Apollo CM Block II PGNCS Navigation Base

Rare “Eval. Test” unit of the Apollo Command Module’s navigation base, or “horse collar”.

The Navigation and Control System (PGNCS) navigation base measures approximately 22′′ x 27′′ x 5′′ and is designed to hold the Inertial Measurement Unit (IMU) and Optical Unit Assembly in precision alignment and, in turn, hold the two precision instruments in alignment with the structure of the Command Module.

Affixed at the bottom is an MIT Instrumentation Lab/AC Electronics label: “Apollo G&N System Navigation Base Assembly, Part No. 2899982, Serial No. ACSK 2, Cont. No. NAS 9-497.” Flanking the label are yellow inspection stamps and an “Eval. Test” stamp. Also attached is a yellow North American Rockwell “Temporary Parts Removal Tag,” dated February 9, 1971.