Deployment Log: Acoustic Node One, Melt Station Sierra, Enceladus South Polar Ice Sheet

Second Watch, Day 11 of Charter. At 0340 station time, Science Officer on duty authorized deployment of Acoustic Node One through the primary melt bore at Station Sierra. Overnight refreezing had narrowed the bore throat by approximately four centimeters. The deicing collar required sustained operation at twice its rated current draw (peak 4.8 kW) before the node assembly cleared the neck. Bore wall temperature at the constriction was logged at 94 K. The node descended on braided tether under controlled winch speed.

At a depth of 212 meters, tether tension dropped to near-zero for approximately two seconds. Winch telemetry attributes the anomaly to transit through a void pocket, likely a relic fracture or brine lens within the ice shell. Load resumed without incident and descent continued. Node One contacted the ice-water interface at 411 meters, consistent with the survey's predicted shell thickness for the Sierra sector (405 to 420 meters). The onboard hydrophone array initialized and passed its first self-test cycle without fault.

The initial acoustic return was not station-generated noise. The hydrophone registered the low-frequency harmonic triplet originating from Vent Field 7, arriving through approximately eighteen kilometers of open subsurface ocean. This signature matches the pattern catalogued under the Deep Chorus record filed by the First Enceladus Survey (ref. 1ES-AC-0041). Commander Meridian ordered thirty minutes of silent running across all station mechanical systems. The signal was monitored on open channel in the habitation module for the duration of the quiet period. No station personnel spoke during the interval.

Deployment of Acoustic Node Two is scheduled for Day 12, contingent on acceptable conditions over the south polar terrain, specifically plume activity levels and thermal fracture propagation rates in the vicinity of Station Sierra.