ET-120 repairs to be completed this weekend – STS-120 on track

by Chris Bergin

Technicians from the Michoud Assembly Facility (MAF) will finish up the repairs to the four LO2 Feedline brackets this weekend.

The process – required after X-rays showed cracks in the foam that surrounds the brackets – will be completed in time to preserve the October 23 launch target for shuttle Discovery’s STS-120 mission.

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The X-rays were ordered due to the foam liberation from one bracket during STS-118’s ascent, causing damage to Endeavour’s TPS.

While leaving the tanks as-is was the most likely option in the aftermath of MMT (Mission Management Team) deliberations, the checks – carried out on both ET-120 at KSC and ET-125 at MAF – showed signs of cracks in the bracket’s foam.

The decision was promptly made to remove the foam from four of the five LO2 feedline brackets on ET-120, before replacing with new foam, minus the denser debris hazard, SLA (Super Lightweight Ablative). By the latter part of this week, MAF technicians had finished repairs to two of the four brackets.

‘Making progress on ET-120 at KSC. Team sprayed two aft stations, 1871 and 1623. Trimming operations (Thursday). Two upper sprays planned (Friday). Team plans to be off tank by September 2,’ noted the latest Stand-Up/Integration report.

‘BX-265 Trim on Bracket XT-1623 & XT-1871 will be continuing today (Friday). Conathane Application on Brackets XT-1129 nad XT-1377 was completed yesterday,’ added processing information. ‘BX-265 Application on Brackets XT-1129 and XT-1377 (stations) will be in work today, with trim scheduled to begin tomorrow.’

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After closer inspections on the brackets, the decision appears to be more than justified, with an image of one of the brackets showing a large visible crack through its SLA area.

‘X-ray of LO2 feedline bracket TPS confirmed subsurface cracking in underlying SLA material near feedline attach location at four bracket locations,’ noted Lockheed Martin – the manufactures of the ETs – to the all-power PRCB (Program Requirements Control Board) meeting on Thursday, which also noted another item of interest with the brackets – although that will not require any work.

‘Continuing assessment of condensate diverters (small recess machined in TPS),’ added the PRCB report. ‘Test results show diverters ‘do no harm’ and provide potential mitigation for gap ice conditions. Implementation will be coincident with trim operations.’

New timelines show the tank will be transferred from its checkout cell inside the Vehicle Assembly Building (VAB) for mating with the twin Solid Rocket Boosters (SRBs) on either September 4 or 5 – depending on how the final work proceeds this weekend. With a rollover of Discovery on September 18, the schedule places rollout to Pad 39A for around September 26.

‘OPF rollover targeted September 19 based on work in test cell on ET, which is going well. ET mate targeted September 5,’ added the Stand-Up. ‘May move this up a day, depending on work progress over next 48 hours.’

Discovery herself had her payload bay doors closed ahead of rollover, with the final processing milestones being completed for her flight.

‘Prepping vehicle for closeout. Performing radiator inspection in midbody, followed by cleaning. Closing payload bay doors Friday,’ added processing information.

‘Working issue with ingress/egress hatch and window switch issue picked up during last two launch countdowns. Looking at rigging of hatch and whether need adjustments. Want this behind them before rolling out of OPF.’

‘Based on Orbiter mate date, will hold Orbiter Rollout Review on September 14.’

NASA and its contractors are due to conduct the Flight Readiness Review (FRR) for STS-120 ‘most likely be October 9 and 10,’ previewed by September’s MOD (Mission Operations Directive) FRR.

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