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photo of OSO in the clean room
Credit: NASA

* Mission Overview

The fourth successful Orbiting Solar Observatory, OSO-4, was launched on 18 October 1967. The objectives of the OSO-4 satellite were to perform solar physics experiments above the atmosphere and to measure the direction and intensity over the entire celestial sphere in UV, X, and gamma radiation. The OSO 4 platform consisted of a sail section (which pointed 2 instruments continuously toward the Sun) and a wheel section which spun about an axis perpendicular to the pointing direction of the sail (which contained 7 experiments). The spacecraft performed normally until a second tape recorded failed in May 1968. OSO-4 was put into a "standby" mode in November 1969. It could be turned on only for recording special events in real-time. One such event occurred on March 7, 1970 during a solar eclipse. The spacecraft became totally inoperable on 7 December 1971.

* Instrumentation

The X-ray telescope consisted of a single thin NaI(Tl) scintillation crystal plus phototube assembly enclosed in a CsI(Tl) anti-coincidence shield. The energy resolution was 45 percent at 30 keV. The instrument operated from ~ 8 to 200 keV with 6 channel resolution.

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