Low-Thrust Many-Revolution Trajectory Optimization

This research project set out and completed the goal to build an efficient and robust capability to optimize spacecraft trajectories that employ low-thrust propulsion through high counts of orbital revolutions while accounting for realistic mission design constraints. Contributions align with the desired outcomes in Technology Area 5.4.2.1, Low-Thrust Trajectory Optimization in a Multi-Body Dynamical Environment. In concert with low-thrust technology breakthroughs, this research enables missions to new science and exploration targets with increased payload mass and reduced costs. The underlying method is to discretize the trajectory and control schedule with respect to phase angle within the orbit and perform the optimization with differential dynamic programming (DDP). The approach is amenable to perturbations in the dynamic model, and has been demonstrated with aspherical gravity and third-body perturbations. Demonstrations include benchmark transfers from low Earth and geostationary transfer orbits to geostationary orbit, within computationally efficient parametric analysis of fuel and time of flight tradeoffs. Many-revolution trajectories are characteristic of orbit transfers accomplished by solar electric propulsion about planetary bodies. This research has contributed methods for modeling the effect of solar eclipses on the power available to the spacecraft and constraining the maximum duration of an eclipse transit. DDP has proved to be a successful design tool in the circular restricted three-body problem. Optimal trajectory design has been presented for transfers between distant retrograde orbits, Lyapunov orbits, and Halo orbits. This contribution aligns with the same area of the NASA Technology Roadmap (TA 5.4.2.1) which states the desired capability to exploit multi-body dynamics.