SPACE travel for man is imminent. Engineers have already supplied us with the vehicles. Admittedly, some of them are still unreliable and, for technical reasons, some will never become reliable. However, certain of them are now operational and have 90 per cent reliability. Although the engineers of these missiles have presented man with the means of travel to outer space, the medical biologists have been slow to accept this fact and find themselves somewhat short on knowledge and understanding of how man can go into space and remain alive. Except within a fairly limited range, we cannot change man’s existing modus operandi, and we can therefore take no other view than that his entry into the new environment is merely an extension of our current knowledge of human biology.
Biologically, the principal problems which will confront man in outer space are: first, the necessity of operating in a virtual vacuum; second, weightlessness, the result of operating under zero or reduced gravity; third, protection against the extremes of solar and nuclear radiation; and fourth, adjustment to high acceleration and deceleration.
No biological system that we know of at present can operate in a vacuum, and therefore an artificial environment compatible with man’s physiological requirements must be contrived. For each of the five components affecting the proper functioning of man — namely, oxygen, barometric pressure, carbon dioxide, humidity, and temperature — there is a relatively narrow limit outside of which his system will not function either efficiently or comfortably. Our failure to recognize such limits has already cost animals their lives while they were still on the launching pad.
Juggling with an artificial environment is a necessity because, except for short flights, the engineers tell us that a life-support capsule operating under reduced atmospheric pressure would be lighter and easier to engineer than one in which the normal sea-level pressure of 14.7 pounds per square inch is maintained. The high-altitude studies which have been going on for a number of years do not provide a solution, because they are carried out with oxygen deprivation, neither necessary nor desirable in a space-capsule environment.
Because we have not had a need to know, we have not tried to find out the relationship between barometric pressure and oxygen percentage in terms both of toxicity from too much oxygen and of hypoxia, a condition of less oxygen in tissues than is required for their proper metabolism. Until experiments to determine this relationship on a shortand long-term basis are carried out both with animals and man, we will be working entirely in the dark. Already the preliminary work being done indicates that the relationship is more complex than we had hitherto estimated.
The safe level of carbon dioxide, which along with water is a respiratory waste product of metabolism, is much easier to control than is the safe oxygen level, and as long as carbon dioxide is kept at less than one per cent, it can do little, if any, harm. However, if at a different atmospheric pressure its percentage increases significantly, we may have problems to solve.
THE TEMPERATURE OF SPACE
One cannot measure the temperature of space with a thermometer because, for all practical purposes, there is nothing to measure. If one puts a thermometer into space, one is measuring the temperature of the thermometer itself; this is the resultant of the radiant heat it is receiving on its sunny side and the radiant heat it is losing on its shady side. Since the heat loss to the cosmos is constant and only the heat gain from the sun varies with distance from the sun, the nearer in space an object is to the sun, the higher will be its final temperature, while the further away, the colder this temperature will be.
Unlike the earth, our space vehicle will have no buffering atmosphere around it, and so we can expect a potential temperature of about 250° F. on the sunny side and about —250 F. on the shady side. It is unlikely that this will actually be the case, especially if the construction materials of the spaceship have good thermal conduction properties and if its atmosphere is assisted in its thermal convection properties by the simple act of stirring. Stirring will occur as part of the system used to remove carbon dioxide and water, the waste products of respiration.
From actual measurements in space, it seems that, in the terrestrial orbit area, we may have trouble in keeping the spaceship atmosphere cooled to the required comfortable temperature. This is especially so since each astronaut gives off an average of 500 B.T.U.’s per hour and since our electronic equipment inside the capsule will also be giving off heat. Fortunately, we can obtain temperature control by varying the ratio between the sunny and the shady side, a relatively simple operation. This system of temperature control would work within certain limits near the terrestrial orbit but should be adequate as long as our exploration is confined to the moon and the neighboring planets. Interstellar travel will pose more difficult questions. Between the area where we lose our solar thermal radiation and that where we gain the radiation equivalent of the next star, we can expect the temperature of the space capsule to drop as low as — 273° F.
The high temperatures encountered on re-entry into the earth’s atmosphere are due to the friction caused by the high speed of the vehicle passing through air, when temperatures of greater than 3000° F. can occur. The production of such an extreme of temperature is the result of the ballisticlike nature of our present missiles. If the costly pay load could be increased to carry enough fuel to allow the spaceship to slow down for a soft landing, high temperature of re-entry could be avoided, but because at present this is not the case, our astronauts are going to have to experience some very warm moments. If this period of high temperatures were short, there would be no great difficulty, but, unfortunately, the very insulation which prevents the heat of surface friction from affecting the capsule too severely also prevents the rapid loss of that heat which is conducted into it. It has already been announced that the temperature of the capsule intended for a man could be kept at around 150°F. during re-entry. During the Able-Baker flight, a deviation of less than one degree Fahrenheit from the specified capsule temperature was achieved.
A nude man is physiologically a tropical animal, and at rest he is most comfortable at temperatures of 80 to 86° F. with a relative humidity of 50 to 60 per cent. In this area, he is in what we call “thermal neutrality.” That part of his circulation which is concerned with the regulation of his normal body temperature is at rest, his sweat glands are at rest, his metabolic needs are minimal, and environmentally he is completely unstressed. Above this temperature range, there are changes in his circulation, respiration, sweating, and metabolism which enable him to maintain the body temperature that nature has chosen for him. Primarily, this increase is costly in fluids, which are lost in the form of sweat. Below this temperature, man has to stoke up the internal fires, a reaction costly in food and oxygen, and to some extent in fluid also.
I would venture to say that, in the recent past, a number of animals have died because of our failure to recognize that the narrow limits of thermal neutrality greatly increase the effects of other physical stresses that are less controllable during preflight, actual flight, and recovery. The best operating temperature for our capsule is determined by the type of clothing its occupant is going to wear. Since in the Able experiment the animal was to be encased in a restraint harness with padding of unknown thermal properties, the thermoneutral range had to be determined by experiment prior to the 72-hour period of the animal’s enclosure within the capsule.
The thermoneutral range of both man and animals can be extended by conditioning. Human subjects have been conditioned to the extent that they are able to sleep in the nude at 50° F. room temperature, and if you do not think this is a neat trick, try it sometime. Conditioning to heat can also be achieved, and, happily, cold and heat conditioning can coexist, greatly increasing the resistance of man to injuries of thermal extremes.
Relative humidity is a less complicated problem, so long as it is kept near the range of 50 to 60 per cent for all temperatures. If humidity is too high, man cannot carry out the normal minimal fluid exchange that should take place, while if it is too low, regardless of temperature, he will suffer from excessive fluid exchange and the tendency will be toward dehydration. Therefore, both the upper and lower limits of relative humidity must be established in the capsule for proper physiological efficiency.
There are some scientists who strongly believe that weightlessness will create a tremendous difficulty in outer space, and to support this theory some very fancy physiological assumptions have been put forward. There are scientists who think that weightlessness will cause only a partial difficulty, similar to seasickness. Still others think that weightlessness will cause no physiological or psychological difficulties whatsoever.
The state of weightlessness is brought about by the absence of gravity in space and cannot be simulated for any useful period of time within the environs of the earth. Earth’s gravitational force, one G, is the unit used not only to describe degrees of weightlessness but also to describe forces which increase the weight of mass above its static weight on earth. Such forces occur during acceleration or deceleration and also when a mass is rotated on a centrifuge. G forces of greater than one G are easy to simulate on earth, either by the use of a centrifuge or by a fast accelerating and decelerating vehicle. What you feel in the seat of your pants when you mash down the accelerator of your car is G force; in reverse, this is also what you feel when you apply the brakes, and both are identically expressed. G forces less than one G cannot be simulated on earth except for a few seconds during high-speed parabolic flight. These few seconds of weightlessness are of no real help in the study of its physiological or psychological effects because the body cannot adjust in the time available. This inability to adjust has led some scientists to believe that there may be a constant feeling of falling and of spatial disorientation as a consequence of weightlessness.
This theory could be quite wrong. Falling is associated with acceleration, while reduced weight or complete weightlessness need not be so associated. The forces of acceleration and deceleration are a changing state which is reported as such by the organs of position and balance, and spatial disorientation is suspected, presumably, because the organs responsible for orientation are now free-floating and without weight. The enigma cannot be solved unless we know whether our organs are mass-weight or mass-inertia dependent. Weight alters during weightlessness in space, but mass and its inertia are always the same, whether on earth or in space.
During Able’s flight through space, she was weightless for about ten to twelve minutes, and there was no physiological change detected as a result of this. The in-flight movies indicate that, psychologically, the monkey was quite undisturbed by finding herself in this strange state. It is probably true that, regardless of the physiological effects, the ordinary acts of living will be somewhat difficult during weightlessness, and especially will this be so on the space satellite stations, which are considered to be a necessity as way stations and take-off points for exploration of the moon, the planets, and of space itself. These satellite stations will orbit around the earth and will be manned by construction crews building true space vehicles.
The engineers and physicists tell us that it is their intention to rotate these satellite stations in order to provide them with artificial gravity by the use of centrifugal force and at the same time to overcome all the problems of weightlessness. These specialists do not appear to realize that rotation creates an interesting but disturbing set of medical problems associated with the organs of balance. If a man or an animal is rotated and the axis of his vestibular apparatus is changed, as in nodding or tilting of the head, some wonderfully fantastic and highly disturbing results take place, similar to those we experience during a ride on a super roller coaster. Very few individuals can tolerate much of this. Some vomit, some manage to emerge with only a pale-green complexion, and others have to go to bed to recover.
Current research has done much to define the psychophysiology of the problem. The adverse effects of rotation vary greatly from one individual to another; professional dancers and acrobats are the least affected. If rotation is necessary, there is some glimmer of hope, for it has been shown that animals and man have a fairly rapid ability to adapt to the effects of rotation.
The space engineers glibly set up conditions without due regard for the biological implications of those conditions. They murmur of weightlessness, but the biologists visualize only an astronaut having difficulties with his balance mechanism. For the past several years, results of experiments indicate that rotation may be a worse problem than weightlessness. Rotation is used not only to establish artificial gravity in space but also to stabilize vehicles in order to overcome the problems of tumble. This is especially important during re-entry into an atmosphere, when violent vibration of the space vehicle takes place. And vibration has a nebulous gamut of biological problems all of its own. This vibration of re-entry appeared to be the only event during flight that caused Able disturbance.
Nuclear radiation in space has been demonstrated by James Van Allen and his colleagues as consisting of a doughnut-shaped belt which surrounds the earth and is primarily centered over the equatorial and temperate regions of the globe, with its inner edge about 400 to 1000 miles distant from it and its outer edge approximately 70,000 miles out. Although the intensity of this belt is fairly well delineated, we have no idea of its effect upon biological systems. Furthermore, we do not as yet completely know what types of radiation compose this band. Animal experiments designed to tell us what harmful effects, if any, may be caused by entry into it would be desirable before we expose an astronaut to its unknown quantity. Of course, in order to cut down the exposure as much as possible, we could rush our astronaut through the Van Allen radiation belt at very high speed, provided that it is as confined as is currently believed, a supposition that seems to become more dubious as the days go by.
Below, within, and beyond the Van Allen radiation belt, we must contend with heavy cosmic particles which travel with a tremendous energy and leave destructive tracks in animal tissue, each of which is about the diameter of twenty blood corpuscles. In the area between the earth’s atmosphere and the inner edge of the belt, we know that these particles occur frequently enough to damage the tissue of animals in high balloon flights. Their strike is apparently not felt by biological specimens, and the effect of their damage is conjectural.
Radiobiologists are of the opinion that if one of these cosmic particles should strike an important area of the brain, a man could be put out of action. It must be remembered that the brain is not composed of finite pinpoint areas but of a large association of cells, the destruction of a small part of which would be unlikely to produce any undesirable effect. The only question that remains is “How many holes in the head can a man or an animal stand?” and to date we are not sure of the answer. We must make sure through adequate animal experiments, especially if we plan to have a manned satellite station rotating around the earth within the area of cosmic radiation.
In this area, the Able-Baker flight lasted approximately ten minutes, and two strikes of such particles occurred on the sensitive plates designed to record the heavy particle concentration. Able’s death from anesthesia five days after the flight allowed exhaustive histopathologic examinations to be made of her tissues, and no heavy particle tracks were found. Baker, who is still alive and well, has shown no evidence that she was in any way affected by such radiation. A conclusion of “no effect" can be made only for a similar flight path and for a similar duration in space. Longer periods in this area of space are required before definite conclusions can be drawn.
ACCELERATION AND DECELERATION
Although acceleration is the process of speeding up and deceleration the process of slowing down, the net effects of the two forces are the same, so that physiologically we can speak of them as being one.
Newton’s first law states that a body either remains at rest or progresses in uniform motion. Because there is no resistance in outer space, the velocity which a body achieves is maintained without any propulsive assistance. The velocity, its direction, and the distance from earth determine whether an object will soar on into space, will fall back to earth, or will go into orbit.
Currently, our methods of propulsion into space consist of giving the space vehicle a high velocity after a short period of time and then allowing the vehicle to continue on its own in free flight without further help. Such a method of propulsion demands that, in order to get into true space, we reach the earth’s escape velocity of about seven miles per second. To achieve this velocity, efficiency of the method requires high accelerative G forces.
A return to earth obviously demands that we apply slowdown methods involving high decelerative G forces. In our present ballistic approach to space travel, deceleration has to be achieved in a relatively short distance, and therefore in a relatively short time, so that, usually, much higher G forces are attained in landing than in take-off. In the Able-Baker flight, G forces during re-entry were three and a half times greater than those during take-off. Although G forces during take-off and recovery can be mitigated by engineering design, which will require larger funds than have so far been made available, the escape velocity of seven miles per second is necessary only because of the current ballistic approach. If we had a long enough ladder and could spare the time, we could climb up into space and back with no G forces of consequence to worry us. This would also be true if we had a space vehicle which could maintain a constant speed when it was pointed toward space. In both instances, we would eventually arrive in outer space; so perhaps future spacemen will look back at our present propulsion methods and smile at the crudity of their forefathers, who contemplated putting a man into a rocket and then firing him off into the blue.
Our chief medical concern with accelerative and decelerative G forces is their ellect upon man’s circulatory system. We need to find out whether there will be impairment of its function of supplying oxygen and nutrition to tissues and carrying away the waste products of tissue metabolism, which the respiratory system eliminates as water and carbon dioxide and the urinary system eliminates as a multitude of end products. The difficulty arises from the fact that, for all practical purposes, the vascular system obeys the laws of hydrostatics.
Fluids are not easily compressed, a fact put into use in the many hydraulic systems, including the braking system of an automobile. And fluids seek their own level. At one G, or the force of gravity on earth, when we are standing up the blood tries to flow out of our toes and is prevented from doing so only by the competence of our blood vessels. Blood cannot go to our brains without the pumping action of our hearts. The heart is sensitive to changes in hydrostatic pressure, to the degree that the mere raising of an arm can be reflected in its compensatory reaction. When we lie down the hydrostatic pressures more or less equalize, and blood goes to the head or to the feet with equal facility.
Under all normal circumstances on earth, the efficiency of the vascular system far outweighs these hydrostatic effects. At zero G, which is weightlessness, these effects do not exist, and any position is as good as the next one. However, at G forces greater than one G, these potencies can be expected to increase in direct relation to the amount of G force applied, so that now position becomes extremely important. Insofar as the direction of the applied G force is concerned, the position which allows no point of the vascular system to be higher than another would give the best results. Under Sufficient G force the position which allows the head to lead in the direction of acceleration would drain the brain of blood and cause a blackout through oxygen starvation. Theoretically, the position where the long axis of the body is perpendicular to the G force would be the best choice.
In the Able-Baker flight, G forces encountered caused Able to increase her heart rate, while little Baker’s rate decreased. I have reported this as being perhaps due to the fact that Able did not have the most important part of her anatomy perpendicular to the G force, while Baker did. If this contention is true, then the dynamics of circulation in the critical anatomical areas require further study, so that our spaceman will not be subjected to unnecessary stress or trauma.
VISION IN SPACE
As an example of some of the lesser difficulties in space medicine, consider the question of vision. Without the buffer of the natural terrestrial atmosphere, the radiation of visual light and infrared and ultraviolet rays will be maximal, so that filters and other specialized protective equipment will be necessary for an astronaut. Also, owing to the absence of an atmosphere, tremendous contrasts between lighted objects and the darkness of space may pose some visual problems.
Perhaps the most serious visual difficulty lor an astronaut may be the condition of empty-space myopia. At rest, our eyes tend to accommodate for a distance of about six feet, so that objects beyond this distance are out of focus and not readily perceived. On the ground and in ordinary flying, this circumstance causes no severe problem, since our eyes can quite rapidly accommodate to distant scenery by progressive accommodations to a series of objects. However, traveling in space, a man does not have this procession of objects in front of him, and with his eyes at the resting accommodation of six feet or less, he has no yardstick by which he may determine whether his eyes are focusing at six feet or at infinity. As a result, objects even as close as a hundred feet can be completely missed visually. For exactly these reasons, the difficulties of vision are a plague to our high-flying jet pilots.
THE NEED FOR BASIC RESEARCH
All of the foregoing might lead one to conclude that space is an outrageously dangerous area to be entered by man. Some have chosen to make an issue out of the difficulties, while others have overminimized them. Doubtless the truth lies somewhere in between. In order to be sure of the extent of likely dangers, biological investigation using animals should have high priority on any program concerning outer space. From what I can glean of the efforts of space scientists in Soviet Russia, the necessity is fully recognized, and Russian biological research is probably ahead of ours. To place a man in space without biological research would be equivalent to developing a polio vaccine by using human subjects instead of animals. The successful efforts carried out in the United States which are worthy of the term bioflight are few.
During the Able-Baker flight. Able had to live restrained inside the capsule and in the artificial environment created for her there for a total period of almost 72 hours — such a lengthy time being required because the biological experiment could not interfere with the primary engineering mission of this particular missile. Even so, the engineers were able to build into the capsule all of the environmental criteria that were requested of them, and they built it to such a degree of exactness that the animals were able to re-enter the world alive and well.
Although some neurological and psychological experiments have been performed using simians, physiological base-line data are relatively lacking for the monkey family. These base-line data take years to collect and evaluate and are already available for other animals, such as the rat and the dog. The claim that the physiology of a chimpanzee or a rhesus is most like that of man is not based upon sufficient research evidence. Physiologists have generally avoided using members of the monkey family as experimental subjects, because of their much greater cost and because they are not the easiest animals to handle. To use them as primary test animals to determine the physiological effects of space is likely to land us in the position of having data which may be difficult to interpret.
In the animal bioflights so far carried out, our knowledge of the biological effects of space is given a good start. But it is only a start. A flight of such a few animals into space for such short periods cannot provide many answers. The variations of the response of biological systems to drugs, environments, or social stresses differ greatly between individuals. If we put ten animals or ten men into a cold room, two might become frostbitten, three might become hypothermic without frostbite, and the other five might be quite happy, although all were in the same situation. We cannot rely upon the meager results so far obtained.
Space medicos understand that grim determination is necessary to carry out a bioflight successfully. They know, too, that their specimens can get back alive, and they will work minutely to see that they do get back alive, never daring to delegate without checking and double-checking. When I hear on a news broadcast that a handful of valueless little white mice have died in an effort to reach outer space, to me there is nothing casual in the implication. There is no exultation when a missile has to be destroyed. To space scientists these things are steps backward in the national effort, for which all of us, no matter to what service we owe our particular allegiance, wish only success and progress.
The topsy-turvy growth of the missile program has affected the medical and biological aspects of space research no less than it has its other aspects. The dream of every space scientist is space travel for man, but up to now the picture of the biological programs necessary to be carried out has not been clear. Injury to our first man in space can put our program back for years, and there would seem to be a need for further animal experimentation before we proceed. There are still many who believe that simulated conditions of space within a laboratory will tell us all, presupposing that we know all the conditions to be encountered during a space flight. Even if they were right, we would have to check our suppositions by the use of animal flights. Furthermore, Van Allen’s belt of radiation, cosmic radiation, and weightlessness cannot be simulated or assessed here on earth.
Space flights using animals cannot be regarded as anything more than a checking process, while in the laboratory we do the basic work, such as the study of the relationship between oxygen and barometric pressure and its effect upon respiration physiology; the study of the effects of radiation upon biological tissue and the protective measures against its ill effects; the study of rotation upon the vestibular system; the study of the dynamics of the vascular system during high G forces.
Space scientists are constantly faced with the question “Why does man wish to explore space?” A mountain climber once told a newspaper reporter that he risked his neck climbing to the tops of mountains simply because the mountains were there, a reply which, despite its complete lack of reasoning, seems to have great public appeal and may be sufficient answer to the present question. Explorations in the past have yielded benefits far beyond what could possibly have been predicted, and it would be unusual if explorations of space did not yield parallel benefits.
It is reported that it took Columbus seven years to induce Queen Isabella to sell her jewels to finance the expedition which has resulted in all that Americans now hold dear. Isabella got very little in return for her investment at the time. The Phoenicians and the Dutch explored for trade; the Egyptians, the Spaniards, the Portuguese, and the British, for King Solomon’s gold; only the Polynesians and the Vikings explored for the sheer joy of practicing the arts of navigation and voyaging.
Today we have other globes to explore, but let us not delude ourselves. Would we rather see our taxes go to efforts to solve the problems of space today, or would we prefer to wait and see them go to a foreign power in payment for the exports from that country’s newest territory, the moon?