Identification of new orbits to enable future mission opportunities for the human exploration of the Martian moon Phobos

Abstract

One of the paramount stepping stones towards NASA's long-term goal of undertaking human missions to Mars is the exploration of the Martian moons. Since a precursor mission to Phobos would be easier than landing on Mars itself, NASA is targeting this moon for future exploration, and ESA has also announced Phootprint as a candidate Phobos sample-and-return mission. Orbital dynamics around small planetary satellites are particularly complex because many strong perturbations are involved, and the classical circular restricted three-body problem (R3BP) does not provide an accurate approximation to describe the system's dynamics. Phobos is a special case, since the combination of a small mass-ratio and length-scale means that the sphere-of-influence of the moon moves very close to its surface. Thus, an accurate nonlinear model of a spacecraft's motion in the vicinity of this moon must consider the additional perturbations due to the orbital eccentricity and the complete gravity field of Phobos, which is far from a spherical-shaped body, and it is incorporated into an elliptic R3BP using the gravity harmonics series-expansion (ER3BP-GH). In this paper, a showcase of various classes of non-keplerian orbits is identified and a number of potential mission applications in the Mars-Phobos system are proposed: these results could be exploited in upcoming unmanned missions targeting the exploration of this Martian moon. These applications include: low-thrust hovering and orbits around Phobos for close-range observations; the dynamical substitutes of periodic and quasi-periodic Libration Point Orbits in the ER3BP-GH to enable unique low-cost operations for space missions in the proximity of Phobos; their manifold structure for high-performance landing/take-off maneuvers to and from Phobos' surface and for transfers from and to Martian orbits; Quasi-Satellite Orbits for long-period station-keeping and maintenance. In particular, these orbits could exploit Phobos' occulting bulk and shadowing wake as a passive radiation shield during future manned flights to Mars to reduce human exposure to radiation, and the latter orbits can be used as an orbital garage, requiring no orbital maintenance, where a spacecraft could make planned pit-stops during a round-trip mission to Mars

Trajectory design and guidance for landing on Phobos

“…provides some physical constants and orbital parameters 4 used in the study, both for Mars (orbit around the Sun) and Phobos [5] (orbit around Mars). The dominant perturbations to this model are the ellipticity of Phobos' orbit around Mars, and the non-spherical gravitational field of Phobos [7,8].…”

Transfers around Phobos via bifurcated retrograde orbits: Applications to Martian Moons eXploration mission

“…Upon arrival, MMX will be inserted into a series of retrograde relative orbits about the Martian moon known as QSO and carry out its scientific observations for more than three years. Alternate orbits to explore Phobos, including liberation point orbits, are systematically studied by Zamaro and Biggs [5].…”

Long-term evolution of mid-altitude quasi-satellite orbits

“…Recent developments on this matter can be separated in numerical and analytical investigations of a point mass subject to the gravitational attraction of a massive primary and a much lighter secondary. In the case of numerical investigations, shooting techniques are typically applied to calculate periodic or quasi-periodic solutions in the vicinity of planetary satellites [8][9][10]. Once these particular solutions are obtained, stability analysis can be carried out using Floquet theory and/or chaos indicators [11][12][13][14].…”