Satellite Power Systems

The Basics

Satellite power modules are widely known as electrical power systems, or EPS. If you are purchasing Cubesat components as a kit, the EPS will come as a self contained unit, usually with batteries attached, and with proper connectors for solar panel arrays and voltage bus distribution. The EPS can be broken down conceptually into four smaller blocks. They are the Power Source, the Energy Storage, the Power Distribution, and the Power Regulation and Control modules.

Power Sources

There are many power sources available to the budding satellite designer. One might find useful applications for nuclear generators (RTGs), or regenerative fuel cells. That being said, most all satellites use photovoltaic cells. When it comes to power generation, this is the one important component you should know. The solar cells are managed via a peak power tracker or PPT unit which is discussed in the [Power Distribution] section.

Energy Storage

Most satellites store their power through a set of primary and secondary batteries. One can find a table of industry standard batteries and their characteristics below.

Table of primary batteries.

Table of secondary batteries

Power Distribution

It is typical to single a single PDS in smaller satellites. In larger satellites it is not uncommon to have multiple distribution systems for collections of components. Typically a distribution bus will contain rails of 5v, and 3.3v for Cubesats. For special applications and different desired rail voltages, a modified EPS may be required. This is the critical module that handles voltage protection, isolation, and fault detection within the power block.

The PDS also typically contains the Peak Power Tracking, PPT module. The PPT monitors the solar panels and places the appropriate load resistance across the solar panel terminals in order to draw the maximum amount of power from them. Solar panels have a non-linear IV curve, which means their output power changes across loads and voltages. As the sunlight changes the voltage, the PPT adjusts the load to match.

Solar cell operating characteristics graph. Caption: the PPT keeps the solar pannels operating along the center line of peak performance.

Power Regulation

Lead into discussion about PPT in Power Distribution.

Change organization to just power sources; solar. Power storage batteries. Power distribution; bus for different sized sats PPT system. Pwr regulation, shunt resistors, Thermal regulation.

Nominal values for Off the shelf components.

Resources to Learn More

MIT open courseware http://ocw.mit.edu/courses/aeronautics-and-astronautics/16-851-satellite-engineering-fall-2003/index.htm