Characterizing Human Spacecraft Safety and Operability Through a Minimum Functionality Design Methodology

Abstract

A systematic methodology is presented for defining a minimum functionality baseline configuration of a human spacecraft. To estimate a lower bound for the spacecraft mass, a set of essential functions is coupled to single-string subsystems with zero fault tolerance. This minimum functionality baseline is defined to meet the physical requirements needed to transport the crew to the target destination and to ensure that their physiological needs are met, but without margin, dispersions, redundancy, or factor of safety. This constitutes a set of nonnegotiable requirements based on fundamental parameters derived from physics and physiology. By definition, this represents a technically feasible solution, but it results in the highest-risk design. Mass additions beyond the minimum functional configuration are allocated to increased safety or operability through the addition of component redundancy, fault tolerance, factor of safety, additional mission functionality, and improved human–system interfaces. This proposed methodology was used to analyze a range of lunar ascent stage spacecraft configurations, and a process was developed to allow systematic estimation of mass for the spacecraft subsystems. The modeled results are verified by comparing them with actual subsystem mass of the Apollo lunar module ascent stage.