Under the Department of Energy's (DoE) Solar Thermal Technology Program, Sandia National Laboratories is evaluating heat engines for terrestrial Solar Distributed Heat Receivers. The Stirling engine has been identified by Sandia as one of the most promising heat engines for terrestrial applications. The Stirling engine has the potential to meet DoE's performance and cost goals . The NASA Lewis Research Center is providing management of the Advanced Stirling Conversion System (ASCS) Project through an Interagency Agreement with the DoE.NASA Lewis is conducting technology development for Stirling convertors directed toward a dynamic power source for space applications. Space power requirements include high reliability with long life, high system efficiency and low vibration. The free-piston Stirling engine has the potential for both solar and nuclear space power applications. Although the space and terrestrial applications appear to be quite different, their requirements are complementary.Parallel contracts continue with Stirling Technology Company (STC), Richland, WA and Cummins Engine Company (CEC), Columbus, IN for two ASCS designs. Each “system” features a solar receiver/liquid metal heat transport system, and a free-piston Stirling convertor which incorporates a linear alternator to directly provide the electrical output of about 25 kW to a utility grid. Both designs have the potential to meet the DoE performance and “long-term” cost goals.The CEC free-piston Stirling convertor incorporates a linear alternator along with hydrodynamic gas bearings to provide non-contacting, wear-free support to the pistons. The STC design incorporates linear alternator technology with flexures that provide non-contacting support while also supplying much of the spring stiffness needed to obtain proper resonance. Both the CEC and STC designs will use technology which is expected to be available in the early 1990's.