Deimos encounter trajectory design for piggyback spacecraft launched for Martian surface reconnaissance

This paper discusses a trajectory design for imaging both Mars and Deimos, which meets the requirements of the next Chinese mission to Mars and Deimos. Compared to Viking-1, being weak in systematic schedules in its original and extended missions, which resulted in the use of more fuel and reducing encounter opportunities, a multipurpose design is addressed in this paper for imaging both Mars and Deimos at Pre-Phase A, not after launch. A frozen and repeating orbit is employed to provide as many as 280 periodic encounters within 100km of Deimos, in contrast to the fly-around mode used by Phobos-1/2 and Phobos-Grunt, requiring much fuel to guide the spacecraft to the vicinity of Phobos from the highly elliptical captured orbit. To enable encounters with Deimos under all of the perturbations and orbital control and determination errors, the station-keeping strategies for the arguments of periareon and latitude are implemented by some corrections to the semi-major axis and inclination, respectively. A numerical simulation is used to verify the encounter opportunities with the help of the station-keeping strategies. Detailed investigations on imaging, lighting and access conditions show that a working orbit is beneficial for imaging both the Martian surface and Deimos. Therefore, it is concluded that designing the trajectory of the piggyback spacecraft to be carried by the main orbiter in the next Chinese Mars mission during Pre-Phase A is practical from the engineering perspective.