Optimal solar sail trajectory analysis for interstellar missions

The optimization of an interstellar probe trajectory using solar sailing is investigated. With a single solar photonic assistance, solar sails can enable the sailcraft to gain high energy to escape the solar system with a cruise speed of greater than 10 AU/year. Based on a reasonable assumption of a jettison point at 5 AU, a new objective function with a variable scale parameter is adopted to solve the time optimal control problem using an indirect method. A technique of scaling of the adjoint variables is presented to make the optimization much easier than before. Acomparison between the current results and previous studies has been conducted to show the advantages of the new objective function. In terms of the mission time, the influence of the departure point of the sailcraft from the Earth orbit is discussed without consideration of the Geo-centric escape phase. Another interesting discovery is that the angular momentum reversal trajectory is achieved as a local-optimal solution in a demonstration mission of 250 AU. Under the same initial condition, the difference between the direct and reversal flybys is discussed in detail through numerical simulations along with their advantages.