Impact of Miniaturized Fixed-Bias Multineedle Langmuir Probes on CubeSats

Kinetic simulation results are presented to study the response of multineedle Langmuir probes of the type used on many satellites. Simulations of isolated probes are used to parameterize the current collected as a function of voltage for a set of densities and temperatures relevant to the Earth's ionosphere. These simulations also serve to assess the validity of analytic results obtained from the orbital motion limited (OML) theory used in recent studies. Computed probe characteristics are then fitted with empirical scaling laws and used to account for electron current collected by needle probes on a typical triple CubeSat. These fits are then used to determine the impact of the probes and guards on the spacecraft floating potential for a nominal configuration of bias voltages, over the plasma parameters of interest. In order for the probes to work as intended, they must operate at a positive potential with respect to the ambient plasma. However, the results show that for the cases considered, the spacecraft floating potential is so low that the probe with the lowest voltage becomes negative. Possible solutions are examined and proposed to ensure that all probes remain at a positive voltage with respect to surrounding plasma.