A CONVEX GUIDANCE APPROACH TO TARGET BALLISTIC CAPTURE CORRIDORS AT MARS

Ballistic capture corridors allow a spacecraft to be temporarily captured about a planet without any thrust firing. They represent a promising approach for future deep-space small-satellites missions, where only limited fuel can be carried onboard. In an effort to enable autonomous interplanetary CubeSats, a guidance algorithm based on convex optimization is exploited to design low-thrust minimum-fuel space trajectories which target ballistic capture corridors at Mars. An Hermite-Legendre-Gauss-Lobatto scheme with nonlinear control interpolation is used to discretize the trajectory. A variable time of flight version of the algorithm is developed and tested in closed-loop guidance simulations, where multiple reference trajectories need to be computed during a simulated interplanetary transfer. The variable time of flight algorithm is of paramount importance when closed-loop guidance is considered to avoid that no feasible solutions are found when the spacecraft is too close to the target celestial body. We show the effectiveness of the variable time of flight algorithm compared to the fixed time of flight one.