Electrically driven pump-fed cycle rocket engine

Abstract

An electrically driven pump-fed cycle for rocket engine is proposed and a viability of the proposed cycle is assessed compared to a gas generator cycle. The maximum possible thrust level is determined considering the technological maturity of the electric motor. Four types of battery cells were assessed in a screening test for the proposed cycle and the necessity of regenerative cooling for the battery pack is shown. The mass expressions of the proposed cycle and gas generator cycle are derived in terms of pump power and burning time. The basic features are demonstrated with respect to combustion chamber pressure, burning time, and thrust level. The results show that it is favorable to maintain a lower combustion chamber pressure, a longer burning time, and a higher thrust level to remedy the payload penalty incurred when the gas generator cycle is not used. In addition to focusing on the battery pack, the regenerative cooling effect on the battery pack mass is discussed. Further, the impact of optimal battery cell discharge time on the payload is explained. To estimate the payload for the proposed cycle quantitatively, hypothetical low earth orbit (LEO) and KSLV-II sun synchronous orbit (SSO) mission cases are used. In the analysis of the hypothetical LEO mission, it is found that the proposed cycle payloads are only 2.1% to 3.5% lower than those of the gas generator cycle when the combustion chamber pressure is 3.0 MPaA. For the KSLV-II SSO mission, the cargo payload is increased by 3.7% compared to that of gas generator cycle if the proposed cycle is employed for the third-stage engine. The effects of independent variables on the total mass are quantitatively evaluated through the sensitivity analysis, and it is found that the batter cell energy density dominates the total mass for the energy-constrained condition, whereas the inverter efficiency does for the power-constrained condition. In addition, the engine reliability is estimated from the known Weibull probability density functions of individual components, and it is shown that the reliability of the proposed cycle engine is higher than that of the gas generator cycle. Finally, the specific transportation cost and first unit cost are evaluated using parametric and bottom-up approaches. As a result, the specific transportation cost of the proposed cycle is estimated to be 14.1~16.5 MY/kg, and the first unit cost of proposed cycle engine is estimated to be 19.8% lower than that of the gas generator cycle engine.