This is a left hand hatch from a Gemini spacecraft. It was used in instrumentation tests and did not fly in space. Made of titanium, it is covered with shingles of Rene 41, which protected the capsule from the tremendous heat generated during reentry.
McDonnell Aircraft made the hatch and donated it to the Museum in 1970.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.