Design and Human Engineering (HE) processes strive to ensure that the human-machine interface is designed for optimal performance throughout the system life cycle. Each component can be tested and assessed independently to assure optimal performance, but it is not until full integration that the system and the inherent interactions between the system components can be assessed as a whole. HE processes, such as defining/applying requirements for human interaction with missions/systems, are included in space flight activities, but also need to be included in ground activities and specifically, ground facility testbeds such as the Bioregenerative Planetary Life Support Systems Test Complex (BIO-Plex). BIO-Plex is a self-contained living, working and crop-growth environment that may ultimately serve as a model for Mars surface habitation. The long duration nature of BIO-Plex brings the issue of habitability to the fore, making it tangible and testable.