by Emil Morhardt
CubeSats are cool. No, actually very cold, since they’re out in space. But they are reproducing like rabbits. There are well over 200 of these little 10 cm X 10 cm X 10 cm cube satellites have been launched into orbit by tucking them into the nooks and crannies in the launch vehicles around much larger satellites. (Some are multiples of cubes, 10 cm X 20 cm, or 30 cm.) They need energy. Until now they have been powered in the main by lithium ion batteries like those in your computer, and charged by the photovoltaic panels that make up a CubeSat’s skin. The thing is that these batteries don’t work very well when they are cold; the speed of electrochemical reactions, just like those of every other chemical reaction, are modulated by temperature—the colder the slower. The current Li-ion batteries don’t work at all below –10°C, yet CubeSats headed for deep space are expected to encounter temperatures of –40°C some of the time. So if you have a CubeSat process that needs power at low temperatures or a short-term burst of power faster than the batteries can provide, you need help.Supercapacitors, even though they don’t hold as much charge per volume as a lithium ion battery, don’t much care what the temperature is plus they charge and discharge much faster than batteries. It makes sense then that some enterprising engineers would combine the two systems to get the benefits of both; the engineers in question are at the CalTech Jet Propulsion Laboratory and at Cal State University, Northridge, nearby. They have just completed a study demonstrating that this hybrid system will solve the problem. The general idea is similar to combining supercapacitors with battery banks to help windpower installations integrate better with the grid (see my Aug 2, 2014 post), but in this case the system is much smaller and in addition to delivering power rapidly without damaging the batteries, it operates at temperatures lower than any wind farm is likely encounter.
Chin, K., Smart, M., Brandon, E., Bolotin, G., Palmer, N., Katz, S., Flynn, J., 2014. Li-ion battery and super-capacitor Hybrid energy system for low temperature SmallSat applications. SSC-14-VII-9, 28th Annual AIAA/USU Conference on Small Satellites. Conference paper at: http://bit.ly/1uEavqH