Jun 21 1975
From The Space Library
NASA successfully launched Oso 8 Orbiting Solar Observatory at 7:43 am EDT from Eastern Test Range on a thrust-augmented Thor-Delta booster, after a 1-day delay because of an electrical malfunction in the launch vehicle. The spacecraft entered a near-perfect circular orbit with a 560-km apogee, 544-km perigee, 95.74-min period, and 32.94° inclination. By 23 June Oso 8 was stabilized and was accurately tracking the center of the sun as planned. All spacecraft systems were operating normally. By 27 June all eight experiments had been activated and were acquiring data.
Primary objective of the Oso 8 mission was to investigate the sun's lower corona and its chromosphere, and their interface in the ultraviolet spectral region, to better understand the transport of energy from the photosphere into the corona. Secondary objective was to study solar x-rays and earth-sun relationships and to investigate the background component of cosmic x-rays.
The 1064-kg spacecraft had two sections: A rotating cylindrical bottom section-the wheel-accommodated experiments that did not require solar reference pointing or that scanned the celestial sphere. The nonspinning rectangular sail section mounted on top of the wheel accommodated experiments that required stable pointing at the sun.
The spacecraft carried eight experiments. The two on the sail section were a Univ. of Colo. high-resolution ultraviolet spectrometer to measure solar-ultraviolet line profiles in the range of 1050 to 2300A and their variation with time and position, and a spectrometer and a cassegrain telescope that would observe the solar chromospheric structure simultaneously in six lines from 1000 to 4000A originating from different levels in the sun's atmosphere. This experiment was provided by France's Laboratory for Stellar and Planetary Physics under a cooperative agreement between NASA and the French Centre National de la Recherché Scientifique.
Other experiments-all on the wheel portion of the spacecraft and supplied by U.S. universities, industry, and government agencies included a high-sensitivity crystal spectrometer to monitor the sun's emission in the 2- to 8-kev range, obtain a complete spectrum of the sun every 10 sec during flares, and obtain high-resolution spectra of many celestial x-ray sources; a mapping x-ray heliometer to measure location, spectrum, and' intensity of intermediate-energy x-rays from individual solar-active regions and to acquire data on extrasolar x-ray sources; an investigation of soft x-ray background radiation using proportional counters; a cosmic x-ray spectroscope to determine the spectra of sources and the diffuse cosmic x-ray background in the energy range of 2 to 60 kev, and to measure intensity variations and identify possible emission lines of discrete x-ray sources; a high-energy celestial x-ray experiment to measure the spectrum of all point x-ray sources observable in the energy range of 0.01 to 1 megaelectron volts, and to search for temporal variations in the intensity and spectrum of the point sources detected; and a study of extreme ultraviolet radiations from earth and space, to determine the behavior of atoms such as hydrogen and neutral and ionized helium in the earth's atmosphere by measuring the intensity and distribution of solar radiation resonantly scattered by these atoms.
Oso 8 was the ninth, and last, in a series of spin-stabilized orbiting solar observatories designed to gather new knowledge of the sun, the earth's atmosphere, and sun-activated terrestrial phenomena over a broad range of the electromagnetic spectrum not detectable by ground-based equipment. Of the eight OSO launches that began with Oso 1 on 7 March 1962, only one, OSO-C, was unsuccessful, because of a launch-vehicle failure. Discoveries made by OSO spacecraft included gamma-ray emissions from the galactic center; a previously unknown isothermal plateau in the chromosphere of the solar atmosphere; differences in the structure of the extreme ultraviolet corona above quiet and active regions on the solar disk; evidence that the corona above the solar poles was significantly cooler than nonactive coronal regions near the equator; and synoptic observations of "holes" in the corona that survived several solar rotations.
Oso 8-built by Hughes Aircraft Co.-was managed by Goddard Space Flight Center under the direction of NASA's Office of Space Science. GSFC was also responsible for the Thor-Delta launch vehicle. (NASA MORs, 4 June 75, 23 June 75, 27 June 75; NASA Release 75-158)
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