End-of-Life disposal design for Near-Rectilinear Halo Orbits

In recent years, there has been a clear increase in space traffic in the cislunarregion, which is expected to become even more pronounced in the future. Given the space debris problem we are facing in near-Earth space and the importance of the cislunarregion, the current plans aim to avoid the same issue from occurring between the Earth and the Moon. To this end, one of the best mitigation strategies to implement is careful planning of End-of-Life (EoL) disposal solutions. To do so would require providing accurate, low-cost disposal options in an efficient and customised manner. Current research on EoL disposal in cislunarspace focuses mainly on studying the problem with a probabilistic approach, for example, to estimate the effect of uncertainties on the system. We propose instead to address the problem of disposal design for cislunarspace by leveraging the system dynamics to minimise the AV cost. This work aims to design and compare disposal strategies for Near-Rectilinear Halo Orbits (NRHOs) in Earth-Moon (EM) Li and L2. These orbits were chosen for the analysis as they are of particular interest for many future missions, such as, for example, the lunarGateway. Of the four disposal strategies usually considered when planning the EoL phase of a mission in cislunarspace, two were selected as the most suitable for these orbits: disposal with insertion on a heliocentric no-return orbit and lunar impact. The former was chosen as it is low-cost and reliable, if supported by long-term simulations. In this case, the disposal trajectory is designed using an energetic approach, which involves a two-impulse manoeuvre: the first in the direction of the unstable manifold and the second to close the Zero Velocity Curves (ZVCs) of the Sun-Earth (SE) system. The latter of the two strategies is chosen due to the natural proximity of NRHOs to the lunar surface. The EoL phase is defined by looking for solutions where the CR3BP dynamics can be exploited to find passive solutions. The disposal trajectory is then optimised to minimise the disposal cost while ensuring lunar historical sites and protected zones on the Moon's surface are preserved. By comparing the two strategies, it is defined which is the most convenient to be applied to NRHOs, highlighting which parameters influence the analysis, such as cost, total time needed for the EoL phase and eventual sensitivity to perturbations.