This unflown horizon sensor was part of the stabilization system used on Agena upper stages. These spacecraft were the first with 3-axis stabilization. Developed by Lockheed Missiles and Space, Agenas carried a number of civilian and military payloads into space from the late 1950s into the 1980s.
This horizon sensor was built by Barnes Engineering and NASA's Manned Spacecraft Center transferred it to the Museum in 1973.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.