Optimal out-of-ecliptic orbits for short-term space-borne infrared telescope missions

This paper presents a new approach for designing orbits for infrared (IR) space-borne observatories using multiple gravity assists. A large displacement normal to the ecliptic plane mitigates the noise generated by the local zodiacal dust, thereby reducing the size, weight, and complexity of the telescope. Although previous works focused on long-term missions, allowing very long transfer times to out-of-ecliptic orbits, this paper considers short-duration missions, for which the transfer times are tightly constrained. To reduce the transfer time, the flyby sequence includes the inner planets only: Venus, Earth, and Mars. Moreover, in order to reduce energy requirements, a fuel-optimal multiple gravity-assisted trajectory is designed. The problem is modeled using the patched-conic approximation and solved using a hybrid genetic algorithm coupled to a pattern search. Efficient trajectories requiring a minimum velocity addition, although providing a maximum observation time, are found and validated using an N-body simulation. The TPF-I mission is used as a benchmark in order to quantify the benefits of an out-of-ecliptic orbit. It is shown that the newly found orbits allow a reduction in the collector area compared to halo orbits.