OSO 5 was launched on 22 January 1969, and lasted until July 1975. It was
the 5th satellite put into orbit as part of the Orbiting Solar Observatory
program. This program was intended to launch a series of nearly identical
satellites to cover an entire 11-year solar cycle. The circular orbit had
an altitude of 555 km and an inclination of 33 degrees. The spin rate of
the satellite was 1.8 s.
The wheel of the satellite carried, amongst other experiments, a CsI
crystal scintillator. The central crystal was 0.635 cm thick, had a
sensitive area of 70 cm2, and was viewed from behind by a pair of
photomultiplier tubes. The shield crystal had a wall thickness of 4.4 cm
and was viewed by 4 photomultipliers. The field of view was ~ 40 degrees.
The energy range covered was 14-254 keV. There were 9 energy channels:the
first covering 14-28 keV and the others equally spaced from 28-254 keV.
In-flight calibration was done with an 241 Am source. The instrument was
designed primarily for observation of solar X-ray bursts. A secondary
interest was the measurement of the intensity, spectrum, and spatial
distribution of the diffuse cosmic background.
The data produced a spectrum of the diffuse background over the energy
range 14-200 keV.