This paper describes a direct-injection, liquid monopropellant powered actuation system, which was developed for the purpose of providing mechanical power to self-powered human-scale robots. The actuation system utilizes the catalytic decomposition of a monopropellant as a hot gas generator for powering pneumatic-type actuators. Specifically, pressurization of a pneumatic actuator is provided via solenoid injection valves, which control the flow of the monopropellant through a catalyst pack

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... the respective sides of the cylinder. Depressurization is provided by a three-way proportional spool valve, which can exhaust one of the two cylinder chambers. A prototype of the actuation system is described, and experimental data is presented that demonstrates good force and motion tracking performance. Experimental results characterizing the energetic performance of the system demonstrate that the prototype provides an energetic figure of merit an order of magnitude greater than that of batterypowered servomotors.