Two flight spare units for the ultraviolet photometers flown on OGO-4 for airglow and Lyman alpha studies. These are simple ionization chambers set behind filters of varying substances and thicknesses, typically lithium fluoride. Orbiting Geophysical Observatory 4 was launched in July 1967. The photometers were transferred to NASM by the Naval Research Laboratory in July 1982.
This object is on display in Space Science at the Steven F. Udvar-Hazy Center in Chantilly, VA.