controlled
     ejection of hydrazine gas from thruster nozzles.  The useful life of a satellite is over when its several
     hundred pounds supply of hydrazine gas is depleted.  (Average life span=10 years)
6.  Transponders-  Electronic mechanisms that amplify the frequency of an uplink signal for
     retransmission to earth.

                                        ""        Created by Wendy Chick, Andrea Boyle,
                                            Last updated  May 19, 1999                                  Mark Helfman, and Matt Poynton.
                    Background borrowed from Digital Satellites.