Summani 



The first four papers discuss the four factors that potentially limit the duration of 

 human space flight. 



• "Biomedical Research" concentrates on physiological deconditioning, which 

 becomes a greater concern the longer the space mission. The commentary 

 addresses the unresolved scientific issues relevant to the following areas: 

 cardiovascular physiology, specifically a more complete characterization of 

 cardiovascular deconditioning; neurophysiology and behavioral physiology, 

 particularly space adaptation syndrome (space motion sickness); bone, 

 endocrine, and muscle physiology, involving total body calcium losses reportedly 

 averaging 3 percent per month during space flight; and hematology, including 

 the significant decreases in red cell mass reported in the Gemini, Apollo, 

 Skylab, and Soyuz flight crews. 



• The "Radiation" paper notes that NASA does not have a focused program of 

 studies concerning radiation effects on space crews. Critical, unresolved issues 

 remain in this field, however, particularly in connection with extended missions, 

 such as a lunar colony, a manned round trip to Mars, and a Mars colony. Much 

 more needs to be known about solar particle events, which could expose a 

 space crew beyond the Earth's magnetic field to debilitating or lethal doses of 

 radiation; the biological effects of high linear energy transfer (LET) radiation, 

 including galactic cosmic rays; radiation-shielding interactions, which produce 

 secondary radiation; and the most effective instrumentation for measuring real- 

 time and cumulative radiation exposures, as well as changes in biological 

 endpoints. 



• The placement of the "Crew Factors" paper, immediately following discussion of 

 biomedical and radiation concerns, emphasizes that human space flight involves 

 not onlv physiological but also psychological survivability. The most pressing 

 issues for extended manned missions, which will offer only limited possibilities 

 for emergency rescue and return to Earth, involve crew /environment interactions, 

 interpersonal interactions, human/machine integration, crew selection, command 

 and control structure, and crew motivation. Answers to the related questions are 

 beyond our direct experience, since the horizons are only beginning to open on 

 long-duration human missions. For the rest of this century, ground-based 

 research will be a practical mode for controlled experiments on group behavior. 



• "Systems Engineering" discusses life support requirements, a factor directly 

 related to both the physiological and psychological well-being of the space crew. 

 The primary concerns in this field, which incorporates a broad range of 

 disciplines, include identifying the requirements for a regenerative food, air, and 

 water system that could support long-duration missions, developing an 

 environmental monitoring system capable of detecting all possible sources and 

 types of contamination, determining the most workable systems to support EVA 

 operations, analyzing habitabilitv requirements (such as the amount ot space 

 required per person) tor extended missions, and identifying the requirements for 

 a variable-gravity facility, such as a centrifuge. 



