Preparing to test a standard triple junction solar cell

Power Systems

Like all other machines, a satellite needs a source of energy in order to function. As it launches away from Earth it will be running off an onboard battery – one last resource from its home planet – but to operate continuously for years on end more long-lived power sources are required. 

What is the Power Systems domain?

Power Systems cover all aspects of power generation, storage, conditioning, distribution and conversion for all types of space applications. Missions can last between a few minutes (launchers) to decades (interplanetary probes or the International Space Station ISS) and request from a few watts (cubesats) to tens of kilowatts (big telecommunication spacecraft, the ISS again). Therefore, finding the optimum combination of primary and secondary sources together with the architecture that will make the best use of them is the key paradigm of Power Systems engineering.

A launcher will live out of electrochemical sources, i.e. primary or secondary batteries, while a satellite in Earth orbit will rely on a solar generator backed by a battery when it is not yet deployed, just after launch, or when the spacecraft goes into the Earth shadow. Today most satellites rely on advanced solar cells with an efficiency around 30% and on Li-ion batteries. When the distance to the Sun becomes too large, i.e. typically beyond Jupiter, then the solar flux can no longer be used effectively and nuclear sources are the only option left.

The power sources being the heaviest equipment of any spacecraft, there is a constant push to increase their performances. Triple junction solar cells, which are the current state of the art, will be replaced by more efficient 4 to 6 junctions ones in the years to come. New battery technologies, like Litihum-Sulfur, are currently the subject of intense efforts to provide a new step forward in energy density.

In the field of power electronics, the trend is toward shrinking the size of the equipment and simultaneously increasing their efficiency, so that the power lost as thermal dissipation is reduced together with the area available to dissipate it. Here too, advanced components like Gallium Nitride (GaN) or Silicon Carbide (SiC) semiconductors are the subject of important development efforts to achieve both goals.

Last update: 17 March 2015

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