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The science operations of the spacecraft and remote sensing instruments for the Martian Moon eXploration (MMX) mission are discussed by the mission operation working team. In this paper, we describe the Phobos observations during the first 1.5 years of the spacecraft’s stay around Mars, and the Deimos observations before leaving the Martian system. In the Phobos observation, the spacecraft will be placed in low-altitude quasi-satellite orbits on the equatorial plane of Phobos and will make high-resolution topographic and spectroscopic observations of the Phobos surface from five different altitudes orbits. The spacecraft will also attempt to observe polar regions of Phobos from a three-dimensional quasi-satellite orbit moving out of the equatorial plane of Phobos. From these observations, we will constrain the origin of Phobos and Deimos and select places for landing site candidates for sample collection. For the Deimos observations, the spacecraft will be injected into two resonant orbits and will perform many flybys to observe the surface of Deimos over as large an area as possible. Graphical Abstract

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The generation of bounded trajectories complying with operational constraints in the complex dynamic environment surrounding Phobos is not an easy task. The vicinity of Phobos is dominated by the gravity field of Mars; consequently, orbiting on a Keplerian orbit about this moon is not feasible. The quasi-satellite orbit (QSO) is a means to orbit Phobos in the sense of relative motion. In particular, the three-dimensional QSO (3D QSO) has been recently suggested as an approach for better meeting mission objectives, such as global mapping. However, the linear stability of QSOs concluded in the simplified three-body model cannot sufficiently ensure a stability domain for operations. In this context, this paper investigates the strategy for designing bounded orbits with desired stability properties and characteristics for observation. Families of periodic 3D QSOs are first computed in the circularrestricted three-body problem. The sensitivity of the QSOs to the initial epoch and operational errors is analyzed, revealing effective stability levels and region that can guide trajectory and operation design. The stability levels are then validated by a dispersion analysis in the full dynamics. Furthermore, being guided by effective stability, a preliminary attempt to maintain low-altitude and high-inclination QSOs in the full dynamics has proven successful.