Artifact: Central Timing Equipment (CTE), Apollo Command Module, Block II

Central Timing Equipment manufactured by General Time Corporation. The 10 pound Central Timing Unit Equipment provided precision square wave timing pulses of several frequencies to correlate all time-sensitive functions. It also generated and stored real time day, hour, minute and second of mission elapse and time in binary-coded decimal format for transmission to Mission Control in Houston Texas via the Manned Space Flight Network (MSFN).

In primary or normal operation, the Apollo Command Module computer provided a 1,024-kiloHertz synch pulse to the CTE for automatic synchronization with the computer. If the pulse failed, the CTE instantaneously defaulted to the secondary mode of operation using its internally provisioned crystal oscillator. For redundancy, the CTE also contained two power supplies, each fed from different spacecraft power bus/breaker sources.

Timing signals generated by the Central Timing Equipment were supplied to the following components on the spacecraft: Pulse Code Modulation (PCM) Equipment (512 Khz square wave for synchronization of the internal clock, 1 Hz frame synchronization, and 25-bit parallel time code input for time-correlation of PCM data); Premodulation Processor (512 KHz square wave for S-Band emergency key transmission); Electrical Power Subsystem Inverters (64 KHz square wave for synchronization of 400-cycle AC power); Digital Event Timer (10 Hz Pulse for digital clock); Environmental Control System (to discharge water from astronaut suits at the rate of 1 pulse every 10 minutes); Scientific Data Equipment (serial time code output for time-correlation of data).