The Orbiting
Solar Observatories (OSO) were a series of eight NASA
satellites that provided a better understanding of the Sun's atmosphere and of the sunspot cycle. The satellites also investigated sources of X-rays beyond. The first seven satellites, built by Ball Brothers Research Corporation, were launched on Mar. 7, 1962; Feb. 3, 1965; Mar. 8, 1967; Oct. 18, 1967; Jan. 22, 1969; Aug. 9, 1969; and Sept. 29, 1971. (OSO C, launched Aug. 25, 1965, failed to achieve orbit.)The
upper section of each OSO was a 57-
cm-high (22-in) semicircular panel covered with 1,860 solar cells continuously pointed toward the Sun. On OSO 1, the scientific instrumentation in this upper section included three X-
ray experiments, a gamma-ray detector, and a micrometeoroid detector. The lower section, a nine-sided aluminum body 22 cm (8.7 in) high and 113 cm (44.5 in) in diameter, rotated at about 30 rpm to spin-stabilize the spacecraft. It contained nickel-cadmium batteries, telemetry processing equipment, a tape recorder, and two radio transmitters. Its instruments studied solar
ultraviolet radiation and solar cosmic rays, measured radiation levels in the Van Allen radiation belts, and detected neutrons. Other experiments were incorporated into both the upper and lower sections of later OSO satellites.OSO 8 was a 1,064-kg (2,346-lb) satellite built by the Hughes Aircraft Company and launched June 21, 1975. The upper section, a 235-cm-high (92.5-in) rectangular panel, contained solar cells, a high-resolution ultraviolet spectrometer, and a French -supplied chromosphere fine-structure analyzer. The lower section, 72 cm (28 in) high and 152 cm (60 in) in diameter, contained a crystal spectrometer and polarimeter, a mapping X- ray heliometer, a soft-X-ray background collimator, a cosmic-X- ray spectroscope, a high-energy celestial-X-ray experiment, and an extreme-ultraviolet-radiation experiment.Of the series, only OSO 2 remains in orbit. It ceased functioning after a few months in space. The OSO satellites obtained the first full-disk photograph of the solar corona, the first X-ray observations from a satellite of solar streamers and of a solar flare in its initial stage of eruption, and the first white-light and extreme-ultraviolet observations of the corona.
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