Discovery has completed her journey back out to Pad 39A with her modified External Tank (ET-137), with first motion at 8pm local on Monday evening, following an issue-free installation of radius blocks on most of its intertank stringers. With a high-level of confidence in the mitigation of further cracks on the stringers during loading and launch, managers have called for the same modifications to take place on STS-134’s ET-122.
In what was the final week Discovery will spend in the Vehicle Assembly Building (VAB) during her role as part of a shuttle stack (she’s expected to be housed in the VAB for a period of time when OPF-3 is handed over to another vehicle, believed to be an X-37) – the veteran orbiter has several days of contingency in her pad flow for what is a target launch date of February 24.
Preparations for her rollout included a final power up, and the removal of platforms which have surrounded the stack during the ET stringer modification work in High Bay 1 (HB-1).
“OV-103 (STS-133) Performed the final power up in the VAB; did some systems snapshots. Closed out the crew module. The aft is closed out for rollout,” noted KSC Ground Operations on the latest Shuttle Standup/Intergration report (L2).
“On the ET stringer repair, the installation of the radius blocks was completed. All the foam has been applied; are in work with trimming and clean up. Will work inspections and any PRs (Problem Reports) on foam damage through the weekend.
“Will get the scaffolding removed and get into platform retraction this weekend. On track for first motion out of the VAB to the Pad on Monday at 20:00 ET.”
It has been a superb effort by United Space Alliance (USA) and Michoud Assembly Facility (MAF) workers, who achieved all of the required modification tasks ahead of schedule, allowing for STS-133’s rollout to occur slightly ahead of a previous February 1 target.
“OV-103 / SRB BI-144 / RSRM 112 / ET-137 (VAB HB-1): ET-137 Stringer Full Modification Update: All mechanical work supporting stringer modifications is complete. Final foam spraying is complete and final foam trimming finished up (Friday),” noted the NASA Test Director (NTD) report (L2).
“Scaffolding removal will continue through Saturday. Preps for A5214 rollout operations and S0009 Pad A validation are in work. VAB platforms retractions will occur on Sunday. Rollout to Pad A is scheduled for Monday, Jan 31 with first motion targeted for 2000 EST.”
The C platform retraction occurred as scheduled on Friday afternoon, followed by the E platform retraction on Sunday morning.
Discovery began her rollout on time at 8pm Eastern, prior to arriving at Pad 39A at around 2:30am on Tuesday.
Discovery’s ET-137 has visible signs of the work around the LO2/Intertank flange during rollout, given the tank has a new coating of BX-265 foam around its circumference – which will be cream/yellow in appearance, contrasted against the rest of the tank’s foam, given the exposure to sunlight ‘darkens’ the untouched older foam.
Other than the band of brighter foam, the TPS material has been trimmed to the prescribed shape of the flange area, which was carried out by MAF technicians – prior to USA engineers double checking the work by working through a handful of miscellaneous collateral damage foam repairs, per their standard process and criteria that allowed for the scaffolding to be removed on Saturday during final rollout preps.
Outside of the VAB, Pad 39A is being readied for the upcoming launch, following the completion of emergency egress training on the pad’s slidewire system.
“Pad A: S1025 emergency egress training on the FSS 195 foot level and at the slide wire bunker area was completed. In all there were three “dry” egress runs on the 195 foot level and 3 runs at the slide wire termination/bunker area,” added the NTD report. “HPU (Hydraulic Power Unit) Cart sampling is complete.”
Preparations for the Delta Flight Readiness Review (FRR) are also ongoing, a review which will be heavily based on the previous Space Shuttle Program (SSP) and Agency FRR content, updated via the ET stringer work. Departmental FRRs are scheduled to take place this week.
Also set for discussion will be the change of crewmember, following the replacement of the injured Tim Kopra with Steve Bowen, with the EVA department noting they have “got a good handle on the STS-133 crew change”, showing the late change is unlikely to have any impact on the launch date.
STS-133 Specific Articles (click for numerous background content on the ET and relating to this article): http://www.nasaspaceflight.com/tag/sts-133/
ET-122 Modification Decision:
Although ET-122 is a much older tank, when compared to STS-133’s ET-137 and STS-135’s ET-138, due diligence was once again placed first by Shuttle managers late last week, as they decided to press ahead of the installation of radius blocks to STS-134’s tank.
Currently located in High Bay 3 (HB-3) of the VAB, ET-122 – stacked with its two Solid Rocket Boosters (SRBs) – is already undergoing shakedown operations for the modification which provides additional strength to the stringers, mitigating the potential of cracks forming.
The opening effort revolved around physical inspections of the stringers via the use of borescope examinations. It is understood that no obvious issues were found during the inspections, which included a check for signs of the “mottled” material on the stringers – one of the root causes for ET-137’s cracks during the scrubbed November launch countdown.
“Borescopes from inside the intertank to detect mottled metal on ET-122 stringers is complete,” noted the NTD report for ET-122. “The data and results are being passed onto the respective engineering organizations for further analysis and discussions.”
In the end, managers decided to approve the modification plan – a mirror of the work conducted on ET-137, bar the doublers which were installed over stringers which had already cracked – as a failsafe, as opposed to any direct observations.
With the investigation team assessment for the ET-122 I/T stringer pedigree, records showed that ET-122’s I/T stringers are from four material heat lots, none of which are the same suspect lots that have affected ET-137. However, unlike material from the newer tanks – which aided the investigation into the root cause – no leftovers or scrap 2090 material was found for ET-122 at MAF.
“All senior program managers agreed that performing the mod, although intuitively may seem unnecessary given the age of ET-122, there is simply insufficient available data to exclude ET-122 from this unstable cracking phenomenon we experienced on ET-137 and in all the associated with testing,” added associated notes on the decision (L2).
By taking the decision to modify the tank at this stage of processing, managers know the schedule for STS-134 will be protected, while additional confidence in the tank during its opening tanking can be assumed via the radius blocks mitigating the formation of cracks.
The decision also leverages the flight rationale that has been developed for STS-133, rather than tasking the investigation team with the added testing and analysis necessary to develop STS-134 specific flight rationale.
It is also likely managers will install a Tanking Test into the pad flow for STS-134, in order to confirm the health of the tank’s stringers via a cyro and pressure cycle.
(Further updates and articles will follow. Refer to live coverage threads linked above. L2 members refer to STS-133 live coverage sections for internal coverage, presentations, images and and updates from engineers and managers. Images used, Larry Sullivan MaxQ Entertainment/NASASpaceflight.com. NASA.gov and via L2 acquired PRCB presentations).