This is an engineering prototype for one of the two X-ray solar telescopes that were flown on the Apollo Telescope Mount on Skylab (ATM), launched in 1973. Known as experiment S056, it was one of eight scientific instruments designed to study x-ray flux from the sun. It consists of a camera assembly with a changeable film magazine. The flight instrument provided in excess of 27,000 exposures of the sun over the course of the Skylab mission. Transferred from NASA.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.