Title: The Medical Challenge of Manned Space Flight
Abstract: As manned space flight becomes a reality, medicine faces new challenges. Contributions from many specialties are required to support human life away from earth. The problems which must be solved can be divided into four areas: 1. Dynamics of Space Flight: Launch, flight, and re-entry involve a complex interplay of forces. The most important hazards arise from acceleration, noise, vibration, and weightlessness. 2. Space Environment: Moving beyond the earth's atmosphere not only means the loss of oxygen and pressure, but also introduces radiation, extreme temperatures, and unaccustomed stimuli. 3. Vehicle Environment: Maintenance of life within the spacecraft requires precise control of many variables. Among the major requirements are supply of food and oxygen, removal of carbon dioxide and waste products, and tolerance of prolonged confinement. 4. Crew Selection, Training, and Support: Astronauts must be carefully chosen and prepared to act under a wide variety of conditions. Dynamics of Space Flight The major dynamic problems are associated with increased and decreased gravitational forces. For orbital flight, the spacecraft must attain a velocity of 18,000 miles per hour, so that the centrifugal force away from the earth balances the gravitational pull toward the earth. For flights to the moon and planets, a minimum of 24,000 miles per hour will be necessary. This involves acceleration loads of eight to ten times the normal force of gravity, or 8 to 10 g. When the force is applied transversely—that is, from chest to back—the acceleration profiles imposed by rockets now in use or under development are not excessive. There are, however, many problems. For example, at 8 g a man can hardly move his limbs. Between 4 and 8 g, thoracic compression reaches the point where only abdominal breathing is possible. Tidal volume then decreases, reducing tolerance to acceleration above 12 g to the time an astronaut can hold his breath. During re-entry, deceleration produced by retrorockets, followed by the braking effect of the earth's atmosphere, produces acceleration forces which are more gradual in onset, and thus less of a problem than those encountered at lift-off. Levels as high as 25 g, however, are possible during impact. As long as the proper transverse orientation is maintained, the brief duration of these forces places them within human tolerance limits. When gravity is decreased and the astronaut becomes weightless, new problems arise. Some of these are practical. For example, special technics are required for drinking when there is no gravity to move liquids into the mouth. Without gravity, crumbs from food and other dÉbris are free to float within the spacecraft. A particularly intriguing question is whether failure of airborne droplets to settle out may increase the chance of infections spreading from one man to another. Another complication may arise from the mechanoreceptors, which ordinarily give rise to the sensation of weight.
Publication Year: 1965
Publication Date: 1965-05-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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