The use of thermodynamic power cycles in space results in much higher conversion efficiencies than the traditional solar cell or thermoelectric couple. This has many beneficial consequences in both solar and nuclear applications. The 20% to 30% cycle efficiency reduces the solar energy collection area significantly, thereby reducing size, weight and drag for low earth orbit missions such as the Space Station. For nuclear fueled systems, the 4 to 5 fold increase in conversion efficiency over thermoelectrics reduces the amount of fuel needed, thereby reducing weight, size, cost and hazard.Two competing dynamic cycles, the Organic Rankine Cycle (ORC) and the Closed Bray ton Cycle (CBC), are being developed by NASA LeRC for solar dynamic systems on the Space Station and by DOE for the U.S. Air Force. For each application (solar or nuclear), the basic cycles are similar. The major variable is power level. The solar dynamic systems being considered are in the 20 to 40 KWe range. Nuclear reactors can be used as the energy source from 10 KWe on up. Radioisotopes are best suited for the 1 to 10 KWe range.As part of the development process for the 1 to 10 KWe sized systems, Grumman has conducted technology demonstrations of critical components of both competing cycles under funding from the U.S. Air Force Space Division.This paper describes the respective critical components, their function, operation, verification test philosophy, test hardware and test results.