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Quick Facts: Orbiting Solar Observatory-8 (OSO-8)

OSO 8 Spacecraft

The 8th Orbiting Solar Observatory (OSO-8) was launched on 21 June 1975. While OSO-8's primary objective was to observe the Sun, four instruments were dedicated to observations of other celestial X-ray sources brighter than a few milliCrab. OSO-8 ceased operations on 1 October 1978. (Courtesy NASA/GSFC)

Mission Introduction

The objectives of the OSO satellite series were to perform solar physics experiments above the atmosphere during a complete solar cycle and to map the entire celestial sphere for direction and intensity of UV, X-ray and gamma radiation.

The OSO-8 platform consisted of a sail section, which pointed two experiments continually toward the sun, and a wheel section, which spun about an axis perpendicular to the pointing direction of the sail and carried five experiments. Gas jets and a magnetic torquing coil performed attitude adjustment. Pointing control permitted the pointed experiments to scan the region of the solar disk in a 40- by 40-arc-min to 60- by 60-arc-min raster pattern. In addition, the pointed section was capable of being commanded to select and scan a 1- by 1-arc-min or 5- by 5-arc-min region anywhere on the solar disk. Data were simultaneously recorded on tape and transmitted by PCM/PM telemetry. A command system provided for at least 512 ground-based commands.

LASP Roles

LASP provided:

OSO-8 spacecraft in construction

The OSO-8 spacecraft under construction. One of the science highlights from the mission was that it set an upper limit on the polarization of radiation from several X-ray binaries. (Courtesy Hughes Aircraft Company)

  • High-Resolution Ultraviolet Spectrometer
  • Spectrometer Principal Investigator, Charles Barth

LASP Instrument

The LASP-built High-Resolution Ultraviolet Spectrometer measured solar ultraviolet lines between 1050 and 2300 A and their variation with time and position on the disk. Spectroheliograms were also generated at selected wavelengths. The instrument consisted of an extended-focal-length Cassegrain telescope, an Ebert monochromator, and a small computer. The telescope focused sunlight on the entrance slit (variable from 1- by 5-arc-s to 1-arc-s by 15-arc-min) of the monochromator. The 3600 lines/mm grating in the monochromator was used in second order. The grating drive mechanism was capable of being programmed to scan: (1) the entire spectrum, (2) selected portions of the spectrum, or (3) selected single wavelengths. Two photomultiplier tubes, one covering the range from 140 to 230 nm and the other covering wavelengths less than 140 nm, detected the radiation. The small computer controlled the experiment and allowed flexible observing programs through automated, data-dependent observing sequences.

Quick Facts

Launch date: June 21, 1975
Launch location: Kennedy Space Center, Cape Canaveral, Florida
Launch vehicle: Delta
Mission target: Earth orbit
Mission duration: 3 1/2 years
Other organizations involved:

  • NASA’s Goddard Space Flight Center
  • Hughes Aircraft Co.