This thesis addresses the optimisation of multi-impulse transfers in the cislunar environment for crewed missions, treating two complementary mission segments under a unified methodology: the trans-lunar leg from a Low Earth parking orbit (LEO) to the 9:2 synodic-resonant southern L2 Near-Rectilinear Halo Orbit (NRHO), and the descent leg from the NRHO to a Powered Descent Initiation (PDI) gate above the lunar south pole. The trajectories are designed in a high-fidelity four-body dynamical model that incorporates the gravitational influence of Earth, Moon, and Sun through JPL SPICE ephemerides, and are optimised for minimum total impulse (ΔV) by a hybrid scheme coupling Particle Swarm Optimisation (PSO) for global search with Sequential Quadratic Programming (SQP) for local refinement.