Natural and artificial orbits around the Martian moon Phobos

Zamaro, Mattia and Biggs, James (2015) Natural and artificial orbits around the Martian moon Phobos. PhD thesis, University Of Strathclyde.

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One of the paramount stepping stones towards the long-term goal of undertaking human missions to Mars is the exploration of the Martian moons. In particular, Phobos is becoming an appealing destination for future scientific missions of NASA and ESA. Phobos is a tiny celestial body that orbits around Mars at low altitude. The unique combination of these two characteristics yields the sphere of influence of the moon to be very close to its surface. Therefore, orbital dynamics around Phobos are particularly complex, because many strong perturbations are involved. The classical models of the Keplerian two-body problem, and the circular three-body problem are not accurate enough to describe the motion of a spacecraft in the vicinity of Phobos. In this thesis, the description of the relative orbital dynamics in proximity of this moon is extended to a more accurate nonlinear model. This is undertaken by the inclusion of the perturbations due to the orbital eccentricity and the inhomogeneous gravity field of Phobos. Subsequently, several classes of non-Keplerian orbits are identified, using the analytical and numerical methodologies of dynamical systems theory. These techniques exploit the improved description of the natural dynamics, enabled by the extended model, to provide low-cost guidance trajectories, that minimize the fuel consumption and extend the mission range. In addition, the potential of exploiting artificial orbits with lowthrust is investigated. The performance and requirements of these orbits are assessed, and a number of potential mission applications near Phobos are proposed. These low-cost operations include close-range observation, communication, passive radiation shielding, and orbital pitstops for human space flight. These results could be exploited in upcoming missions targeting the exploration of this Martian moon. Furthermore, the new model can provide evidence to support the accretion theory of Phobos' origin, and to explain the formation of the craters and grooves on Phobos.