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The Floating Potential Measurement Unit (FPMU) has been operational on board the International Space Station (ISS) since 2006. One of the instruments in the FPMU suite is a spherical wide‐sweeping Langmuir probe, referred to as the WLP, which is sampled at a temporal cadence of 1 s giving in‐situ measurements of the plasma density and electron temperature. In this study we present our refinements to the Langmuir probe analysis algorithm that address the uncertainties associated with photoelectron emission current from the metal probe. We also derive the fraction of O+ ions as a secondary data product, which shows decrease in O+ abundance in the post‐midnight sector during solar minimum. The derived plasma parameters are compared and validated with an independent in‐situ measurement technique, overlapping ground‐based incoherent scatter radar measurements, as well as International Reference Ionosphere model output. The reduced data set spans the entire solar cycle 24 and shows the F‐region ionosphere variance at ISS altitudes. Key Points: Langmuir probe measurements of plasma parameters in Earth's F‐region ionosphere over Solar Cycle 24Reduced parameters include plasma density, electron temperature, and O+ fraction which are validated using plasma impedance probe and Incoherent Scatter Radar observationsAlgorithm details of analyzing a Langmuir probe IV curve in ionospheric space plasma are provided [ABSTRACT FROM AUTHOR]

The validation of the floating potential measurement unit (FPMU) plasma density and temperature measurements is an important step in the process of evaluating International Space Station (ISS) spacecraft charging issues including vehicle arcing and hazards to crew during extravehicular activities. The highest potentials observed on the Space Station are due to the combined Vsp x B effects on a large spacecraft and the collection of ionospheric electron and ion currents by the 160-V U.S. solar array modules. The ionospheric plasma environment is needed for input to the ISS spacecraft charging models used to predict the severity and frequency of occurrence of ISS charging hazards. The validation of these charging models requires the comparison of their predictions with measured FPMU values. The FPMU measurements themselves must also be validated for use in manned flight safety work. This paper presents preliminary results from a comparison of densities and temperatures derived from the FPMU Langmuir probes and plasma impedance probe with the independent density and temperature measurements from a spaceborne ultraviolet imager, a ground-based incoherent scatter radar, and ionosonde sites. [ABSTRACT FROM AUTHOR]