History of Research in Space Biology and Biodynamics
[33] Among the phenomena to be encountered in manned space flight, few, if any, have inspired as much scientific and popular speculation as that of subgravity,* including both pure weightlessness or zero-gravity and the various fractional states that lie in between zero-gravity and normal gravity conditions. In recent years, this has also been a subject of intensive research both in the United States and abroad; and the Space Biology Branch of the Aeromedical Field Laboratory, at the Air Force Missile Development Center, is one of the agencies that have made significant contributions to the research effort. This aspect of the Center's human factors program is less well known than either the rocket-sled experiments of Doctor (Colonel) John Paul Stapp or the program of high-altitude balloon flights culminating in the record Man-High (II) ascent of 19-20 August 1957. Yet the current program of subgravity research has roots at Holloman Air Force Base that go back before the rocket track was even built, and before the first balloon with biological payload was launched.
Subgravity research as a clearly defined field of study had its real beginning just after World War II. It has its primary application in the field of ultimate space flight, where gravitational attraction will still be present but will be normally counterbalanced by other factors, rather than in conventional aviation. Nevertheless, brief exposures to subgravity can and do occur in aircraft flight, so that the problem attracted some slight attention even earlier from specialists in aviation medicine. Moreover, even before World War II, a limited amount of subgravity experimentation had already taken place.
A German aeromedical scientist, Doctor Hubertus Strughold--now at the now at the School of Aviation Medicine, Randolph Field, Texas--staged a particularly memorable experiment to study human orientation when deprived of gravitational cues from the external pressure sense. This is only one of the sense mechanisms that supply information on bodily weight and direction, but it is important in flying, where it is activated by the pressure of the aircraft seat on a flier's skin and thus provides the familiar "seat-of-the-pants sensation." In order to simulate a weightless condition as far as this one sense is concerned, Strughold anesthetized his buttocks with novocaine. He then flew a series of acrobatic maneuvers, and in his peculiar condition he found the experience very disagreeable.1 Another German investigator, Heinz von Diringshofen, whose main work concerned human tolerance to multiple g-loads, began exposing test subjects in 1938 to a few seconds of subgravity simply by putting an aircraft through a vertical dive.2
The early experiments of Von Diringshofen and Strughold did not lead to any concerted or continuing program of subgravity research in Germany. In the immediate post-war years, German scientists contributed some valuable theoretical studies relating to subgravity, as did scientists in other European countries. The first major landmark in actual subgravity experimentation, however, was a series of high-altitude rocket flights with animal subjects started in 1948 by the United States Air Force.3 The agency immediately in charge was the Aero Medical Laboratory at Wright Field, which then formed part of the Air Materiel Command and which is now a unit of Wright Air Development Center. The vehicle used at first was the German V-2 rocket, of which large numbers had been captured and brought to White Sands Proving Ground in south-central New Mexico to be used in high-altitude research. No less than five V-2 animal flights were launched from White Sands, and in each case the project obtained a wide variety of support services from Holloman Air Force Base, on the opposite side of the same Tularosa Basin. For all flights except the very first, actual preparation of the nose cone including the animal capsule took place in Holloman laboratory facilities. And when, in 1951, the Aero Medical Laboratory began using the newly-developed Aerobee research rocket for its experiments, launch operations as well were transferred entirely to Holloman.
The Aero Medical Laboratory's animal rocket flights were not designed [34] purely for subgravity studies. Their purpose was to expose living subjects to as many as possible of the potential hazards of space flight. In practice, however, a rocket trajectory was too brief to obtain significant exposure to such hazards as primary cosmic radiation, while fairly moderate g-forces were involved both in rocket acceleration and in the opening shock of the parachute recovery system that was designed to carry the capsule safely back to earth. The far-reaching significance of these flights lies rather in the exposure of animals to subgravity lasting for as much as two or three minutes, during the period of coasting and free fall from rocket burnout to the point where the descending capsule again met appreciable atmospheric drag. At that time, no other experimental method could come close to providing as long an exposure. Moreover, for subgravity research, unlike cosmic radiation studies, two or three minutes was not too short a period for some disturbing symptoms to make themselves felt, if in fact any were likely to occur.
The hero of the first animal rocket flight was a nine-pound rhesus monkey named Albert. He was brought to New Mexico by a team from the Aero Medical Laboratory at Wright Field that included Doctor (Captain and later Lieutenant Colonel) David G. Simons, who now heads the Aeromedical Field Laboratory at Holloman. Albert was carefully instrumented to record both heart and respiratory action. On 18 June 1948 he was finally launched toward space. Unfortunately, his brief trip in a V-2 to an altitude of thirty-seven miles was plagued with a series of operational failures, and no data were obtained. Neither did Albert manage to get back alive: the parachute system failed.
A year later the Wright Field scientists, including Doctor Simons, tried again. On 14 June 1949, Albert (II) reached an altitude of about eighty-three miles. There was still no live recovery, since the parachute system failed again. However, data were successfully recorded throughout the flight and indicated that the second Albert suffered no serious ill effects from weightlessness, cosmic radiation, or any other hazard of space flight.
After two more monkey flights, of which one was marred by unsatisfactory rocket performance and the other essentially repeated the outcome of the Albert (II) flight, a mouse was chosen as passenger in the fifth and last of the space biology V-2's. The mouse was not instrumented for heart action or breathing since this time the primary objective was to record the conscious reactions of an animal under changing gravity conditions. For this purpose, the animal capsule was equipped with a camera system to photograph the mouse at fixed intervals. As usual, the recovery system failed--the mouse did not survive impact. But photographic evidenced showed that the mouse retained "normal muscular coordination" throughout the subgravity phase, even though "he no longer had a preference for any particular direction and was as much at ease when inverted as when upright relative to the control starting position."4
With the first aeromedical Aerobee firing, on 18 April 1951 from Holloman Air Force Base, project scientists ed to the pattern of the V-2 monkey flights. The result was quite familiar: physiological data on a monkey's breathing and heart rates were successfully recorded there was no sign of any gross disturbance in the subject, and the parachute failed again. Finally, with the second Aerobee animal flight of 20 September 1951, the long-awaited breakthrough in parachute recovery was successfully accomplished. An instrumented monkey was safely brought back from peak altitude of 236,000 feet, and so was a grand total of eleven mice that had gone along with him. Successful recovery was again accomplished on the third and last Aerobee flight of the series, which took place on 21 May 1952. All passengers--two monkeys and two mice--returned safely to earth, and one of the monkeys is still alive and health., Washington, D. C., zoo.
Nine of the second Aerobee's mouse contingent served primarily as cosmic radiation subjects, but all other mouse like the mice on the last V-2, were studied photographically for their reaction during the subgravity state. One of these had undergone a prior operation removing the vestibular apparatus of the inner ear that is responsive to gravitational force helps give both mice and human beings a sense of equilibrium. The mouse was already accustomed to orient himself by vision and touch exclusively and did not seem troubled by loss of gravity during the flight. One of the three normal mice as subgravity test subjects was also free from any sign of disorientation during exposure to subgravity, apparently because it had a paddle to cling to and retained full possession of tactile as well as visual references. But the two remaining mice did show some signs of disorientation.
Since May 1952, there have been [35]  more rocket experiments with animal subjects either at Holloman Air Force Base or elsewhere in the United States. For a few years, at least, experiments of this type have become a monopoly of the Union of Soviet Socialist Republics, where the first animal-carrying rocket is said to have been launched in 1951. The Russians preferred dogs as test subjects, and refrained from giving them anesthesia before takeoff. They have also claimed that no dog was ever lost through failure of his breathing equipment or "effect of external factors," but they have not specified how many may have been lost for other reasons.5 If United States experience is any guide, one is tempted to assume that the Russians must regard parachute failure as an "internal" factor! Be that as it may, the Russian methods and test results generally resembled those of the earlier Air Force animal rocket flights--until, of course, they used a rocket to place a dog in orbit in November 1957.
From the standpoint of subgravity studies, the unique quality of this last achievement was the length of the exposure obtained, from the final rocket burnout until the death of Laika, the satellite dog, roughly a week after launching. Technically speaking, a minor limitation of this experiment was the presence of fractional g-forces caused by the tumbling of the satellite vehicle. A more obvious limitation for subgravity studies or any other research objective was failure to bring back either the dog itself or a photographic record for later study and observation.6
According to results published so far concerning the Russians' satellite experiment, the effects of rocket acceleration on Laika's heart beat, though tolerable, persisted much longer after acceleration ceased than would have been the case if recovery from the same high g-load had been made in a normal one-g field. Russian scientists attributed this result directly to the influence of a post-acceleration subgravity state. However, there was still no sign of disabling ill effects on the test subject as a result of subgravity exposure. The dog's eyesight allegedly "compensated to a certain degree the disturbance of locomotive power" that was due to subgravity, although under the conditions of the test it is hard to see how this could be anything more than a reasonable hypothesis.7
Even before the United States abandoned the field of animal rocket experiments to the Russians, at least for the present, scientists at different Air Force installations had branched out into still another fruitful type of subgravity research, using the airplane as test vehicle. In May 1950, two former German scientists working at the School of Aviation Medicine, Doctors Fritz and Heinz Haber, delivered a paper in which they explained how to achieve over thirty seconds of subgravity in aircraft flight. The method was to fly the plane in a parabolic arc or "Keplerian" trajectory in which centrifugal force would exactly offset the downward pull of gravity and engine thrust would counterbalance air friction. This was not an easy thing to do, and even with an expert pilot at the controls one could expect absolute weightlessness for only part of the total subgravity trajectory. Nevertheless, the Habers' proposal offered the first method for obtaining a really significant subgravity exposure in manned flight.8
During 1951, the new procedure was tested at Edwards Air Force Base in California and at Wright Field in Ohio. At Edwards, the noted test pilot Scott Crossfield and the Air Force's Major Charles E. Yeager both flew a number of Keplerian trajectories, the former working on behalf of the National Advisory Committee for Aeronautics. At Wright Field, similar experiments were conducted by Dr. E.R. Ballinger. Apparently none of these early experiments achieved more than a few seconds, at most, of true zero-gravity, but total subgravity trajectories were in reasonably close accord with the Habers' predictions. Test results showed a tendency for subjects to overreach with their arms during subgravity. Symptoms of disorientation also appeared in some cases, but, on the whole, these flights indicated no major difficulties in orientation as long as the subjects were firmly belted in and had full visual references.9
This sudden burst of subgravity flights in the United States was followed by a period of relative inactivity during 1952-1954. Meanwhile, related experiments were being conducted during these same years in Argentina by the Austrian-born scientist Dr. Harald J. A. von Beckh, who had left Germany for South America shortly after the war. Von Beckh introduced still another animal to the menagerie of subgravity test subjects, the South American water turtle. He had one turtle whose vestibular function had been injured accidentally; and he found that this turtle showed much better coordination and orientation during an aircraft subgravity flight than his normal companions. Like the mouse that had a special vestibular [36] operation before going up in the second aeromedical Aerobee, the turtle had apparently learned to compensate visually for the lack of normal gravitational cues. Even the normal turtles, however, gradually improved their performance after a sufficient number of flights. 10
In his turtle experiments, Von Beckh achieved subgravity exposures up to seven seconds by means of vertical dives. Subsequently he, too, adopted the parabolic flight pattern and shifted from turtles to human subjects. The latter submitted to a series of eye-hand coordination tests, in which they showed the familiar tendency to overreach during subgravity but resembled Von Beckh's turtles in their capacity to improve with later flights. Von Beckh was also much interested to observe that when the plane entered its subgravity arc by a maneuver causing high acceleration forces, the recovery from acceleration-induced blackout took appreciably longer than usual.11 In a sense this foreshadowed the experience of the Russian satellite dog, and suggested a special topic for further experimentation. However, Von Beckh cut short his stay in Argentina to take a position in the United States with the Human Factors Division of the Martin Company. Later still, in January 1958, he joined the staff of the Air Force Missile Development Center's Aeromedical Field Laboratory. There he assumed direction of the present subgravity program which had been started--perhaps it would be better to say reactivated--in 1954.

* The term "subgravity" will normally be used in this study to denote all states in which the gravitational force is less than the normal one "g". "Weightlessness" is commonly used in the very same broad sense, but can be confusing. The word literally suggests a complete absence of weight, or zero-gravity, whereas the writer often is referring in fact to a small fractional gravity state-- "virtual" weightlessness as it is sometimes expressed.