With just over two weeks to launch, engineers will disassemble the Ground Umbilical Carrier Plate (GUCP) at the pad, after it was noted the troublesome hardware failed a leak check. Several contingency days exist in the STS-133 pad flow, as engineers press on with S0024 hyper loading tasks on the Solid Rocket Boosters (SRBs).
Over the weekend, S0009 Launch Pad Validation tasks were completed, following Discovery’s return to Pad 39A last week. Discovery is tracking an opening launch attempt on February 24 – providing the Ariane 5 ECA launch with ATV-2 launches on its opening attempt on February 15.
Tasks over the last few days included the removal and replacement of a Range Safety battery, a GPS retest, SSME (Space Shuttle Main Engine) Ball Seal leak checks and a temperature transducer mass spec leak check on Discovery’s Main Propulsion System (MPS), allowing for the transition into S0024 operations on Monday morning.
The loading of the toxic hydrazine fuel into the Hydraulic Power Units (HPUs) on the SRBs – which requires the pad clearing of workers for specialist engineers to carry out the loading in their Self-Contained Atmospheric Protection Ensemble (SCAPE) suits – began at 9am local.
“S0024 SRB HPU hyper load: The orbiter is powered up and being configured for remote ops. HPU load call to stations should be completed shortly,” noted Monday’s NASA Test Director (NTD) report (L2). “Pad A is scheduled to be cleared by 0800L this morning. HPU hydrazine load is scheduled to begin at 0900L this morning.”
Three relatively minor Interim Problem Reports (IPRs) were also listed; one of which is already in the process of being closed, another relating to troubleshooting on a flight cap on a SRB and one issue on Space Shuttle Main Engine 1 (ME-1) likely to receive a waiver. IPRs at this stage of the pad flow are common.
“OV-103/SRB BI-144/RSRM 112/ET-137 (Pad A): New IPR 0083 to MPS. During Engine FRTs (Flight Readiness Tests), ME1 (SSME Number 1) Reg B pressure exceeded OMRSD (Operational Maintenance Requirements and Specifications) limit twice (Actual was 782.2 psia, OMRS limit is 780 psia.),” the NTD added.
“Engineering plans to discuss regulator transducer R&R and/or OMRS waiver. Constraint: S1287 Op 30-105.
“New IPR 0084. During the modified un-commanded extend for HYD-257, ET actuator extension did not stop as expected. Engineering is evaluating a troubleshooting plan. Constraint: S1287 Op 30-105 (Current plan is to close the IPR as an explained condition).
“New IPR 0085. While removing the left tilt GN2 press & purge QD (Quick Disconnect) flight cap, techs noticed vapors as well as liquid coming from the poppet. The poppet was sniffed hot, therefore the techs flushed with IPA and reinstalled the flight cap.
“TVC’s (Toxic Vapor Concentrations) with the cap installed are 0.0 ppm. PC goal does not show any pressure deltas during the time of cap removal. The system was drained prior to rollback to the VAB and any commodities present are just residual vapors. Engineering plans on troubleshooting today after getting into SCAPE ops. Constraint is to left tilt system loading.”
STS-133 Specific – Including ET Stringer Issue – Articles: http://www.nasaspaceflight.com/tag/sts-133/
Other work which was completed prior to hyper loading included the Orbiter Mid Body Umbilical Unit (OMBUU) mate/leak checks, ET camera functional test, 1st motion test, and the GUCP leak checks.
No issues with the GUCP were listed during the early Monday NTD report, however sources noted that later in the morning a call to disassemble the GUCP at the pad was made by mangers, due to what was noted as a failed leak check.
While the system can detect leaks in realtime via instrumentation, the tank is unpressurized and won’t reach cryo temperatures until the day of launch during tanking, meaning engineers can only carry out ambient temperature tests on the hardware – as per scheduled.
Sources have noted that Friday’s leak check did result in a small leak, so small that it was initially thought to be nothing more than noise in the detection system, though it is possible that due to the troublesome history of the GUCP of late, managers decided the system should be dismantled to be absolutely sure everything appears as it should.
UPDATE: Although note of a separate leak – after Friday’s schedule leak checks and ahead of Monday morning – was listed at this time. The NTD did cite a small leak being noted during helium leak checks on Monday.
GUCP leaks caused scrubs on both STS-119 and STS-127 in 2009, prior to being the reason STS-133 scrubbed during the transition from reduced fast fill to topping of the LH2 tank during tanking, when a leak was detected – exceeding the 40,000 PPM limit in the Launch Commit Criteria (LCC – HAZ-9).
While the observed cracks on ET-137’s LO2/Intertank flange stringers – seen after the scrub was called – have been the main focus of attention since the scrub, a root cause for the GUCP leak was successfully found via concentricity measurements, which spotted a misalignment in the system.
With engineers called to “clock” the GUCP’s placement on the tank – and a new two-part flight seal installed – engineers were provided with “free” test of the GUCP via December 17 Tanking Test. This test was called for to aid the investigation into the stringer cracks, but showed the GUCP did not leak at any point during the tanking, adding confidence to the mitigation procedure.
It is likely that the call to disassemble the GUCP at the pad is solely to protect against any potential issues during the tanking for launch next month, with enough contingency time in the pad flow to allow the work to take place without any impact to the NET (No Earlier Than) February 24 launch date.
Once the hardware has been re-installed, engineers will be able to carry out another leak check to confirm the health of the system.
(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, Larry Sullivan MaxQ Entertainment/NASASpaceflight.com and via L2 acquired PRCB presentations).