National Aeronautics and Space Administration

Also on board was a small spark chamber experiment called MIMOSA for observations of gamma-rays from 70-300 MeV. The instrument was equipped with a stereoscopic TV system viewing through the chamber portholes to record the particle tracks. It operated from March-October 1972. There was a significant particle-induced background, despite an anti-coincidence system. Numerous gamma-rays were detected, but no gamma-ray point sources could be identified.

There were two stellar ultraviolet experiments on board. The Utrecht Orbiting Ultraviolet Stellar Spectrometer S59 used a small telescope and a three-slit scanner covering three bands between approximately 2100 and 2800 Å. About 200 bright stars were observed by the instrument and were later published in a catalog. The S2/68 spectrophotometric sky survey telescope was developed jointly by the UK and Belgium. It operated in the range 1350 and 2550 Å. This experiment used an off-axis reflecting telescope to focus radiation onto a set of entrance slits. These in turn fed a photometer and a three-channel spectrophotometer. The light falling on the spectrophotometer entrance slit was reflected onto a diffraction grating, and the dispersed light then passed through one of three slits and then onto individual photomultipliers. The orbital motion of the satellite caused the dispersed beam to scan across the exit slits.