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Many on-going European Space Agency (ESA) science and earth observation missions are based on precision attitude control and formation flying. All these missions impose strong requirements on propulsion system which should provide low thrust, low noise, and high-precision thrust vectors in up to \mathbf 16 directions. Also as most of these missions have a platform with limited solar cell arrays, the power consumption of the propulsion system should be as low as possible. The idea of using a small high-efficiency multistage plasma thruster (HEMPT) system for such missions is very attractive because of its relatively low complexity and low system mass. Thus, the ability of down-scaling a HEMPT to the \mu N range is investigated experimentally. A measurement campaign studying systematically the influence of the geometrical dimensions of main thruster parameters on operation, beam profile, and ion acceleration is presented. Additionally the anode material was varied and showed relevance to ion acceleration distribution. The minimum achieved thrust was \mathbf 50~ \mu N at an anode voltage of 600 V, corresponding to a specific impulse of 230 s. Operation points with thrusts of \mathbf 180 and 360~ \mu N demonstrate a specific impulse of 610 and 860 s, respectively. [ABSTRACT FROM PUBLISHER]