Gravitational Biology 



impact upon animal physiology. Rats and primates exposed to hypergravity during 

 development experience a modification in their neural thermoregulatory system 

 that causes a delay in their ability to return their body temperature to pre- 

 experimental levels. The biorhythms of growing rats exposed to hypergravity stay 

 depressed for several days and do not synchronize with light/dark cycles as do 

 ground-based control animals. Space flight has also been shown to influence the 

 rat's circadian timekeeping system. Bone-forming cells (osteoblasts) developed by 

 rats flown in space exhibit significantly inhibited rates of bone deposition. Skeletal 

 unloading has been shown to reduce the accumulation of dense, highly 

 mineralized, mature bone, in addition to reducing bone formation. However, if 

 strain is placed upon an unloaded bone via muscle tension, bone growth 

 inhibition is reduced. 



Plant Adaptation to Different Gravity Levels. Plant adaptation research is 

 focused on studying the effects of hypo- and hypergravity on metabolism, 

 especially carbohydrate, lignin, and lipid synthesis; on the composition, 

 organization, and size of plant structures; and on fluid dynamics and distribution 

 in plants. Also of interest is to determine how plants respond to the interaction of 

 gravity with various environmental factors, such as light and ionizing radiation, to 

 understand the mechanisms involved, and to separate these effects from those 

 due solely to microgravity exposure. 



Findings and Recommendations 



On-Orbit Variable-Gravity Facilities 



Findings 



• On-orbit variable-gravity facilities, which include centrifuges, are required for 

 scientific studies of microgravity: 



— Variable-gravity facilities are needed to isolate the effects of microgravity 

 from all others associated with space flight, including forces encountered 

 during launch and reentry, solar and cosmic radiation, and environmental 

 contamination. 



— Research specimens need to be subjected to different g levels for varying 

 periods of time so that the acute effects of micro- or fractional-g exposure 

 and readaptation to higher g levels can be understood. 



— Long-duration human habitation of the Moon and Mars will require prior 

 long-term studies of the effects of exposure to 1/6 g and 1/3 g on animals 

 and, eventually, humans, including studies of multigenerational exposure to 

 varied g levels. 



— Variable-gravity facilities will play a crucial role as part of a program to 

 evaluate artificial gravity as a potential countermeasure designed to reduce 

 the debilitation caused by prolonged exposure of humans to hypogravity. 



• Centrifuge size and design are governed by several factors: the physical 

 limitations imposed by spacecraft volume, the size of research specimens to be 



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