A survey on descent trajectories from Gateway orbit to the Moon

Kurzfassung

Since the end of the Apollo program in 1972, no human has set foot on the Lunar surface. Now, with the start of the Artemis program by National Aeronautics and Space Administration (NASA), a permanent human presence on the Moon is planned. This presence is intended to serve as an outpost for human research and as a launch point for missions deeper into our solar system and to Mars. To achieve this goal, a station called Gateway is planned to be built, which will orbit around the Moon. The orbit in which it will move has also been specified by NASA. It is a Near Rectilinear Halo Orbit (NRHO) of the L2-Southern-Family with an average radius at pericenter of 3366 km. The orbit has a 9:2 Lunar Synodic Resonance, resulting in an orbital period of approximately 6.5 days. One important reason for choosing this orbit is the absence of eclipses by Earth until at least 2030. The aim of this thesis is to analyze descent trajectories from the Gateway’s orbit to the Lunar surface. For this purpose, both orbital mechanics and operational aspects have been considered. The descent itself has been divided into two parts. The first part consists of the descent from the Gateway’s NRHO to three circular parking orbits at an altitude of 100 km. The three orbital planes of the chosen Low Lunar Orbits (LLOs) are orthogonal to each other. Descent trajectories have been calculated using the Python library SEMpy. In the second part of the descent, a landing from the corresponding parking orbits on the Lunar surface has been considered based on theoretical principles. In the course of the analyses, two case studies, the Orion capsule (NASA) and the Starship (SpaceX), have been examined. The results of the analyses showed that a polar parking orbit is best suited for performing a landing. It was also found that the descent should start as close as possible to the apocenter of the Gateway orbit due to the required change in orbital plane. It was shown that the Orion capsule, with respect to its fuel capacity (full tanks), is only capable of performing the transfer to the parking orbit. The fuel capacity of the Starship (full tanks) is sufficient for a descent to the Lunar surface and an ascent back to a parking orbit. From an operational point of view, there are hardly any restrictions. However, it should be noted that direct communication with Earth is not possible when the transfer passes behind the Moon from Earth’s perspective. Additionally, there may be eclipses of up to half an orbit period on the respective parking orbit.