The Floating Potential Probe (FPP) for ISS: Operations and Initial Results

In this paper we report early results from the Floating Potential Probe (FPP) recently installed on the International Space Station (ISS). The data show that FPP properly measures the electrical potential of ISS structure with respect to the plasma it is flying through. FPP Langmuir probe data seem to give accurate measurements of the ambient plasma density, and are generally consistent with the IRI-90 model. FPP data are used to judge the performance of the ISS Plasma Contacting Units (PCUs), and to evaluate the extent of ISS charging in the absence of the PCUs.