This is a high fidelity 1:8 scale model of the J-2 liquid fuel rocket engine. The J-2, using liquid hydrogen and liquid oxygen, was the powerplant for the second and third stages of the Saturn V launch vehicle that took astronauts to the Moon in the Apollo program. The J-2 produced a thrust of 200,000-230,000 pounds.
The Saturn V's second (S-II) stage used a cluster of five J-2's for a combined thrust of 1,150,000 pounds while the third (S-IBB) stage was fitted with a single J-2 with restart capability. This object was donated to the Smithsonian in 1974 by Rocketdyne.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.