The primary application is spacecraft thermal management. If the program is successful, the TPTMS proposed here will provide a two-phase thermal management solution for spacecraft that is versatile with respect to heat load requirements and location, allows for efficient use of available mass, volume, and power budgets, can handle heat load transients, and is capable of scaling heat rejection with cooling demand through control of accumulator pressure. In addition, these functions are accomplished using relatively simple, low-cost components, such as a single-phase pump and the accumulator design. Applications for this thermal management system would include spacecraft with thermal demands beyond the capabilities of capillary systems and those interested in low-cost alternatives to conventional thermal management systems. In addition, since the TPTMS aims to provide gravity-independent and acceleration-resistant operation, ACT will also investigate potential aircraft applications. In Phase II, ACT will develop two additional test systems. The first will demonstrate an on-demand TPTMS using a dynamic, automated control system. The second will demonstrate reduced gravity operation aboard NASA or private test aircraft. During this phase, ACT will investigate application with the growing commercial satellite and spacecraft market. Depending on the phase separation performance of the MVS integrated with the TPTMS, ACT will also consider military and commercial aircraft applications.