  The commercial interest in producing low-cost space missions by exploiting
the superior propellant management of low-thrust propulsion technology has
become increasingly popular. Typical to such missions is the design of transfer
trajectories between desired targets. This is a complex and computationally
expensive process. Additionally, the optimal solvers used to generate these
trajectories are extremely sensitive to initial guesses. One way to overcome
this challenge is to use a reasonably approximate trajectory as an initial
guess on optimal solvers. This paper presents a flexible approach to generating
very low thrust trajectories. The initial guess is obtained from a flexible
semi-analytic approach that can provide both planar and three-dimensional
initial guess trajectories for various design scenarios like orbit raising,
orbit insertion, phasing, and rendezvous. NASA's Evolutionary Mission
Trajectory Generator (EMTG) and General Mission Analysis Tool (GMAT) are used
as optimal solvers in this analysis. Numerical case studies are presented in
this paper.
