Why is Power and Energy Conversion important?
A reliable, ongoing power supply is essential to a space mission's success. The Sun provides around 1.4 kilowatts of power per square metre in low-Earth orbit - a bountiful resource that spacecraft designers do their very best to take advantage of. This is why the majority of spacecraft incorporate wing-like solar arrays or else have them layered across their hull.
These are composed of linked photovoltaic cells which produce an electrical current when light shines on them –working like the light emitting diodes of (LEDs) in a modern car dashboard but in reverse.
But this free availability of power does not mean designing a satellite's power system is an easy task. Photovoltaic cells efficiency remains comparatively low at 28% for the latest designs, and their efficiency is further reduced by heating from the Sun and radiation damage during a satellite's lifetime. This means solar arrays have to built on a large scale to deliver useful power levels, on the order of tens of square metres for a typical communications satellite.
Most satellites have orbits that will take them out of the Sun into shadow behind the Earth – for a low-Earth orbiting spacecraft that occurs once per orbit – so they are also equipped with rechargeable ('secondary') batteries to keep them powered in the meantime.
A satellite's electrical loads will generally vary depending on which instruments or subsystems are running at a particular time. So the supply needs to be regulated to ensure they are producing a level of power equal to that required by the satellite. The electricity is then distributed to the various elements requiring it, overseen by the power system.
The power system also incorporates conditioning and conversion devices to prevent harmful current surges and switch voltages as required – power leads for home computers having their own versions of these.
Last update: 18 November 2009
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