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Handling the recording of voice and data aboard the Command Module was a very sophisticated unit - the Data Storage Equipment (DSE). This self-contained device includes two eight-inch reels that spooled through read-write heads approximately 2,250 feet of one-inch Mylar magnetic tape. The 14-track tape had a storage capacity of over four hours of voice and data. Subsystem information, normally sent directly from the spacecraft, was recorded by the DSE along with voice at a high or low bit rate and could then be transmitted to the ground by Mission Control. The DSE was used during the critical Lunar Orbit Insertion (LOI) burn performed by the CSM while on the far side of the Moon when the spacecraft was out of communication with the Earth. During this period, the DSE recorded crew voices, along with important engine and system parameters, that were then dumped to the ground for engineering analysis as soon as the vehicle flew into Earthrise and regained radio communication with Mission Control.
The equipment, manufactured by Leach Corporation was installed in the lower equipment bay and had tape speeds of 3.75, 15, and 120 inches per second. The tape speed was selected automatically based on the data rate, The tape has fourteen parallel tracks, four Command Module Pulse Code Modulated (PCM) digital data, one digital clock, one allocated to Lunar Module (LM) PCM data, one CM-LM voice, three scientific data and four spare.
The DSE had several modes of operation, including Single Directional with rewind mode, Automatic Selection (in which the tape speed is determined by the data rate); Remote Control (complete remote operation of the DSE was achieved from Mission Control via the Up-Data Link/S-Band). A total of 2250 feet of tape on the real yielded recording times of 2 hours at 3.75 inches per second and 30 minutes at 15 inches per second.