This is part of the internal resonant portion of a Hemispherical Resonator Gyro (HRG). It measures the vibration of the cup-shaped resonator, which is an indicaiton of acceleration. An HRG senses acceleration by the change in phase of vibration of a cup-shaped resonator, similar to the way a wine-glass resonates when rubbed by a wet finger. The device is rugged and accurate, and it has replaced other models of mechanical gyroscopes on most deep-space missions, as well asn other applications.
Northrop Grumman donated this to the Museum in 2011.