Preliminary Design of a 30 kN Methane-Oxygen-powered Electric-Pump-fed Liquid Rocket Propulsion System

Abstract: The design of a liquid rocket propulsion system, unlike that of a standalone system, is intertwined with the overall development of a number of associated systems and is influenced by a multitude of conditions and considerations: from the requirements needed to accomplish the mission to the rationalizations involved behind the development of each rocket system and/or component. In my thesis, the preliminary design of a “new generation” 30 kN rocket engine driven by an electric pump feed system and running on liquid methane and liquid oxygen is performed. The propulsion system would be employed on a hypothetical small-lift orbital-class twin-stage rocket to deliver a light payload of about 200 kg into a circular 500 km LEO. Such topics as the selection of bipropellant combinations, the feasibility of electric pump feed systems, design methodologies for thrust chambers, for nozzles in particular, management of the high thermal energy and the selection of compatible wall materials, as well as the design of an injector have been looked comprehensively into. It is realized that methalox is indeed better than both hydrolox (with regard to density impulse) and kerolox (in terms of specific impulse). Besides, a suite of attractive characteristics makes the bipropellant a combination of choice to power rockets of the future. Yet more notably, an electric-pump-fed engine cycle is, under the right circumstances of engine operation, established to outperform both the pressure feed system and the turbopump feed system. With constant advancement in battery technologies, improvement of both power density and energy density to achieve much higher performance is but a matter of time. The adoption of a propulsion system such as ours for a mission objective as outlined above, therefore, is not just viable but unquestionably realistic. Two thrust chamber versions—a sea-level variant for the booster stage and a vacuum-optimized variant for the upper stage—are developed for our rocket. And both the nozzles employ a TOP “thrust optimised parabolic” contour; also, the booster stage comprises a cluster of 9 engines in a parallel burn arrangement. Concerning thermal management, the entirety of the booster-stage thrust chamber implements regenerative cooling (using Inconel 625), whereas the aft of the upper-stage nozzle section implements radiative cooling (with Niobium C-103). Further, the injector faceplate (also of Inconel 625) comprises two concentric patterns of unlike impingement doublet sets: with 80 pairs on the outer ring and 40 pairs on the inner ring. With rational assumptions, our hypothetical launch vehicle is deemed to have a mass of roughly 17200 kg (200 kg of which is the payload) and a delta-v of approximately 9600 m/s—quite within the desirable range of specifications for small-lift orbital-class twin-stage rockets of today.