Atlantis due back at KSC Tuesday – STS-125 ET foam liberation event reviewed

Atlantis’ piggyback ride back to the Kennedy Space Center (KSC) is expected to come to a conclusion between 6pm and 6:30pm at the Shuttle Landing Facility (SLF). Meanwhile, managers have been reviewing the foam loss from STS-125′s External Tank (ET-130) as part of the STS-127 Flight Readiness Review (FRR).
Atlantis Latest:

With Atlantis riding on top, the modified 747 SCA (Shuttle Carrier Aircraft) was reversed out of the MDD (Mate Demate Device) at 4:43am local time, with a departure around 8am local on Monday - following approval by the Ferry Flight Readiness Review (FFRR).

Tuesday Update: Based on weather, the current plan on Tuesday involved heading to Lackland AFB (San Antonio), before heading to Columbus, MS, prior to an eventual arrival back at KSC around 6pm local time.

Refer to live update pages for the latest information.

Dryden farewell:

“Teams are preparing space shuttle Atlantis for its cross-country ferry flight from California to Kennedy,” noted a memo to KSC workers earlier today. ”Atlantis is mounted on top of a modified Boeing 747 and is expected to depart Edwards Air Force Base at 11 a.m. EDT (8 a.m. PDT) today.

“The ferry flight will travel to Biggs Air Force Base in El Paso, TX and will stay there overnight before continuing the trip to KSC. Weather permitting, Atlantis could be back at its Florida home Tuesday night.”

Bar a slight problem during mating late on Sunday, all remaining closouts were completed without issue.

“Orbiter: OV-104 / Landing – Edwards AFB Turn Around Operations: Post Landing Ops Completed Over the Weekend: MPS (Main Propulsion System) decay checks. The 44 door and the drag chute door installations. Platform removals,” noted Monday processing on L2.

“The Ferry Flight Readiness Review; the team was given a ‘GO’ to proceed. The lift onto the Shuttle Carrier Aircraft (SCA). The Ferry flight is scheduled to depart Edwards AFB soon after completion of the Weather Briefing scheduled for 0600 PDT this morning.”

The results from the initial testing of Atlantis Aerosurface Servoamplifer (ASA) wiring have come back with no obvious issues. The failure of ASA Channel 1 as STS-125 launched held no mission impact, but a root cause would be deemed as helpful, as managers meet this week at the STS-127 Agency level Flight Readiness Review (FRR).

“ASA-1 initial troubleshooting for IPR-0002; no anomalies were found in orbiter wiring,” added Monday’s processing, with further testing scheduled for when Atlantis is back inside the Orbiter Processing Facility (OPF) at the Kennedy Space Center.

More will follow.

ET-130 IFR Review:

Also part of STS-127′s FRR is the IFA (In Flight Anomaly) of the foam loss observed from Atlantis’ External Tank (ET-130) during STS-125. While ET-130 was yet another “clean” tank, the loss of foam from the LOX Ice Frost Ramp (IFR) occurred during the “dangerous” period of ascent, where resulting impacts have the potential to cause damage.

a7The liberation did strike the orbiter, but only caused minor damage on her starboard Chine area of her Thermal Protection System (TPS). The damage failed to expand during the return home, backing up the DAT (Damage Assessment Team) findings the damage was of no concern.

Regardless, the foam loss made up the majority of Lockheed Martin’s ET IFA (STS-125) and FRR (STS-127) documentation (all available to download on L2), mainly thanks to the lack of other issues, and also to provide further understanding of the risks associated with similar foam liberations over the remainder of the shuttle program.

“STS-125/ET-130 post flight performance assessment in-work: Prelaunch and preliminary post launch assessments to be summarized. No constraints to STS-127 launch identified to date,” outlined the FRR presentation.

“ET-132 identified as STS-127 LON tank: First implementation of FSW welding on LH2 tank barrels 3 & 4 (longitudinal welds only)/ Provides more robust and producible design. Nominal processing with no issues for STS-127 LON (Launch On Need) requirement.”

Specific to ET-130, the presentation outlined that the tank performed as expected, with only four areas of foam loss observed imagery – which was initially gained from handheld photography, due to the failure to download the ET Umbilical Well camera footage. That footage has since been manually downloaded, following Atlantis’ arrival in California.

“Pre-launch Performance Assessment: All ET systems performed nominally – No (criteria) violations. No leakage observed at hydrogen vent system ground interface. Typical TPS observations acceptable per (requirements),” added the presentation.

“Post Flight Performance Assessment: Structural, electrical, and MPS systems performed nominally. TPS system performed nominally. Four (4) foam loss events observed in imagery review. Debris size / timing consistent with expectations

a2“One item observed to impact Orbiter chine at 104 secs. LO2 IFR debris location Xt 718 possible cause of damage. Time of release not observed but expected based on physics-based understanding of design and failure mode (void / delta pressure). Chine impact at 104 sec also observed via SRB video (multi piece event).”

Lockheed – who operate the Michoud Assembly Facility (MAF) in New Orleans – presented assessments related to the mass of the liberation, and any potential manufacturing changes that may have led to the foam shedding event. Importantly, the mass of the shedded foam was well below the risk assessment numbers.

“Performance consistent with physics-based understanding of hardware / failure mechanism (PDL pour with void/delta pressure divoting). Conservative mass estimate below risk assessment mass limit (0.020 lbm). 0.007 lbm max debris mass conservatively assuming single piece release.

“Assumed 104 secs MET time of release consistent with analytical prediction. Divoting potential starts at 95 secs. (combination of external heat and vacuum loading). Imagery and test data review support multi-piece liberation event. Review of SRB video shows additional debris observed within 1 sec. of chine impact with similar trajectory.

“Review of previous ascent imagery and test data shows successive foam release likely for PDL material. Thrust strut flange on STS-117 and LH2 IFR thermal / vac tests

“Reviewed ET-130 configuration, processing and repair history. No unique events or changes identified for STS-125. Design and process previously flown with no debris. Process revalidated since RTF – 3rd flight following re-validation of application process.”

“Performance consistent with debris cloud inputs and results used in integrated Probabilistic Risk Assessment (PRA). Divoting potential starts at around 95 secs. Largest single piece (assuming multiple events) ~< 0.007 lbm and consistent with debris cloud expectations (~0.005 lbm).

“Documented observations less frequent than predicted by debris cloud. 17 void / delta pressure debris events < 0.010 lbm expected per flight. Two debris events (divots) observed since RTF (XT 634 & 718). Erosion / popcorning typically observed on forward ramps due to high heating environment.”

Thanks mainly to the low mass of the liberation, the event will not require any further investigation.

“Summary / Forward Plans: Performance assessment results show all ET systems performed nominally. Four (4) debris events observed in umbilical well imagery. Mass estimates in-work but expected to remain below risk assessment mass limits. Time of release within expected performance for all observed losses.”

The performance of the External Tanks since the PAL ramp liberation event of STS-114 has been nothing short of spectacular. Several phases of redesigns – mainly focusing on reducing areas of foam on the tank that has the potential to shed and impact the orbiter – have proved to be highly successful.

ET-130 – despite the IFR event – can be added to the list of successes.

L2 members: Documentation – from which most of the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

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