STS-122: ET-125 repairs to be completed on Friday

by Chris Bergin

Work is finalizing on External Tank ET-125, following a huge effort to bounce back from the ECO (Engine Cut Off) sensor anomalies that placed a temporary halt on the surge of ISS assembly.

The trimming of the newly applied foam around the LH2 Feed-through connector worksite is scheduled for Tuesday evening, with “closeouts” targeted for completion this coming Friday.

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STS-122 ECO related news content: *Scrub 1* – *MMT Debate* – *Scrub 2* – *Hale Memo* – *Forward Plan* – *Culprit Found* – *Tanking Test* – *Repair Options* – *MAF Plan**PRCB Debate* – *Plan Approved* – *Repair Schedule* – *Launch Date* – *New Issue* – *Hale Rallying Call* – *PRCB Launch Dates* – *New Connector Installed* – *Positive Test Results* – *Manifest Impacts* – *Optimism with forward plan* – *Flight Rationale*

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The effort has involved engineers and technicians from the United Space Alliance, Lockheed Martin and others, added to several NASA centers being at the center of testing and analysis.

A review of the documentation surrounding the changeout of the LH2 Feed-through connector with a modified connector – which has had its pins soldered to avoid the problem that is believed to have caused the ECO sensor anomalies – will start on Friday, during the Level 2 Delta Flight Readiness Review (FRR).

Meanwhile, at the pad, work is coming to an end on the replacement work, which is now focusing on the finalization of foam TPS (Thermal Protection System) work over the J Box – which houses the connector assembly – and SRB (Solid Rocket Booster) PAL (Protuberance Air Loads) ramp.

‘Sensor Feed-through connector update: The environmental enclosures were reinstalled Monday morning and thermal conditioning was re-established. Conathane application was completed around noon yesterday,’ noted processing information on Tuesday morning.

‘BX-265 spray was completed last night at about 00:30. Initial BX trimming is scheduled to pick up about noon today with final trim and sell later tonight, after 16 hour cure is complete. ECO closeouts and PAL ramp rework completion are still targeted for 1/25 (Friday).’

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Atlantis herself is proving to be no problem in the push towards the start of S0007 Launch Countdown operations in two weeks time, with the only recent issue of note – a problem with Fuel Cell 2 – no longer a concern.

‘Fuel Cell #2 Voltage Increase Update: (Engineering) position is that this IPR/ PR (Interim-Problem Report) should be closed as either explained condition or as a procedure error,’ added Tuesday’s processing information.

‘The general consensus being developed is that the increased voltage was due to minor regulator flow in the presence of residual O2 in the manifold. Additional data collection continues in an effort to support closure rationale.’

Launch On Need (LON) capability also appears to be on track, with ET-126 – the tank that will fly with Endeavour on STS-123, but also required as part of LON rescue support for STS-122 – undergoing similar connector testing.

As part of that process, test results from the weekend showed that the connector appears to be in good condition, with no observation of ‘glass cracking’ – which was found with ET-125’s removed LH2 Feed-through connector.

The issue of glass cracking won’t halt STS-122, but will continue to be evaluated, due to the potential concern of LH2 leaking through the crack, at pressure, during ascent. This would be a safety threat to the shuttle.

The crack found on the removed connector from ET-125 was not seen in subsequent testing on a connector from ET-120, and even one from the now defunct X-33.

However, a recent memo notes a request for off-tank qualification testing in order to closely replicate the in-tank environment, thus be more representative of the real-life conditions these parts are under during cryo conditions.

‘ET-120 glass seal failure is a different failure mode than ET-125 – suggests loading conditions (imposed stresses) for ET-120 differ significantly from ET-125,’ noted a memo that was quoting documentation that was drawn up from the ‘Glass Team.’

‘Raises concerns that current test plan will not replicate ET-125 failure mode. Raises concerns that future planned testing will create more chaos than answers. Time to regroup!’

However, these comments – typical of an engineering discussion – are not central to the status of ET-125’s newly modified connector, which has no observed cracking, but instead are part of a drive to increase the database of information, which should prove useful for the new connectors that are due to be installed in future tanks.

‘Revise test plan to more accurately reflect flight conditions. Dedicate more than 2 units to life testing to understand scatter. Establishing clear pass/fail criteria based on hazard control,’ added the information.

‘Consider accepting fewer cryo cycles in demonstrated life (do we really need 13 tankings?). Get glass experts down to MAF (Michoud Assembly Facility) to participate directly in test planning and analysis.

‘The best approach is to test to failure a minimum of two (four would be better) using a test method to duplicate as closely as practical the cryo-cycling stresses during tanking/detanking.’

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