The calculus of variations is used to obtain optimum three-dimensional interplanetary transfer trajectories for a specified power-limited vehicle. The constant thrust program with coast capability used is governed by two-body orbital mechanics. The trajectory is broken up into departure and arrival spirals and a heliocentric transfer. The initial and terminal states for the spacecraft are circular-equatorial parking orbits about the departure and arrival planets. A minimum heliocentric distance for the spacecraft of .723 AU was maintained. The values of the parameter for the propulsion system modeled reflect those for Inertial Electrostatic Confinement (IEC) fusion and plasma linear driven Magnetized Target Fusion (MTF). The majority of the launch dates are from the years 2024 to 2026 Numerical results are presented for optimal Earth-Mars and Earth-Jupiter trajectories obtained using VariTOP (Various Trajectory Optimization Program), which is a low to mid-thrust trajectory optimization and analysis program developed at the Jet Propulsion Laboratory (JPL).