The launch vehicle industry is undergoing a major shift as new commercial organizations are staking claim to large market shares with bold technologies. To stay competitive in this new era, launch vehicle companies must develop new technologies to reduce launch costs while serving the growing demand for space accessibility. A possible solution is to use additive manufacturing in combination with topology optimization to relieve manufacturing and assembly burdens in addition to reducing launch mass. Topology optimization is a mathematical method that optimizes the distribution of material in a design domain for a given combination of loads, boundary conditions and constraints with the objective of maximizing mechanical performance. Now an increasingly popular design tool in the aerospace and automotive industries, topology optimization is used to redesign structures to reduce mass while increasing stiffness. To effectively apply this design tool to launcher structures, the optimization process must take into account multiple load cases to represent the large number of load cases such structures are subjected to, throughout the various flight phases. In this thesis, a design methodology was established for topology optimization of launcher structures under multiple load cases by redesigning a launcher structure produced by Airbus Defence and Space Netherlands. The thesis used two analytical models; a simple cantilever beam model to set baseline expectations of design methodologies which were then verified on the launcher structure demonstrator model. To achieve the objective, a suitable multiple load case objective function was identified for the design problem at hand by testing different objective functions on both analytical models. In the process, efficient ways to accommodate the large number of load cases in the objective were also studied through which promising methods to reduce the number of load cases were identified. The final optimized design was compared to the original launcher structure which showed that the optimized design exhibited organic design features, higher stiffness with the same mass. This thesis provided insight into multiple load case topology optimization which is expected to accelerate its adoption in the launch vehicle industry and pave a new path for more efficient space travel.