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The interest for near-Earth asteroids for scientific studies and, in particular, for potentially hazardous asteroids requires the space community to perform multiple-asteroid missions with close-up observations. To this end, multiple near-Earth asteroid rendezvous missions can help reduce the cost of the mission. Given the enormous number of asteroids, this work proposes a method based on artificial neural networks (ANNs) to quickly estimate the transfer time and cost between asteroids using low-thrust propulsion. The neural network output is used in a sequence search algorithm based on a tree-search method to identify feasible sequences of asteroids to rendezvous. The rendezvous sequences are optimized by solving an optimal control problem for each leg to verify the feasibility of the transfer. The effectiveness of the presented methodology is assessed through sequences of asteroids of interest optimized using two low-thrust propulsion systems, namely solar electric propulsion and solar sailing. The results show that ANNs are able to estimate the duration and cost of low-thrust transfers with high accuracy in a modest computational time.

This report presents a mapping between the elements of highly non-Keplerian orbits and classical orbital elements. Three sets of elements are discussed and mappings are derived in closed, analytical form for both the direct and inverse problem. Advantages and drawbacks of the use of each set of elements are discussed. A sensitivity analysis is performed on all mappings presented. The spacecraft thrust-induced acceleration used to generate families of highly non-Keplerian orbits is extracted from the inverse mapping from the osculating orbital elements. The key signatures of highly non-Keplerian orbits in Keplerian elements tracking data are determined through a set of representative test cases.

The scientific interest for near-Earth asteroids (NEAs) as well as the interest in potentially hazardous asteroids from the perspective of planetary defense led the space community to focus on NEA mission studies. A multiple NEA rendezvous mission with close-up observations of several objects can help to improve the characterization of these asteroids. This work explores the design of a solar-sail spacecraft for such a mission, focusing on the search of possible sequences of encounters and the trajectory optimization. This is done in two sequential steps: a sequence search by means of a simplified trajectory model and a set of heuristic rules based on astrodynamics, and a subsequent optimization phase. A shape-based approach for solar sailing has been developed and used for the first phase. The effectiveness of the proposed approach is demonstrated through a fully-optimized multiple NEA rendezvous mission. The results show that it is possible to visit 5 NEAs within 10 years with near-term solar-sail technology.