The innovation is a Multi-Use Non-Intrusive Flow Characterization System (FCS) for densified, normal boiling point, and two-phase cryogenic flows, capable of accurately measuring several fluid parameters in real-time. Cryogenic fluids are ubiquitous in the aerospace industry. Their low temperatures inherently promote heat transfer from the ambient environment which often results in two-phase flows that cannot be adequately characterized by existing instrumentation. FCS was originated to address this issue and greatly enhance the quantification, reliability, safety, and autonomous operations of propulsion test operations. FCS handles both transient and steady state flows, and is anticipated to have a fast response time. The technology can non-intrusively operate in the following five modes: 1) on-line analysis of fluid mixtures; 2) mass flow rate measurement; 3) temperature measurement; 4) fluid conditioning and health monitoring; and 5) model validation for a cryogenic or non-cryogenic fluid flow. Phase I has been structured to provide design, analytical, experimental, and data analysis groundwork toward the successful development of the proposed technology, including the characterization of high pressure LOX flows. The Phase II program will produce a prototype commercial FCS System for delivery to NASA Stennis Space Center, and use at several other NASA centers and commercial facilities.