Performance Requirements for a Descent and an Ascent Lunar Engine

The renewed interest in lunar exploration and the need to extend the crew's time on the Moon, has led to the conceptual development of several manned landing systems, characterized by numerous architectures that differ mainly in the number of stages and the peculiarity to be re-used or not. Each architecture will depend on the type of assumptions made, the manoeuvres performed by the landing system and the type of orbit used. Generally, the tendency is to choose as an outpost a near-rectilinear halo orbit (NRHO) that serves as a reusable command and service module in lunar space. The purpose of the following discussion is to preliminarily define the requirements for lunar descent and ascent propulsion systems based on data associated with previous Apollo missions. After an introduction on the main parameters of a rocket engine and the major influencing factors, the oxidizer and fuel pair used in the current mission and the performance provided by that propellant will be analysed. Choosing the design parameters appropriately, the masses of the individual stages will then be calculated. These values will be compared with approximate models and with known data from the Apollo lunar descent and ascent modules, to obtain reasonable estimates to be used in subsequent sizing of pressurizing gas systems. In addition to the required masses, the most common tank geometries and the stresses to which they are subjected, generated by the high storage pressures of the fluids in question, will be analysed. Then, the solutions provided by the space market will be evaluated and compared with those previously calculated. Once the particular geometry and the number of tanks has been chosen, the architecture of the descent, ascent and attitude control systems will be realized, whose fundamental requirement is the redundancy of the single components. The valves used by the systems will then be selected appropriately. Finally, once the fundamental principles associated with the geometry of a rocket engine have been analyzed, the thrust chambers will be sized and the substantial differences between the main stages evaluated.