Ball valves are a critical component in a plethora of liquid propellant propulsion systems. The Spanish company PLD Space is considering the usage of these valves in their new series of KER-LOX liquid propellant rocket engines, the TEPREL-C & TEPREL-C Vacuum engines. These will be operating on-board the Miura 5 launch vehicle. The purpose of this research is to re-design and analyze an unoptimized ball valve design, as to make it suitable for cryogenic service while minimizing its mass. The secondary objective of the research is to inquire into the aspects of ball valve operation. This includes investigating the required operating torque of a ball valve and the achievable flow factor as a function of a ball valve's opening angle. The results of this thesis are scripts which can estimate the torque and flow factor values, a methodology to mass-optimize a ball valve, and a re-designed ball valve suitable for cryogenic service.