STS-131: Discovery rolls out to Pad 39A – ET repaired following bird vandalism

by Chris Bergin

Discovery has rolled out of the Vehicle Assembly Building (VAB) just after midnight on Wednesday morning in preparation for her April 5 STS-131 launch date. With rollover to Pad 39A is completed, further repairs will take place on the stack’s External Tank (ET-135), following “avian induced damage” to the tank’s TPS (Thermal Protection System) foam.

STS-131 Processing Latest:

Following the delay of the March launch date – based on cold temperature constraints for Discovery’s rollover to the VAB, and a Dual Docked Operations (DDO) constraint relating to a Russian Soyuz docking at the International Space Station (ISS) – Discovery now has over a week’s worth of contingency in her flow.

Thus, the one day delay to rollout – caused by a passing weather system – holds no impact to what should be a relaxed pad flow.

“Last week, got rolled over to the VAB. Completed all mating activities, and powered up Friday. Over the weekend, completed all planned power-up testing for the VAB,” noted Ground Operations on the latest Shuttle Standup/Integration report on L2. “Wrapping up all inspections and platform retractions.

“Shuttle Interface Test and T-0 Umbilicals and Orbiter/ET Interface Leak Checks were completed Saturday. Rollout inspections and VAB HB-3 platform retracts picked up Friday and conclude on Monday in support of SSV (Space Shuttle Vehicle) Rollout to Pad-A.

“On OV-103 (Discovery), after engine installation and getting into leak checks, had a couple of leaks on the LOX side on Engine 1 and 3 where they replace seals. Were scheduled to get into re-leak checks (completed on Monday).

“Rollout to Pad A was delayed 24-hours due to the potential for severe weather; revised call-to-stations is Tuesday at 2000 EST with first motion is expected at 0001 EST tomorrow (Wednesday morning).”

“Once it gets to the Pad, will get into normal Pad validations on a Wednesday/Thursday timeframe, and pick up with TCDT (Terminal Countdown Demonstration Test) on a Thursday/Friday timeframe.

STS-131 Specific Articles:

Pad 39A is ready to welcome Discovery, with nominal processing continuing as a hypergolic valve was repaired during Monday night.

“Pad-A: Hyper valve R&R on the 107’-level was completed as scheduled on 2nd shift Monday night,” added the NASA Test Director (NTD) processing report. “GH2 recharge at the GH2 battery is scheduled for tomorrow (Wednesday).”

ET-135 Damage:

Ahead of rollout, engineers noticed some damage to the External Tank, which was repaired inside the VAB, prior to some additional work being scheduled once the stack is out at the pad. The damage was caused by birds that had managed to access the tank, and decided to peck away at the TPS foam.

“On ET-135 in the VAB, last week had some avian induced damage (some birds pecked on it). Smoothed it out with a combination of sand and blend, and some minor PDL repairs,” added the Standup report. “The repair is complete, but the touch up of the top coat will take place out at the Pad.”

The tank will be the main topic at the upcoming SSP (Space Shuttle Program) FRR (Flight Readiness Review) – scheduled for next week – following continued losses from the intertank region of the tank on recent flights.

While the cause is understood to be related to dust contamination on the metal surface of the intertank, prior to the application of foam, pull/plug tests are still carried out on the intertank ahead of rollout, so as to ensure the stringers do have an acceptable level of adhesive strength.

The delay to rollover, and subsequent slip to the launch date, allowed for ET-135 to have additional areas – most notably on the -Z side (backside) of the tank – to undergo pull/plug tests, thanks to the erection of additional platforms inside the VAB.

The additional tests were via the orders of SSP management, who noted early results showed ET-134 (STS-130) shed 21 areas of foam from the intertank – and mirrored similar areas of loss as ET-131 on STS-127.

“In lieu of the Intertank foam losses observed on STS-130/ET-134 (see photos, left), an additional 60 Bond Adhesion Tests are to be performed on ET-135 per the SSP Noon Board (request),” noted a SSP Top Risks presentation to the Program Requirements Control Board (PRCB), available on L2.

“Twenty-one losses were identified on the intertank of ET-134. Preliminary assessment indicates these losses are similar to the ET-131 intertank foam loss per the special investigation in terms of apparent failure mode and location.

“Failure mode: Potential Contamination. Preliminary assessment indicates all ET-134 intertank observations are bound by the ET-131 intertank losses in terms of size, location and observed timing. ET Project Hazard T02, Loss of ET Thermal Protection System, is being assessed for an increase in risk due to these losses.”

Although noted as similar to ET-131 losses, the amount of TPS liberations were considerably less with recent flights, especially when compared to STS-127.

“STS-127/ET-131 launched on July 15, 2009 (sixth attempt). Post-launch camera and film review showed loss of foam at several locations on the Intertank (IT),” added the Top Risk presentation.

“There were 38 Intertank foam losses observed on ET-131/STS-127, with the largest loss area occurring on Stringer 11 of Panel 1 at Station (location) 1052. The dimensions for this loss are approximately 34.7″ L x 5.2″ W x0.6″ D, with a mass of 0.255lbm (unknown if one piece).”

Most importantly, foam losses from the -Z side of the tank hold little to no impact threat with the orbiter, and the majority of liberations on any area of the intertank occur over two minutes into ascent – and are unlikely to hold enough mass or energy to damage the orbiter TPS should there be an impact.

The SSP FRR will be updated on the latest findings, based on collective data gained on intertank losses since STS-127.

L2 members : Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4500 gbs in size

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