**7. Artificial gravity as a total countermeasure for spaceflight deconditioning**

For human space voyages lasting several years, such as those envisioned for the exploration of Mars, astronauts will be at risk of catastrophic consequences should any of the systems that provide air, water, food, or thermal protection fail. Beyond that, astronauts will face serious health and/or safety risks resulting from marked physiological deconditioning associated with prolonged weightlessness [1, 79]. The principal physiological deconditioning risks are related to physical and functional deterioration, and the loss of regulation of the several systems, including blood circulation, decreased aerobic capacity, musculoskeletal systems, and altered sensorimotor system performance. These physiological effects of weightlessness are generally adaptive to spaceflight and present a hazard only following G transitions upon returning to Earth or landing on another planet [80]. Among them, bone mineral metabolism will be greatly affected during prolonged spaceflight.

## **7.1 Why artificial gravity**

Space biomedical researchers have been working for many years to develop "countermeasures" to reduce or eliminate the deconditioning associated with prolonged weightlessness. Intensive and sustained aerobic exercise on a treadmill, bicycle, or rowing machine coupled with intensive resistive exercise has been

**27**

as Mars expeditions.

*Effects of Microgravity on Human Physiology DOI: http://dx.doi.org/10.5772/intechopen.90700*

loading in space is warranted.

used on US and Russian spacecraft to minimize these problems. The procedures were uncomfortable and excessively time-consuming for many astronauts, and their effectiveness for maintaining bone, muscle, and aerobic fitness has not been demonstrated due in part to the low reliability of the devices flown to date. Furthermore, they have had inconsistent effects on postflight orthostatic hypotension or sensorimotor adaptive changes. With the exception of fluid loading before reentry, other countermeasures (e.g., diet, lower body negative pressure, or wearing a "penguin suit" to force joint extension against a resistive force) either have been

To succeed in the near-term goal of a human mission to Mars during the second quarter of this century, the human risks associated with prolonged weightlessness must be mitigated well beyond our current capabilities. Indeed, during nearly 45 years of human spaceflight experience, including numerous long-duration missions, no single countermeasure or combination of countermeasures that is completely effective has been developed. Current operational countermeasures have not been rigorously validated and have not fully protected any long-duration (>3 months) astronauts in low Earth orbit. Thus, it is unlikely that they will sufficiently protect astronauts journeying to Mars and back over a 3-year period.

Although improvements in exercise protocols, changes in diet, or pharmaceutical treatments of individual systems may be of value, they are unlikely to eliminate the full range of physiological deconditioning. Therefore, a complete research and development program aimed at substituting the missing gravitational cues, and

The urgency of exploration-class countermeasures is compounded by the limited availability of flight resources for validating a large number of system-specific countermeasure approaches. Furthermore, recent evidence of the rapid degradation of pharmaceuticals flown aboard long-duration missions, putatively because of radiation effects, raises concerns regarding the viability of some promising countermeasure development results. Although the rotation of a Mars-bound spacecraft will not be a panacea for all human risks of spaceflight (artificial gravity cannot solve the problems associated with radiation exposure, isolation, confinement, and environmental homeostasis), artificial gravity does offer significant promise as an effective, efficient, multi-system countermeasure against the physiological deconditioning associated with prolonged weightlessness. Virtually all of the identified risks associated with cardiovascular deconditioning, myatrophy, bone loss, neurovestibular disturbances, space anemia, immune compromise, and neurovegeta-

Although a short-radius centrifuge has been proposed several times, loading with artificial gravity has not been demonstrated to be effective at preventing spaceflight deconditioning on its own. Making a human-powered short-arm centrifuge is an effective method to create exercise loads for astronauts. Considering the size of the ISS, it is appropriate to employ a short-radius centrifuge rather than a large-radius human centrifuge; however, it may be beneficial to rotate the spacecraft itself to provide the artificial gravity for long-duration spaceflight such

In 1999, Iwase proposed the creation of artificial gravity by ergometric exercise, and it was installed at Nagoya University [33]. Several studies were performed using this short-radius centrifuge with an ergometer. In 2002, a bedrest study was carried out to evaluate the effectiveness of artificial gravity with ergometric exercise. In 2005, the facility was moved to Aichi Medical University, and bedrest studies

marginally effective or presented an inconvenience or hazard.

tive state may be alleviated by sufficient artificial gravity.

**7.2 Why artificial gravity with exercise**

### *Effects of Microgravity on Human Physiology DOI: http://dx.doi.org/10.5772/intechopen.90700*

*Beyond LEO - Human Health Issues for Deep Space Exploration*

with a significant increase in glutathione content.

and cause hemolysis due to suppressed erythropoiesis.

quickly disappear upon returning to 1 G on Earth.

which leads to susceptibility to viruses.

**6.2 Immunological changes during weightlessness**

increased plasma volume, reduced hemoglobin concentration, and increased serum erythropoietin. This reflects a decrease in the RBC life span and slower production. Rizzo et al. [76] analyzed the cause of the shortened RBC life span and reported altered cell membrane composition and an increase in lipid peroxidation products. They suggested that antioxidant defense systems in the erythrocytes were induced,

The mechanism underlying anemia was also confirmed by measuring the erythropoietin (EPO) level [77]. Radioimmunoassay revealed that the EPO level decreases after 24 hours of flight and is reduced by 30–40% on the third day compared with preflight levels. This low secretion of EPO will inhibit RBC maturation

Other changes in leukocytes (WBC) are in their polymorphonuclear characteristics. The composition of WBC is changed such that there is a slight increase in neutrophils and decrease in eosinophils. The percentage of lymphocytes, especially T cells, decreases, whereas that of monocytes slightly increases. These changes

Recent studies confirmed dysregulation of the immunological response in humans and the reactivation of latent herpes virus, which persisted for the duration of a 6-month orbital spaceflight [78]. Blood samples from ISS crew members demonstrated that long exposure to microgravity reduced their T lymphocyte counts, suggesting the attenuation of cytotoxic function and viral reactivation in the space

As the immune system is highly sensitive to different types of stressors, including psychological, physical, and local environmental stressors (e.g., oxidative and radiation exposure), exposure to the space environment suppresses T helper cells,

For human space voyages lasting several years, such as those envisioned for the exploration of Mars, astronauts will be at risk of catastrophic consequences should any of the systems that provide air, water, food, or thermal protection fail. Beyond that, astronauts will face serious health and/or safety risks resulting from marked physiological deconditioning associated with prolonged weightlessness [1, 79]. The principal physiological deconditioning risks are related to physical and functional deterioration, and the loss of regulation of the several systems, including blood circulation, decreased aerobic capacity, musculoskeletal systems, and altered sensorimotor system performance. These physiological effects of weightlessness are generally adaptive to spaceflight and present a hazard only following G transitions upon returning to Earth or landing on another planet [80]. Among them, bone mineral metabolism will be greatly affected during prolonged spaceflight.

Space biomedical researchers have been working for many years to develop "countermeasures" to reduce or eliminate the deconditioning associated with prolonged weightlessness. Intensive and sustained aerobic exercise on a treadmill, bicycle, or rowing machine coupled with intensive resistive exercise has been

**7. Artificial gravity as a total countermeasure for spaceflight** 

**26**

environment.

**deconditioning**

**7.1 Why artificial gravity**

used on US and Russian spacecraft to minimize these problems. The procedures were uncomfortable and excessively time-consuming for many astronauts, and their effectiveness for maintaining bone, muscle, and aerobic fitness has not been demonstrated due in part to the low reliability of the devices flown to date. Furthermore, they have had inconsistent effects on postflight orthostatic hypotension or sensorimotor adaptive changes. With the exception of fluid loading before reentry, other countermeasures (e.g., diet, lower body negative pressure, or wearing a "penguin suit" to force joint extension against a resistive force) either have been marginally effective or presented an inconvenience or hazard.

To succeed in the near-term goal of a human mission to Mars during the second quarter of this century, the human risks associated with prolonged weightlessness must be mitigated well beyond our current capabilities. Indeed, during nearly 45 years of human spaceflight experience, including numerous long-duration missions, no single countermeasure or combination of countermeasures that is completely effective has been developed. Current operational countermeasures have not been rigorously validated and have not fully protected any long-duration (>3 months) astronauts in low Earth orbit. Thus, it is unlikely that they will sufficiently protect astronauts journeying to Mars and back over a 3-year period.

Although improvements in exercise protocols, changes in diet, or pharmaceutical treatments of individual systems may be of value, they are unlikely to eliminate the full range of physiological deconditioning. Therefore, a complete research and development program aimed at substituting the missing gravitational cues, and loading in space is warranted.

The urgency of exploration-class countermeasures is compounded by the limited availability of flight resources for validating a large number of system-specific countermeasure approaches. Furthermore, recent evidence of the rapid degradation of pharmaceuticals flown aboard long-duration missions, putatively because of radiation effects, raises concerns regarding the viability of some promising countermeasure development results. Although the rotation of a Mars-bound spacecraft will not be a panacea for all human risks of spaceflight (artificial gravity cannot solve the problems associated with radiation exposure, isolation, confinement, and environmental homeostasis), artificial gravity does offer significant promise as an effective, efficient, multi-system countermeasure against the physiological deconditioning associated with prolonged weightlessness. Virtually all of the identified risks associated with cardiovascular deconditioning, myatrophy, bone loss, neurovestibular disturbances, space anemia, immune compromise, and neurovegetative state may be alleviated by sufficient artificial gravity.
