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The long-term storage of cryogenic propellants on orbit under thermal and pressure control is a promising enabling technology for future space exploration. Composite insulation composed of polyurethane foam (Foam), variable density multilayer insulation (VD-MLI), and a vapor-cooled shield (VCS) is considered as an effective passive thermal control method for such missions. This paper presents a theoretical model that considers three heat transfer mechanisms simultaneously within the VD-MLI and convective heat transfer inside the VCS, to predict and optimize the thermal performance of the insulation combination. The model is validated by experimental data. The influences of VCS position and warm boundary temperature (heat flux) on the thermal insulation performance are investigated for LH2, LN2, LO2, and LCH4 tanks. The temperature profiles within the insulation material with or without VCS are compared. In addition, the contributions from the VCS to reduce the heat flux into the tank are evaluated. The conclusions are valuable for the optimal design of future composite insulation with Foam/VCS/VD-MLI for cryogenic storage tanks on orbit.

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.

In this paper, the C ( t ) and C ∗ integrals, stress redistribution time t red and creep crack-tip stress distributions in the compact tension (CT) specimens with various thicknesses have been calculated by the three-dimensional (3D) finite element method, and the out-of-plane creep crack-tip constraint induced by specimen thickness is quantitatively characterized and analyzed in detail. The results show that the out-of-plane creep crack-tip constraint in the CT specimens could be characterized and analyzed by the new constraint parameter R . The 3D creep crack-tip constraint increases with increasing specimen thickness, and the 3D effect becomes more pronounced with increasing the parameter C ∗ . There is a central region with higher creep constraint along the crack front, the size of the region increases with increasing specimen thickness, and decreases with increasing creep time and parameter C ∗ . The factors of influencing the out-of-plane creep crack-tip constraint are analyzed.

In this paper, the C ( t ) and C ∗ integrals, stress redistribution time t red and creep crack-tip stress distributions in the CT specimens with various crack depths have been calculated by the finite element method (FEM), and the creep constraint induced by crack depths are quantitatively investigated in detail. The results show that the creep constraint could be characterized by the new constraint parameter R . The constraint effect induced by crack depths at non-steady-state creep is more pronounced than that at steady-state creep. The effects of the crack depths, load levels ( C ∗) and distances from the crack tips on the creep constraint parameter R are analyzed.