Abstract:

Occulter-based telescopy offers a promising new terrestrial planet-finding methodology that involves the formation flying of a conventional space telescope with a large external occulter, which will block the light of a star and allow imaging of its dim, close-by planetary companion. Recent advances in shaped-pupil technology have enabled the design of occulters that have superior diffraction performance and that can be manufactured easily. This approach is attractive because it eliminates the precision-optical requirements of the alternative coronagraphic or interferometric approaches. However, it introduces new scientific challenges in the area of precise dynamics and control, which is the topic of this dissertation.

Due to the large distances between satellites, realignment is fuel intensive, which increases the mission cost and reduces its lifetime. In order to overcome this problem, this dissertation focuses on the trajectory design of the mask satellite and conducts an optimization study to select the order and timing of imaging sessions.

The optimal configuration of satellite formations consisting of a telescope and multiple occulters around Sun-Earth L2 Halo orbits is studied first. Focusing on the Quasi-Halo orbits, which are of interest for fuel-free occulter placement, the phase space around L2 is examined. The periodic orbits of interest around L2 are numerically computed and their stability properties analyzed.

Quasi-Halos are good candidates for occulter placement, as they are fuel-free orbits and have large sky coverage with respect to the Halo orbit, where the telescope is placed. With the aim of identifying these orbits, a new fully numerical method that employs multiple Poincar? sections to find quasi-periodic orbits is developed. This methodology has the advantage of very fast execution times and robust behavior near chaotic regions that leads to full convergence. Its numerical implementations for Lissajous and Quasi-Halo orbits are explained. These results are then extended from the simplified three body model to find the orbits in the real solar system that have the same characteristics.

Trajectory optimization of the occulter motion between imaging sessions of different stars is performed using a range of different criteria and methods. This enables the transformation of the global optimization problem into a Time-Dependent Traveling Salesman Problem (TSP). The TSP is solved first for a formation consisting of a telescope and a single occulter. Then, with the insight from the dynamical analysis, multiple-occulter formations are analyzed and the global optimization is performed for the multiple-occulter case.

For a concrete understanding of the feasibility of the mission, the performance of an example spacecraft, SMART-1, is analyzed. The mission is shown to be feasible with the current technology.