This paper describes the evolution and maturation of the thermal isolation technologies over several decades at LM and discusses options and relative merits for reduction of boil off for propellants. The emphasis is on missions of 6 months or longer and storage of LH2. Thermal isolation includes multilayer insulation (MLI), composite supports, and low heat leak plumbing. The boil off loss is typically dominated by MLI system performance, which is difficult to implement and has a high degree of unpredictability and repeatability. A summary and comparison of the MLI experience on instrument Dewars and large propellant tanks is included. Additional boil off reduction approaches discussed include conductive shields cooled by cryocoolers and/or vented vapor. The difficulty of achieving low temperature gradients in the shields and the role of coolant circulation loops is discussed. The benefits and techniques of Sub-cooling propellants prior to launch is discussed. The benefits of low mass vacuum shells and the associated weight penalty are assessed.
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