These are samples of a simulated solid propellant (called grains), manufactured by the Atlantic Research Corporation, a maker of small rocket motors for civilian and military applications. Founded shortly after World War II, Atlantic produced grains of this type (and the actual propellants) by way of extrusion.
The grains shown here simulate the solid propellants used in the U.S. Army's shoulder-launched Stinger surface-to-air missile.
Transferred to NASM from the Atlantic Research Corporation.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.