Atlas of Optimal Low-Thrust Rephasing Solutions in Circular Orbit

Abstract

In this paper, the time- and propellant-optimal low-thrust rephasing problems in circular orbit are studied to depict their solution spaces in an atlas. The rephasing problem is known as the same-orbit rendezvous from different angular positions. It is generally solved by some optimization methods, but its whole solution space is rarely investigated due to many key parameters. To reduce the number of parameters, a set of linearized equations of motion is developed based on the Sundman transformation, and two reduced shooting functions are formulated using the minimum principle and symmetry properties. Only one key parameter is identified for the time-optimal problem, while two key parameters are obtained for the propellant-optimal one. Numerical investigation of the relationships between these parameters and shooting variables reveals that they can be depicted by some curve (or contour) maps and approximated by piecewise functions (or linear interpolations). For the relatively short- or long-term rephasing cases, some analytical time- and propellant-optimal solutions are proposed and consistent with the numerical solutions. Numerical results demonstrate that the proposed solutions can provide good initial guesses to solve the low-thrust rephasing problems with nonlinear dynamics. Moreover, the approximations of the performance indexes can be used in the preliminary mission design.