In-situ Measurements of Particle Size and Charge Distributions for Mars and Lunar Missions

摘要

E-SPART analyzer is an instrument capable of measuring aerodynamic diameter and electrostatic charge distributions on a single particle basis in real time. A frequency biased Laser Doppler Velocimeter (LDV) is used to make non-contact in-situ analysis of the particles under ambient conditions, with respect to the temperature, pressure, and composition of the gaseous medium in which the particles are suspended. We report here new developments related to LDV optics, signal processor, and miniaturization of the E-SPART analyzer so that it can be applied on the surface of Mars and the Moon for characterization of dust particles. The conventional LDV was replaced with a diode laser based MiniLDV and we eliminated the frequency biasing device that requires either use of Bragg Cells or rotating diffraction grating with a new LDV beam geometry. The new optical system, a Stationary Fringe LDV (SFLDV), in which the fringe pattern in the sensing volume is stationary, is able to resolve directional ambiguity of an oscillating particle motion without a frequency bias between the two laser beams. Thus the complexity of the frequency biasing system is absent allowing both stability and robustness of the miniature E-SPART analyzer. For comparison between the conventional E-SPART analyzer and the new miniaturized instrument, experimental results on size and charge distributions for different test particle clouds are presented. The advantages of the new instrument for in-situ particle characterization for different industrial, pharmaceutical, and space explorations applications are discussed.