scope:

A gaseous hydrogen (GH2) leak occurred on 03/11/09, during the STS-119/ET-127 cryogenic loading for flight, and was repaired with a "fix to fly" approach by replacing the flight seal and the Ground Umbilical Carrier Assembly (GUCA) quick disconnect (QD. There was no attempt to determine the cause of the leak before the repair. An anomaly resolution team was assembled after the launch to determine the long-term approach.

In successfully mating the GUCA QD to the External Tank Carrier Assembly (ETCA), the following factors play key roles: Ground Umbilical Carrier Plate (GUPC) concentricity, QD probe/flange concentricity, two-piece seal, the GUCA QD's Inconel bellows, vent line loads, alignment between the ETCA and the flight carrier plate, alignment of the hinge support brackets, and the pyrotechnic bolt. Of these eight factors, GUCP concentricity and QD probe/flange concentricity can be adjusted within limitations.

Attached to this lesson is the GUCA GH2 Leak Investigation White Paper, which provides details of the investigation and process changes.