Solar–Electric Planetary Missions with an Initial Out-of-Ecliptic Thrust Phase

A solar-electric propulsion mission profile with Earth gravity assist is considered that differs from more conventional mission designs by letting the thrust phase preceding the Earth swingby be inclined with respect to the ecliptic. The thrust acceleration is oriented normal to the orbit plane thus adding inclination without increasing the 1-astronomical unit solar distance. The out-of-ecliptic mission phase serves to accumulate a major relative velocity increase, directed normal to the spacecraft's orbit plane as thrust time progresses, This effect is essential to gaining greater effectiveness of the subsequent Earth swingby maneuver that converts this relative velocity component to the desired outbound direction, for example, in missions to Jupiter or other outer planets. This mission profile considered here offers considerable flexibility in the selection of launch dates and simplifies a trade between mission duration and solar-electric power, An initial inbound thrust phase in outbound missions is avoided, and thereby, the spacecraft design is simplified. The various characteristics of the modified mission profile that differ from the conventional profile are described, and the respective advantages that are due to these modifications are shown. It is shown that the out-of-ecliptic thrust phase, in combination with Earth swingby, offers considerably greater flexibility in the overall mission profile design, which in turn relieves launch date constraints and simplifies thrust vector control requirements, These factors have not been sufficiently explored as yet in previous contributions to the electric-propulsion mission and system design literature.