PASP Plus solar array parasitic current collection flight results

Solar cells at potentials positive with respect to a surrounding plasma collect electrons. Current is collected by the exposed high voltage surfaces: the interconnects and the sides of the solar cells. This current is a drain on the array power that can be significant for high-power arrays. In addition, this current influences the current balance that determines the floating potential of the spacecraft. One of the objectives of the Air Force (PL/GPS) PASP Plus (Photovoltaic Array Space Power Plus Diagnostics) experiment is an improved understanding of parasitic current collection. We have examined current collection flight data with the arrays facing the ram direction. Overall, the collecting area rises about two orders of magnitude as the applied bias rises one order of magnitude. This is typical of leakage current when snapover plays a role in the current collection process. The collecting area does not depend strongly on the plasma density. The collecting area is larger for lower densities (longer debye lengths). The dependence on density is stronger for lower densities. And there is a large amount of scatter. The current collected under similar conditions varies by a factor ten. We are using the flight data to validate the analytic formula developed. The formula can be used to quantify the parasitic current collected. Anticipating the parasitic current value allows the spacecraft designer to include this interaction when developing the design.