This is a 25-pound thrust Gemini Orbital Attitude Maneuvering System (OAMS) thruster. OAMS thrusters provided thrust for the U.S. manned Gemini spacecraft to rendezvous with the Agena target vehicle. They also controlled the spacecraft in orbit, enabled the separation of the Gemini from the second stage Titan launch vehicle and inserted it into orbit. They also provided abort capability.
The thrusters used hypergolic (self-igniting) propellants of nitrogen tetroxide and monomethylenehydrazine that made the system simple and reliable and eliminated the need for an igniter. OAMS thrusters were used on all Gemini flights up to the end of the program in 1966. This object was donated to the Smithsonian in 1973 by Rocketdyne.
This object is on display in Rockets & Missiles at the Steven F. Udvar-Hazy Center in Chantilly, VA.