Human Adaptability to Space
Justin Armetta
Human biological nature has evolved over millions of years on the surface of the Earth. Gravity has shaped our bones and muscles. An oxygen-rich atmosphere has nourished our bodies and shielded us from harmful radiation. Our psychological cycles of sleep, heartbeat, and aging have reflected the rhythm of earthly time.1 In the last hundred years scientific achievements have allowed us to leave this surface environment and travel into space. Airplanes carrying people to the upper reaches of the atmosphere are a common means of transportation. Astronauts in the Apollo spacecraft have traveled to the moon and back. Today, the National Aeronautics and Space Administration (NASA) is building the International Space Station with Russia and other European countries. This will allow humans in space to orbit the Earth for months at a time. In the planning stage, there is a more aggressive and high risk three-year manned trip to the planet Mars.2 This trip will test human adaptability to space.
Scientific concern is high over human ability to go to such extremes. In the three-day 1972 Apollo mission, astronaut Eugene Cernan, fatigued and filthy with rock dust on the moon, barely made it back to the spacecraft for a return to Earth. A trip to Mars will multiply the hazards of space travel. Scientist Michael Long suggests a troubling scenario.3 He says, "Imagine a radiation-sick, sleep-deprived astronaut stepping onto Mars. Challenged by a different gravity and with his bones, muscles, and immune system weakened by the long trip; he falls and breaks his leg. How would NASA respond?" Today NASA is concentrating on known environmental problems in space and experimenting to find methods to solve them. These issues range from physical problems of weightlessness and radiation, to psychological problems of isolation, sleep deprivation, disorientation, depression, and time changes.4 These problems are serious and affect many parts of the human body. For these reasons, only the major ones will be examined.
Weightlessness
Weightlessness is a constant problem in space but hard to simulate on Earth. In a cosmonaut training center in Moscow, there is a special airplane that flies astronauts in maneuvers simulating weightlessness. This helps astronauts prepare for adaptation to the zero-gravity conditions of space. During zero-gravity periods, people bounce off the ceiling, do airborne gymnastics, and are thrilled by the sensation of weightlessness. Others are not amused, but sick. This free motion causes many to be nauseous. Motion sickness affects two-thirds of all astronauts.5 Though most recover after a few days in space, longer exposure severely stresses and significantly changes body systems.
The weightless problem is better appreciated by examining its physiological effects. Deprived of gravity information, the human brain is confused by visual illusions. Body fluids rush to the head and chest while neck veins bulge. Faces puff as the heart and other internal organs enlarge. Sensing too much fluid, the body begins to discharge it. This includes electrolytes, calcium, and blood plasma. The production of red blood cells decreases, rendering astronauts slightly anemic.6 With the loss of fluid, legs shrink. Spinal discs expand and so does the astronaut. A six-foot man can soon measure six-foot-two and suffer a backache.
Though this sounds terrible, in an outstanding feat of adaptation, most astronauts adjust to weightlessness and even come to enjoy it. They learn to control their movements and their senses regain balance7. Through a process of biofeedback, many adverse reactions are reduced in severity. After short trips in space lasting the span of only several weeks, astronauts quickly readjust to Earth's gravity and seem no worse for their experience in space.
During longer flights there is alarming evidence that weightlessness can cause permanent damage to the physiology of the human body. Russia's Institute for Biomedical Problems watched cosmonauts return from long space flights wobbly, pale, and unable to stand without fainting. Some needed to be carried from the spacecraft and had to spend time recuperating in the hospital.8 Americans returning from flights of several months duration also paid a price. They suffered from loss of weight, bone size, and density. NASA is especially concerned about flights lasting a year or more. During long durations, the heart loses muscle mass, while the large, weight-bearing muscles of the legs gradually atrophy. Density in the bones of the pelvis and legs decreases relentlessly. This decrease is one to two percent a month on average. Severe osteoporosis could result. Doctors believe that a process begins with atrophy of large weight-bearing muscles. These weakened muscles exert less torsion and compression on bones, initiating a little-understood process that drastically reduces bone renewal.
The obvious countermeasure seems to be exercise that keeps muscles fit. The Russians have established rigorous schedules of bungee stretching, followed by sessions on bicycles and treadmills. Gymnastics will be required of astronauts in all space flights. The message is, "Do your exercises. Don't and we will have to carry you off the spacecraft."9 Although the Russian exercise program is impressive, not one astronaut has returned from long-duration flight without bone loss. A few have lost as much as 20 percent of their hip density. NASA believes that we must find better ways to stop this loss of bone and muscle tain at least 95 percent of density during the long trip, the risk of bone fracture is too high to take.
Unusual alternatives are being studied to preserve the bone structure of astronauts. One idea is to add drugs to their diet to prevent osteoporosis. Another is the use of a costly artificial gravity device that would provide short doses of gravity. The issue on the need for artificial gravity grows with respect to long duration flights in the future. Both Russia and the United States are debating this step. The problem here is that such a device would disrupt other systems of the spacecraft. Even more bizarre is the idea of vibrating astronauts. Scientists have discovered that by vibrating floors under turkeys and sheep they have increased the density of their bones.10 So far, no men have volunteered to be vibrated.
A more detailed account of how humans' cardiovascular systems adjust to microgravity is interesting. In flight, the body no longer experiences the downward pull of gravity to distribute the blood and other fluids to the lower parts of the body, especially the legs. These fluids make what is called a "headward shift," meaning they are redistributed to the upper parts of the body. This causes the astronauts to have puffy faces and thinner legs, sometimes called "bird legs." The regulatory systems of the body sense this excess fluid and direct the kidneys to eliminate much of it by urination.11 Thirst is adjusted so that intake of fluids is reduced. With decreased drinking and increased fluid elimination, the body's fluid level falls below its normal level on Earth. With less work, the heart shrinks in size in what doctors call the "space-normal" condition.
When returning to Earth's gravity, the human body senses that it does not have enough fluid to function properly and a reverse adjustment takes place. The heart enlarges and the body tissues retain more fluid. Normal pre-flight conditions return in two to three weeks. This shows an astronaut's amazing adaptability. It is clear that man's cardiopulmonary system adjusts quickly to Earth and the presence of gravity once out of a weightless environment.12
Radiation
Radiation presents yet another array of problems to astronauts in space. Earthlings who enjoy the sun's benign warmth may find radiation explosions difficult to believe.13 A coronal mass ejection discharges billions of tons of electrically charged gas into space. Colliding with Earth's magnetic field in March 1989, one such pulse shorted out power in large areas of North America like a power surge from a lightning strike. These solar flares explode regularly with the force of a hundred million Hiroshima bombs. This could potentially launch harmful rays toward any spacecraft in the vicinity. Solar flares present a lethal threat because they deplete bone marrow and kill cells in vital organs. To alleviate this problem, NASA has developed a monitoring system to warn astronauts of such events. When flares occur, the crew is immediately notified. They will then scurry into the space equivalent of a storm cellar enclosed with heavy polyethylene shielding that will absorb the radiation.14
A more serious threat is the radiation from cosmic rays that travel from the Milky Way and other galaxies. They possess too much energy and too much speed for shielding to be effective. Heavy ions of iron forged in supernovae can travel 185,000 miles a second, nearly the speed of light. These are unavoidable. They pass through the body tissue, bombarding cells and leaving them unstable, mutated, or dead. Understanding the biological effects on astronauts is a major priority.15 The long-term cancer risk is unknown.
Researchers studying this problem have bombarded rats with non-lethal doses of heavy iron particles. This caused significant reduction of the brain chemical dopamine, which is necessary in motor ability, cognition, and memory. Remarkably, when they were fed a diet that included blueberry extract rich in antioxidents, the rats improved. Other researchers have found that tamoxifen, an anti-cancer drug, heals tumors in rats irradiated with heavy iron particles.16 Human adaptation to cosmic rays will probably require special diets and drugs to offset their damage.
Psychological Problems
In addition to these physical problems, astronauts face a variety of psychological problems. NASA finds that the stresses of isolation and confinement are increased if people have too few tasks to perform. NASA psychiatrists worry about the mental health of astronauts, including depression.17 The risk of depression remains high but it is difficult to identify. Researchers at the University of Pennsylvania are searching for a quantitative means of recognizing stress and depression. They plan to build a computer program that can recognize emotional states. The computer will be taught to recognize facial expressions with human emotion (e.g., the slanted eyebrows of sadness or the wide eyes of surprise). Information is recorded in tiny pixels, enabling it to determine subtle changes in expression. Would astronauts consider such a computer program an invasion of privacy? It is probable.
Disorientation is a psychological problem that occurs in space because of the weightless environment. We have within the inner ear a balance mechanism called the vestibular organ. This organ senses our body's position and movement in relation to the Earth's gravity. Information from our senses of sight and touch and information from our muscles and joints, are integrated by the brain in order to understand the body's actions.18 In space, without a gravitational foundation, the astronaut becomes confused. The brain adjusts in a day or two, learning to rely on visual observations. Placement of directional symbols will tell an astronaut the spacecraft's position in relation to the Earth. With orientation restored, astronauts can now function with comfort and confidence.
Space Time
As astronauts venture farther into the extremes of space, they must adjust to the enigma of time. This presents them with an obstacle not well understood. For two centuries, scientists were satisfied with Isaac Newton's definition. It established that time is absolute and flows unvarying without relation to any outside force.19 In 1907, Albert Einstein shattered this understanding with his theory of relativity. It predicted that time was not just a constant measurement of events, but a limiting dimensional force in space. The implications of this phenomenon to space travel are wide ranging. A clock on board a space ship traveling 87 percent the speed of light would tick only half as fast as the same clock on the surface of the Earth.20 Of course humans will need radically new propulsion systems to achieve such speed. Even today, at much slower speeds, some problems in space may be related to time change. For example, there is a problem of sleep deprivation. On early trips, it was attributed to noise, improper scheduling, and uncomfortable bed restraints. Even after these conditions were corrected, however, sleep patterns remain unchanged. Today, astronauts average only six hours sleep per day in space versus eight hours on Earth.21 NASA does not know why. Within the brain, various biological clocks respond to the passage of time. These clocks, through an interconnecting of billions of neurons, regulate all our bodily functions.22 There is little doubt that these most complicated mechanisms in the universe are tuned to Earth time. Scientists can only speculate what will happen when their atomic structures are subjected to a slower time in space travel.
There is some reason to be optimistic about our ability to travel at time-changing speeds. The human body has demonstrated its ability to adjust to the lack of gravity. It most likely has the same natural instinct to adjust to time changes. Consider the fact that slower time may have the effect of slowing our rate of biological metabolism. If the body's atomic structure adapts to time changes by slowing this rate down even more, astronauts may feel better and age more slowly. During a high speed, three-year trip in space-time, astronauts may age only two Earth years.
In Houston, astronauts are training for a trip to Mars. It is a trip that will test their physical and psychological adaptability to the frontiers of time and space. NASA is optimistic about the human ability to go to these extremes.
End Notes
- J. Boslough, "The Enigma of Time." National Geographic Magazine (March 1990).
- Sir C. Clarke. "Beyond Gravity." National Geographic Magazine (January 2001).
- Ibid.
- R. White. Human Physiology in Space. The National Institutes of Health (February 1995).
- Clarke.
- The Mars Society. Countermeasures to Long Duration Spaceflight. <http://www.drfast.net/mars/aero3.html> February 11, 2001.
- Clarke.
- White.
- Ibid.
- J. Parker Bioastrautics Data Book. NASA, 1985.
- White.
- Parker.
- M. Long. "Surviving in Space." National Geographic Magazine, January 2001.
- Space Studies Board. Radiation Hazards to Crews of Interplanetary Missions. <http://www.nap.edu/readingroom/book/rim/> February 12, 2001.
- Ibid.
- White.
- Long.
- White.
- J. Boslough. "The Enigma of Time." National Geographic Magazine, March 1990.
- Ibid.
- Long.
- Boslough.
Works Cited
Boslough, J. "The Enigma of Time," National Geographic Magazine (March 1990).
Brown, J.H.U. Physiology of Man in Space. Academic Press, January 1963.
The Challenge Project. Parallel Processes? The Study of Human Adaptation to Space. <http://quest.arc.nasa.gov/space/challenge/background/pp.html> February 12, 2001.
Clarke, Sir C. "Beyond Gravity," National Geographic Magazine (January 2001).
Long, M. "Surviving in Space," National Geographic Magazine (January 2001).
The Mars Society. Countermeasures to Long Duration Spaceflight. <http://www.drfast.net/mars/aero3.html> February 11, 2001.
Parker, J. Bioastronautics Data Book. NASA, 1985.
Sawyer, K. "A Mars Never Dreamed Of," National Geographic Magazine (February 2001).
Space Studies Board. Radiation Hazards to Crews of Interplanetary Missions. <http://www.nap.edu/readingroom/book/rim/> February 12, 2001.
White, R. Human Physiology in Space. The National Institutes of Health, February 1995.