Presheath formation and area design limit satellite-based Langmuir probes

In this article, the effect of the finite conductive surface area of a satellite on the use of satellite-based Langmuir probes is reviewed in light of the basic theory of asymmetric double Langmuir probes (ADLPs). Recent theoretical and experimental studies have discussed electron sheath/presheath formation and the electron Bohm criterion along with their implications for satellite-based Langmuir probes. The effects predicted by the latest theory of the electron Bohm criterion were not experimentally observed and the experimental results remain supportive of a critical area ratio (A_L/A_S)_crit = (m_i/(2.3m_e))^1/2 between the probe area A_S and the satellite area A_L as conventionally believed. A satellite-based Langmuir probe must satisfy this criterion to physically act as a single Langmuir probe. However, experimental investigations also found that high-energy electrons adversely affect (A_L/A_S)_crit and a Langmuir probe's signal quality by giving additional electron current to A_L. Based on these results, a number of limitations of the maximum probe area are derived when designing satellite-based Langmuir probes, with consideration of both the aim of the satellite and the plasma where the satellite-based probe works. These proposed measures are expected to only partially alleviate the effect of the inadequate satellite surface area on the application of satellite-based Langmuir probes. Using a larger satellite to carry a Langmuir probe remains the most viable means to obtain precise space plasma parameters.