Martian Moons eXploration transfer analysis between planar and spatial QSOs around Phobos

Quasi-satellite orbits (QSO) are stable retrograde parking orbits around Phobos that are currently being considered for JAXA's upcoming robotic sample return mission MMX. During the proximity operations of MMX, the spacecraft inserted in a high altitude QSO will gradually descend to lower altitude QSOs with suitable transfer and station-keeping techniques between different relative QSOs. Preliminary analysis of two-impulsive planar transfers between relative retrograde orbits utilizing the bifurcated QSOs families is studied to estimate the DV costs and time of flights of the transfers. In spatial transfer problem, trajectories utilizing the invariant manifolds of unstable 3D-QSOs are weakly to highly unstable and require additional station-keeping strategies to perform MMX scientific observations. These transfer trajectories have a longer flight time and might need minor correction maneuvers along the transfer paths. In this paper, an orbital maintenance strategy that suppresses and eliminates linear dynamical instability of the unstable 3D-QSOs has been considered for shortlisting feasible 3D-QSOs for high-latitude observations. Differently from previous works, we utilize the initial guesses found through the preliminary results that provide two-impulsive transfer DV execution points and optimize the transfers between relative QSOs around Phobos. Primer vector theory is applied to investigate the primer vector of the transfer trajectories to evaluate whether intermediate maneuver or initial/final coasting times along the trajectories can minimize the total DV cost between the transfers.