August 6, 2003

Power is everything

All satellite systems need electricity. It is usually supplied by solar panels made up of photovoltaic cells, which convert energy from photons in the Sun's rays into electrical energy. 

On a satellite in low-Earth orbit, solar energy incident on the solar cells provides a power of 1,400 watts per square metre.

But solar power systems are not very efficient, since only 200 watts per square metre of this energy is retrieved and used. As a result, the cells must be turned towards the Sun all the time to gain maximum power.

Certain interplanetary probes operating in deep space a very long way from the Sun have solar panels spanning 30 square metres and use nuclear radioisotope thermoelectric generators (RTGs) as a supplementary power source.

Power generated is used immediately by the satellite or stored in batteries so that systems can continue to function when the satellite passes in the Earth’s shadow or when it needs to draw extra power. 

Most energy consumed is converted to heat, which does not dissipate easily. Heat exchanges therefore have to be controlled to avert overheating or excessive cooling.
The satellite’s internal temperature is regulated by reflective and insulating blankets. Excess heat is rejected to space by radiators.
Did you know?
Heat transfer
In space, heat only propagates by radiation in the form of waves. On Earth, two other natural processes dissipate heat and regulate temperatures:
  • Conduction is the process by which heat is transferred by communication of kinetic energy from particle to particle
  • Convection is the process by which heat is transferred by displacement through a fluid

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