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.
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.