2. What are satellites

Satellites are basically equipment platforms located in space. Each satellite has a 'payload' which describes its purpose. For example a satellite fitted with radio equipment is a 'communication satellite'. On the other hand a satellite fitted with weather measuring instruments is a 'weather satellite'.

Communication satellites send and receive data from one point on the Earth to another point on the Earth.

The flat parts extending above the satellite are solar panels. They convert sunlight into power that is then stored in a set of on-board batteries.

The batteries allow the satellite to work on the dark side of the planet.

The spiky bits are radio antennas that communicate with Earth stations located around the world. Some antennas are dished shaped, these are designed to only cover (illuminate) certain parts of the Earth. This area is called the 'satellite footprint'.

Satellites also contain small thruster motors.

Ground control can fire these thrusters every now and then to keep the satellite in its correct orbit.

In fact this is what sets the lifetime of the satellite - as soon as it has run out of motor fuel, it has to be switched off.

Otherwise it drifts and interferes with other satellites sharing the orbit.