A car without wheels or an engine is of little value. In the same way, there are certain parts that must be built into a satellite.
Most spacecraft depend on batteries and solar cells for their power supply. Solar cells are wafer-like pieces of silicon or other materials which produce electricity when sunlight falls on them.
If thousands of these cells are linked in large panels to form the solar panels, they can power a sizeable spacecraft. The cells also charge batteries whenever they are in sunlight. When a spacecraft goes into shadow, the batteries take over.
Spacecraft carry several antennas. These function like ears and provide communication links with Earth. The most important of these is a dish up to 2 m across that can send and receive large amounts of data and information.
The spacecraft’s brain is its computer system. Data can be stored in the computer memory or sent back to Earth in real time via the antennas.
The computer also stores instructions on how to operate the spacecraft. This provides a back up in case contact is lost or a breakdown occurs.
Spacecraft also need small engines to navigate in space. There are different types of engines.
Spacecraft turn and roll by firing thrusters. These send hot gases into space at high speed. Some satellites have ion engines. These use a strong electric field to propel gas into space.