During the past 40 years of manned spaceflight, some insight has been gained about human performance in space. Unfortunately, it has been largely about astronauts and cosmonauts on short-duration missions, and is of limited value for those who will live for much longer periods aloft. But, we have learned that, deprived of Earth's gravity for extended spaceflights, the body gradually acclimatizes to microgravity, but cardiovascular deconditioning sets in, human bones lose calcium, a demineralization process begins, and the "space adaptation syndrome'' of nausea, disorientation, or discomfort can be overcome by most spacefarers .
The mission records for days aloft were first established by Skylab (three astronauts in 1974 for 84 days) and Salyut 7 (three cosmonauts in 1984 for 237 days). Between the Skylab days and the era of the Shuttle-Mir link-ups, American experience in space was limited to orbital Shuttle flights. Thr longest such mission was the STS-80 flight of Columbia in November 1996 when the crew of five spent 17 days 15 hours aloft, carrying out many tasks including deploying two satellites and successfully recovering them after they had performed their tasks. The first American to carry out a long-duration mission aboard Mir was Dr. Norman Thagard, who spent 115 days aloft in 1995. Currently, Russian cosmonauts hold the long-duration honors for stays in Earth orbit. Space medic Dr. Valeri Polyakov spent 438 days in orbit (over 14 months) between January 1994 and March 1995. His combined space experience is 679 days (over 22 months). By contrast, the record for the longest single space mission by an American is 215 days, helf by Michael Lopez-Alegria. Such timespans offworld will constantly be extended to years and eventually decades. At present, assignments are for six months aboard the International Space Station, as well as at a lunar outpost when it is completed by 2020.
Our extraterrestrial human experience to date proves that steps can be taken to improve crew efficiency, ranging from automation and environment control systems, to exercising and scheduling alterations. In 1987, some of this accumulated information benefited two Soviet cosmonauts on their Soyuz TM-2/TM-3 missions. Alek-sander Aleksandrov stayed in orbit for 160 days, and his companion, Yuri Romanenko, spent 326 days aloft. During this time, Romanenko grew one centimeter taller and lost 1.6 kg of body weight, and experienced fatigue, listlessness, and homesickness during his long flight. In December 1988, cosmonauts Vladimir Titov and Musa Manarov spent over a year in space on the Mir station, returning in the Soyuz TM-6 capsule with their three-week visitor, Frenchman Jean-Loup Chretien. Radio Moscow reported that immediate medical check-ups on landing showed them feeling well, and subsequent physical evaluation of the two spacefarers at Star City revealed no serious difficulties after their prolonged weightlessness for 366 days. This was partially attributed to exercise twice a day by Manarov and Titov on both a treadmill and an exercise bicycle. They also had special space suits which forced blood to concentrate in the lower parts of their bodies, simulating the effect of gravity, so that they would not become accustomed to weightlessness. Despite these precautions against calcium loss in long spaceflights, they did shrink in size as their legs lost calcium, but managed to return to Earth in better shape by use of vitamin supplements. During their 12 months plus on the station, the then record-holders conducted extensive astrophysical studies, technological experiments, and medical tests, as well as studying sources of radiation and taking more than 12,000 photographs of the Earth's surface (Los Angeles Times, December 22, 1988, p. 8). In January 1994, cosmonaut physician Valery Polyakov, 51 years of age, blasted off for 438 days in space, circling the Earth over 7,000 times in Mir. Such accounts confirm high performance in space by both astronauts and cosmonauts, feats which will be continuously surpassed by spacefarers to follow! These duration records for orbital assignments made by space pioneers are the precursors for long-term colonists in space.
NASA director of life sciences Arnauld Nicogossian confirmed the paucity of knowledge concerning human physiology and performance in the weightless environment. Unless research is expanded on the biomedical, psychological, and biospheric factors of spaceflight, long-duration manned missions may be jeopardized. Nicogossian, the author of Space Physiology and Medicine, made these pertinent observations :
• ground training in biogenic or autogenic feedback may precondition some people to spaceflight so they may master motion sickness aloft;
• after four days in space, the body adapts to weightlessness, yet we do not fully understand the influence of visual perception;
• drugs have different effects aloft than on the ground, so use of that therapy for motion sickness or other ailments has to consider issues of metabolism in space;
• although the Russians have had missions as long as 237 days or more, NASA is presently confident operationally with scheduling for 90 days aloft in terms of providing adequate medical support;
• a health maintenance facility is proposed for inclusion on the International Space Station to deal with incapacitating illness or injury, as well as dental problems— all of which impact performance;
• ignorance exists on closed environments for long-term flights, especially relative to out-gassed material and their contribution to headaches, irritability, drowsiness, and depression; meal times have been demonstrated as of psychological importance for on-orbit socialization;
• insufficient research has been done on matters of decor (color scheme, number of windows, etc.) and privacy influences on performance;
• inadequate data on human factors exist for a manned Mars mission.
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