IMECE 2004-59029 RISK ASSESSMENT AND CONTROL THROUGH COUNTERMEASURE SYSTEM IMPLEMENTATION FOR LONG-TERM CREW EXPOSURE TO MICROGRAVITY
Experience with the International Space Station (ISS) program demonstrates the degree to which engineering design and operational solutions must protect crewmembers from health risks due to long-term exposure to the microgravity environment. Risks to safety and health due to degradation in the microgravity environment include crew inability to complete emergency or nominal activities, increased risk of injury, and inability to complete safe return to the ground due to reduced strength or embrittled bones. These risks without controls slowly increase in probability for the length of the mission and become more significant for increasing mission durations. Countermeasures to microgravity include hardware systems that place a crewmember’s body under elevated stress to produce an effect similar to daily exposure to gravity. The ISS countermeasure system is predominately composed of customized exercise machines. Historical treatment of microgravity countermeasure systems as medical research experiments unintentionally reduced the foreseen importance and therefore the capability of the systems to hnction in a longterm operational role. Long-term hazardous effects and steadily increasing operational risks due to non-functional countermeasure equipment require a more rigorous design approach and incorporation of redundancy into seemingly nonmission-critical hardware systems. Variations in the rate of health degradation and responsiveness to countermeasures among the crew population drastically increase the challenge for design requirements development and verification of the appropriate risk control strategy. The long-term nature of the hazards and severe limits on logistical re-supply mass, volume and frequency complicates assessment of hardware availability and verification of an adequate maintenance and sparing plan. Design achievement of medically defined performance requirements by microgravity countermeasure systems and incorporation of adequate failure tolerance significantly reduces these risks. Future implementation of on-site monitoring hardware for critical health parameters such as bone mineral density would allow greater responsiver.ess, efficiency, and optimized design of the countermeasures system. INTRODUCTION Human beings are adapted to live and work in the 1-g environment of Earth. Once that biological system is placed in the near-zero-gravity environment of low Earth orbit (LEO), it reacts to the changing stimuli in ways that are deleterious both to continued function on-orbit, and especially to return to normal life back on Earth’s surface. As expected, some of the most serious effects on the body involve those systems involved in resisting the pull of gravity including the skeletal system and skeletal muscle groups involved in posture and locomotion. Effective countermeasures against the effects of microgravity on human beings must be developed if we are to continue to safely complete long-term missions in Space or other worlds with reduced gra-vitj;. NASA research of the effects on the human body of long-term living in Space dates back to the Skylab missions of the 1970s, when U.S. astronauts first lived in LEO for up to 84 days. As medical ethics require, NASA has always provided crewmembers with the best countermeasures available at the time, so little data is existent on the wholly unmitigated effects of microgravity on humans. However, the mitigated effects demonstrate the critical nature of
Main medical results of extended flights on space station Mir in 1986-1990.
During 1986-1990 seven prime spacecrews (16 cosmonauts) have flown on-board the Mir orbital complex. The longest space mission duration was 366 days The principal objectives of the medical tasks were the maintenance of good health and performance of the spacecrews and conducting medical research programs which included study of the cardiovascular, motor, endocrine, blood, immune, and metabolic systems. Results obtained point to the ability of humans to readily adapt to a year-long stay in space and maintain good health and performance. Readaptation had a similar course as after other previous long-term space flights of up to 8 months in duration. Primary body system changes were not qualitatively different from findings after flights aboard the Salyut 6 and 7 space stations. In this case, during and after an 11-12 month flight, body system alterations were even less severe which was a result of adequate countermeasure use, their systematic and creative employment and maintenance of required environments to support life and work in space.
Modifications of spontaneous oculomotor activity in microgravitational conditions.
Investigations on spontaneous oculomotor activity were carried out prior to and after (five cosmonauts) and during space flight (two cosmonauts) on the 3rd, 5th and 164th days of the space flight. Recording of oculomotor activity was carried out by electrooculography on automated data acquisition and processing system "Zora" based on personal computers. During the space flight and after it all the cosmonauts with the eyes closed or open and dark-goggled showed an essential increase of the movements' amplitude when removing the eyes into the extreme positions especially in a vertical direction, occurrence of correcting saccadic movements (or nystagmus), an increase in time of fixing reactions.