Busek proposes to develop a radio-frequency discharge, gridded micro ion engine that produces µN level of thrust precisely adjustable over a wide dynamic thrust range. Rf discharge was chosen to eliminate the life-limiting internal cathode of a dc discharge ion engine. Thrust actuation on the order of 0.03µN resolution is proposed with a closed-loop control system. This controlling scheme can be achieved by varying only one parameter: the rf power with a feedback from the beam current. Uniquely, the rf ion engine can also produce enough thrust for coarse constellation corrections or reconfigurations. Argon will be the base-lined propellant to ease concerns of propellant condensing on optics or other cryogenic surfaces. This feature can be critical for close formation flying as micro-thrusters such as field emission electric propulsion (FEEP) and colloids could potentially coat neighboring spacecraft. The proposed rf ion engine, combined with Busek's space-qualified carbon nanotube field emission cathode (developed for the ST7 DRS mission) as a neutralizer, will create a new opportunity in precise thrust actuation. Further implementation of a simple propellant feed system and power electronics will create a compact, low power, high performance spacecraft propulsion system.