This is a cutaway model of injector for the the M-1, a liquid oxygen/liquid hydrogen rocket engine of 1.2-1.5 million pounds thrust. The M-1 was designed by the Aerojet as an advanced, high-performance first or upper stage powerplant for heavy-lift, deep space missions of the post-Saturn V (post-Apollo) era. The engine was conceived for use in the contemplated Nova super booster.
Nova was NASA's largest planned vehicle and went through several configurations in proposals. One envisioned as many as 14 M-1 engines to power the first stage. That vehicle had a first stage thrust of 17 million pounds. However, funding reductions caused Nova to be cancelled.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.