Mass optimization of a recompression supercritical nitrous oxide and helium power system for space exploration

Abstract

Due to high output power, long lifetime, high efficiency, and compact structure, the space nuclear power (SNP) system is considered an ideal choice for future large-scale and deep space missions. The system's mass, volume, and thermoelectric conversion efficiency directly affect and determine the system's performance compared with ground nuclear devices. The mass of the space nuclear power system is a vital parameter due to the limitation of cost, volume, and transportation. This study designed and optimized the recompression supercritical with nitrous oxide and helium (N2O–He) Brayton cycle with a small modular reactor for mass. Each Brayton cycle component model was developed to estimate the cycle performance systematically. The mass estimation model of the Brayton system includes a nuclear reactor, radiation shadow shield, Brayton cycle unit, recuperator, and radiator. A small modular reactor was designed to predict the minimum mass reactor suited to the given cycle conditions. The system mass optimization explored the trade-offs between the reactor, radiation shield, Brayton cycle unit, recuperator, and radiator to obtain the minimum mass of the space nuclear energy system to satisfy the operating requirements. Sensitivity parametric investigations are considered to evaluate the effects of crucial decision variables on the whole Brayton cycle mass. Furthermore, multi-objective optimization is performed to find optimum operating parameters to minimize the system mass. The results illustrate that the specific mass of the system is less than 20 kg/kW. The total mass of the whole system is 5605.93 kg using near-term materials, of which the Baryton Rotating Unit, radiator, and shadow shield mass dominate the total mass. The Brayton Rotating Unit, radiator, and radiation shield account for 44.64%, 32.53%, and 14.29%, respectively. It is concluded that after the dual-objective optimization analysis, the mass of the cycle decreased by 18.44%, which used the existing technical materials.