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This report presents the results of an investigation conducted to obtain experimental heat transfer data on a liquid hydrogen tank insulated with 34 layers of MLI for warm side boundary temperatures of 630, 530, and 150 °R. The MLI system consisted of two blankets, each blanket made up of alternate layers of double silk net (16 layers) and double-aluminized Mylar radiation shields (15 layers) contained between two cover sheets of Dacron-scrim-reinforced Mylar. The insulation system was designed for and installed on a 87.6-in.-diameter liquid hydrogen tank. Nominal layer density of the insulation blankets is 45 layers/in. The insulation system contained penetrations for structural support, plumbing and electrical wiring that would be representative of a cryogenic spacecraft. The total steady state heat transfer rates into the test tank for shroud temperatures of 630, 530, and 152 O R were 164.4, 95.8, and 15.9 BTU/hr respectively. The noninsulation heat leaks into the tank (12 fiberglass support struts, tank plumbing, and instrumentation lines) represent between 13 to 17 percent of the total heat input. The net heat transfer through the MLI is 0.94, 0.53, and 0.09 BTU/hr-ft z for the 630, 530, and 152 O R shroud temperatures. These heat input values would translate to liquid hydrogen losses of 2.3, 1.3, and 0.2 percent/day, with the tank held at atmospheric pressure.

A cryogenic liquid oxygen storage system for providing oxygen to a fuel cell powered underwater vehicle has been proven feasible through a research program with the Office of Naval Research. A system has been designed that meets the Navy specifications of storing 50 kg and delivering 0.1 to 100 gimin of oxygen in an unmanned underwater vehicle. The total system mass has been shown to be practical for an underwater vehicle and the oxidizer mass ratios have been shown to be significantly greater than alternative oxygen storage techniques such as chemical or high pressure gas. Waste heat from the fuel cell has been shown to he a plentiful and effective heat source for vaporizing and pre-heating cryogenically stored liquid oxygen. The pre-hazard analysis has identified the potential hazards and countermeasures have been developed that will enable the liquid oxygen system to meet the high safety standards set forth by the Navy. A system design tool has been created that integrates a cryogenic reactant storage and delivery system with fuel cell design models using Visual Basic Application language. The system design tool is useful for conducting sensitivity analyses of key design parameters on overall system performance.

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SUMMARYThe storage of cryogenic propellants such as liquid hydrogen (LH 2 ) and liquid oxygen (LO 2 ) for the future Space Exploration Initiative (SEI) will require lightweight, high performance thermal protection systems (TPS's). For the near-term lunar missions, the major weight element for most of the TPS's will be multilayer insulation (MLI) and/or the special structures/systems required to accommodate the MLI. Methods of applying MLI to LH 2 tankage to avoid condensation or freezing of condensible gases such as nitrogen or oxygen while in the atmosphere are discussed. Because relatively thick layers of MLI will be required for storage times of a month or more, the transient performance from ground-hold to space-hold of the systems will become important in optimizing the TPS's for many of the missions. The ground-hold performance of several candidate systems are given as well as a qualitative assessment of the transient performance effects.