Tanks still causing headaches

by Chris Bergin

Thursday’s PRCB meeting revealed continuing concerns on ensuring ET-118 is delivered to the Kennedy Space Center within its required timelines. The External Tank (ET) is required for Atlantis and her supporting STS-300 mission.

The meeting also raised concerns over the ET’s propulsion line hardware (specifically two areas of the GO2 pressline) “mission life requirement” – which is being evaluated by engineers and technicians.

The resulting information was collated from information presented to the Shuttle PRCB meeting today, all of which is available in full document form on L2. To join L2, click the advert —>

ET-118 is currently manifested to be completed at the end of this month, although that is in danger of slipping for a variety of reasons, most notably the requirement to replace its ECO (Engine Cut Off) sensors.

‘ET-118 production continuing for planned 5/30 completion,’ noted today’s PRCB document. ‘Additional up-shifting and staffing required to maintain date.’

Lockheed Martin had already noted they were moving all available workers to the 118 task, in order help mitigate the delay on the tank, much to the detriment of ET-123 – the next tank due to leave the Michoud Assembly Facility (MAF) after ET-118.

ET-123 is now under a complete review of its timelines as a result, although the concentration on ET-118 is understandable, given it has to make it to KSC to allow STS-121 to fly by a certain processing date, with the support of STS-300 a mission requirement.

While the issue is being given a lot of attention by Shuttle managers, sources note that it is highly unlikely the tank will slip to the extent of affecting STS-121’s July launch window.

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A new issue that has come to light from the meeting on Thursday is the ‘ET propulsion line hardware safe life’ analysis.

The issue was noted as the ‘ability of propulsion line hardware to meet mission life requirement (>4x),’ following ‘(an) assessment of propulsion line hardware (for penetrant inspection issues) resulted in concern of 90/95 probability of detection (POD) flaw size screened by radiographic inspection.’

The problem has been spotted during tests on the modified External Tank – following the removal of the PAL ramp from all future ETs. Two areas of the GO2 pressline are in question.

‘Analysis of preliminary PAL ramp elimination environments indicated potential violations for subsequent environment increases. Subsequent analysis using final PAL ramp elimination steady/unsteady airload environments (May delivery)resulted in violations at 2 locations on the mid flex segment of the GO2 pressline.

Order Now - Countdown Creations‘Review of ET-119 radiographs at MAF indicated potential issue at one location. Disposition was no defect (weld solidification). Further review of radiograph by independent source identified indication as suspect defect.’

No info has been made available on how this could affect STS-121, given more work is needed to look into the initial data, as the ‘resolution’ noted: ‘Refined analysis technique to eliminate mach consistent max/max resultant moment calculations.’

Marshall Space Flight Center (MSFC) have been brought in to look at the information – through their Fracture Control Board – with a test article being fabricated via a contingency plan to perform simulated service tests.

More will follow on this story in the coming days

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