The effect of surface contamination of tiny satellite on DC probe ionosphere measurement

The DC Langmuir probe is a widely-used instrument for the plasma measurement in the space missions. But to apply DC Langmuir probe to a tiny satellite, such as a cubesat, for ionosphere study is difficult to get accurate electron density (ne) and electron temperature (Te) for two reasons: the contamination on both satellite surface and the electrode to be used, and a lack of conductive surface area of the tiny satellite. Under the charging effect of the satellite with an insufficient area ratio between the surface of the probe and the spacecraft, the contaminations on the surface of both probe and the satellite, acting as equivalent capacitances and resistances, modify both the potentials on the satellite and the probe, and an elevated Te and a suppressed ne are derived incorrectly. In this paper, the effect of the surface contamination on the DC Langmuir probe measurements onboard a tiny satellite is investigated in detail. The effects of the accumulated charge and the impedances on the contamination layers have been identified in the experiments done in a ground chamber with similar plasma conditions in the Earth’s ionosphere, and the characteristic dependences of the probe sweeping frequency and the plasma density are presented. The experiment result suggests that a contamination-free instrument TeNeP, operated at 0.2∼10 MHz probe sweeping frequency and sweeping potentials below 500 mV, is a better solution to obtain accurate Te and ne, onboard a satellite with a surface area ratio below 100.