Supercritical CO2 Brayton cycle for space exploration: New perspectives base on power density analysis

High-power-density space energy systems are crucial for establishing colonies on the lunar or Mars and exploring the solar system's outer edges. This study develops a space CO2 Brayton cycle thermodynamic and mass predicted model. Exploring how critical thermodynamic parameters influence power density, identifying pathways for optimizing energy efficiency and mass, analyzing differences between space sCO2 Brayton cycles and conventional ground systems, and proposing improved routes. Results indicate that the peak power density is 38.99 W/kg for 100 kW power output, with the radiator nearly 40% of the total mass due to low radiative heat transfer efficiency in the space environment and the compressor inlet temperature far from the CO2 vapor dome. The high-efficiency advantages of sCO2 near its critical region cannot be realized. Two improved strategies include using CO2-base mixture to raise the critical temperature or switching to a subcritical cycle for enhanced safety. Adding H2S has the best improvement, increasing power density by approximately 7.8 %. Reducing the high side pressure from 15.8 MPa to 7 MPa, power density decreased to 34.3W/kg due to lower heat transfer performance. Until the stability of the CO2-H2S mixture and high-pressure sealing is solved, the subcritical CO2 Brayton cycle may be a more promising technical approach.