Endeavour rolls out for STS-400 role at Pad 39B – GUCP anomaly status

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Shuttle Endeavour has completed her rollout to 39B, where she will be put through a part flow as the STS-400 LON (Launch On Need) support for Atlantis’ STS-125 mission. During this flow, engineers will test the alignment procedures with the Ground Umbilical Carrier Plate (GUCP) – following the leak during STS-119’s opening launch attempt.

STS-400/127 Flow:

Endeavour spent a week inside the Vehicle Assembly Building (VAB), prior to rolling out of High Bay 1 shortly before midnight local time.

Engineers were called to stations two hours ahead of first motion, after completing the retraction of platforms that had surrounded the vehicle during ET mate and Shuttle Interface testing (S0008).

“A5214 Shuttle Transfer and Mate to Pad B: “E”, “D” and “B” platform retracts are complete. S0008 Shuttle Interface Testing is complete. SRB HPU checks are complete,” noted pre-rollout processing information on L2. “The SSV has been powered down in preparation for rollout. SRB Hold-down Post Firing Line Checks are complete.”

Only three minor issues of note were worked during Endeavour’s VAB flow, two relating to orbiter camera systems, and one relating to Endeavour turning herself off during an unexpected power loss inside the famous building.

“During S0008, an unexpected power loss occurred resulting in Orbiter/SRB power down (resolved),” added processing information. “During ET Sep Camera testing, the flash module did not flash during testing,” which has also been resolved, although engineering evaluations will continue, due to similar issues with Discovery’s ET camera during STS-119.

“While attempting to download images from ET/TPS DCS Camera to A31P laptop, the following error message was received: ‘An error was detected with reading images from card, retry’,” was noted as the only other problem during the VAB flow. Further troubleshooting resolved the issue.

The Rotating Service Structure (RSS) is not due to be retracted around Endeavour until Monday, which – thanks to Atlantis’ RSS on Pad 39A being retracted on Friday – will allow for the stunning photography of both shuttles being visible on the pads, as was last seen prior to the on orbit issues with Hubble, which ultimately delayed STS-125 last year.

See more: Click here for recent STS-400 related articles
See more: Click here for recent STS-127 related articles

GUCP Testing and Status:

Once Endeavour is put through her STS-400 flow on 39B, engineers will keep a close eye on the mating and installation process of the GUCP, in order to try and gain more data on a potential root cause to the leak observed during STS-119’s opening launch attempt – which caused the launch to be scrubbed.

a312“STS-119 / ET-127 Performance Summary: Pre-launch: 1st loading resulted in scrub/LCC (Launch Commit Criteria) violation due to GH2 leakage at GUCA (>40,000 ppm. Flight seal/QD (Quick Disconnect) replaced,” noted a post mission IFA (In Flight Anomaly) review presentation on L2, written by the MAF (Michoud Assembly Facility).

“Leakage occurred during transition from fast fill to topping. Vent valve opened when 98 percent level sensor indicated wet. Detected by leak detectors (LD 23 & 25) located in ground umbilical shroud. Isolates leak to either ground side quick disconnect (QD) or interface with flight seal.

“Contingency plans (vent valve cycling) unsuccessful in controlling leakage within acceptable limits. Launch scrubbed, flight seal/disconnect replaced. No GH2 leakage observed during subsequent loading. No other anomalous performance observed during loading.”

No root cause has yet been found, although the leading candidate has been noted on the latest documentation relating to the incident.

“No first-time hardware changes implemented for STS-119/ET-127 GH2 vent system. 31 previous loadings with only 1 leak observed (13,500 ppm). Previous leaks also observed during fast fill to topping transition,” added the MAF presentation.

a47“Most probable cause identified as momentary breach in flexible flight-seal to bellows probe due to ‘thermal shock’ of GH2/LH2 with vent valve in open position.

“Significant Disassembly Observations: Lower left pad was hard against skin. Other locations were not touching (0.014 – 0.030 gap / 0.001 requirement) indicating a pull downward and to the left. Peripheral seal compressed more on left side and toward bottom of GUCP.

“Left side pivot assembly in hard contact with pivot pin (pin would not rotate). Stain observed on external surface of bellows guard and peripheral seal at 6 o’clock position. Flight-side seal asymmetrically compressed at 3, 7 and 8 o’clock positions.”

However, as per usual, engineers will ensure the problem isn’t related to another factor, such as a problem with the alignment of the hardware on the tank. In order to check their procedures, STS-400’s flow included the addition of tape markers on the alignment pins, to allow the monitoring of the hardware for any movement during the process.

“GUCP Checkout: Engineering added a dev to apply tape to GUCP alignment pins,” noted Endeavour processing information. “The tape application is complete. The procedure on the GUCP Alignment will be worked at the Pad.”

The MAF document also included a full run down on what is required when mating the umbilical and plate to the tank, which is more complex than may be assumed.

a211“Installation Process: GUCP installed using three (3) guide pins to align. Install / torque pyro bolt to verify distance from tank (7.0 – 7.06”) and ensure proper bellows preload. Adjust pivot assembly feet to contact the umbilical hinge bracket pins and remove guide pins (recent change from hard-down preload requirement, last year).

“Adjust pads between GUCP periphery and tank skin to lightly touch (4 places). Install QD with use of 4 guide pins. Adjust pads (4 places) to verify parallelism and take measurements (Checkout cell and integration cell). Helium leak check at around 6 psig.

“Post vent line installation. Adjust pads (4 places) to ensure around 0.001 clearance and ensure feet contact hinge pins. Helium leak check at around 6 psig.”

Engineers don’t expect the same issue to cause a problem for STS-125’s countdown in less than a month’s time, but have taken precautions on both Atlantis’ ET-130 and Endeavour’s ET-131.

“ET-130 vent disconnect hardware removed, inspected/re-built and replaced in VAB. Micro-fibers observed on flight seal emanating from corners of seal (around 1” length, 0.0003” dia., max). Fibers inherent to manufacturing process and accepted use-as-is,” added the presentation.

“Seal compression (>10x max fiber dia.) due to probe loading sufficient to either liberate or cold flow fibers into seal parent material. Similar fibers observed on seal installed and successfully flown on ET-127. No significant observations noted during disassembly and rebuilding of QD.”

“ET-131 flight seal re-inspected and replaced due to small, isolated indention on sealing surface. Indention not observed / documented during multiple visual / tactile inspections at MAF and initial inspection at KSC (cause indeterminate). Condition not consistent with observations noted on ET-127 seal.”

These precautions have already avoided the STS-119 issue from becoming a topic of concern at next week’s SSP (Space Shuttle Program) Flight Readiness Review (FRR), with managerial approval to fly as-is with the next two tanks.

“Root Cause Fault Tree Investigation and Tests In Progress .STS-125 (ET-130) and LON (ET-131) Hardware and Installation Re-Verified,” confirmed the document. “No Constraints to Flight Identified.”

L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

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