This is a back-up instrument for the Bragg crystal X-ray spectrometer experiment flown in the pointed sail section on OSO-4, launched on 18 October, 1967. It was designed and built at the Naval Research Laboratory (NRL) by Talbot Chubb in Herbert Friedman's group. The spectrometer was transferred to NASM from NRL in 1982. It was acquired still in its original display box with other OSO-era solar instrumentation.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.