Shuttle engineers like to check, double check, and check again, whenever there’s a flight safety concern – and that was more than the case with the pull tests that have been conducted on External Tank ET-132, following an increased number of foam liberation events during ET-131’s ride to orbit with Endeavour. The test results show the tank is good to fly, allowing Discovery to make her journey to the VAB on Sunday.
Discovery’s been patiently sat on the Orbiter Transporter System (OTS) for a number of days, as engineers carried out pull tests on ET-132’s intertank – the area from which several unusual foam liberations occurred during Endeavour’s ride uphill on STS-127.
Initial testing concentrated on the adhesive properties between the foam and the tank’s structure in 26 locations in the intertank region. Those initial results showed positive margins.
“TPS-ET-132 Foam Bond Adhesion Verifications: All 26 locations now tested and have adhesion failures only. ET-132 Foam Adhesion: All 26 locations had COHESION failures not adhesion failures,” noted a memo (L2) outlining the good news from the initial testing.
While those areas were being repaired, the pull test results went to the “Noon Board” – a daily meeting between shuttle managers – at the Johnson Space Center (JSC) in Houston.
“11 of the 26 (reapplication of foam) and in trim now on the +Z side. 13 on the -Z side have Conathane applied and (reapplication of foam),” added the memo. “Noon Board today will determine the next course of action and if more pulls are required.”
The decision of the Noon Board resulted in a call for a further 125 pull tests to take place, in order to be absolutely sure all areas of ET-132’s intertank aren’t threatening to shed foam as per its predecessor.
“TPS-ET-132 Foam Bond Adhesion Verifications: 24 of the original 26 plugs have been repaired. Lockheed Martin (engineers) will perform 126 bond adhesion pull tests on one panel on the -Z side (back side) of the tank.
“Once all pulls are complete and good, meaning any failures would be cohesive failures, then we will be cleared for the Orbiter to rollover.”
The results of those additional tests were relayed to Discovery’s engineering teams at 8pm on Saturday evening, citing the tank has been cleared for flight, thus allowing Discovery to make the short trip over to the VAB during Sunday’s first shift. This roll has now been completed at 8:22am local time.
“The following operations have been rescheduled to support inspections resulting from the STS-127 launch debris events: Rollover to VAB for integration is scheduled for July 26; first motion targeted for 0700. Shuttle Interface Testing will pickup immediately following Orbiter/ET mate,” added processing information based on the now-confirmed good news from the pull tests.
This places STS-128 – a logistics mission to the International Space Station (ISS), with the MPLM (Multi-Purpose Logistics Module) Leonardo as Discovery’s primary payload – on a NET (No Earlier Than) launch date of August 26.
Now she’s inside the VAB, Discovery will be lifted over to the awaiting ET-132 and twin Solid Rocket Boosters (SRBs) for mating. The estimated 23 day pad flow will be challenging, especially if the transfer of Discovery’s payload to the pad is delayed.
“Engineering is reviewing a potential challenge with payload weight and center-of-gravity; the team continues to work toward payload move to Pad 39A on July 30 with canister lift operations scheduled to begin on 3rd shift July 31. SSV (Space Shuttle Vehicle) rollout to Pad 39A on August 5.”
Next up for STS-128 is the Flight Readiness Review (FRR) season, with the opening meetings set to take place on August 3. This will be followed be additional departmental meetings ahead of the main two-day Space Shuttle Program (SSP) FRR – one week ahead of the Agency FRR that confirms the launch date.
The TPS (Thermal Protection System) events during STS-127’s launch will make up a large part of the discussions at the FRR. While Endeavour suffered no more than cosmetic dints to her starboard chine area, the “potential” for such liberations to cause damage will be fully evaluated.
While it gained less of a mention in the media than the intertank foam losses, the liberation from the LO2 Ice Frost Ramp during Endeavour’s launch has a greater threat of causing damage – based on mass and location – thus remains under review.
The results of that review – along with a full outline of the intertank liberation events – will make up part of next week’s STS-127’s IFA (In Flight Anomaly) review, which in itself will also become a major element for the STS-128 FRRs.
“The STS-127/2JA In-Flight Anomaly (IFA) Review will be discussed at next week’s SSP PRCB (Program Requirements Control Board). Follow-up work will be done as needed,” noted the latest Shuttle Standup/Integration report on L2. “The Orbiter Pre-FRR for STS-128/17A is currently scheduled for the afternoon of August 3.
“The team is analyzing the damage tolerance of tile, particularly the chine area, to foam release from the intertank. It is thought that due to the thinness of the foam and the fact that it is perforated, it may present less of a risk to tile than pieces released from the acreage area. Preliminary testing has begun at Southwest Research Institute (SwRI).
“Xt-718 LO2 Ice Frost Ramp: (performed) digital X-ray and Terahertz analysis. Imagery will be provided to MSFC (Marshall Space Flight Center) for use in IFA troubleshooting and in next week’s IFR TIM (Technical Interchange Meeting) at MSFC. Any future rework to the IFR may be worked post Orbiter Mate.”
Thanks to the stunning work by the Damage Assessment Team (DAT) – a group of engineers that review, highlight, and analyze any areas of interest via the Flight Day 2 surveys and Flight Day 3 RPM ((Rbar Pitch Maneuver) imagery – the IFA review will have all the TPS data they require.
The DAT imagery analysis also allowed for a potential modification on Discovery, via lessons learned from Endeavour’s flight.
“Thermal barrier sleeving around the arrowhead was protruding on the current flight of OV-105 (Endeavour). In an effort to prevent this from reoccurring on OV-103’s (Discovery) flight of STS-128/17A, it was decided to put some black Room-Temperature Vulcanizing (RTV) around the sleeving,” added the Standup.
However, engineers decided against the idea, citing the process was troublesome via mock-up testing.
“A simulator was mocked up to practice the technique, but it is very difficult to cleanly and successfully inject the RTV into the space. It has been decided to leave the area as is for flight.”
STS-128 will be more than “just” a logistic mission when Discovery launches next month, with a special DTO (Detailed Test Objective) – on behalf of the Orion Project Office – to be carried out during her re-entry.
The TriDAR AR&D Sensor Detailed Test Objective and the next Boundary Layer Transition (BLT) DTO, will also be carried out by the veteran orbiter.
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.