Research on Trajectory Design of Launch Vehicle Based on Linear-gravity Field

Abstract

To solve the problem of optimal ascent trajectory design in case of small thrust-weight ratio of launch vehicle's last stage, and send payloads into orbit with much less velocity loss and propellant consuming, a new trajectory design method based on more accurate line-gravity field was proposed by simplifying yaw program angle and co-states, which transfered the optimal thrust direction in vacuum flight into a two-point boundary value problem containing five constraints, and got the optimal trajectory by integrating motion equations. Furthermore, the initial values of iteration were analyzed according to launch vehicle's flight features, and an estimation method of initial values of co-states and flight time was deduced, and a means and process of launch vehicle trajectory design in whole ascent flight based on linear-gravity field was put forward. The simulations show that this method generates the same results with the conventional method in situation of normal thrust-weight ratio, and pitch program angle varies nearly linearly. In situation of small thrust-weight ratio, this method generates much less velocity loss, saving 2.9% and 2.1% propellant compared with the conventional method and iterative guidance respectively, and pitch program angle varies non-linearly. This method is of good convergence and optimization effect, and can be well applied in trajectory design of small thrust-weight ratio and launch vehicle's whole ascent flight. This method can also supply a new means of online trajectory planning, etc.