Multi-Needle Langmuir Probe System for Electron Density Measurements and Active Spacecraft Potential Control on CubeSats

In this paper, we present the CubeSat version of a scientific instrument called the multi-Needle Langmuir Probe (m-NLP). The m-NLP instrument measures the electron density in the ionosphere with kHz sampling rate, yielding meter scale resolution on low Earth orbit satellites. The sounding rocket version of m-NLP has flight heritage from nine sounding rockets. However, to get an in-orbit demonstration of the system a CubeSat implementation has been developed. The m-NLP measurement principle is based on several fixed bias probes, where each probe has to be biased above the spacecraft potential. To ensure that this requirement is fulfilled, the CubeSat version of the m-NLP will feature a new miniaturized thermionic electron emitter, which can actively control the potential of the satellite. The emitter is designed to accommodate the low size, weight, and power challenges of the CubeSat platform. Together with the in-flight determination of the spacecraft floating potential, it can autonomously control the potential of the spacecraft by emitting electrons. Preliminary, test results from the plasma chamber at the European Space and Technology Center in Holland are shown, verifying that a miniaturized electron emitter is able to actively control the floating potential of the spacecraft and, hence, improve the accuracy of the electron density measurements.