Space Radiation

In addition to weightlessness, g loads, air, water, and food supply, isolation, and meteoroids, the problems of space flight included protecting the passenger from different kinds of electromagnetic radiation found above the atmosphere. Of the varieties of radiations in space the most mysterious is cosmic radiation, the source of which presents one of the grandest puzzles in nuclear astrophysics. Some of this radiation possibly comes from the Sun, but the preponderance of the cosmic rays bombarding Earth's atmosphere evidently originates outside the solar system - thus the term "cosmic" radiation. High-energy cosmic ray primaries - subatomic particles, of which about 90 percent are protons of hydrogen and helium - slam into the atmosphere at velocities approaching the speed of light. Fifteen to 25 miles above Earth, the cosmic ray primaries collide with atoms and molecules in the thickening atmosphere, are broken up, and are converted into lower-energy rays called secondaries. Above 25 miles the atmosphere becomes too thin to absorb the cosmic ray primaries; since they are capable of penetrating a thick lead wall, it was futile to try to shield a spacecraft pilot completely. So in the early 1950s medical researchers, assuming that a space pilot would be exposed to some cosmic radiation, approached the problem primarily from the angle of establishing how large a dose a human being could tolerate.54

As with weightlessness and g-load research, the best postwar device for studying cosmic radiation was the instrumented sounding rocket. But the last of the rocket experiments with primates occurred in May 1952. From that time until animal rocket shots resumed in 1958, the only upper-atmospheric research rockets fired in the country were occasional Aerobees, launched by the Air Force to altitudes of about 150 miles.55 These shots, carrying only instruments, brought back a modicum of data on cosmic rays. The prime instrument for cosmic ray [50] research from 1952 to 1958 was the oldest vehicle for human flight, the balloon. The postwar development of sturdier, larger, polyethylene balloons to replace rubber aerostats made possible higher and higher ascents with increasingly heavier loads. At the same time the expansion of balloon technology, leading to an increasing number of giant, shiny spheres floating over the United States, multiplied reports of and popular interest in "Unidentified Flying Objects."56

In the balloon-borne space radiation experiments of the fifties, the Navy carried out some notable manned ascents into the stratosphere. On November 8, 1956, for example, Lieutenant Commanders Malcolm D. Ross and M. L. Lewis, as part of the Navy's Strato-Lab program of manned ascents from northern latitudes, reached 76,000 feet, then an altitude record. Less than a year later Ross and Lewis sat in their cramped sealed gondola as their huge polyethylene balloon ascended to nearly 86,000 feet. And in late June 1958 the same two Navy aerostation veterans remained in the 70,000-80,000-foot region for almost 35 hours.57

The Navy also pioneered in the use of balloon-launched rockets (rockoons). The first successful rockoon launch occurred in August 1952 when, from a ship off the coast of Greenland, a University of Iowa team headed by physicist James A. Van Allen sent up a balloon from which a rocket ignited at 70,000 feet and climbed to an altitude of nearly 40 miles. The Navy did most of its upper-atmospheric research, however, with instrumented balloon flights carrying small organisms and insects. In May 1954, for example, General Mills, Incorporated, under contract to the Office of Naval Research, launched a polyethylene balloon, with a capacity of 3 million cubic feet, that carried cosmic ray emulsions - plates designed for recording the tracks of ionizing particles - to an altitude of 115,000 feet. Five years later, from Sioux Falls, South Dakota, Raven Industries launched an Office of Naval Research balloon biological package to a record altitude of 148,000 feet.58

The center of Air Force balloon research in the early 1950s was the Aeromedical Field Laboratory in New Mexico. From July 21, 1950, when Air Force personnel launched the first polyethylene balloon at Holloman Air Force Base, to December 18, 1958, the scientists at the field laboratory sent up 1000 research balloons, although only a small number of these ascents were designed expressly for cosmic ray study. In 1953 the Holloman researchers moved most of their balloon experiments to the northern United States, in the higher geomagnetic latitudes, where they could obtain increased exposure to cosmic ray primaries. During the next year they sent aloft a collection of radish seeds on a series of flights, compiling some 251 hours of exposure of the seeds above 80,000 feet. Monkeys, mice, rats, hamsters, and rabbits also drifted upward in balloons launched by Winzen Research, Incorporated, as a Holloman contractor, from Sault Ste. Marie, Michigan. The most interesting effect observed among the various test subjects was a striking increase in the number of gray hairs on black mice exposed to the high altitudes.59

The first solo manned ascent into the stratosphere was also principally an undertaking [51] of the field laboratory at Holloman. In 1956 field laboratory experimenters inaugurated Project Manhigh, a series of flights from northern sites using Winzen balloons, to test man's ability to live for prolonged periods in a sealed-cabin environment like that inside a spacecraft and to gather new data on cosmic radiation. David Simons, head of the Space Biology Branch at Holloman, was project officer for the Manhigh ascents. The initial flight, from Fleming Field, Minnesota, took place on June 2, 1957. Captain Joseph W. Kittinger stayed aloft inside his sealed gondola for nearly seven hours, breathing pure oxygen, making visual observations, and talking frequently with John P. Stapp, the flight surgeon, and other physicians on the ground. Kittinger spent two hours above 92,000 feet; his maximum altitude during the flight was 96,000 feet.60

About nine weeks later Simons himself entered the space equivalent region, suspended in a sealed capsule below a 3-million-cubic-foot polyethylene balloon launched from an open-face mine near Crosby, Minnesota. Simons exceeded Kittinger's mark for both duration and altitude, staying aloft 32 hours and remaining at 101,000 feet for about 5 hours. Simons was the first man in history to see the Sun set and then rise again from the edge of space. In the Manhigh I gondola he spent more time than anyone before him looking upward at the blackness of space and outward at the white and blue layers of the atmosphere. "The capsule seemed like a welcome window permitting a fabulous view and precious opportunities, not a prison or an enclosure," he related after the flight.61

In October 1958 an excessive temperature rise in the capsule forced a premature termination of the third Manhigh flight, carrying Lieutenant Clifton M. McClure.62 Yet McClure's ascent, together with those of Kittinger and Simons, proved the workability of the sealed cabin for sustaining human life where "the environment is as hostile and very nearly as different in appearance as one would expect to observe from a satellite."63 The environmental control system of the Manhigh capsule and the instrumentation for physiological telemetering were strikingly similar to those later used in the Mercury spacecraft.

With regard to cosmic radiation, however, the Manhigh flights, like numerous rocket, balloon, and laboratory experiments of previous and succeeding years, returned data that were either negative or inconclusive. During the Manhigh II ascent two containers of bread mold were attached to the underside of the capsule, and Simons wore emulsion plates on his arms and chest to measure cosmic ray penetration. The plates did show indications of several hits by so-called "heavy" primaries - cosmic ray particles made up of nuclear particles heavier than are found in hydrogen or helium - but years later the skin in the area of the plates revealed no effects of radiation.64

All these experiments left most scientists as reluctant to speculate about the hazards from cosmic rays in flight as they had been in the early fifties. Simons felt that in manned orbital flights following roughly equatorial orbits, where the spacecraft remained within the protective shielding of Earth's magnetic fields, the spacecraft pilot would be in no danger from cosmic radiation. Yet he remained [52] troubled by the possibility that a solar flare, a sudden burst of energy from the Sun, might precipitate a great increase in cosmic ray intensity during a space mission. About a twentyfold multiplication of cosmic radiation accompanied a solar flare of February 1956. Simons' concern with solar flares led him to the conclusion that continuous voice contact between ground stations and the space pilot would be essential, as well as stepped-up efforts to predict the flares.65

All proponents of manned space flight were alarmed when information transmitted from the first three Explorer satellites, launched during the first half of 1958, disclosed the existence of a huge envelope of radiation beyond the ionosphere. Evidently consisting of protons and electrons trapped in Earth's magnetic field, the radiation layer begins about 400 miles out in space and doubles in intensity about every 60 miles before tapering away about 1200 miles from Earth. This discovery was the first "Van Allen belt," named after James A. Van Allen, United States director of the International Geophysical Year radiation experiments. The Pioneer III probe, launched in December 1958, failed to reach escape velocity, but it did reveal that the radiation zone consisted not of one belt but of two at least - an inner belt of high-energy particles and an outer belt of less energetic particles. Two earlier Pioneer shots, in October and November, had shown that while the radiation zone was several thousand miles deep, it did not extend into space indefinitely.66 Quite obviously, the doughnut-shaped Van Allen belts would pose a serious threat for manned travel in high orbits or interplanetary voyages. In the early manned ventures into space, however, a spacecraft could be placed in an orbit 100 to 150 miles from Earth, high enough to be free of atmospheric frictional drag, yet low enough to stay under the Van Allen radiation.67

The radiation hazards of space flight also include solar radiation. Solar heat, ultraviolet rays, and x-rays all become much more intense beyond the diffusive atmosphere of Earth, but they can be adequately counteracted by space cabin insulation, shielding, refractive paint, and other techniques. Advanced space missions may subject astronauts to dangers from other kinds of radiation, such as the radiation belts surrounding other planets or the radioactivity produced by a spacecraft with a nuclear powerplant.68


54 On cosmic radiation see, for example, James A. Van Allen, "The Nature and Intensity of the Cosmic Radiation," in White and Benson, eds., Physics and Medicine of the Upper Atmosphere, 239-266; Joseph A. Connor, "Space Radiation Protection," NASA-MSC fact sheet No. 106; Hermann J. Schaeffer, "Appraisal of Cosmic-Ray Hazards in Extra-Atmospheric Flight," in Alperin, Stern, and Wooster, eds., Vistas in Astronautics, 291-298; Gerathewohl, Principles of Bioastronautics, 133-138; and C. Frederick Hansen, "The Characteristics of the Upper Atmosphere Pertaining to Hypervelocity Flight," Jet Propulsion, XXVII (Nov. 1957), 1155-1156.

55 Emme, Aeronautics and Astronautics, 77, 82.

56 On Unidentified Flying Objects see several works by Donald E. Keyhoe, especially Flying Saucers in Outer Space (New York, 1953); and Donald H. Menzel, Flying Saucers (Cambridge, Mass., 1953).

57 Malcolm D. Ross, "A Consideration of the U.S. Navy Strato-Lab Balloon Program and Its Contributions to Manned Space Flight," in Proceedings of the Second National Conference on the Peaceful Uses of Space, Seattle, Washington, May 8-10, 1962, NASA SP-8 (Washington, 1962), 261.

58 Gerathewohl, Principles of Bioastronautics, 475-476.

59 David G. Simons, "The 1954 Aeromedical Field Laboratory Balloon Flights: Physiological and Radiobiological Aspects," Journal of Aviation Medicine, XXVII (Apr. 1956), 100-110; Simons interview; Bushnell, "Major Achievements in Space Biology at the Air Force Missile Development Center," 2-12.

60 David G. Simons, "Psychophysiological Aspects of Manhigh," Astronautics, IV (Feb. 1959), 32-33; Bushnell, "Major Achievements in Space Biology at the Air Force Missile Development Center," 27-34.

61 David G. Simons, "Manhigh II," Technical Report 59-28, Air Force Missile Development Center, Holloman Air Force Base, N. Mex., June 1, 1959; Simons, "Psychophysiological Aspects of Manhigh," 33, 62; Simons, "Observations in High-Altitude, Sealed-Cabin Balloon Flight," in Gantz, ed., Man in Space, 133-160; Simons et al., "Personal Experiences in Space Equivalent Flight," in Flaherty, ed., Psychophysiological Aspects of Space Flight, 39-41; Bushnell, "Major Achievements in Space Biology at the Air Force Missile Development Center," 34-41; Simons, "Space Medicine - the Human Body in Space," monograph No. 6, Journal of the Franklin Institute Series, Dec. 1958, 169-178; Simons interview. For a popularly written personal account of the Manhigh II flight see David G. Simons and Don Schanche, Man High (Garden City, N.Y., 1960).

62 "Manhigh III: USAF Manned Balloon Flight into the Stratosphere," Tech. Report 60-16, April 1961; Simons, "Psychophysiological Aspects of Manhigh," 63; Simons et al., "Personal Experiences in Space Equivalent Flight," 41-43.

63 Simons, "Observations in High-Altitude, Sealed-Cabin Balloon Flight," 146. See also Simons, "Manhigh Balloon Flights in Perspective," in Proceedings of the Second National Conference on the Peaceful Uses of Space, 243-248. Simons' record for a manned ascent stood until May 4, 1961, when Cdr. Malcolm Ross and Lt. Cdr. Victor G. Prather reached 113,740 feet in an Office of Naval Research Strato-Lab High V balloon, launched from the carrier Antietam. Prather was killed during helicopter recovery when he stood up in the "horse collar" sling and fell into the ocean.

64 Simons, "Manhigh II," 272-294; Hanrahan and Bushnell, Space Biology, 171-172; Simons interview.

65 Simons, "Observations in High-Altitude, Sealed-Cabin Balloon Flight," 137; Simons, interview. On Air Force solar flare observatories, see David Bushnell, "The Sacramento Peak Observatory, 1947-1962," Air Force Office of Aerospace Research, 1962.

66 Gerathewohl, Principles of Bioastronautics, 136-138; Hanrahan and Bushnell, Space Biology, 180-187; Connor, "Space Radiation Protection"; James A. Van Allen, "On the Radiation Hazards of Space Flight," in Benson and Strughold, eds., Physics and Medicine of the Atmosphere and Space, 2-11; House Committee on Science and Astronautics, 86 Cong., 1 sess. (1959), U.S. Aeronautics and Space Activities, Jan. 1 to Dec. 31, 1958: Message from the President of the United States, 3, 4.

67 Simons, "Space Medicine - the Human Body in Space," 162.

68 Connor, "Space Radiation Protection"; Hanrahan and Bushnell, Space Biology, 179-180, 187-188.


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