Anna Wilson, of Ilam School, asks :-

What are satellites made out of?

Roger Emery, a space scientist with the Rutherford-Appleton Laboratory in England, and who helped build the Infrared Space Observatory (ISO) satellite for the European Space Agency (ESA), responded.

Satellites are made of lots of materials. Each has to be tested to make sure it does not change in the high vacuum of space and can withstand the temperatures which can be very cold. Space agencies keep long lists of materials and components which they have tested for use in space, to help the engineers. These are often materials which combine strength with lightness, such as aluminium alloys or carbon fibre for the structure, since the cost of launching the satellite is mainly determined by its weight.

Apart from the structure of the satellite, there are many other parts, much of which involve electronics and the use of semiconductors, like silicon. These are needed for the satellite to receive command signals from the Earth and to send signals back, all controlled by a computer. This electronics looks much like the insides you find in a radio or television, but made using components selected for space, and specifically components that are not easily affected by the radiation in space. To provide the power for all this, photocells are used in the form of large panels to convert sunlight into electricity, and batteries are also used to store this power.

With these basic parts of the satellite sorted out, it also needs to include instruments so that it can perform its special jobs. Examples are cameras to look down at the Earth for weather satellites (Meteosat) or telescopes to look up for astronomy (Hubble Space Telescope). Some of these need the satellite to be controlled very carefully in position. For this, small gas jets are used, often with the actual position being measured by a camera designed to look at the stars.

So you can see, metals, special plastics and glasses are used to make satellites - with great care being taken in their selection and testing - and sometimes even gas or liquids in special containers.