Solar Array in Dense Plume Plasma

Abstract

Testing of large solar array (2m x 4 m) in the arc jet plume plasma environment revealed many interesting features like sharp increases in current collection, light em ission, and sputtering. This test was conducted in voluminous vacuum chamber (12 m diameter and 18 m height) that prevented the back reaction of chamber walls on plasma distribution. Vacuum equipment (ten diffusion pumps) provided background pressure about 1 µTorr. Plume plasma diagnostics was performed by using spherical and cylindrical Lamgmuir probes, emissive probes, and Faraday cup. Optical spectra of hot plasma near the nozzle were measured and analyzed. Contamination of solar array surfaces was deter mined by employing two Quartz Crystal Microbalance ( QCM ) probes. Chemical composition of plasma was monitored by quadrupole mass spectrometer. Current collections and arc thresholds were measured by biasing array with an external power supply. Acquired da ta were used to make important conclusions concerning the influence of plume plasma on solar array operation. In order to elucidate physical mechanisms of array – plasma interactions, a few experiments were conducted in smaller chamber filled with xenon pl asma. Special samples were manufactured to simulate solar array design, and these samples were undergone the same test procedures as it was done for large solar array. Arcing, light generation, and sharp increase in current collection were observed, and re spective characteristics were measured and analyzed. The explanation of these effects is given in current paper. Nomenclature Aik = transition probability, s -1 V = hydrogen ion velocity, m*s -1