Asteroid mining is rapidly becoming a popular topic amongst space community, primarily due to the potential resources that the asteroids can provide for future spacefaring. One of the interesting resources that can be obtained from asteroids is water, which can also be processed into oxygen and fuel. An intriguing concept would be to process fuel from asteroid, and establish a fuel depot in an Earth-centered orbit. This thesis considers a mission concept consisting of travelling to an Arjuna near-Earth asteroid from a lunar distant retrograde orbit as a depot orbit, processing fuel in-situ from the water on the asteroid, and bringing back 100 tons of fuel to the depot orbit.

In order to minimize fuel consumption for such a trip, the thesis develops an optimization method that can obtain the best trajectory for different phases of the round trip, given certain constraints to ensure the spacecraft successfully reaches the asteroid and comes back to the Earth system.

The optimization model consists of four steps, i.e., the outbound trip, the first phase of the return trip, the second phase of the return trip, and the optimization for the combined phases of return trip. The outbound trip is the trajectory from the depot orbit to the asteroid. After at least three months of mining, the spacecraft brings back the processed fuel to the vicinity of the Moon. This phase is called the first phase of the return trip. The spacecraft is then captured without an insertion burn to an Earth-centered orbit by a lunar gravity assist maneuver, and travels to the point where the insertion maneuver to the depot orbit begins. This is the second phase of the return trip. The last step of the optimization is the combination of the two phases of return trip, in addition to the final maneuver for entering the lunar distant retrograde orbit.

The optimization method uses MATLAB fmincon solver, and it was applied to 29 synthetic asteroids. There were 19 converged solutions, but for 10 asteroids the optimizations was not able to converge. The lowest minimum fuel consumption for a trip is 19965.5 kg, and the highest minimum fuel consumption is 61821.4 kg. For the lowest minimum fuel consumption, the duration of the trip is nearly 7 years, and the duration for the highest minimum fuel consumption is about 2.6 years.