Abstract
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.
Highlights
Szuszczewicz[19] has investigated the area influences of RE in LP measurements
The experiments in this paper suggest that this approach is inappropriate because that the contamination layers on the surface of both the probe and satellite distort the potential variation curves inevitably in practical measurements, and this distortion can not be corrected by other means
The electrons in SPOC is generated from the BDPS by its driving current through six Nickel cathodes painted with BaO powder
Summary
Szuszczewicz[19] has investigated the area influences of RE in LP measurements. It is shown that the theoretical minimum ΓRE for undistorted current-voltage (I-V) curve is 10,000. The size of the probe is limited by the gain of the amplifier circuit and the sheath effects,[21] so the increase of ΓRE is usually achieved by enlarging the conductive surface area of the spacecraft by the mechanical deployment. This deployment for a tiny satellite, such as small cubesats, sometimes is technically challenging, or even impossible. The satellite potential is balanced by the electron emitting device and a stable potential on the satellite is formed, the satellite charging effect on a Langmuir probe measurement can be eliminated. The contamination effects are carefully investigated by in-lab experiments in a plasma chamber with plasma of similar density and temperatures in a low earth orbit (LEO).[6]
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