Oivnriew 



Space Medicine and Biology 



The overall tasks of Space Medicine and Biology are to assure the health and safety 

 of U.S. space crews and to understand the biological effects of space flight on 

 organisms. Four factors that may significantly limit mission duration are physiologi- 

 cal deconditioning, the biological effects of ionizing radiation, potential psychologi- 

 cal difficulties on the part of the space crew, and environmental requirements, 

 including the need of life support on missions of extended duration. Each factor 

 has many unknowns, and flight personnel may exhibit marked variability in their 

 susceptibilities to serious or limiting damage. 



Physiological deconditioning during space flight is a significant concern because its 

 effects are not well understood. Soviet cosmonaut Yuri Romanenko returned to 

 Earth on December 29, 1987, after a record 326 days in space. His return, covered in 

 the world press, suggested that humans can exist for considerable periods in space 

 and successfully readapt to conditions on Earth. However, the experience of one 

 man, particularly a veteran cosmonaut, cannot alone provide a sufficient basis for 

 broad and highly optimistic conclusions. Moreover, hard data are not generally 

 available concerning Romanenko's physiological and psychological condition during 

 his mission and following his return to Earth. 



Space Medicine and Biology is responsible in part for ensuring that American 

 crews can maintain acceptable levels of physiological conditioning throughout 

 extended space missions, ranging from the 1 to 3 years that could be required for a 

 round trip to Mars. Before the U.S. embarks on such missions, research needs to 

 be conducted to determine the limits of human endurance in space, to find the 

 physiological point of no return for space crews, to assess, prior to launch, the sus- 

 ceptibility of individuals to the various stresses, and to develop effective counter- 

 measures to the effects. 



Experiments conducted on the ground and in space have identified a few of the 

 physiological effects of microgravity on humans, which relate to the redistribution 

 and reduction in blood volume, muscle atrophy and calcium loss, and disturbances 

 (including space motion sickness) caused by confusing sensory signals. This 

 research has also tested countermeasures that will be useful on missions lasting 

 manv months. Information has not been collected, however, on the effects of longer 

 exposures to microgravity. One of the greatest challenges for life sciences research is 

 to develop countermeasures to muscle loss and bone demoralization, which will 

 probably be continuous during prolonged exposures and may not be completely 

 reversible upon the astronaut's return to Earth. Such research must be conducted in 

 space. 



Ionizing radiation poses some significant questions for extended human missions 

 i space. Considerable information is available about radiation beyond the protec- 

 ifluence ot the Earth's magnetic field but little concerning the biological effects 

 of I l/l (high atomic number, Z, and high energy, E) particles or the shielding 



d to protect crews on interplanetary missions from galactic cosmic radiation 

 partic le events. 





