OSO 3
OSO 3, or Third Orbiting Solar Observatory was launched on March 8, 1967, into a nearly circular orbit of mean altitude 550 km, inclined at 33° to the equatorial plane. Its on-board tape recorder failed on June 28, 1968, allowing only the acquisition of sparse real-time data during station passes thereafter; the last data were received on November 10, 1969. OSO 3 reentered the Earth's atmosphere and burned up on April 4, 1982.
Like all of the early Orbiting Solar Observatory series satellites, it had two major segments: one, the "Sail", was stabilized to face the Sun, and carried both solar panels and Sun-pointing experiments for solar physics. The other, "Wheel" section, rotated to provide overall gyroscopic stability and also carried sky-scanning instruments that swept the sky as the wheel turned, approximately every 2 seconds.
OSO-8, the final spacecraft in this series, had 3-axis pointing.
Instrumentation
| Name | Target | Principal Investigator |
| High Energy Gamma Ray | anti-solar | Kraushaar, W. L., Massachusetts Institute of Technology |
| Cosmic Ray Spectrum Detector and Gamma Ray Analyzer | Sun, all-sky | Kaplon, Morton F, University of Rochester |
| Directional Radiometer Experiment | Earth | Neel, Carr B Jr, NASA Ames Research Center |
| Earth Albedo | Earth | Neel, Carr B Jr, NASA Ames Research Center |
| Solar EUV Spectrometer 0.1 to 40.0 nm | Sun | Neupert, Werner M, NASA Goddard Space Flight Center |
| 0.8- to 1.2-nm Solar X-Ray Ion Chamber | Sun | Teske, Richard G, University of Michigan |
| Solar and Celestial Gamma-Ray Telescope | Sun, all-sky | Laurence E. Peterson University of California, San Diego |
| Thermal Radiation Emissivity | near-Earth space environment | Neel, Carr B Jr, NASA Ames Research Center |
| Extreme Ultraviolet Spectrometer | Sun | Hinteregger, Hans E, Phillips Laboratory |
The Sail carried a hard X-ray experiment from UCSD, with a single thin NaI scintillation crystal plus phototube enclosed in a howitzer-shaped CsI anti-coincidence shield. The energy resolution was 45% at 30 keV. The instrument operated from 7.7 to 210 keV with 6 channels. The Principal Investigator was Prof. Laurence E. Peterson of UCSD. Also in the wheel was a cosmic gamma-ray sky survey instrument contributed by MIT, with PI Prof. William L. Kraushaar.
Scientific results
OSO-3 obtained extensive hard X-ray observations of solar flares, the cosmic diffuse X-ray background, and multiple observations of Scorpius X-1, the first observation of an extrasolar X-ray source by an observatory satellite.The MIT gamma-ray instrument obtained the first identification of high-energy cosmic gamma rays emanating from both galactic and extra-galactic sources.