This hatch was attached to Faith 7, the spacecraft in which L. Gordon Cooper, Jr., made the last Mercury flight, Mercury-Atlas 9 (MA-9). Cooper made 22 orbits of the Earth on May 15-16, 1963, a mission that lasted 34 hours, nearly four times the length of previous mission. The one-man Mercury capsule had, except in its earliest versions, a hatch that was attached on the launch pad with explosive bolts. If the astronaut needed to exit the spacecraft, either on the launch pad, or after landing, he could hit a plunger that would fire the bolts and eject the hatch.
This was transferred to NASM from the NASA - Johnson Space Center in 1971, but not accessioned until 1977.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.