Multiple fly-by for interplanetary missions

Current state-of-the-art of propulsion system for space vehicles does not allow to deliver therequired payload for the mission to all bodies in the Solar System. Therefore, alternatives havebeen developed to reach those bodies without having the necessary technology. Gravity AssistManoeuvres take advantage of the encounter of the spacecraft with one or more celestial bodies tomodify the velocity vector of the spacecraft. These manoeuvres have already been used previouslyto reach high v targets with a very low propellant consumption.This thesis models a Gravity Assist Manoeuvre to later apply the model to a space mission to reacha target with multiple gravity assist manoeuvres around the Moon to reduce the fuel consumption.In the first part, the gravity assist manoeuvre is designed based on the angle that the normal vectorof the plane of the fly-by forms with the perpendicular vector to the velocity of the spacecraft onthe Moon reference frame and the velocity of the Moon. The second designed parameter for thefly-by is the angle that the velocity of the spacecraft relative to the Moon rotates about the planeof the fly-by modifying the direction of the spacecraft’s velocity.The second part of the project applies the previous concept of gravity assist manoeuvres to aspace mission. A spacecraft orbiting on a Geostationary Transfer Orbit is injected into an orbitto the Moon. Once the spacecraft reaches the Moon, it flies by the Moon modifying the directionand magnitude of the velocity of the spacecraft in the Earth reference frame. The orbit obtainedafter the fly-by is then propagated for a given period of time before injecting the spacecraft againinto an orbit to the Moon. After arrival to the Moon, the direction and magnitude of the velocityof the spacecraft in the Earth reference frame is modified through a second fly-by. Afterwards,the previous process is repeated again for a third fly-by before transforming the velocity of thespacecraft into the Heliocentric reference frame. The orbit is propagated for a period of timebefore getting injected into an orbit to the target of the mission.The third part of the project aims to optimise the mission developed in the second part, thoughonly two fly-bys will be considered in this part to simplify the optimisation process. The previousmission has been developed in several sections and the minimum fuel consumption has beendetermined individually for each section, obtaining a local minimum. Unfortunately, the globalminimum fuel consumption determined as the addition of those local minimum fuel consumptionmight be different, i.e. different sections might influence other sections leading to a lower globalminimum fuel consumption that has not been considered before.The fourth and last part shows future work that might be done to the project. It includes themodification and application of the code for the optimisation, the study of powered fly-bys tomodify the previous parts, and the addition of perturbations and space interactions to develop amore realistic mission