The application of cryogenic fluid storage systems to manned spacecraft is considered attractive primarily because of the substantial weight and volume saving afforded compared with high-pressure gaseous storage at ambient temperature. The major use of the stored fluids has been as a metabolic support (oxygen) and as reactant supply (hydrogen and oxygen) to the fuel cell for power generation. In addition cryogenic helium is used for descent propellant tankage pressurization aboard the lunar module.The subsystems developed for the NASA Gemini program, the firts full-scale operational application of this type of equipment, are discussed as a baseline for comparison with more advanced designs for subsequent programs. State-of-the-art design improvements are presented in some detail.Current programs (i.e., Apollo, Lunar Module, Biosatellite (primate), Manned Orbiting Laboratory, and the Air-lock Module) utilize cryogenic storage and supply subsystems for the usages mentioned earlier. A comparison of the physical and thermodynamic characteristics of these subsystems indicates a well-controlled evolution of the basic Gemini design concept. Further advantageous evolution of this concept of storing the cryogen as a single-phase supercritical fluid is anticipated for programs, such as the Apollo applications mission. However, it does not appear likely that further significant performance gains are to be expected in equipment with design limitations which are imposed by the peculiar fluid characteristics of supercritical storage.Concurrent with operational supercritical production has been development of subcritical storage concepts for zero-“g” operations. Air Force-, NASA- and AiResearch-sponsored development of subcritical storage has resulted in the investigation of phase control and of various gauging systems. The design concept is followed through early developmental phases to the in-orbit experience of the Saturn-Apollo Flight 203.Advanced missions under consideration require storage capacity for periods beyond the 14- to 30-day missions currently underway. The advanced missions will require storage capacity for 60 days to one year. Although present design concepts can be used to provide storage for 60-to 90-day missions, the systems become relatively heavy and have limited performance capability.These drawbacks have led to the advanced design concept. A long-mission cryogenic storage vessel has been fabricated and tested. Results of testing indicate that the test unit is capable of a one-year mission, with a mission performance flexibility far beyond the capability of present state-of-the-art designs. The storage concept provides for mass flow rates small enough to provide for minimum metabolic needs of a typical manned mission, or high enough for rapid pressurization of large volumes, while operating isobarically with no parasitic power requirements.Data are presented to show thermodynamic/heat transfer and certain dynamic and environmental testing. In addition, the simplification of manufacture and the mission growth potential of the long-missions storage concept are discussed.