PRCB debates STS-122 options – includes rollback and tank swap

Two options were debated by the all-powerful PRCB (Program Requirements Control Board) meeting, one of which will allow Atlantis to aim for a late January – or more likely – early Febuary launch date, the other involving rollback.

Currently, “Option A” appears to have the support of shuttle management, which will involve the soldering of the LH2 Feed-through connector pins. “Option B” involves rollback and a tank swap with ET-126.

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**COMPLETE Section on ECO/Feedthrough Connector issues and troubleshooting, graphical and data based – expansive.**

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ET-125 Troubleshooting Latest:

A large contingent of engineers are calling for ‘Option B’ – which will involve the STS-122 stack being rolledback to the Vehicle Assembly Building (VAB), due to the requirement of having to enter the tank to remove the entire Feed-through assembly. Such work at the pad is no longer considered as an option.

Once inside the VAB, Atlantis would be de-mated from ET-125 and re-mated with ET-126 – the next tank that was scheduled to fly, with Endeavour on STS-123.

‘SE&I, NESC, KSC and JSC engineers recommend Option B: Remove entire feedthrough assembly, rollback, put orbiter onto ET-126, take ET-125 apart. Keeping everything intact improves chances of finding root cause.’

‘Option A’ – which, according to preliminary schedules, would allow for Atlantis to launch in around four weeks time, has the support the ECO team, who were tasked with finding a solution to the cause of the two launch scrubs earlier in the month.

 
‘ECO Team recommends option A: remove external plug and feedthrough, keeping intact, for root cause testing (internal plug not removed.)’

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Shuttle management is believed to be in favor of following ‘Option A’ – however, the large ranging support of ‘Option B’ may derail their wishes.

The forward plan for the interim is to go ahead and remove the external plug and feed-through connector, intact, to allow for cryogenic testing at the Marshall Space Flight Center (MSFC). Access to this hardware has already been gained via work by engineers at the pad over Christmas.

This is part of Option A, to test out the connector for any clues as to the cause of the recent ECO (Engine Cut Off) system issues.

‘Inspect Feed-thru assembly pins/sockets, cracks in the silicon rubber grommet, and contamination or workmanship issues. (External Plug/Feed-thru assembly will not be separated),’ noted one of several presentations that were reviewed by the PRCB.

‘Examine and photograph feed thru assembly for signs of damage. Sample Feed-thru Internal plug pins for contamination. Nano-Focus X-ray for bent pins, engagement, cracked grommet and tolerance issues.

‘Measure distance from glass surface of connector to face of connector. Perform pin retention test of feed thru internal pins. Send to TS-300 for Cryo-Testing.’

‘Cryogenic Bench Testing’ will allow engineers to compare data gained from previous connector testing, and the recent tanking test. The hope is the additional data will help confirm the specific location of the fault on the LH2 Feed-through connector system, currently believed to be related to the pins on the external plug contacts.

Option B involves rollback due to the need to enter the tank, in order to remove all of the Feed-through connector, both internal and external. This would require the tent-like clean room, last seen during the ECO sensor changeouts. 

‘Remove Entire Feedthru Assembly (External Plug/ Feedthru/Internal Plug). Partial removal of TPS for in-situ inspection of feedthru connector hardware and TPS (Same as Option A),’ added the presentation on the two options. 

‘Detailed dissection of TPS within J-box (surrounding connector) planned to identify any potential contributors (i.e. excessive cracking or intrusion into connector body) – Not expected based on results from ET-120

‘Visual inspections of connector hardware internal / external) with moisture proofing and TPS material in place. Inspections provide baseline of hardware configuration prior to removal. Remove Assembly intact by cutting within the cable tray and into the Tank wiring. Install Temporary Blankoff Plate at the Feedthru hole.’

As far as actually solving the issue of the open circuit on the connector, engineers are favoring the approach last used by the Atlas program, that of soldering the pins and wires in place. This plan is still being worked.

ET-126 operations in the VAB will continue to be placed on hold, while more data is gathered, before what currently appears to be a final decision on the forward plan – on rollback or R&R at the pad – at the next PRCB, due on January 3.

Option A’s timeline has already been mapped out, with work at the pad showing a schedule that would allow for completion and certification by the end of January. Returning to a launch posture, post R&R, would allow for a launch date to be set in early February.

However, this remains a fluid situation, with further debate on which option to take set to take place over the coming week.

Further articles, based on the expansive PRCB presentations acquired by L2, will follow.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.

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