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Cryogenic propellant storage on orbit is a crucial part of future space exploration. Efficient and reliable thermal insulation is one of the dominant technologies for the long-duration missions. This paper presents theoretical and experimental investigation on the thermal performance of variable density multilayer insulation (VDMLI) with different configurations and spacers. A practical method for optimizing the configuration of VDMLI was proposed by iteratively predicting the internal temperature profiles and maximizing the thermal resistance based on the basic layer by layer model. A cryogen boil-off calorimeter system was designed and fabricated to measure the temperature profile and effective heat transfer coefficient of the VDMLI samples over a wide range of temperature (77–353 K). The experimental data confirm that the optimized sample as predicted does have the minimum effective heat transfer coefficient in the control group. The results indicated that the insulation performance of MLI could be improved by 45.5% after replacing the regular uniform configuration with the optimized variable density configuration. For the same optimized configuration, the performance was further improved by 54% by changing the spacing material from none-woven fiber cloth to Dacron net. It was also found that the effective heat transfer coefficient will be much less sensitive to the MLI thickness when it exceeds 30 mm for on-orbit thermal environment. [ABSTRACT FROM AUTHOR]

Abstract: A saturation vapor pressure equation, p(T), is an essential component in the 3He state equation currently under development. The state equation is valid over the range 0.01–20K with pressures from 0 to the melting pressure or 15MPa. The vapor pressure equation consequently must be valid from 0.01K to the critical temperature. This paper surveys available 3He critical temperature and pressure measurements, leading to new recommended critical values of 3.3157K and 114603.91Pa. The ITS-90 temperature scale is defined by the 3He vapor pressure from 0.65 to 3.2K. A new vapor pressure equation is developed for the interval from the upper end of the T 90 scale to this newly defined critical point, employing a mathematical form in which the second derivative d2 p/dT 2 diverges in agreement with scaling laws at the critical point. Below 0.65K, an empirical vapor pressure expression is adopted, consistent with a theoretical expression valid in the limit T →0. These two new components are fitted to be piecewise continuous with the EPT-76 p(T) scale rather than the ITS-90 T(p) scale between 0.65 and 3.2K. Probable deviations between this vapor pressure scale and PLTS-2000 melting pressure–temperature scale are recognized, but not reconciled. [Copyright &y& Elsevier]

The computation with heat transfer, fluid flow and thermodynamics indicates that higher pulse tube refrigeration performance can be achieved with He–H2 mixtures as working fluids than that with pure He in the cooling temperature region of 30 K. In addition, it is found that Er3Ni, a regenerative material, is able to absorb H2 and forms Er3NiHx. The hydrogen absorption capacity of Er3Ni is about 3.5 H/Er3Ni in the H2 pressure region of 0.1–2.0 MPa at 30 °C. The calculation shows that the regenerative performance of Er3NiH3.5 is better than that of Er3Ni due to its higher volume specific heat. Experimental results show that the pulse tube refrigeration performance in 30 K cooling temperature region is obviously enhanced with He–H2 mixtures and Er3NiHx regenerative material. [Copyright &y& Elsevier]