Studying the Effects of Gravity

Abstract

The force of earth's gravity, universal and inescapable, is unique among the forces influencing terrestrial life. Yet very little is known about its effect on biological systems. For hundreds of years, scientists have speculated about the physiological changes which might result from extensive periods under increased or decreased gravity, but little experimentation was either possible or necessary until men began to fly. Even then, the effects of increased g loads on pilots were often treated symptomatically without much understanding of the nature of the effects themselves. Within the past decade however, the prospects of travel to other planets, where gravity could be several times that of the earth, and the plans for extrnded space-station living under conditions of zero gravity, have made research in gravity effects more urgent. The apparently reversible effects of weightlessness on Gemini and Apollo astronauts and Soyuz cosmonautsstability problems, transient blood abnormalities, increased white-cell and decreased red-cell counts, abnormal red-cell proteins and bone-calcium and muscle-nitrogen deficiencies-provided some data. Despite this input, however, and additional bits and pieces of insight gained from animals and plants exposed to weightlessness for varying periods of time, space-flight doctors are still looking for more complete information. They have felt the need for some kind of earth-bound simulator that would permit them to draw some general conclusions about the real-time effects on living things of changes in gravity. Although true weightlessness cannot be simulated for long periods on earth, increased gravity levels can be simulated in centrifuges. The Navy and Air Force have been using such instruments for years to explore pilot ability to function under the increased g loads which occur in flight. The National Aeronautics and Space Administration uses large centrifuges at the Manned Spacecraft Center in Houston, in which astronauts train for the six to seven g's of launch and reentry into the earth's atmosphere. Such training and post-exposure examinations have led to the development of protective gear and an understanding of some momentary effects. But scientists would still like to know in real time exactly what is happening to body functions and systems during exposure to abnormal gravity. For a study of the effects of increased g loads Photos: NASA