ACE staff has contributed extensively to advanced power systems technology. The ACE staff has performed detailed technical analyses and evaluations of alternative energy conversion and mobile power systems. This work includes the Automobile Power Systems Evaluation Study that the California Institute of Technology performed for the Ford Motor Company, a systems definition of alternative mobile power and environmental control systems performed for the US Army, and a systems analysis of alternative fuel cell power systems for railroad locomotives performed for the South Coast Air Quality Management District. These analyses included emissions, performance, design, and cost evaluations of conventional Otto cycle engines, Diesel engines, Rankine cycle engines, Stirling cycle engines, Brayton cycle (gas turbine) engines, and fuel cells. A laboratory research Stirling engine built under NASA funding at the Jet propulsion Laboratory was conceived and the conceptual design defined by an ACE staff member.