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.
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.
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