The fifth Orbiting Geophysical Observatory, OGO-5, was launched on 4 March
1968. The satellite, primarily devoted to Earth observation, was in a highly
elliptical initial orbit with a 272 km perigee ... and an 148,228 km apogee. The
orbital inclination was 31.1 degrees. The satellite took 3796 minutes to
complete one orbit. Two experiments aboard OGO-5 produced cosmic high- energy
results, although their intended target was the Sun. The spacecraft attitude
control failed on 6 August 1971 and it was placed in a standby mode on 8
October 1971. Three experiments (none of which were related to cosmic
high-energy detection) were reactivated from 1 June to 13 July 1972. Operation
of OGO 5 terminated completely on 14 July 1972.
The Anderson et al. (University of California, Berkeley) Energetic Radiations
from Solar Flares experiment was operational from March 1968 - June 1971.
Primarily devoted to solar observations, it detected at least 11 cosmic X-ray
bursts in time coincidence with gamma-ray bursts seen by other instruments. The
detector was a 0.5 cm thick NaI(Tl) crystal with a 9.5 sq-cm area. Data were
accumulated into energy ranges of: 9.6-19.2, 19.2-32, 32-48, 48-64, 64-80,
80-104, 104-128, and > 128 keV. The data were sampled for 1. 15 seconds once
every 2.3 seconds.
The gamma-ray instrument on-board, sensitive to energies from 25-100 MeV, was a
six gap spark chamber with an effective area of ~ 100 sq-cm. It was called the
Energetic Photons in Primary Cosmic Rays experiment (Hutchinson et al.,
Southampton University). It had an angular resolution of ~ 30 degrees (FWHM).
The satellite was Earth-pointing and passed regularly through the radiation
belts, which led to severe restrictions on the sky regions which could be
examined by the gamma-ray instrument. Other problems, such as an efficiency
reduction in the anti-coincidence shield and data system difficulties, severely
degraded the scientific return from the experiment. Data collection ceased
altogether after 5 months. Gamma-ray emission from the galactic plane was
monitored. No point sources were detected.
[Summary provided by NASA.]