Application of a Two-Level Targeter for Low-Thrust Spacecraft Trajectories

Applications of electric propulsion to spaceflight in multi-body environments require a targeting algorithm to produce suitable trajectories on the ground and on board spacecraft. The two-level targeter with low thrust (TLT-LT) provides a framework to implement differential corrections in computationally-limited autonomous spacecraft applications as well as the larger design space of pre-mission planning. Extending existing two-level corrections algorithms, applications of the TLT-LT to spacecraft with a range of propulsive capabilities, from nearly-impulsive to low-thrust, are explored. The process of determining partial derivatives is generalized, allowing reduced logical complexity and increased flexibility in designing sequences of thrusting and ballistic segments. Various implementation strategies are explored to enforce constraints on time and other design variables as well as to improve convergence behavior through the use of dynamical systems theory and attenuation factors. The TLT-LT is applied to both nearly-impulsive and low-thrust spacecraft applications in the circular restricted three-body problem to demonstrate the flexibility of the framework to correct trajectories across the spectrum of thrust magnitude. Finally, parameter continuation is employed to extend a family of trajectories from a solution with nearly-impulsive thrust events to the low-thrust regime, and the characteristics of this transition are investigated.