Time-optimal trajectory design for a dual-satellite sailcraft interstellar mission with probe release

In this paper, a time-optimal trajectory design for a novel dual-satellite sailcraft is presented to accomplish mid or far-term interstellar missions. The mission considered also requires the release of a probe at the perihelion point of the sailcraft. Consequently, the lightness number of the sail undergoes a positive jump at probe release, reaching a value significantly greater than one, thus allowing the sailcraft to reach a very high terminal speed at a sail-jettison distance of 5 AU. An ideal sail force model and the two-body dynamic equations are utilized in the current study. The sail cone and clock angles are the control variables. The mission requirements result in a discontinuous, time-optimal control problem, which is solved by the application of an indirect method, involving the solution to a multi-point boundary value problem. A number of mission scenarios are investigated by varying relevant parameters, such as the mass of the probe, the minimum perihelion distance and the initial sail lightness number. The paper presents data regarding flight time and terminal speeds at distances ranging from 5 to 500 AU. In some cases, the final jettison velocities are as high as 60 AU per year, indicating the possibility of a dramatic reduction in the flight time to make the 500 AU missions feasible.