Some satellites can divide their signal into many movable spot beams. Like a tight, bright flashlight beam, a spot beam can be aimed at an exact small area on earth, then moved elsewhere to reach new or different customers. The area of the earth's surface covered by a satellite's signal is called the satellite's footprint. Satellites have a great deal of equipment packed inside them. A satellite has seven subsystems, and each one has its own work to do.
Satellites drift out of position because of solar wind or gravitational or magnetic forces.
When that happens, the thrusters are fired to move the satellite back into the right position in its orbit. The power subsystem generates electricity from the solar panels on the outside of the spacecraft. The solar panels also store electricity in storage batteries, which provide power when the sun isn't shining on the panels. The power is used to operate the communications subsystem. A Boeing 702 generates enough power at the end of its service life to operate two hundred 75-watt light bulbs.