Weightlessness

Fossils in the geological record reveal that humans have existed on Earth for over three million years. Further, we know that vertebrates roamed the Earth for hundreds of millions of years before the emergence of Man. Throughout these eons, all evolution and human development have been influenced by the Earth's gravitational field. In countless subtle ways, humans have responded to this ubiquitous force and have learned to cope with it. Not only are we molded and constrained by gravity, but Earth's whole blanket of life, the biosphere, with all its component species, is in some respects a product of the effects of gravity.

So intimate is the relationship between gravity and life that, before the advent of spaceflight, no one could predict precisely how or even whether any particular biological process would function in the absence of gravity. Weightlessness cannot be experimentally produced within the Earth's atmosphere for more than a few seconds at a time in aircraft. We had to wait until spacecraft could be launched into orbit around the Earth before the effects of prolonged weight lessness could be investigated.

Before the Space Age, scientists predicted many dire consequences if a human being were suddenly thrust into weightless flight. Often, the predictions contradicted each other. Various specialists said that the heart would race or that it would stop, that a person could not sleep or would sleep constantly, and that an astronaut would become euphoric or profoundly depressed. It was said that the bones would soften, that eating would be impossible, and that the ability to think would be impaired. So acute was the concern for the unknown medical effects of weight lessness that numerous animals were flown, first in ballistic suborbital trajectories and finally in complete Earth orbits, before either Yuri Gagarin or Alan Shepard first flew their Vostok and Mercury spacecraft. Happily, most of the predicted dangers did not occur. Weightlessness in general turned out to be surprisingly benign and tolerable. However, some significant changes in the human body were noted, even in the earliest flights. How long these changes last, and how serious they are in the long run, continue to be the subjects of intense investigation by space medicine specialists in both the United States and the Soviet Union.

Before Man flew.
The chimpanzee "Ham" was the live test subject for the Mercury Redstone 2 flight on January 31, 1961. Here the 17-kg (37-pound) primate is fitted into a special "biopack" couch prior to flight. The 680-kilometer (420 statute miles) suborbital mission was a significant accomplishment in the American route to manned spaceflight.

monkey test subject preparing for space flight

Travellar's reward.
Ham reaches for an apple following his brief ride in space.

Circlatory changes

The first impairments observed in astronauts that were definitely caused by space flight were the changes in heart rate and blood pressure exhibited by Walter Schirra following his 9-hour flight in October, 1962 and by Gordon Cooper after a subsequent 34-hour flight, each in a Mercury spacecraft. Immediately after returning to Earth the astronauts tended to become dizzy on standing, and each showed a decrease in the total volume of blood. These effects were confirmed by medical studies of other astronauts during the later Gemini and Apollo flights, and they were investigated in much greater detail over a period of months during the long-duration Skylab flights in 1973-1974.

astronaut Owen Garriott performing biomedical reseach

Biomedical research in space.
Owen Garriott ties in the Lower Body Negative Pressure Device aboard the Earth-orbiting Skylab. The instrument was used to monitor the time course of cardiovascular adaptation to spaceflight and to predict the degree of difficulty to be encountered during and after return to Earth.

The Skylab studies showed that the circulatory changes which occur level off after four to six weeks of flight. After that, no further changes occur, nor do the changes impair crew health or performance aloft. Exercise tolerance during the space flight itself is unaffected, but the ability to per form vigorous exercise is temporarily diminished after return to Earth.

Scientists and doctors are begin ning to understand these changes. When a human is suddenly thrust into weightlessness, apparently blood shifts from the legs and lower parts of the body, where it is normally held by gravity, upward toward the head. Sensitive receptors, located in the upper part of the body, mistakenly interpret this sudden and sustained shift of blood as an increase in total blood volume. The body then tries to reduce the blood volume to its "normal" value by eliminating fluid and some electrolytes, either by increasing urine flow or by cutting water in take (reducing the feeling of thirst). These changes lower the blood volume to a level that is perfectly compatible with weightless life in space but that is too low to support vigorous activity back on Earth. Just after return, the astronaut is like someone who hasjust given a blood transfusion and cannot immediately engage in heavy exercise. This diminished performance after return from space continues for a few days until the missing blood volume is restored; there seem to be no long-term effects.

If the circulatory changes, technically called "cardiovascular deconditioning", are caused entirely by lowered blood volume, simple precautionary measures can be used to correct the problem during critical reentry maneuvers and immediately after return to Earth. However, because it it possible that other, more serious circulatory changes may occur in space, scientists monitor the cardiovascular system of an astronaut in flight as well as the red and white cells and other components of the blood.

astronaut in shorts pedals exercise bicycle in spacelab

Only way to jog.
Pete Conrad exercises on the astronauts' bicycle ergometer in-side the Skylab Workshop.

The opportunites to study humans in space are still somewhat limited and can involve only a few subjects, so methods have been devised for simulating some of the physiological effects of spaceflight here on Earth. By immersing humans and animals in water baths for extended periods or by confining them to bed or in plaster casts in a slightly head-down position, many of the same cardiovascular changes that occur in space can be produced on the ground and studied in detail.

Using his head.
Weightless in Skylab, Owen Garriott supports him self on the bicycle ergometer by pressing against the compartment "above" him.

Bone and muscle loss

When they are not used to work against the gravity field of Earth, bones tend to deteriorate and muscles tend to atrophy, that is, to shrink or waste away. Similar problems occur in space. The limited mobility within the small earlier spacecraft and the lack of appropriate stress, even in the larger Skylab and Salyut space stations, produced a continuous loss of bone and muscle tissue in the astronauts. The loss appears slow enough to enable space missions of from six to twelve months to be undertaken without instituting any preventive or remedial measures. On longer flights however, steps must be taken to pre vent these losses. In-flight exercise was tried on the Skylab and is being used by the cosmonauts aboard Salyut missions, but so far the correct combination of measures to be applied to prevent bone and muscle loss has not been found. The search is continuing in the Space Shuttle missions as well as in laboratories on the ground.

photo of astronaut exiting Apollo 9 for space walk with earth far below

The hatch is open.
David Scott's extravehicular activity on the fourth day of the Apollo 9 Earth orbital mission takes place with the Mississippi River valley in the center background.

Motion sickness

Starting in 1968, eleven missions in volving astronauts were undertaken during the five-year span of the Apollo program. These missions added motion sickness (the "space sickness" of generations of science fiction writers) to the significant biomedical problems produced by space flight.

Although nausea had been noted earlier by Soviet cosmonaut Gherman Titov during his one-day Vostok 2 flight on August 6, 1961, as well as by some crew members of subsequent Soviet flights, no American astronauts had yet experienced the symptoms. (In retrospect, however, the lack of appetite observed on certain Gemini flights may have been an early sign of this illness.) The crewmen of Apollo 8 and 9 were especially plagued with stomach uneasiness, nausea, and vomiting. In Apollo 9, an Earth orbit mission, astronaut Rusty Schweickart was sick for a considerable time and had to postpone the first test of the Lunar Module in space.

photo of astronaut sitting on special zero gravity scale

Behind straps and bars.
Alan Bean "weighs" himself on a mass measuring device aboard Skylab.

astronaut breathing through tube during exercise collecting data for research

Life and breath in space.
Measurements of gas exchange and heart activity are made as astronaut Bean pedals the bicycle ergometer.

Throughout the remainder of the Apollo program, during subsequent Skylab missions, and during Soviet missions, symptoms of motion sick ness continued to manifest themselves.

It is a serious problem; almost half of the astronauts sent into space have been affected. The illness appears to last for only the first two or three days in space and in almost all cases disappears within a week. The occurrence of motion sickness during the first few days of space flight is of great operational concern during the forthcoming Space Shuttle flights, many of which last only a few days. Unfortunately, at the present time, the factors responsible for motion sickness are unknown. Scientists believe that the vestibular apparatus, or machinery of the inner ear which controls our sense of balance, is profoundly influenced by weightlessness. Humans are not the only creatures affected. Experiments carried out on the Skylab spacecraft produced pictures of disoriented fish swimming in loops in their containers. Furious nervous activity was recorded from the brain of a frog that was suddenly rocketed into weightlessness. In humans, the disorientation arises when sensations from the eyes and from other parts of the body conflict with those from the vestibular (inner ear) apparatus and with information stored in our brains as a result of experience at "1 G". This condition apparently can be over come. After a few days in space, a repatterning of the central memory network occurs so that unfamiliar sensations from eyes and ears start to be correctly interpreted and the person adjusts to his new environment. More effective means whereby adaptation can be accelerated and motion sickness symptoms suppressed are being sought in many laboratories. Hopes are high that this search will be successful and that, unlike so many hapless sailors, aviators, and other travelers, future astronauts will be freed of space motion sickness as an occupational nuisance.

Food and diet

It is almost always true that an astronaut or cosmonaut who returns from space to Earth weighs from one to ten pounds less than upon launch. Spring-loaded mass measuring devices, carried aboard the American Skylab and Russian Salyut spacecraft, were used to "weigh" the astronauts in the absence of gravity. These records showed that about half of the weight loss occurs within the first few days of flight while the remaining loss takes place much more slowly. Scientists believe that, just as in any person who starts to lose weight, the early losses consist mainly of water, while muscle, fat, and bone comprise the later losses.

Weight loss can be reduced by combining appropriate exercise with a complete and balanced diet. How ever, most of the early astronauts paid little attention to the dietary advice they received prior to flight and could not be convinced that life in weight less flight requiredjust as much food energy as it did on Earth. The commander of one lunar flight insisted that he, wanted nothing but a few candies on the way to the Moon. Some Gemini astronauts traded their individually planned metabolic rations with each other, much to the consternation of the dietitians. In later long term flights such as Skylab, food was taken more seriously. Daily intakes were calculated by computer, and supplements were automatically prescribed to each astronaut to make up deficits incurred the previous day. Insuring that the space food tastes good is one way to promote eating enough. This always has been difficult because of the need to process the food to save as much space and weight as possible, but the individual meals on Skylab were a major advance over the primitive edibles available to the Mercury astronauts. Food preparation and use will provide increasingly complex challenges in the future, when "closed ecology" food systems will generate food from the waste products of human metabolism.

astronaut in t-shirt sits down to a weightless dinner in the Skylab

Mess call.
Oven Garriott reconstitutes a container of freeze-dried food at the crew quarters wardroom table in Skylab.