ET-120 foam repairs begin – Discovery’s flight still on for October

by Chris Bergin

Technicians inside the VAB (Vehicle Assembly Building) have begun to repair four LO2 feedline brackets on External Tank (ET-120) – the tank that’s set to fly with Discovery on STS-120 late October.

A team of Michoud Assembly Facility (MAF) engineers are also arriving at KSC on Saturday to oversee the repairs. Discovery can still make the launch target, with the main constraint relating to making room inside the VAB – within schedule – for the build up of the STS-122/Atlantis stack.

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Initially, the tank looked like it was going to be clear to fly without any modifications. However, due diligence checks on the brackets on ET-120 (STS-120) and ET-125 (STS-122) – called after the foam liberation event during Endeavour’s ride uphill during STS-118 – found ‘linear indications’ via X-Ray checks on the brackets.

These indications imply a crack in the SLA (Super Lightweight Ablative) material in the brackets, leading to a NASA decision to repair the brackets, before mating operations with STS-120’s twin Solid Rocket Boosters (SRBs) can take place.

‘Decision made yesterday to repair Feedline brackets,’ noted launch processing documentation on Friday. ‘Preps and paper were completed last night. Three brackets will be repaired and potentially one more.

‘Removal of Closeout Foam and SLA will be in work today, with MAF is scheduled ‘on-site’ tomorrow (Saturday) to begin repairs on the Feedline Support Brackets. Analysis is in work on the 4th bracket.’

That fourth bracket is also deemed to have ‘linear indications,’ and will be repaired. Meanwhile, at MAF, ET-125 – due to be completed for shipping at the end of the month – has one bracket on its 17in LO2 feedline bracket that showed similar indications, thus will also be repaired.

‘All five X-Rays were completed on the LO2 feedline. Preliminary results see a linear indication on stations 1129, 1377, 1623 and 1871. Station 1974 was nominal,’ added a separate processing report on Friday morning. 

A delay to the STS-120 stack rolling out to Pad 39A can be buffered by the two week advancement that was built in to clear space in the VAB High Bay 1 for the commencement of STS-122 stacking. HB1 the only available section of the VAB for shuttle stacking, due to maintenance being carried out on High Bay 3.

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The latest rollout target for STS-120 was aimed at around September 16 – based on the September 9 rollover of Discovery into the VAB. This rollout date is earlier than required for pad processing, but allows an on time start for the build up of the STS-122 stack – with Atlantis’ flight scheduled for December. Originally, STS-120 was set to rollout to the pad on September 13.

New information on Friday points to a change in the processing dates, with repairs completed by around September 3, Discovery rolling over to the VAB no earlier than September 18th – with rollout to Pad 39A delayed to September 25. Launch processing would still be able to make October 23.

This key issue of ensuring the VAB flow remains on track during processing for the two missions was emphasized by shuttle manager Wayne Hale, who found media reports pointing at a stand-down for the remainder of the year, as ‘amusing’.

‘Been amused to read press reports in last 36 hours on what Shuttle plans to do regarding next mission,’ noted the minutes from Thursday’s stand-up meeting. ‘Everyone is working hard on determining what we need to do in the short/long term. This story is still coming forward. Not appropriate to jump to a conclusion until we have data in front of us.

‘Have a fair amount of contingency time according to schedule. Will not have any of the team slow down their preparations for October 23 launch. Do have interesting implications to flight after that because of VAB situation. May need to make adjustments. Message to team is to keep working to dates on book so you don’t become the long pole. Just give ET folks a few days to sort through recommendations. Will come to good conclusion and then send out schedules.’

One potential solution is being looked at, involves moving STS-120’s stacked boosters out of VAB High Bay 1 into High Bay 2, which is used as a Hurricane Protection Bay – in the event of an emergency rollback of a stacked shuttle from the pad. This would then allow the build-up of the STS-122 boosters while ET-120 was repaired. The two stacks could then switch positions when ET-120 was ready to be mated, if HB1 was the only bay still available.

ET-120 has had an eventful life already, having been one of four ETs that were sent back to MAF in New Orleans from the Kennedy Space Center for modifications, following the loss of Columbia.

ET-120 was originally set to fly on Discovery’s RTF mission STS-114, until it was replaced by ET-121, following ECO (Engine Cut Off) sensor problems during tanking. Ironically, more sensor problems came to light with the tank just prior to its shipping back to KSC – which have since been resolved as ok to fly without replacement.

The tank was also at the center of the NASA decision to remove the PAL ramps from all tanks ahead of STS-121, after visible cracks were observed on ET-120’s foam surface. The PAL ramps came into focus following a liberation event during STS-114, where a chunk of the ramp came loose during ascent.

Hale classes the tank as valuable due to the huge amount of data that is being gathered from successfully correcting the issues it’s had, which can be applied to problems with future tanks.

‘Mr. Hale noted how valuable ET-120 is. Still continuing to learn from it. Confident will use it as a flight article,’ added the Stand-up minutes from Thursday. ‘This is a lesson for new programs on importance of taking hardware to flight condition to see performance.

Appreciate MAF Team; they’ve shown resilience in face of technology/material problems and keep working hard on every issue. He looks forward to seeing team at MAF tomorrow (Friday) and wants to tell them how much he appreciates their hard work. He’s confident the bracket concern will be resolved and the tank will fly in the near future.’

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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