III.

Space Medicine

The U.S. National Aeronautics and Space Administration (NASA) is responsible for nonmilitary space flight for scientific purposes, which include medical studies. Specialists in space medicine—also known as bioastronautics—study the human factors involved in flight outside the atmosphere. Most of the potential dangers in space travel (such as acceleration and deceleration forces, the need for an artificial atmosphere, and noise and vibration) are similar to those encountered in atmospheric flight and can be compensated for in similar ways. Space medicine scientists, however, must consider two additional problems—weightlessness and the increased radiation outside the atmosphere.

A.

History

The first information about human performance during space travel was gathered in Germany in the 1940s under the direction of Hubertus Strughold. In 1949 Strughold was made director of the department of space medicine at the School of Aviation Medicine at Randolph Air Force Base, Texas (now the School of Aerospace Medicine at Brooks Air Force Base, Texas). Both the United States and the Union of Soviet Socialist Republics (USSR) conducted rocket tests with animals beginning in 1948. In 1957 the USSR put a dog into earth orbit, and the U.S. used a monkey for tests in 1958. The tests suggested that few biological dangers existed in space flight. This was confirmed when human space flight began on April 12, 1961, with the launching of the Soviet cosmonaut Yuri Gagarin into orbit.

The United States followed with the Mercury-Redstone suborbital flights and then the orbital Mercury and Gemini flights, the Apollo moon landings, the experimental orbital vehicle Skylab, and Space Shuttle flights. Then, in the 1980s, when Soviet cosmonauts began setting records for time spent in the gravity-free or “microgravity” environment, the effects of long-term weightlessness began to be viewed as a serious medical problem.

B.

Physiological Findings

Few serious biological effects were noted during the early years of space flight. Even the 21-day quarantine of astronauts returning from the Apollo moon mission was subsequently abandoned, because no infectious agents were identified. The body functions that were monitored (often with specially designed miniature instruments) included heart rate, pulse, body temperature, blood pressure, respiration, speech and mental alertness, and brain waves. Few changes occurred. Changes in the hormones and in the concentrations of salts in the blood did take place, but these were not detrimental. Eating in weightlessness was accomplished by packaging food in containers that could be squeezed directly into the mouth, and special systems were designed for collection of fluid and solid wastes. The lack of a natural time cycle in space was compensated for by keeping the astronauts’ schedules synchronized with earth time.

Psychological changes were anticipated because of the close confinement of a few individuals in a small space with limited activity. Few psychological problems were noted, however, perhaps because the astronauts were chosen for emotional stability and high motivation and because they were assigned enough tasks to keep them almost constantly busy. Irradiation was also found to have little effect. Short orbital flights produced exposures about equal to one medical X ray—about the same as suborbital flight. The crew on the longer Skylab flight sustained many times this dose. Space flights are planned to avoid periods when solar flares are expected to occur, as these can emit dangerous levels of gamma radiation.

However, although it was assumed that gravity is necessary for normal growth, the magnitude of physiological changes induced by extended periods in a microgravity environment came as something of a surprise. Serious medical problems, including loss of bone matter and muscle strength, were observed to result from long-term weightlessness, as during the 237-day mission of three cosmonauts aboard a Salyut space station in 1984. Moreover, atrophy of certain muscles, particularly those of the heart, was seen to be especially dangerous because of its effect on the functioning of the entire cardiovascular system. The blood itself was found to be affected, with a measurable decrease in the number of oxygen-carrying cells.

On a seven-day Challenger Space Shuttle mission in 1985, these effects were studied in an experiment using 24 rats and 2 monkeys. Post-flight examination revealed not only the expected loss of bone and muscle strength but a decrease in release of growth hormone as well.

These findings are taken into consideration now whenever plans are made for manned space flight. Astronauts’ busy work schedules in space are designed to include regular exercise periods, thereby maintaining muscle tone. And plans for the operation of permanently manned space stations now include provisions for changing crews on a regular basis, so as not to subject astronauts to weightlessness for indefinite periods of time.