This paper describes the design of a power supply And actuation system appropriate for position or force controlled human-scale robots. The proposed approach utilizes a, liquid monopropellant to generate hot gas, Which is utilized to power a pneumatic-type actuation system., A prototype of the actuation system is, described,and closed-loop tracking data are shown, which demonstrate,good motion, control. Experiments to characterize, the energetic performance of a six-degree-of-freedom actuation system indicate that the proposed system with a diluted propellant offers;in energetic figure of merit five. times. greater than battery-powered dc motors. Projections based on these experiments. indicate that the same system powered by undiluted Propellant would, offer an energetic figure of merit an order of magnitude greater than a comparable battery-powered dc motor actuated system.