OSO 3

OSO 3

The third Orbiting Solar Observatory, OSO 3, showing its "Sail" (upper), carrying solar experiments pointed at the Sun, and its rotating "Wheel" (lower), carrying two sky-scanning survey instruments: the UCSD hard X-ray experiment, and the MIT gamma-ray telescope
Operator	NASA
Major contractors	Ball Brothers Research Corporation (BBRC)
Mission type	Solar Physics
Launch date	March 8, 1967 at 16:19:00 UTC
Launch vehicle	Thor-Delta
Launch site	Cape Canaveral, United States
Mission duration	2 yr 8 mn
COSPAR ID	1967-020A
Mass	281 kg
Orbital elements
Eccentricity	0.002164
Inclination	32.87°
Altitude	550 km
Apoapsis	464.0 km
Periapsis	534.0 km
Orbital period	95.53 min.
Orbits per day	15.07

OSO 3 (Orbiting Solar Observatory 3), or Third Orbiting Solar Observatory (known as OSO C before launch) 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 the American OSO-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 sec.

Instrumentation

Experiments on board OSO 3

Name	Target	Principal Investigator
High Energy Gamma Ray (> 50 MeV)	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 (0.32- to 0.78-µm)	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 (7.7 to 200 keV)	Sun, all-sky	Peterson, Laurence E, 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(Tl) scintillation crystal plus phototube enclosed in a howitzer-shaped CsI(Tl) 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 (PI) was Prof. Laurence E. Peterson of UCSD. Also in the wheel was a cosmic gamma-ray (>50 MeV) sky survey instrument contributed by MIT, with PI Prof. William L. Kraushaar].

Scientific results

OSO-3 obtained extensive observations of solar flares, the cosmic diffuse X-ray background, and the observation of a single flare episode from 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.

See also

• Orbiting Solar Observatory
• X-ray astronomy

External links

The content of this article was adapted and expanded from NASA's HEASARC: Observatories OSO 3 [2] and NASA's National Space Science Data Center: OSO 3 [3] (Public Domain)