The main goals of NASA's Evolvable Mars Campaign (EMC) include expanding the human presence on Mars by 2030 to promote scientific progress, innovation and international collaborations. This campaign, therefore, requires the development of new technologies to support the human presence and to transport heavy cargo to Mars. Thus, the development of multifunctional and reusable landers including the Mars Ascent Vehicle (MAV) is critical. This thesis addresses the preliminary sizing of the major subsystems of a manned Mars lander with the ability to descend and ascend from Mars orbit. The goal is to deliver a tool requiring a limited set of users’ inputs to select that will allow for a set of outputs calculated through specific algorithms.