Attempting to predict human responses to space travel, physicians and researchers of the 1950s speculated that microgravity and spaceflight itself would present significant challenges‐if not barriers—to the human body. They hypothesized that the combined stresses of launch acceleration, weightlessness, radiation, and heavy deceleration upon reentry would be incapacitating. At the very least, they predicted that the bodily systems sensitive to gravity‐based cues would function improperly or not at all. Given this grim forecast, the initial focus was to demonstrate that life, away from Earth, could survive space travel and subsequent return to Earth's gravity. Faced with this challenge, both the United States and Soviet Union turned first to ground simulations, such as immobilization studies, and then to the study of animal test subjects launched on board high‐altitude balloons, suborbital, and orbital rockets. What followed is a series of biological satellites that carried a variety of living specimens, from isolated cell cultures to whole instrumented organisms. The Soviet Union relied primarily on canines to provide such data, whereas the United States chose primates for such experimentation.
This article attempt to present a concise overview of life in space, physiological responses to this new environment, and associated health implications for future space travelers. Consideration must be given to the hostile, and yet dynamic environment of space; to the craft that protects the crew members from the harsh environment, allowing them to navigate in space; and to life itself as it adjusts to this novel environment. Today it is known that some adaptive changes, such as immune and hormonal responses, are primarily the response to the stresses of confinement, isolation, and spacecraft design, not necessarily to the unique effects of the space environment.