Many more candidates were trained for the Gemini, Apollo, and Skylab programmes. The emphasis shifted towards academic qualifications, and scientists were accepted in addition to pilots. The advent of the space shuttle in the 1980s made space flight almost routine, and civilians were allowed to fly as passengers with relatively little training. Indeed, instead of going to war, the Soviets and Americans vied with each other to offer rides in space to political allies and 'minority' groups. The official route into the space shuttle for civilians is to become a payload specialist (PS), the job being to look after some specialist aspect of the mission, such as a scientific or industrial experiment. The PS initially trains for one mission only, though some individuals continue as career astronauts. Much of the mission training is carried out in the laboratory of the payload developer, and in ground mock-ups of the spacelab and shuttle orbiter. PS applicants go through the screening procedures of their own countries and those of NASA (the National Aeronautics and Space Administration) or ESA (the European Space Agency), a small number then being selected to train for a particular mission. Final selection usually depends partly on performance in training, and partly on political and other considerations. For future long-duration international missions more attention will be paid to the compatibility of crew members.
The number of scientific experiments has increased enormously, several hundred having been carried on Spacelab missions (attached to NASA's shuttle) and on Mir (the former USSR space station). Civilian scientists have an important role in running space experiments, and they, too, must train to play their part in the complexities of a scientific mission. They have to participate in 'timeline' simulations, and learn how to use the communication systems.
1. The mission
2. The return to earth
3. The future
1. The mission
Many of the difficulties of living in space occur in other confined environments. These include isolation from the normal world and limited communication with it; problems of living in a small space; lack of privacy; social interactions within a small group; artificial day–night cycles, and shift of circadian rhythms (see biological clock); anxieties about the life-support system and a safe return to the normal world; tiredness due to long work schedules; delays in completing assigned tasks and coping with apparatus failures; and boredom on long missions. All of these difficulties are shared by deep-sea divers operating from submersible chambers.The unique aspect of space travel is weightlessness. An orbiting spacecraft is in a state of free fall, because the earth's gravitational acceleration is exactly balanced by the radial acceleration produced by the curved flight path of the spacecraft. The resulting microgravity (near zero gravity) causes various physiological changes, such as a shift of body fluids to the head, loss of calcium in the bones, muscular atrophy, and changes in blood composition. One of the most distressing effects is that of space motion sickness, which affects about half of all astronauts during their first two to four days in space. Motion sickness was not a problem on early NASA missions, but the incidence appears to have increased. One reason for the increase is that crew members move around more in larger spacecraft. The other reason is increased detail in reporting symptoms: for example, a crew member of Spacelab 1 gave magnitude estimates of his feelings of discomfort during the first fourteen hours in orbit (Fig. 1).
Space motion sickness — like other forms of motion sickness — is probably due to sensory conflict. The normal correspondence between visual, vestibular, and tactile stimulation breaks down, and the traveller may feel disoriented and nauseated until his brain learns to reintegrate the sensory information (see spatial coordination). It is perhaps remarkable that this learning can occur within two or three days. There is little evidence for a relationship between susceptibility to motion sickness on the ground and in space. This may be because astronauts usually avoid making provocative movements in space, and may not fully report any symptoms. Also, the nature of the sensory conflict is different: passengers on earth are passively subjected to unusual changes in acceleration, whereas astronauts move actively in a constant microgravity environment.
The vestibular system consists of the semi-circular canals (whose sense organs respond mainly to rotary acceleration) and the otolithic organs (which respond mainly to linear acceleration and gravity). Head movements on earth produce a familiar combination of signals from the canals and otoliths. Under weightless conditions the canals operate normally, but the otoliths do not. They can no longer indicate head orientation with respect to gravity, but only linear acceleration fore–aft or left–right or up–down. The astronaut must therefore learn to reinterpret otolithic information. Pitch and roll head movements are particularly provocative, as are ambiguous visual stimuli such as the view of the spacecraft from an 'inverted' orientation, or seeing another crew member 'upside-down'. Unlike terrestrial travellers, astronauts can remove themselves from provocative stimulation: they can wedge themselves into a corner, close their eyes and keep their head still. Drugs can provide some protection against motion sickness, both on earth and in space, but they may produce unwanted side-effects such as drowsiness or dry throat.
Many investigators have studied how perceptual-motor skills adapt to a microgravity environment. Early in a mission, astronauts rely more heavily on visual than other cues to determine bodily orientation and the direction of gaze. There may be a reduction in the vestibular contribution to reflex eye movements and spinal reflexes. Astronauts learn how to move themselves around in space, using the hands and arms rather than the legs. They learn new patterns of hand–eye coordination, and reprogramme rapid arm movements so as not to overreach in microgravity. They also partially adapt to their own loss of arm weight, and learn to judge the mass of objects through inertial cues rather than weight. There is some initial rapid improvement in these skills, followed by gradual improvement over a few days; but mass discrimination in space remains poorer than weight discrimination on earth.
Astronauts report good visual acuity for details seen on earth, and current research shows no consistent changes in near vision or the visual contrast sensitivity function.
Fig. 1. Magnitude estimate of discomfort for one subject during the first fourteen hours in orbit. A score of 20 indicates vomiting. Curves between data points were interpolated by the subject. The diamond represents medication (scopolamine and Dexedrine), followed by the horizontal bar representing the period of maximal effectiveness.
2. The return to earth
Returning astronauts are rather like swimmers staggering ashore after a long swim. They feel heavy and clumsy. In addition, their vestibular coordination is disturbed, and they may see the world swing round in an unusual manner with head movements. 'I felt like my gyros were caged,' explained one astronaut. It takes a relatively long time for complete readaptation to the earth's gravity. For example, after the ten-day mission of Spacelab 1 some crew members were still showing neurophysiological and perceptual after-effects a week later. Soviet missions of several months' duration produce more serious and prolonged physiological effects. Astronauts differ in their after-effects, and it is not clear whether prolonged after-effects are correlated with slow or rapid adaptation in space.Some after-effects may be due to the continued reinterpretation of otolith signals as linear accelerations rather than as head tilt: this causes postural instability with the eyes closed, and an increased reliance on visual orientation cues. There may also be some changes in sensitivity to linear acceleration in different body axes. Other effects may be due to changes in proprioceptive and tactile sensations, such as feelings of heaviness, impairment of weight discrimination (Fig. 2), under-reaching for objects, and faulty awareness of limb position.
Readaptation to gravity is not the only problem faced by astronauts. They may be short of sleep, or be required to shift their circadian rhythm to local time. They may face several long days of medical, physiological, and psychological tests, debriefing sessions, and press publicity. They must then face the reality of readjustment to normal life, and of difficult career decisions. The life of the astronaut is not quite as rosy as is sometimes pictured.
Fig. 2. Dr Ulf Merbold, a European payload specialist, tests himself on return from the Spacelab 1 mission, and shows impaired weight discrimination.
3. The future
The Challenger disaster in January 1986 reduced enthusiasm for manned spaceflight, and made satellites and robotic instruments more desirable. Nevertheless, the usefulness of humans in space had been amply demonstrated, and NASA's shuttle programme continued. The USA and other nations also cooperated with the former USSR in the use of the Soviet space station Mir. Helen Sharman became the first British astronaut when she joined Mir in 1991, and Michael Foale (NASA, but originally British) helped with on-board repairs to the ageing Mir in 1997. Mir met its final demise in March 2001. Meanwhile the USA, Canada, Europe, Russia, and Japan are cooperating in building the International Space Station, a new manned orbiting space station, where the crews will include more scientists and technicians, and will stay in space for weeks or months at a time. There is talk of a manned base on the moon, and a manned mission to Mars, in the next fifteen years. Research on space psychology is likely to move away from the causes of motion sickness (which ceases to be a problem after about four days) to the longer-term effects of living in space and returning to earth. Simultaneously, research will go on into the automation of astronauts' tasks, and efforts will be made to replace humans with robots or teleoperators. This is unlikely to be practicable for many tasks, and we can expect to keep the 'human-in-the-loop' for the foreseeable future.(Published 2004)
— Helen E. Ross
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