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A condition known as \u201cpopcorning\u201d can occur, but holds no threat to the orbiter, due to the small mass associated with such liberations, and the late stage of ascent during which this condition usually occurs.<\/p>\n
The mechanics of foam loss relates to when TPS cell pressure at substrate exceeds bond adhesion strength. Voids in the foam can also suffer from \u201ccryopumping\u201d \u2013 although such events have not been seen on the intertank.<\/p>\n
What is for certain is the complex material sciences associated with the control of TPS foam loss during the pressures of launch, which is near-impossible to avoid. Modifications to the tanks since Columbia have mainly focused on reducing the most \u201cat risk\u201d areas of foam, thus removing the debris threat.<\/p>\n
![\"T3\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/07\/T31.jpg\" "\\"T3\\"")
Although it was late in ascent when Endeavour\u2019s ET-131 intertank started to shed foam \u2013 thus holding no serious debris impact threat to the orbiter due to the lack of atmosphere that would result in a high velocity impact \u2013 engineers are looking into its root cause.<\/p>\nCurrently, that root cause remains elusive, with the initial conclusions focused on a potential issue with the adhesive\/bond properties between the foam and the intertank\u2019s structure. That in turn placed doubts on the next tank set to fly, ET-132 \u2013 kick-starting an investigation to gain confidence the same event was unlikely to occur during next month\u2019s launch.<\/p>\n
Spaceflight
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\u201cET-132 Bond Adhesion Evaluation: Purpose: Provide plans and obtain approval to inspect ET-132 \/ STS-128 Intertank TPS (Thermal Protection System \u2013 Foam) at KSC. Additional data needed to provide confidence in the as-sprayed TPS integrity,\u201d noted an overview presentation available on L2.<\/p>\n
Interestingly, the presentation appears to cover other foam loss events from ET-131, such as the debris shower noticed at T+104 \u2013 which was initially claimed as not originating from the intertank, when it caused cosmetic damage to Endeavour\u2019s starboard Chine area. However, this is now unclear.<\/p>\n
\u201cBackground: Multiple \/ unexpected Intertank TPS loss events observed on ET-131. 1st observation occurred at around 104 seconds MET (Mission Elapsed Time). Losses occurred around entire periphery of tank. Majority of foam loss events appear to extend to the primed substrate.<\/p>\n
\u201cIndication of inadequate TPS adhesion due to unique processing anomaly. Timing (> 100 secs. MET) consistent with physics-based understanding of bond adhesion failure mode. Losses occur due to vacuum \/ ascent heating load affects at TPS \/ primer bond.\u201d<\/p>\n
![\"T2\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/07\/T21.jpg\" "\\"T2\\"")
Root cause may have been easier to pinpoint had a manufacturing change been noted by MAF in relation to the intertank. However, the presentation confirms no changes to the application of the foam have been made.<\/p>\n\u201cNo engineering changes (design or process) to Intertank acreage for ET-131 \/ STS-127 or ET-132 \/ STS-128. NCFI 24-124 TPS applied using automated spray process. Majority of material power machined (optimize weight) and perforated (+Z, debris minimization).<\/p>\n
\u201cMajority of material thickness around 0.5\u201d (nominal). Nominal as-built density around 2.6 pcf. On-part lead-in\/out bond tension tests performed in cryo regions near flanges (>30 psi required).\u201d<\/p>\n
ET-132 Pull Tests:<\/p>\n
Already inside the Vehicle Assembly Building (VAB), mated with the twin Solid Rocket Boosters (SRBs) and awaiting the arrival of Discovery for mating, access to ET-132 is already in place.<\/p>\n
This has allowed the majority of the pull tests \u2013 used to check the adhesive properties on ET-132 \u2013 to take place, ahead of scaffolding being installed for access to the remaining test areas on the intertank.<\/p>\n
\u201cPlan focused on determining root cause in parallel with performing tests\/inspections of as-built hardware,\u201d added the presentation. \u201cPlanning bond adhesion pull tests on ET-132 \/ STS-128 to provide confidence in Intertank TPS application integrity.<\/p>\n
\u201cTwenty-six (26) tests planned with samples from each panel (8 panels). Majority of tests (12 of 26) being performed on three (3) +Z panels. Locations selected based on observed ET-131 performance and debris potential (i.e. CDZ).<\/p>\n
\u201cTests planned on stringer top and sidewall leading \/ trailing edges. Tests provide best method to determine integrity of bond strength. Additional testing may be required based on ET-132 process data review.\u201d<\/p>\n
![\"T4\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/07\/T41.jpg\" "\\"T4\\"")
As of Tuesday morning, 18 of the 26 pull tests have been conducted, with results showing encouraging signs that ET-132\u2019s intertank has the required adhesive strength between its structure and TPS foam.<\/p>\n\u201cOf the 26 test sites 18 were completed (all the walk up access). All tests were 100 percent cohesive failures (broke in the foam \u2013 which is good news) and the pull numbers ranged from 14.25 to 84.9 psi with only two values below 43.77,\u201d noted engineering logs on the test (L2).<\/p>\n
\u201cThe two that broke between 14 and 16 and these had some issues during the testing (the cores were not completely perpendicular, and the plug was bonded slightly crooked) and could have technically been declared a no test.\u201d<\/p>\n
Access was being built via scaffolding to conduct the remaining tests \u2013 now expected to show the same positive results \u2013 while repairs on the previous test areas are soon to take place.<\/p>\n
\u201cHigh Crew is in the process of completing installation of scaffolding this morning. 13 of the 18 locations are being prepped for repair,\u201d added STS-128 processing information for Tuesday morning (L2). \u201cThree require additional photo work and two others are under Engineering Evaluation.<\/p>\n
\u201cUSA (United Space Alliance) will begin repairing the 18 locations starting with any primer touch up that is required, less the two areas that had lower pull values.\u201d<\/p>\n
Should the tests continue to show good results, shuttle managers will have the confidence to clear the tank to fly near the end of August.<\/p>\n
UPDATE: All 26 Pull Tests now conducted by Tuesday night, all with good results.<\/em><\/p>\n
![\"T6\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/07\/T6.jpg\" "\\"T6\\"")
\u201cPath to Flight Rationale for STS-128 \/ ET-132: Root Cause is isolated to ET-131 with positive test \/ inspection results. Similar foam loss not expected during STS-128,\u201d noted the presentation based on good pull test results.<\/p>\nHowever, even the worst case results would have only incurred around a few weeks worth of delay to the schedule, due to the low threat from such foam liberations from the intertank during ascent.<\/p>\n
The only requirement would have been to \u201cremove and replace suspect NCFI (foam) with BX manual spray,\u201d which can be carried out inside the VAB.<\/p>\n
Other work taking place relates to the Damage Assessment Team (DAT) creating models to show the main flow paths of foam liberations from the intertank, and the worst case damage such a liberation could threaten.<\/p>\n
The results will be overviewed at the STS-128 Space Shuttle Program (SSP) Flight Readiness Review (FRR) next month.<\/p>\n
ET-132 Damaged During Tests:<\/p>\n
As luck would have it, the tests caused new damage to ET-132, when part of the new scaffolding fell on to the tank. Thankfully the damage is minor.<\/p>\n
\u201cDuring build up of scaffolding on platform E around the external tank, a technician was tightening a tube-lock for a handrail,\u201d added Tuesday processing information. \u201cThe tube-lock broke and fell from the scaffolding, impacted the ET and landed on B platform roof directly.<\/p>\n
\u201cIn the area contacted, there is minor damage to a stringer just below the flight door. Dimensions and repair technique to be addressed in PR (Problem Report).\u201d<\/p>\n
![\"T5\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/07\/T51.jpg\" "\\"T5\\"")
This incident should not cause additional delays to the rollover of Discovery, which is tracking both the finalization of testing and subsequent repairs to ET-132, and the completion of repair work that is taking place on Pad 39A\u2019s flame trench, which lost some of its refractory concrete during Endeavour\u2019s launch.<\/p>\n\u201cPad-A: MLP-3 (Mobile Launch Platform) transfer to the East Refurb Site is complete. Flame trench repairs continue; completion is expected by the end of the week,\u201d noted processing information, which confirms the Pad will be ready well ahead of Discovery\u2019s current date for rollout on July 30 \u2013 based on a Thursday rollover to the VAB for Discovery.<\/p>\n
\u201cThe STS-128 Shuttle Final Countdown Phase Simulation (S0044) for team certification is scheduled for today,\u201d added Tuesday processing information.<\/p>\n
\u201cThe following operations have been rescheduled to support inspections resulting from the STS-127 launch debris events: Rollover to VAB for integration is scheduled NET July 23. Shuttle Interface Testing will pickup immediately following Orbiter\/ET mate. Payload transport to Pad-A on July 27. SSV (Space Shuttle Vehicle) rollout to Pad-A on July 30.\u201d<\/p>\n
Discovery is being prepared for a 13 day, 3 EVA, mission to the ISS that will include the flight of the TriDAR AR&D Sensor Detailed Test Objective (DTO), the next Boundary Layer Transition (BLT) DTO, and the first flight of the OI-34 flight software. The mission was swapped from Atlantis to Discovery, following the changes in the 2009 manifest.<\/p>\n
Also riding uphill with Discovery will be a new crew member for the ISS \u2013 Nicole Stott \u2013 as well as MISSE (Materials on International Space Station Experiments) 6A and 6B, SIMPLEX, MAUI, and SEITI.<\/p>\n
However, the primary payload for Space Shuttle Discovery will be the MPLM (Multi-Purpose Logistics Module) Leonardo, and the Lightweight Experiment Support Structure Carrier with an Ammonia Tank Assembly.<\/p>\n
L2 members<\/em><\/em>: Documentation \u2013 from which the above article has quoted snippets \u2013 is available in full in the related L2 sections, now over 4000 gbs in size.<\/em><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"
The foam liberation from Endeavour\u2019s External Tank (ET-131) intertank may have been a one-off event, as all 26 pull tests on ET-132\u2019s intertank show no signs of weakness in the tank set to fly with Discovery next month. However, minor damage was sustained on the tank after a tube-lock broke loose and fell from scaffolding […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[9212,9213,9038,9205,7935],"class_list":["post-41044","post","type-post","status-publish","format-standard","hentry","category-news","tag-et-131","tag-et-132","tag-sts-127","tag-sts-128","tag-tps"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/41044"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=41044"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/41044\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=41044"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=41044"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=41044"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}