In total, they went through 39 variants of the future lunar human landing system, also modeling the cost for the most promising options. The team went through a comprehensive approach for assessing alternative concepts of lunar human landers, looking at a broad number of options using architectural screening models. Finally, they analyzed the resulting tradespace and identified preferred architectures for consideration by stakeholders concerned with the design of human lunar landers. Lunar human landing system architecture tradespace modeling, Acta Astronautica (2021). Lunar human landing system architecture tradespace modeling,(2021).