Perspectives on Spacecraft Human-Rating

Abstract

The term 'human-rated' is typically used to differentiate the increased safety requirements imposed on crewed spacecraft relative to unmanned satellites, including the launch vehicle as an integrated element. At a fundamental level, human-rating attempts to ensure the vehicle(s) and mission are designed to 'accommodate, protect, and utilize' the crew to the maximum extent possible, while also safeguarding ground personnel and uninvolved public. This definition drives life support needs, risk mitigation strategies, and vehicle and operational functionality, among other design requirements. The end result can generally be reduced to a single metricthe ability to accomplish the mission objectives with an acceptably low probability for Loss of Crew (LOC). Although this overarching goal may be well agreed upon, the means for achieving human-rating remain the subject of debate. This paper presents an overview of published literature and various NASA documents governing spacecraft human-rating, considers the relevance of analogies such as FAA airworthiness certification and housing certificates of occupancy, and offers a framework for further discussion of 'What does human-rating mean?' and 'How do we achieve it?'.