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摘要

The impact on spacecraft contamination of the emission of cesium droplets by cesium field effect electricnpropulsion is investigated. This paper focusesmainly on identifying worst-case contamination scenarios, rather thannassessing a fully quantitative contamination level. Evaporation of droplets and sputteringmechanisms are comparednand the second is shown to be negligible. Cesium droplet evaporation is shown to be self-inhibited by evaporation-ninduced cooling down. As a consequence, evaporation rate is only controlled by external power deposition onndroplets. Evaporation stimulated by solar light absorption and by ion bombardment in the plume are compared andnthe latter can be neglected, except in the field effect electric propulsion thruster vicinity (a few centimeters). Dropletnacceleration by ion beampressure is consideredwithin the beam, and free transport at constant velocity is considerednout of the beam. Contamination levels normalized by the totalmass of droplets are estimated in a plane normal to ionnbeam main direction and containing the thruster. Levels depend on droplet size, initial velocity, and direction ofnemission (within or out of the beam). Worst-case contamination of, respectively, tens of angstroms, hundreds ofnangstroms, and thousand angstroms for 1 g of emitted droplets were computed at, respectively, 1m, 10 cm, and 1 cmnfrom the field effect electric propulsion thruster.