Investigation of a single spraying site of a colloid thruster

Abstract

A repetitive time-of-flight system is used to study a colloid thruster spraying site which is isolated on the tip of a sharpened wire. The mean specific charge of sprayed droplets does not seem to be related to wire sharpness, but is strongly dependent on the propellant mass flowrate to the site. Spraying site characteristics are determined as a function of propellant mass flowrate (in a novel way) and of propellant temperature. The dependence of mean specific charge on mass flowrate is found to be <q/m>αm−0·57, in excellent agreement with the findings of Pfeifer and Hendricks (1968). The mean specific charge is found to be a weak function of propellant temperature, and this result may have important implications in the control of capillary-fed colloid thrusters.