The American manned spaceflight program officially began in November 1958, when the new National Aeronautics and Space Administration (NASA) received authorization to launch a man into Earth orbit. That effort, Project Mercury, was the first phase of a program that would lead to a series of manned lunar landings between 1969 and 1972 and the Skylab missions of 1973-1974, which qualified man for space missions lasting up to 84 days. Between Mercury (which included animal flights before single manned flights) and Apollo, the Gemini and Skylab projects successfully launched and recovered two and three men, respectively. The Skylab missions of 1973 and 1974 exposed men to a spaceflight duration of 84 days. That the space program moved so far so quickly is a testament to NASA's ability to harness and coordinate a diversity of talents and resources. It also testifies to the nation's capabilities in biomedicine and the behavioral sciences and to NASA's ability to encourage and sustain a working relationship among biomedical and behavioral scientists, clinicians, physical scientists, engineers, and mission planners.
This working relationship, though unusual, was not unprecedented. Within the military services, life scientists, engineers, and mission planners were accustomed to close interaction. For more than 50 years before the first manned spaceflight, these diverse specialists had worked together to solve human factors problems in aeronautics, to identify and measure human limitations at increasingly higher altitudes and speeds, and to develop equipment that would enable man to transcend these apparent limitations. Those charged with planning for Project Mercury and the Subsequent phases of the manned space program were products of this experience.
MEDICINE AND MANNED FLIGHT BEFORE 1958
 A new phase in human exploration began on November 21, 1783, when two Frenchmen rose over the French countryside in a balloon1. Their flight introduced men to an era in which exploration would be inextricably bound to the machinery of exploration and to man's ability to cope with the conditions of unusual, and increasingly hostile, environments. Given the role of medicine in extending the frontiers of flight, it was fitting that one of the two persons on that first balloon flight was a physician. Numerous physicians flew on subsequent balloon flights. An American, John Jeffries, made several balloon flights after 1784 and may have been the first to investigate the effects of flight on man. He recorded a significant decrease in temperature, oxygen, and pressure with altitude and described a painful sensation in his ears. A contemporary, British surgeon John Shelton, discovered that nausea and irrational behavior can be effects of flight. Neither Jeffries nor Shelton understood the connection between diminished oxygen supply and diminished barometric pressure and the observed physiological effects.2
The manner in which Jeffries and Shelton investigated the conditions and environment of flight-using themselves as test subjects-became a tradition that continued into the period of powered flight. Steadily increasing speeds and altitudes and maneuvering capability raised new questions concerning human physiology and performance, and these questions naturally attracted the attention of flight-oriented physicians. These physicians, most of whom were military flight surgeons, generally were not research scientists, but more pragmatic, mission-oriented investigators. They sought to understand the factors that affected the health and performance of flight crews and to identify methods for reducing or eliminating ill effects.
Flight physicians often took heroic approaches to their investigations of the human factors problems of flight, using themselves as test subjects. Col. Randolph Lovelace I I gave a dramatic demonstration of this approach in 1943. Lovelace hypothesized that the decreased density of the atmosphere at high altitudes would intensify the shock of parachute opening during emergency escapes. To test this hypothesis and evaluate several items of equipment intended to minimize the shock, he bailed out at an altitude of 12,195 meters. He proved his hypothesis and the value of the backup equipment: the shock nearly killed him, but the equipment saved his life.3 Other flight physicians have made comparable heroic efforts. In most cases, their objective was to identify the causes of, and develop preventive measures against, specific problems, while developing a scientific understanding of the physiological and behavioral dynamics associated with flight operations.
 Biomedical interest in flight was not entirely limited to flight surgeons, however In the 1860s, French physiologist Paul Bert began to investigate systematically the physiological effects of diminished oxygen and barometric pressure. He realized that he needed to be able to simulate, on the ground, the flight environment. Accordingly, he constructed the world's first pressure chamber, in which he could simulate altitudes up to 10,980 meters. Using himself and dogs as experimental subjects, he conducted 670 experiments in which the percentage of oxygen in the air was constant and barometric pressure was the variable. He discovered that heart and respiration rates and digestive gases vary in direct proportion to altitude. Above 4,880 meters, he experienced nausea and dimming of vision. These symptoms of altitude sickness disappeared when he breathed air enriched with oxygen.
Bert followed these investigations with inflight research on two occasions. Two of his associates, both scientists, ascended to 7,991 meters in a gondola that was equipped with bags of oxygen having special mouthpieces. Both flights confirmed his belief that the use of oxygen-enriched air above 1,840 meters would eliminate the effects of altitude sickness. These experiments nearly ended in disaster, however, because Bert did not realize that the passengers would have to breathe oxygen continuously above the critical altitude.4
Bert had correctly identified the need for supplementary oxygen at high altitudes, but he failed to recognize that the critical factor was not the quantity of oxygen available, but the oxygen saturation within the blood, which in turn was a function of atmospheric pressure. Several European physiologists discovered this factor during balloon flights between 1900 and 1903. Their work led to conclusions that became part of the theoretical framework of aerospace medicine: man cannot survive above 7,930 meters without extra oxygen; oxygen must be force-fed through a closed mask in order to ensure optimum blood saturation; and man requires protection within a sealed structure or pressure suit at altitudes above 12,200 meters. 5
The advent of powered flight and its rapid development after World War I augmented biomedical interest in the human factors of flight. Increased speeds and variable accelerations associated with maneuvering drew attention to the effects of these factors on physiology and performance, while developments in the machinery of flight raised concern over the possible clinical effects of noise, vibration, and toxic fumes. These and other factors gave increasing impetus to research in biotechnology-the application of information derived from human research to the development of life support and protective equipment to improve human performance in flight operations.6 During the interwar period, aviation medecine came under the nearly exclusive control of the military services.
 Research, development, and training facilities established by the Army and Navy remained the primary centers for aviation and space biomedicine through the mid-1960s. The activities at these facilities reflected the developing interaction among biomedical and engineering personnel and a pragmatic approach to aerospace medicine.7
The development of jet aircraft following World War II, like the advent of powered flight 30 years earlier, generated renewed interest in human factors. The jet age placed new emphasis on the identification of human capabilities and limitations, the design of systems and equipment to maximize these capabilities and minimize the limitations, and the definition of standards for selecting and training the individuals best qualified to endure the stresses and hazards of high-speed, high-altitude flight.8 The development of jet flight strengthened and sustained the traditions of biomedical involvement in manned flight and mission-oriented biomedicine that had slowly emerged with propellor-powered flight.
While flight-oriented physicians and biomedical scientists gave primary attention to the human factors problems of aeronautics during the postwar period, interest in human factors aspects of spaceflight grew steadily during the 1950s. A cadre of German specialists in rocketry, biotechnology, and aviation medicine were the primary force behind this growing attention to space biomedicine. Between 1946 and 1948, the Army transferred 34 of these specialists to American military facilities, a few to Navy facilities.9
The dean and principal theoretician of the group was Hubertus Strughold, a physician and physiologist who had been engaged in aviation medical research since the mid-1920s. A Rockefeller Foundation Fellow, he gained international stature as a professor of aviation medicine and as director of the German Aeromedical Research Institute.10 Strughold established the world's first department of space medicine at the Air Force School of Aviation Medicine in 1950. Under his leadership, the school became a major center for basic and clinical investigations into the physiological and behavioral effects of spaceflight and the space environment. During the 1950s, researchers at the school conducted (or sponsored) investigations into the biodynamics of spaceflight (physiological effects of stress factors and weightlessness), human performance (psychological, psychophysiological, and neurological effects), and metabolic, psychological, and other human requirements in space. The results of these investigations were regularly communicated to scientists worldwide through publications and symposia. 11
Strughold contended that the distinction between space and atmosphere was artificial and misleading, at least as far as human biology was concerned. He maintained that man begins to experience "space equivalent" conditions at an altitude of 15,250 meters, where he is  exposed to most of the hazards of the space environment and cannot survive unless protected by a sealed capsule or a pressure suit. For this reason, he argued, manned spaceflight is a natural extension of aeronautical flight, and space medicine a logical extension of aviation medicine. Biomedical investigations into the human factors of spaceflight, he concluded, must build on and extend knowledge already gained from aviation medicine.12 Strughold's views had both practical and political value. They encouraged confidence in the nation's fundamental capability for proceeding with manned spaceflight, and they provided a rationale that Air Force officials would later use to justify the claim that the Air Force should direct manned spaceflight.
A number of other German scientists, particularly Otto Gauer and Henning von Gierke, were assigned to the Aviation (later Aerospace) Medical Laboratory at the Wright Air Development Center. Since the 1930s, this center had sponsored research into human physiological requirements in flight and had applied the results to the design and engineering of pressurized cabins, pressure suits, protective equipment (couches, restraints, cushions), and life support equipment (for example, oxygen masks for high-altitude flights).13
Like Strughold at the School of Aviation Medicine, Gauer and his associates introduced a theoretical approach to aerospace medicine at the Wright facility. Gauer theorized that multiple G acceleration followed by weightlessness could have serious physiological effects. He observed that the acceleration forces encountered during spaceflight launch and reentry would depress circulatory function and cause certain conditions that had been observed in high-altitude aeronautical flights: pooling of blood in the extremities and the brain ("redout") or insufficiency of blood supply to the brain (blackout). Weightlessness, he theorized, would compound the problem since, in the absence of gravity, the blood vessels would relax and would not perform the capillary action that normally aids the heart in the circulation of blood. Consequently, the heart, already overtaxed by multiple G acceleration, would be further strained by the loss of capillary action. This combination of factors, he believed, could lead to conditions such as heart failure, pneumonia (from pooling of blood and fluid in lungs), or severe muscle cramps (from pooling of blood in muscles). He suggested that this combination of factors could also disrupt the normal processes of the nervous system, through which the brain sends signals to the body systems in response to sensations. Because the sensations derive from pressure exerted at various points on the body, the multiple G and null G states, and their rapid succession, could cause the brain to receive and send mixed or conflicting signals. This, in Gauer's view, would affect balance, spatial orientation, and the body's efforts to compensate for circulatory dysfunction.14
 In practical terms, Gauer's theories implied that these effects could he negated, or at least significantly reduced, if some means could he found to reduce the multiple G forces experienced during launch. Following this suggestion, researchers at the Wright center conducted tests of the relationship between body position and the physiological effects of G forces. After numerous tests with a centrifuge between 1952 and 1957, researchers concluded that maximum physiological tolerance results when the forces are applied transversely perpendicular to the head-to-foot axis.15
The Wright center was also responsible for designing equipment that would protect pilots of high-altitude, high-speed aircraft. This responsibility later included space crews, who would face similar, but more extreme, hazards. The major protective devices developed were pressure suits, couch and restraint systems, emergency escape hatches and seats, enclosed flight cabins, and life support equipment. By the end of the 1950s, scientists and engineers at Wright had become increasingly interested in the modification and redesign of aeronautical equipment for spaceflight.16
At the Aeromedical Field Laboratory (an extension of the Wright center) at Holloman Air Force Base, New Mexico, investigators conducted inflight biomedical investigations. Space-related biomedical research included exploration of the effects of weightlessness and radiation on small mammals and primates, human tolerance of the forces of acceleration and impact physiological and performance effects of environmental extremes (cold, diminished oxygen, low barometric pressure), and human responses to brief periods of weightlessness. Biomedical operations at Holloman began in 1948 in a field then termed space biology," the investigation of the space environment through observation of its effects on animals. On four occasions, rhesus monkeys in pressurized capsules were fired into the upper atmosphere aboard V-2s. In each case, the monkey survived the hazards of flight, but died when its parachute failed. From 1949 to 1952, in the Aerobee series, rhesus monkeys and mice were launched to altitudes above 70,000 meters on four flights. These animals were successfully recovered, with no adverse effects attributable to weightlessness and acceleration.17
The space biology program was terminated in 1952, when the Air Force began to give priority to ballistic missiles. By this time, Holloman had other biomedical commitments. Fritz Haber and Heinz Haber at the School of Aviation Medicine and Harold J. von Beckh at Holloman shared Gauer's anxieties about the potential hazards of weightlessness. A method for simulating weightlessness was obviously needed. The Habers, who were physical scientists and engineers, speculated that a brief period of weightlessness could be created by having an airplane make an abrupt  descent following a sharp ascent. In 1951, test pilots flying such parabolic patterns proved the Speculation to be substantially correct. They experienced about a half-minute of zero G and two to six minutes of low G. Von Beckh Suggested a modification of the Habers' technique in order to assess both weightlessness itself and the pilot's reactions to reentry forces following weightlessness. He suggested that immediately following the half-minute of weightlessness, the pilot drop the plane into a steep downward spiral.
Missions between 1953 and 1958 using the combined Haber-von Beckh technique dispelled some concerns while raising new ones. The flights resulted in temporary disorientation and nausea (though it was impossible to determine whether this resulted from weightlessness or the nature of the flight pattern), but showed that humans quickly learn to perform in the new environment. The von Beckh trajectories provided concrete evidence that physiological tolerance of the forces of acceleration declines following exposure to weightlessness. This further confirmed Gauer's theories and reemphasized the need to keep G loads to a minimum.18
Holloman was also a center for investigations of the effects of linear acceleration and high-speed impact. Usually identified with Col. John Stapp, who rode the facility's high-speed "sled" a significant number of times between 1947 and 1955, these studies were intended to determine the limits of human tolerance to the multiple G forces of linear acceleration (straight-line, continuous force) and to high-intensity impacts. By 1958, these studies had revealed that humans have the potential to withstand 46 G and a force of 10,000 pounds for a quarter of a second, forces that were well in excess of those anticipated for spaceflight.19
Finally, Holloman was the center for the Air Force's Man-High high-altitude balloon f lights between 1956 and 1961. Seven missions were flown to measure the intensity of cosmic radiation, test the effectiveness of a sealed cabin, and evaluate instrumentation for remote medical monitoring of a pilot's physiological responses above 30,500 meters. The most important results were in the areas of heat and humidity control and biomedical telemetry.20
While the Air Force was the unquestioned leader in aerospace medicine and biotechnology, the other military services made contributions. The Naval School of Aviation Medicine at Pensacola had responsibilities similar to, but narrower in scope than, those of the Air Force school. The naval school trained flight surgeons, but offered no specialized training in space medicine The facility did sponsor research in areas that would later prove relevant to space medicine, such as designing and evaluating Psychological profiles for the selection of pilots, and studying the effects of stress factors and extreme environments on the vestibular apparatus (Components of the inner ear that control balance and orientation).
 The Navy also sponsored biomedical research and development at its Aviation Medical Acceleration Laboratory in Johnsville, Pennsylvania, and the- Naval Equipment Center in Philadelphia. The activities of these two centers together were similar to those of the Wright center. Johnsville had responsibility for human factors research, while Philadelphia oversaw biotechnology. As at Pensacola, these facilities were oriented toward aviation research and development with little direct interest in spaceflight before 1957.21 Johnsville operated a centrifuge to study effects of acceleration and decceleration. The centrifuge, with NASA input, was modified to simulate interaction between the pilot and a control system that regulated centrifuge motion and G force. This dynamic motion simulator was used to develop the space reaction control system for the X-15 research airplane and later for tests of piloted reentries of the Mercury spacecraft.
The Army had no active program in aviation and space biomedicine, though it did staff a bioastronautics office at the Army Ballistic Missile Agency within the Wernher von Braun group at Huntsville, Alabama. The Army also had a major physiological research facility, the Armed Forces Institute of Pathology in Washington, D.C., which sponsored a wide-ranging program of basic research. Finally, the Army and Navy cooperated in 1958-1959 in a series of biological investigations in space with rhesus monkeys. These flights, launched by Jupiter missiles, provided additional evidence that higher organisms could endure the rigors of spaceflight if adequate life support was provided, and they were important for testing and evaluating biomedical monitoring techniques, instruments, and operational procedures.22
SPACE BIOMEDICINE IN 1958
As the United States prepared to respond to the challenge presented by the Soviet Union's successful launch of Sputnik 1 in October 1957, few within the American aerospace community doubted that the nation could place a man into orbit and return him safely, possibly in advance of the Soviets. The military services had the basic capabilities for launch, operations, and recovery. Biomedical investigators had evidence that man could tolerate the G forces and brief periods of weightlessness anticipated for an orbital mission. The hardware for sustaining man in near-space already existed and could be modified to meet the requirements of an orbital mission. Perhaps most important, the military services, the National Advisory Committee for Aeronautics, NACA (NASA's predecessor), the aerospace industry, and many universities collectively had the scientific, biomedical, and engineering talents and the research, development, and operations facilities required for the task.
 Nonetheless, manned spaceflight remained a formidable challenge, and the human factor was a major element in that challenge. Adapting and modifying hardware, techniques, and knowledge derived primarily from aeronautical research posed significant engineering and operational problems, problems that were exacerbated by a dearth of hard data on human capabilities and limitations in space. While biomedical scientists were certain that humans could tolerate the conditions and forces of Earth-orbital flight, the precise short-term and long-range clinical and behavioral effects of spaceflight were not predictable. Nor could scientists provide the engineers with the baseline (normative value) specifications required for design and development of space capsule protective, life support, communications, and control systems.23
Physicians were particularly concerned about the environmental variables of space (radiation, weightlessness, magnetic fields), the spacecraft (toxic contaminants, fuel leakage, artificial atmosphere, abnormal pressure), and the spaceflight experience (acceleration, isolation, confinement, discomfort, disruption of day-night cycle). Among these. the most worrisome was weightlessness, because it could not be simulated effectively for sustained periods. So little was known about the effects of prolonged weightlessness that a broad range of possible debilities had been predicted, including disorientation and circulatory failure. Biomedical scientists were also worried about interactional factors, that is, the combined effect of two or more stress and environmental factors. The severe problems predicted by Otto Gauer were early examples. I n addition, there was an apparent correlation between the level of oxygen in the bloodstream and tolerance to G forces. Biomedical scientists feared that weightlessness, by upsetting the normal rhythm of the circulatory system, would reduce tolerance to the multiple G forces of reentry. That, in turn, could degrade the ability of flight crews in a critical portion of any mission.24
In the absence of predictive values, space physicians realized that f light crews would have to be selected on the basis of exceptional physical and mental health and then carefully trained. Consequently, the selection and training of astronauts was a major area of biomedical concern. This would not be a simple task, however, given the absence of consensus on the physiological and psychological parameters that should be measured, and the unproved reliability of the instruments that would be used in making these measurements.25
The absence of hard biomedical data had a direct bearing on engineering and operations. To develop a space capsule that would meet human requirements without exceeding weight limitations and without unduly complicated systems, engineers required precise human factors values.26 Mission planners, too, required precise biomedical data to ensure that the  duration, configuration, and progression of missions would not exceed human tolerance. Since weightlessness was the major unknown variable and could not be simulated effectively, flight plans would have to be configured to increase gradually the duration of exposure. To do so, planners needed to know the levels of acceptable risk" for each mission and decide which biomedical functions should be made part of overall monitoring procedures.27
The human factors requirements as known were fully documented by Dr. W. Randolph Lovelace II, a retired Air Force flight surgeon and international expert in aerospace medicine. Between February and October 1958, Lovelace chaired a Working Group on Human Factors and Training-a committee of aerospace physicians, human factors engineers, and test pilots who met under the auspices of the NACA-sponsored Special Committee on Space Technology (Dr. H. Guyford Stever, chairman). This group issued a report, authored by Lovelace, in which biomedical problems were cited as major obstacles to manned orbital flight. An "immediate requirement" exists, Lovelace wrote, for "detailed information on human tolerance limits" to prolonged weightlessness, isolation and confinement, linear and variable acceleration, and space radiation, as well as the application of this information to the "verification of space capsule design." This required, in Lovelace's view, a multidisciplinary approach to human factors research and applications and a coordinated national program of research in space biology and medicine.28
COORDINATION OF THE MANNED SPACE PROGRAM
Although in early 1958 the United States had the resources and facilities needed to provide research, development, and operational support for manned spaceflight, these capabilities were dispersed among different agencies and the various space-related activities were largely uncoordinated. Between January and July 1958, President Eisenhower, key members of Congress, and leading scientists and spokesmen for the aerospace community became increasingly aware of the need for direction of the national space program by a single agency. In January 1958, Eisenhower authorized establishment of the Advanced Research Projects Agency within the Department of Defense to seek means for coordinating the nation's space programs and to recommend a single agency to carry out the task. Subsequently, the three military services and the NACA vied for authorization to manage and direct the space program, particularly the manned effort.
The Air Force seemed the likely choice, inasmuch as it had launch capabilities superior to those of the other military services, major launch  sites on both coasts, and the most experience in launch operations. It was also the unquestioned leader in the field of aerospace medicine, with three times the biomedical personnel and four times the biomedical research and development budget of its closest competitor, the Navy.29 Perhaps most important, the Air Force had shown more interest over a longer time than had any of the other claimants, and it could argue that this interest evolved logically from its historical role as the nation's principal aviation agency. The Air Force, as its space-oriented officials pointed out, had always been moving toward space: "From the first aircraft to enter the inventory to the futuristic X-15, Air Force goals have changed in degree only; the basics have been constant-greater speed, longer range, and higher altitude. 30
The Air Force was also the most advanced in manned spaceflight planning and development. It had three separate programs at different stages of development, but each was conceived as an integral part of the overall Air Force space program. The X-15 rocket-powered research airplane, a joint NACA-Air Force project intended to "fly to the edge of space," was the most recent in a long series of high-performance research aircraft flown since 1947. Although it was plagued by development problems the X-15 was promoted by the Air Force as the first step in its plans to place a man in space.
The second Air Force program, Dyna-Soar, was still on the drawing board in 1958, but the Air Force argued that it was a logical extension of the X series of research aircraft. With design features similar to those of the X-15, Dyna-Soar was to be a lifting body. Launched into orbit by a missile, it would be capable of maneuvering in orbit briefly to set up its reentry and glide to Earth. The Air Force was also proposing a third manned program, Man-in-Space-Soonest (MISS), an extensive program that would achieve both military and civilian objectives in space. MISS was planned to begin with a series of unmanned biological satellites, proceed to a manned orbiting satellite (about 1960), a manned orbiting laboratory (about 1963), and conclude with a manned lunar landing in 1965.31
Neither the Army nor the Navy could set forth a comparable claim to the space mission. The Navy had excellent biomedical, human research, and biotechnology resources and facilities, but it lacked the Air Force's launch capabilities and lengthy experience in high-altitude and astronautics research, development, and planning. Moreover, the Navy's lone proposal for a manned spaceflight project, Project MER (for Manned Earth Reconnaissance), was overly ambitious, requiring the development of completely new hardware and systems. Further, the Navy's failure to place an unmanned satellite (Vanguard) in orbit cast doubt on its ability to sponsor a successful manned operation in space.32
 The Army had launch capabilities and experience to match those of the Air Force. Its Ballistic Missile Agency, led by von Braun, probably had the best launch organization outside the Soviet Union and had been responsible for the United States' first successful orbiting satellite. However, the Army had limited capabilities in aerospace biomedicine and biotechnology, as was evident in its manned space proposal, Project Adam. Adam was simplistic in conception: a man would be hermetically sealed into a capsule atop a ballistic missile. The missile would launch the capsule into space; the capsule would orbit once and reenter as its orbit decayed. In terms of biomedicine, the plan required only that the passenger be protected against the more obvious hazards and forces. No effort would be made to monitor the passenger's physiological reactions in flight or to test human performance capabilities.33
The NACA was the least likely candidate for authorization to manage the manned space program. It had no launch capabilities or facilities, no biomedical resources, no tradition of space-related research and development, and no clearly defined proposal. What the NACA had, however, was an extensive and effective aeronautical research and technology development team, several decades of experience doing advanced research on the ground and in flight (i.e., the X series of research aircraft) in support of military and civilian aeronautical technology development programs, and an intense interest in expanding the scope of its activities to include astronautics. Perhaps most important, the NACA was a civilian agency. 34
President Eisenhower, concerned that a national venture in space would nourish the growth of a politically powerful "military-industrial complex," was suspicious of military ambitions for a space program. Key members of Congress, leading scientists, and other influential public figures shared Eisenhower's concern. It was also believed that an open space program under civilian management would illuminate the contrast between the American and Soviet governments. Many scientists feared that a military space program would stifle communication among scientists and subordinate legitimate research to weapons systems development.35
On April 2, 1958 President Eisenhower recommended that Congress create a new agency, structured around the NACA, to manage the national space program. Congress did so on July 16. The National Aeronautics and Space Administration became operational on October 1, 1958 and received formal authorization to direct the manned orbiting satellite program (soon to be named Project Mercury) several weeks later.36 How this new agency, with no biomedical personnel, no biomedical research facilities, and little experience in human factors research and engineering (with the exception of aircraft flight control), would manage a program that depended so much on biomedicine, remained to be determined.