A tiny washer has been removed from External Tank ET-134, after an engineer spotted the rouge item embedded into GO2 pressline guide rail. Engineers had to dig out the washer, prior to carrying out foam repairs to the area of the tank – which have since been completed. The STS-130 stack will remain in the Vehicle Assembly Building (VAB) over Christmas, ahead of a January 6 rollout.
STS-130 Tank Troubleshoot:
The STS-130 stack is fully configured for rollout to Pad 39A, but will wait until the new year for departure out of the VAB – as the workforce enjoy the holidays and power outage work takes place out at the Pad 39 complex.
“Platform C retraction was completed Wednesday,” noted the final processing report for the year (L2), as the stack remains powered down over Christmas. “The vehicle is configured for Rollout to Pad-A; preparations will resume on Jan 4 with the actual Rollout is planned for 1/6/10.”
Most of the work on the stack had been completed last week, until a walkdown of the vehicle resulted in an engineer spotting a washer embedded into the tank – documenting it as an “Out of Place Processing Materials (OOPPMs).”
As per usual, shuttle managers took even this small issue very seriously, as it became the main topic of a daily Program Requirements Control Board (PRCB) meeting at the Johnson Space Center (JSC) in Houston.
“Issue: During Orbiter mate operations in the integration cell, a technician noticed a single washer between the GO2 Pressline guide rail and the Cable tray bracket. Attempts to remove washer were unsuccessful,” noted one of two presentations created by the PRCB, and available on L2.
“Concern: Debris potential created from ‘loose’ washer. Metallic debris is not allowed. Washers required to ensure min/max gap requirements between guide rail and pressline (0.0” min – 0.032” max).”
It is not known how the washer managed to find its way into its out of place location, though a similar issue was reported back on ET-42.
Engineers at the Michoud Assembly Facility (MAF) in New Orleans were also asked to check ET-135 – currently enroute to the Kennedy Space Center (KSC) for STS-131, and ET-136 – which will be used on STS-132. No issues were found on either tank.
“Similar condition does not exist on ET-135 or ET-136. Similar condition has occurred previously at KSC on ET-42. Hardware removed and re-installed per design,” added the presentation, which moved into options for several removal technics – or if they could fly the tank without removing the washer.
“ET Project identified potential solutions to address concern: 1) Remove closeout and entire assembly to access washer and replace entire closeouts. 2) Partial trim of closeout, break torque and repair. 3) Spot bond washer – Pending debris risk assessment. 4) Use as is – Pending debris risk assessment – Risks and benefits for each option characterized.”
STS-130 Specific Articles: http://www.nasaspaceflight.com/tag/sts-130/
Three main options were then presented, with managers opting for the compromise approach of removing just a small area of surrounding foam, prior to removing the washer. This option ensured no negative impact would be felt on the rollout schedule of STS-130.
“Recommendation: Proceed with Option 2 – Eliminates debris potential with minimal technical and schedule risk,” added the PRCB presentation.
“Option 2: Removal of washer – Use as repaired. Approach: Trim out minimum required foam from subject area. Remove hardware and IB rail. Break joint on nut/bolt to open gap. Ensure washer removed, Do not reinstall washer, re-torque to requirements – check gaps to drawing. Reassemble IB rail and Repair foam.
“Benefits: Less work than full R&R required. Less schedule impact risk. No tooling mods required – no demo required. Engineering requirements maintained. Risks: Low technical risk. Washer debris potential eliminated. All TPS (Thermal Protection System) repairs / applications are within experience base. Lower schedule risk than Option 1.”
Engineers wasted no time in implementing the procedures, spending just a couple of days to carry out the work listed in Option 2, with the replaced foam now curing during the vehicle’s stay inside the VAB. Option 1 would have involved a four day impact to STS-130’s pad flow.
The flawless removal of the waster and repair of the worksite was praised by Shuttle managers, with the entire process of spotting the washer, to working and carrying out corrective work on the issue, taking just a few days.
“As reported by the Flow Director, this was a great effort by the team to complete this work with minimal repairs,” noted Shuttle management, who are expecting the arrival of the next tank – ET-135 – at the turn basin at KSC on December 25, ahead of offloading in the new year.
L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size