Functional integration of humans and spacecraft through physics, physiology, safety and operability

Design criteria for human-rated space systems can be broken down into four top-level functional categories grouped by parameters of physics, physiology, safety and operability. Starting with a minimal function design baseline, a set of non-negotiable requirements can be derived that provide the requisite physical protection from the space environment and meet the basic physiological needs of the crew, but nothing more. This can be thought of as a `technically feasible, but programmatically unacceptable' initial solution from which to start the iterative trade study process that will ultimately make the system safer and/or nicer (i.e., more operable). Safety aspects include risk mitigation approaches such as added redundancy, increased factor of safety or consumable margins. Operability can be further categorized into accommodation (what the vehicle provides the crew beyond the bare necessities) and utilization (what the crew does for the vehicle/mission), which can be evaluated through human factors analysis and testing. This framework provides clear and relatively simple guidelines for defining a set of baseline, minimum functionality conceptual design requirements that can theoretically accomplish the stated mission objectives. It can also serve as a verification and validation method to be used throughout the design process for ensuring that any additional features requested to be incorporated into the spacecraft beyond the minimal baseline are systematically rationalized for inclusion. Employing this philosophy from the beginning of a program can help to reduce the typical mass overruns that tend to occur from baselining legacy solutions and to minimize `scope creep' by making it necessary to rigorously justify each function that is added over and above the minimum baseline in terms of improved safety or operability. This work outlines how a human spacecraft design scheme such as this can be defined and implemented.