System scheme design for LOX/LCH4 variable thrust liquid rocket engines using motor pump

Abstract

With the development of both cryogenic and motor pump technologies, the cryogenic variable thrust liquid rocket engine that uses a motor pump is becoming an advanced power system for use in various aerospace missions. In the present study, this kind of engine system scheme is originally developed. The technical metrics of the engine system are primarily obtained based on the time history of the thrust for the descent engine in the lunar process as the mission profile. Subsequently, to satisfy the general mission requirements, the system schematic diagram is designed, followed by the design of the according subassemblies. The design highlights the pressure-drop models of the pipe and the cooling channels, and the mass model of the chamber. These models may improve computation precision. In this design scheme, based on the theoretical models and derivations, the state and structural parameter distributions for the system scheme are first proposed. Moreover, the influences of the tank material type, the battery type, and other parameters on the system scheme are analyzed. The results demonstrate that the pressurization system, due to its heavy battery and motors, constitutes the largest portion of the dry mass of the entire system, which may weaken the advantages compared with the conventional turbine pump system. The second-largest portion of the dry mass is composed of the propellant tanks, due to the restricted minimum wall thickness and the use of cryogenic materials. It is reported that, during the throttling process, there is a linear relationship between the route pressure losses of the cooling channels along with pipes and the 1.75 power of the chamber pressure. Based on this analysis, a better understanding of the proposed system scheme of the LOX/LCH4 variable thrust rocket engine that uses a motor pump can be obtained.