This is the lens cap to a lunar mapping camera, certified as the flight backup to those used on the last three Apollo missions. Mapping the lunar surface was a high priority during Apollo 15, 16, and 17. Mounted in the service module, the mapping camera captured high-resolution images of the Moon as the spacecraft orbited. While returning to Earth, command module pilots performed spacewalks to retrieve the film canisters, mounted on the right side of the camera.

This flight backup, available for those missions if the installed cameras were damaged or malfunctioned before launch, is the best surviving example of the Fairchild-built camera. The flown versions remained in the service modules, which burned up when they reentered the Earth's atmosphere.

NASA transferred this camera lens cap to the Museum in 1978.