This document contains a sustainability study of a permanent Martian outpost. It involves a preliminary introduction to the exploration of Mars and concepts related to sustainability such as sustainable development, carrying capacity or impact, as well as an overview of previous studies regarding human exploration of Mars. The methodology proposed to carry out the sustainability study is a brand-new approach to the analysis of space exploration missions that focus on the impact of the mission elements regarding the Earth, the Outer Space, and Mars itself. It also provides a framework that will allow to extend the study to location-related carrying capacity assessment, and In Situ Resource Utilization and Environmental Control and Life Support Systems’ circularity. After a discussion of the results obtained from the quantitative analysis performed, an extensive proposal of future work is provided, as well as orientation on what to expect from future missions to the red planet.