Ioonos

A real ball of energy

Energy is vital for life in general and satellites in particular. Mid-air refuelling is impossible! So satellites can only rely upon two sources of energy: fuel on board, which must be used as sparingly as possible, since it is what is used to correct the satellite’s orbit, and electricity that it has to produce, store and distribute itself in order to operate. To do that, when their direction towards the sun permits, we use solar panels, which are a sort of second skin made up of sensors that cover the satellite’s entire shell. So does this strange insect, the satellite, have wings or not?

Where is the electricity socket?

That’s right, you’ve understood, we have to be able to catch solar energy. And it’s not as simple as that. It requires photovoltaic cells, often made of gallium arsenide, a semiconductor that transforms solar photons into electrons and then into electricity. But this requires a very large amount of photovoltaic cells, and thus very large solar panels, since energy is lost on the way.

Can’t one stop moving a bit?

Actually, no. Everything moves, even in space. The solar panels must be perpendicular to the sun’s rays to work properly. So you have to constantly change the position of the panels (which requires even more energy!) and separate the movement from the rest of the satellite, which has to keep facing the Earth to communicate with it. What’s more satellites, especially those in orbit" >low orbit that pass very quickly over the Earth often find themselves in its shade. So they need batteries that can store energy for distribution when there is no sun. And as you will have already found out with your digital Walkman, a battery does not last forever…

Be ECONOMICAL

Communications satellites are very greedy: normally they have to receive a signal, amplify it and rebroadcast it. Satellites that are equipped with passive instrumentation, that is, which only receive data, use less. But they all have to be economical: for example, their onboard electronics is designed to use power frugally. As a result, a “greedy” satellite only uses about 10 kilowatts of electrical power, which is the electrical power of a medium-sized flat.