Very high power planar power distribution for spacecraft bus control

Typical spacecraft power distribution system include some type of spacecraft power bus controller that serves as the summing point for the solar array, the battery, umbilical power and general spacecraft loads. A bus controller for a 3.2 KW spacecraft routes currents in excess of 135 A leading most manufacturers to use manual, expensive, point to point wiring to accomplish this task. By its very nature, such a connector pin and labor intensive operation has questionable reliability issues. A planar solution would be simple and ideal but is actually quite difficult since existing standards for a printed circuit board's current carrying capability stop at 35 A. SwRI has invested Internal Research funds to explore the limits of heavy copper PC boards for very high current power distribution. This paper discusses the processes and results of this internal research project. The research entailed fabricating a conceptual power board using standard printed circuit material and using the division's unique heavy plane manufacturing capability. The goals of this project were to answer key questions: can high currents (135 A) can be reliably routed within the planes of the printed circuit board in a space application and can division assets achieve adequate solder flow for the through-hole components in a thermally challenging printed circuit board. As part of this investigation, SwRI also implemented a current shunt as part of the planar assembly. Such an embedded current shunt reduces the number of manual operations and increases the overall reliability and manufacturability of the product. The concept employs methods to compensate for copper plane resistance change due to temperature. Several board designs were manufactured and instrumented with thermal sensors. Boards were selective soldered and solder flow evaluated. Various current levels up to and in excess of 135 A were then applied across the board assembly and the embedded current shunt while the self heating characteristics of the board were measured at atmospheric conditions. This paper provides the results of this study.