M.Sc Thesis

M.Sc StudentNir Gali
SubjectDesign of Out-of-Ecliptic Orbits for Space-Borne Telescopes
DepartmentDepartment of Aerospace Engineering
Supervisor PROF. Pinchas Gurfil
Full Thesis textFull thesis text - English Version


In this research, a method for obtaining optimal out-of-ecliptic orbits suitable for space-borne IR telescopes is developed. These orbits are characterized by a significant normal displacement with respect to the ecliptic plane, and therefore allow a dramatic reduction of the noise caused by the local zodiacal dust. These out-of-ecliptic orbits yield a considerable reduction in the mass and the costs of an IR mission.In order to reduce the energetic requirements, the transfer trajectories were planned using multiple gravity-assist maneuvers. The preliminary trajectory plan was based on a patched-conic approximation, which reduces the complete trajectory into a concatenation of two-body conic arcs, and therefore saves  considerable computational time. The problem is described as a constrained global optimization problem and is solved using an optimization procedure based on a hybrid genetic algorithms and pattern search method.

The design is carried out for both long and short-duration missions. In the long-duration case, Jupiter is used as the main energy source. The design problem is divided into two sub-problems: Minimizing the energy costs to reach Jupiter without considering the transfer time, and maximizing the observation time without any additional delta V.  In the short-duration case, on the other hand, arriving to Jupiter is not an option, since the required transfer time is higher than the total mission time. The trade-off between energy requirements and observation time is taken into account. In both cases, different optimal fly-by sequences and launch windows are obtained.

The obtained optimal trajectories are examined in a realistic environment using an N-body simulation. Since the actual trajectory is not able to follow the planned one without velocity corrections, a matching procedure was developed, which includes a series of small optimization problems.

The systematical benefits of out-of-ecliptic orbits are illustrated using NASA's TPF-I mission as a case study. Since the out-of-ecliptic orbit allows a dramatic reduction in the noise levels, it is possible to reduce the main mirror size without affecting the mission's features and goals. This modification dramatically reduces the mass and costs of a mission.

The main contribution of this research is the development of a method for obtaining optimal out-of-ecliptic orbits, which allows significant reduction in the mass and costs of an IR mission. The obtained trajectories are proven to allow a dramatic reduction in the cost per image of an IR telescope, and therefore, are very promising for future space-borne IR missions.