Comprehensive Performance Evaluation of Densified Liquid Hydrogen/Liquid Oxygen as Propulsion Fuel

Densified liquid hydrogen/liquid oxygen is a promising propulsion fuel in the future. In order to systematically demonstrate the benefits and challenges of densified liquid hydrogen/liquid oxygen, a transient thermodynamical model considering the heat leakage, temperature rise, engine thrust, pressurization pressure of the tank, and wall thickness of tank is developed in the present paper, and the performance of densified liquid hydrogen/liquid oxygen as propulsion fuel is further evaluated in actual application. For liquid hydrogen/liquid oxygen tanks at different structural dimensions, the effects of many factors such as temperature rise during propellant ground parking, lift of engine thrust, mass reduction of the tank structure, and extension of spacecraft in-orbit time are analyzed to demonstrate the comprehensive performance of liquid hydrogen/liquid oxygen after densification. Meanwhile, the problem of subcooling combination matching of liquid hydrogen/liquid oxygen is proposed for the first time. Combining the fuel consumption and engine thrust lifting, the subcooling combination matching of liquid hydrogen/liquid oxygen at different mixing ratios and constant mixing ratios are discussed, respectively. The results show that the relative engine thrust enhances by 6.96% compared with the normal boiling point state in the condition of slush hydrogen with 50% solid content and enough liquid oxygen. The in-orbit time of spacecraft can extend about 2–6.5 days and 24–95 days for slush hydrogen with 50% solid content and liquid oxygen in the triple point state in different cryogenic tanks, respectively. Due to temperature rise during parking, the existing adiabatic storage scheme and filling scheme for densification LH2 need to be redesigned, and for densification LO2 are suitable. It is found that there is an optimal subcooling matching relation after densification of liquid hydrogen/liquid oxygen as propulsion fuel. In other words, the subcooling temperature of liquid hydrogen/liquid oxygen is not the lower the better, but the matching relationship between LH2 subcooling degree and LO2 subcooling degree needs to be considered at the same time. It is necessary that the LO2 was cooled to 69.2 K and 54.5 K, when the LH2 of 13.9 K and SH2 with 45% was adopted, respectively. This research provides theoretical support for the promotion and application of densification cryogenic propellants.