This thesis details the mechanical design and analysis of the MSL BitBox, which allows the robotic arm of a specially designed Mars rover to replace a drill bit assembly that is attached to the robotic arm with an identical back-up. This is all accomplished though built-in functionality of the robotic arm along with additional mechanisms of the BitBox. The thesis begins by providing an overview of the BitBox and then moves into detailing the design of the components. Then a presentation of the finite element analysis utilized to refine the design is discussed. Finally, the thesis provides an overview of the operation of the BitBox and its interaction with the MSL Rover's robotic arm. The resulting design proved to be very functional, and two BitBoxes were implemented rather than one as originally planned. Variations of the BitBox design could be used for other rover missions that utilize a robotic arm, both on terrestrial planets as well as in deep-sea operations.