Study on Earth-to-Mars direct transfer trajectory by the Long March launch vehicle

In order to solve the problem of searching for optimized launch period lasting 2-3 weeks for an engineering-oriented Earth-to-Mars transfer trajectory, with constraints from the launch azimuth scope and the longest coast time on parking orbit of the cryogenic final stage, adding coast constraint into models firstly, a forward-backward bi-directional differential correction scheme which is different from the B plane vector method is proposed. It also greatly reduces the required time to accurately design and match all the six orbital elements at the separation point with probe. The hyperbolic orbital elements at the injection point of launch vehicle are directly solved from the boundary velocity at the sphere of influence of the Earth. Meanwhile the flight arc of the ground track is given analytically as a function of the coast time. Initial launch trajectory satisfying the constraints are quickly found. The problem of launch trajectory optimization is solved when considering a small deep space maneuver of Mars probe. High-precision results are obtained using this bi-directional differential correction scheme in the high-precision mechanical model. The analysis shows that the accuracy is matched with the commercial software STK under the same condition. The transfer trajectory starting from liftoff to the nominal periapsis of Mars probe is optimized as a whole, which ensures that our first Mars exploration mission implements successfully.