Shuttle Atlantis has arrived back inside the Vehicle Assembly Building (VAB) Sunday, ahead of repairs to ET-124, which was damaged by a freak hail storm last week.
Platforms and scaffolding has already been erected inside the VAB, in readiness for engineers to take a detailed look at the state of the damaged areas of the STS-117 stack. An initial repair plan has been put into place, with work currently estimated to continue until mid April.
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The completion of the payload transfer to the PCR was completed on Saturday, as engineers worked towards the rollback of the RSS (Rotating Service Structure) – usually reserved for the final day of the launch countdown.
However, despite STS-117 being the smoothest pre-launch flow for many a year, Mother Nature decided to throw a spanner in the works, with an unprecedented hail storm causing over 7000 areas of damage, primarily to the top of the LOX tank on the ET.
Now Atlantis is back inside the VAB, she was greeted by special platforms and scaffolding that were erected on Saturday night, with first evaluations to take place on Monday.
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‘LO2 platforms and scaffolding installation will be continuing through Sunday night. Engineering Evaluation Team Pretest Briefing is scheduled for Monday at 0830 hrs (VAB 2K6),’ noted a NASA memo. ‘Inspections and grid marking will be continuing throughout Monday. Remaining platforms and scaffolding will be in work through Monday night.
‘QC inspections are scheduled to begin on lower platforms (B & D) on 2nd shift Monday. ET-124 Damage Assessment & Repair. Initial planning is complete for platforms, access control, initial engineering inspection, tank grid mapping and quality inspection. Details are currently being worked.’
Lockheed Martin – in charge of ET production at the Michoud Assembly Facility (MAF) in New Orleans – are deeply involved with the repair plan, which they claim won’t be completed until mid April, making the NET (No Earlier Than) April 22 launch target less likely than at the start of May.
LM, speaking at last Thursday’s PRCB (Program Requirements Control Board) meeting at the Johnson Space Center noted: ‘Early estimates indicated mid-April completion (subject to change pending results of detailed inspection).’
‘Adequate inspection requires hands on inspection to determine depth of damage,’ added a LM presentation to the PRCB. ‘Concern is GO2 seal – which is expected to take the longest to repair – land waviness ascent heating / re-entry and ice/TPS debris. Rollback required to adequately assess damage and repair.’
Repairs will continue after the assessment on a 24 hour, 7 days a week basis, with an initial plan already drawn up by LM/MAF.
‘Developed approach for repair of damaged areas/General Assumptions: Pencil sharpener repair is tall pole, other repair areas performed in parallel with certified USA resources.
‘BX-265 is viable repair, requires mission specific heating rates – spray similar to PAL ramp spray. Spray extends to nosecone aft skirt. Nose cone remains installed. 24 hr / 7 day activities. ICD requirements (waviness) maintained by hand sanding. Michoud resources allocated as required.’
Work on the top of the ET is not something KSC workers aren’t experienced at carrying out, having previously used the platforms in the VAB to repair ET-100, which caused the last rollback, on STS-96. Workers also replaced the LOX vent and relief valve on ET-119 in a similar fashion.
‘Processing similar to ET-119 LO2 tank damage,’ added Lockheed Martin’s presentation. ‘Standard process controls for manual sprays within the critical debris zone (mock-ups required for BX spray). Schedule driven by longest span activity (expected to be GO2 seal land repair).’
Although this repair plan will take up to six weeks, it still remains a better option than having to destack Atlantis from the tank, and wait for the mid April arrival of ET-117, which is currently set to fly with Atlantis on STS-118. Such a worst case scenario would delay STS-117 to the summer.
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