 The Air Force launched an intensive study of the human factors involved in spaceflight. By then we had solved such mechanical problems as vehicle design, guidance, tracking, re-entry techniques. Now, through 1960, we sought to determine if a 1G oxygen-breathing creature accustomed to the protection of the Earth's atmosphere could survive in the hostile environment of space. The problems encountered were both physiological and psychological. But an active man functioned in spacecraft-type high-carbon dioxide content air. Dr. Bruno Balk and others of the Air Force School of Aviation Medicine exercised in a sealed chamber at 11,000 feet altitude on Mount Evans, Colorado. He breathed air that had been given at 12 percent CO2 content. Sea level normal is one-thirtieth of one percent. The findings of the experiments indicated that man could increase his ability to cope with high altitude through conditioning and that space pioneers must possess physical stamina and great emotional stability. Weightlessness in spaceflight was given great attention. The human nervous system, blood circulation, and muscular control are normally adjusted to the influence of gravity and low altitudes, what we call 1G. Here the absence of gravity was created in a fast C-131, flying a path in which for a brief time, centrifugal force is exactly balanced by the Earth's gravitational pull. The men are in a state of free form. They feel no gravity. Psychological reaction to this strange state of affairs varied considerably. But the tests proved that during the period of zero gravity, man could retain his ability to use his arms and legs. Potential astronauts undergo this experience of weightlessness. A float in a crystal ball told the pilot of the C-131 when he attained the right speed and flight path to produce zero G. In orbit in mercury capsules they will be in a weightless state for hours, not a mere 15 seconds. But here they begin to get used to the strange sensation of zero G. Man's neuromuscular coordination in the weightless state was determined by studies in other flights. In an MC-2 full pressure suit, this man occupied a chamber designed to simulate the temperatures which the crew of a space vehicle would experience at hypersonic speed during re-entry of the Earth's atmosphere. The tube infrared lamps raised temperatures 100 degrees a minute. As specialists of the aerospace medical research laboratory, studied skin and body temperatures, pulse rate and heart reactions. This helped determine the limits of heat stress on human beings and the protection needed in space flights. During the test, the chamber temperature was raised to 500 degrees. At Wright-Patterson Air Force Base, from 7 through 15 April 1960, Courtney Metzger, research scientist, volunteered to spend seven full days in an airtight capsule in order to test life-sustaining space equipment in a simulated space environment. He communicated by squawk box with observers outside the capsule. As men must do in spacecraft, he took his food from tubes. The water he drank was under pressure. He maintained his muscular tone by exercise. Throughout the seven days, the temperature, moisture and oxygen levels within the capsule were recorded. In good shape at the end of a full week in the capsule, he was congratulated by Colonel John Stapp, famed for his historic sled runs at Solomon Air Force Base. Then there was a much longer test of how men will react to prolonged stays in the environment of space. From 15 August through 15 September 1960, Captain John J. Hargreaves and Captain William B. Habluzzo spent 30 days, eight hours and 21 minutes in a space cabin simulator at the School of Aerospace Medicine. They had a supply of 80 pounds of pre-cooked, dehydrated food and an oxygen system. They shared the duty of continuously manning the control panel 24 hours a day. They ate, slept and kept house in this 8 by 12 sealed cabin for a whole month. Outside the cabin, instruments recorded their physiological and psychological reactions. Findings of the long and trying ordeal indicated that men can maintain efficiency during extended space flights. At Rider Development Division, a space suit was developed to provide part of the protective and life-sustaining equipment that a space traveler would need. This man, in an altitude chamber, is not only wearing the full pressure suit that he will need in the near vacuum of space, but on his back he carries a pack that supplies him with oxygen by a new system. Poses, recycle his breath through the pack. Carbon dioxide and moisture are removed. Pure oxygen is added and his breath is returned to him to be breathed again. A striking feature is that the equipment is free from attachments to the spaceship's own oxygen system. This means that the wearer could move outside the vehicle into space, taking with him the oxygen he needs. G-loads that men must endure during the acceleration and deceleration of space vehicles have been under study since the early 1950s and became a matter of general interest when Colonel Staff made his famous ride in 1954. At Holloman Air Force Base in New Mexico, sled runs carried man and animals into extreme G-load condition. More than men will ever be required to experience in actual spaceflight. During each run, instrumentation recorded data on rates of acceleration and deceleration and on the peak G-loads. It was not unusual to sustain G-loads from 25 plus to 45 plus. An extraordinary event occurred in 1958 when Captain Eli L. Beading of the Air Force, a program task scientist, took a perilous ride that subjected him for four hundredths of a second to 82.6 Gs. The limit of tolerance of G-forces was proved to be high. Another significant factor explored during the 1950s was the effect of cosmic radiation on the space traveler. To verify information gathered in numerous animal balloon flights, Air Force Major David Simons in 1957 ascended to 102,000 feet in a semi-sealed cabin. He suffered no adverse effects from radiation. Tests with animals were of great value. chimpanzees are the best adapted to tests under space conditions because their liver, heart, and intestines are in the same location as in man. At Holloman Air Force Base, a large colony of these intelligent animals was maintained by the Air Force Aerospace Medical Laboratory. They were given the best of care. They became trusting and friendly with the veterinarians who had them in charge. They submitted willingly to test flights. They learned to perform complex tasks in manipulating an instrument panel. They willingly cooperated in tests made in the space environmental chamber, while technicians checked their pulse, blood pressure, temperature, and respiration rate, and while the chimp was working as he might when in orbit. Men who go into space must be equipped to survive launch and re-entry G-load, long periods of weightlessness, low pressures, and other factors of the hostile environment in which he will find himself. Before these risks can be faced, an immense amount of research and testing must be accomplished. Major parts of this research were conducted during the 1950s, a play, and progressively, by the United States Air Force.