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Spacecraft human-rating: Historical overview and implementation considerations

The fundamental tenets of a human-rated space system are to accommodate the needs of the crew, effectively utilize their capabilities to accomplish the mission objectives, and protect the crewmembers, as well as ground teams and the uninvolved public, from hazardous events. The concept of human-rating (previously referred to as man-rating) was originally primarily aimed at improving the reliability of launch vehicles for human use and increasing safety through the addition of escape/abort systems. The earliest use of this term found in the aerospace literature was in reference to the X-series experimental rocket planes. Later sources began including `human in the loop' design aspects driven by ergonomics and human factors, which essentially extended the application to explicitly address crew utilization. Accommodating basic human needs in the hostile environment of space is primarily achieved by incorporation of a life support system. Beyond this basic provision, however, human factors and related medical considerations can also be used to improve overall health and performance of the crew. Throughout the years, the human-rating process itself evolved from providing general guidelines to being mandated as a set of prescribed requirements. Considered collectively, the ultimate goal is to help ensure safety and mission success through proper space system design and operations. This paper provides a brief historical overview of human-rating and considerations for its implementation throughout all phases of spacecraft design and operations.