Pending acceptable weather conditions on Friday, all systems are go for ET-137’s Tanking Test – a key milestone in the effort to gain data on both the health of the tank and the root cause investigation into four cracks sustained during the previous STS-133 tanking. The November launch attempt was scrubbed due to a leak at the Ground Umbilical Carrier Plate (GUCP) – which will also be tested during Friday’s loading.
Delayed by two days due to cold weather and high winds interrupting the engineering efforts to install instrumentation into two locations on the tank, the realigned target of entering Call To Stations (CTS) on Wednesday night was achieved thanks to the completion of foam application tasks, covering nearly 100 sensors, and returning the tank to a nominal configuration.
“OV-103/SRB BI-144/RSRM 112/ET-137 (Pad-A): S0037 ET Tanking Test: Acceptable enclosure, ET skin/substrate, and Conex box temperatures were maintained allowing conathane and foam applications to be completed. The foam (was then) in cure,” noted the NASA Test Director (NTD) reports on pre-Tanking Test preparations (L2).
On Wednesday morning, technicians started to trim the new BX foam on the two stringer locations, prior to adding markers which will be monitored via OTV cameras and later by the Final Inspection Team (FIT) during the tanking process.
“Winds at Pad A finally relaxed enough to allow photogrammetry dot placement to be performed. Dot placement completed early this morning on panel 6 of the -Z side of the ET utilizing the scaffolding on the intertank access arm.”
The next task was to remove the enclosures used to install the instrumentation and reapply foam on the tank, prior to testing the sensors – which proved to be successful. Upcoming key events open with the retraction of the Rotating Service Structure (RSS) on Thursday night, ahead of the start of the Tanking Test at 7am on Friday.
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“ET Instrumentation: The intertank was closed out Wednesday for the Tanking Test. ET sensor channelization test completed Thursday. S0037 ET Tanking Test: LO2/LH2 ET load preps will begin Thursday morning. RSS rotation to park is scheduled for 2130L tonight. Tanking is scheduled for 0700L tomorrow morning.”
Classed as a ‘free’ test, the loading of ET-137 will provide confirmation that the engineering work to resolve the GUCP leak has been successful, following a root cause investigation determining a misalignment of the GUCP assembly – which has since been corrected.
“During the transition from reduced fast fill to topping of the LH2 tank, a leak exceeding 40,000 PPM was detected. Measurements and inspections were performed at each step of disassembly. Measurements showed that the GUCP had shifted since the final measurements were taken prior to S0007 (Launch Countdown),” outlined investigation notes (L2).
“The GUCP and the QD (Quick Disconnect) probe had an offset clocked in a direction that contributed to the leak. The investigation identified 8 key factors in obtaining a successful mate of the GUCA QD to the External Tank Carrier Assembly (ETCA) – GUCP concentricity, QD probe/flange concentricity, 2 piece seal, GUCA QD’s inconel bellows, vent line loads, ETCA flight carrier plate alignment, hinge support brackets alignment, and the pyro bolt.
“Of these 8 factors, the GUCP concentricity and the QD probe/flange concentricity can be adjusted within limitations. The GUCP and QD were replaced and the QD clocked to minimize the concentricity offset. Analysis of the fault tree identified residual risk due to the relative motion between the GUCP/QD and flight seal due to vent line loads and dynamics, bellows spring force, bellows binding/interference, and the pyro bolt assembly.”
Although the engineering community is in agreement that they are in the best posture they can be without changing certified processes and procedures, the Tanking Test will provide the opportunity to watch for any movement during loading, especially in relation to any leak detections.
“STS-133 Tanking Test: Baseline GUCP measurements taken before tanking test. High definition camera 4 is installed on Intertank access platform haunch. LH2 and LO2 will be loaded per nominal timelines. Like standard tanking if a GUCP leak is detected the loading team will implement steps to maximize the amount of time the 98 percent sensors stay Wet facilitating vent valve cycling,” added the Tanking Test presentations (L2).
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“Based on GUCP performance loading may continue to standard stable replenish configuration and beyond. LCC (Launch Commit Criteria) HAZ-09 is a Tanking Test mandatory LCC. Current limit of 40,000 PPM remains applicable for Tanking Test. Team will initiate new IPR (Interim Problem Report if reading is above 20,000 PPM.”
Following the Tanking Test, a 48 hour review of the data will be carried out, while preparations pick up for the rollback of the STS-133 stack to the Vehicle Assembly Building (VAB) for another key milestone in returning the tank to flight status – the full 360 degree scanning of the two flanges on the Intertank.
“S0038/A5217 Rollback to the VAB: Following the Tanking Test, the vehicle will be rolled back to the VAB to perform 360 degree NDE (Non Destructive Evaluation) of LO2 and LH2 flanges, remove instrumentation, and repair foam areas associated with the instrumentation,” added the NTD report.
“Preps for rollback are tentatively scheduled to begin on Monday, December 20. First motion for rollback is tentatively scheduled for 0001L Tuesday, December 21. S0072 HPU (Hydraulic Power Unit) Offload is scheduled for 1100 EST on Sunday, December 19 following LH2 boil-off.”
The STS-133 stack will be returned to the VAB for the Christmas holidays by Crawler Transport 2 (CT-2), following a problem with CT-1.
“Crawler Transporter (CT-1): A PR (Problem Report) was picked up on CT-1 for an intermittent PLC input/output fault and unplanned shut down. As a result, CT-2 will substitute and be moved to the Pad-A gate this morning to support STS-133 rollback to the VAB.”
The stack is scheduled to return to Pad 39A early in January.
(Further updates and articles will follow. Refer to live coverage threads linked above. L2 members refer to STS-133 live coverage sections for internal coverage, presentations, images and and updates from engineers and managers. Images used, Lead: Larry Sullivan, MaxQ Entertainment/NASASpaceflight.com. Within the article: via L2 acquired PRCB presentations and NASA KSC).