Final Launch Reviews Reveal Modifications to Endeavour for STS-134

by Chris Gebhardt

With Endeavour zipping through S0007 (launch countdown) ops, teams at Launch Complex 39A have completed PRSD load for Endeavour’s three electricity-producing Fuel Cells. Meanwhile, with no outstanding issues for the baby orbiter’s launch Friday at ~15:47.52  EDT on the STS-134/ULF6 mission to the International Space Station, final launch reviews have been completed – reviews that highlighted several “first time” configurations and modifications to Endeavour.

Previous Endeavour flight (STS-130) In-Flight Anomaly Review:

Overall, Endeavour’s previous mission, the highly successful and all-star STS-130/20A mission to deliver Node-3 Tranquility and Cupola to the ISS in February 2010, was an extremely clean mission – with only 9 In-Flight Anomalies (IFAs) recorded.

In fact, only four of those IFAs were charged to Endeavour herself, with the remaining 5 IFAs charged to the Government Furnished Equipment aboard her.

Of these three orbiter IFAs, only two gained mentioned on STS-134 Flight Readiness Review (FRR) documents: a protruding Elevon flipper door-to-door seal and two TPS (Thermal Protection System) anomalies.

For the protruding door-to-door Elevon Flipper seal, the SSP (Space Shuttle Program) FRR notes that, “Upper elevon sliding seal between flipper doors 12 and 13 identified as protruding ~ 3.8 inches,” during in-flight photographic assessment.

The seal itself is 0.025 inches x 3″ x 31″. All pre-flight images showed nominal configuration and installation.

Post-flight inspections in OPF-2 revealed no change to the seal’s condition, nor did the inspections turn up any indication of thermal degradation – which confirmed the in-flight analysis that the seal issue was safe for reentry.

Following the investigation, the seal itself was removed and replaced. Post-removal inspections of the seal revealed no “material or fabrication discrepancies;” however, “Wear marks on the upper surface of the adjacent trailing edge seal [indicated] the part was dislodged and experienced multiple elevon cycles prior to peeling up on ascent.”

Further assessments revealed that the most likely cause of the seal peel up during ascent was a combination of “reduced seal overlap due to trailing edge seal deformation combined with increased friction due to common debris resulting in the leading edge of the seal catching the tangent of the trailing edge seal allowing the seal to become displaced after installation but prior to launch.”

Modeling tool assessments have confirmed that there is adequate design overlap at all seal locations across the orbiter fleet. The only other occurrence of this type of situation in Shuttle Program history was on two early program flights of OV-104/Atlantis.

Therefore, since the seal and adjacent seal were replaced with new parts, the issue has only been seen on two early program flights, and all thermal & structural assessments concluded that all temperatures & stresses would not result in loss of structural integrity, the seal peel up issue is not a concern for STS-134.

Aside from the seal, there were only two other TPS anomalies noted from STS-130, the first being a protruding ceramic insert around Endeavour’s windows.

“During on-orbit inspection, a tile ceramic insert was found protruding ~0.4″ between windows 1 & 2,” notes the Orbiter SSP FRR presentation – available for download on L2.

The protruding insert was quickly cleared for reentry based on its low potential for reentry liberation and positive structural & thermal margins at all possible vehicle impact locations should liberation have occurred. 

The insert, which was still in-place upon initial post-flight inspections of Endeavour, was “easily removed” by ground crews.

A review of insert closeout documentation revealed that bondline defects exceeding baseline requirements were present at this insert location.

Furthermore, inspections found that the insert plug made contact with the carrier panel fastener head and resulted in undesirable loads on the insert bondline.

A Chit (J6604A) was created to “inspect for plug-to-fastener head interference and to perform pull tests on suspect inserts” across the fleet. On OV-103/Discovery, several loose and missing plugs were discovered.

Subsequently, all necessary insert plugs requiring modification were removed and replaced using a stiffer cord as the “locking feature” for high plug installation torque.

STS-134 Specific Articles:

For STS-134, all forward- and mid-body insert plug locations have been inspected and either cleared for flight for R&Red using the new modification requirements – mods that have already flown three times (STS-131/Discovery, STS-132/Atlantis, STS-133/Discovery).

Finally, the last IFA noted by the STS-134 Orbiter SSP FRR presentation was “suspect cracked canopy tile adjacent to previous RTV repair (performed in 2007).

This issued was cleared relatively quickly during STS-130 based on the low potential for liberation and positive thermal margins in the event of a complete or partial liberation during reentry.

Post-flight inspections revealed missing coating that gave the appearance of an offset along with a very slight crack. The RTV repair was still firmly attached and was not loose.

Configuration Changes to OV-105/Endeavour for STS-134:

Debuting on the final flight of Endeavour are several modifications designed to improve vehicle safety and mission success. 

In all, five modifications were made to Endeavour herself.

These included Fuel Cell CPM dedicated power feed circuit fuse mods, Main Engine Ignition acoustic sensor filter mods, Thermal Protection System ceramic insert plug modifications, and the inclusion of the Boundary Layer Transition (BLT) Detailed Test Objective (DTO) protuberance tile and associated hardware.

More specifically, though, several Sharpie reference marks were applied to Endeavour’s port and starboard Wing Leading Edge (WLE) Reinforced Carbon-Carbon (RCC) panels.

“With the planned OBSS stowage on ISS during STS-134, the docked late inspection procedures requires a unique scanning sequence,” notes the Orbiter SSP FRR presentation.

To aide with this docked late inspection, incorporating lessons learned from the STS-123/Endeavour and STS-131/Discovery, 15 reference marks were added to Endeavour’s starboard wing (one reference mark to the port wing) to help the crew identify pause points for the RCC scan and to aid in determining proper pan and tilt angles for the LDRI (Laser Dynamic Range Imaging) scanner on the OBSS (Orbiter Boom Sensor System).

The remaining 7 modifications for Endeavour are in the form of mission kit changes, including the STORRM DTO installation, Port and Starboard Tool Stowage Assembly cushion modifications, sleep restraint strap modifications, payload cable harness modifications for AMS-2’s ROEU, and added length to cables.

Specifically, engineers also removed low priority Low Pass filters for MEI (Main Engine Ignition) instrumentation.

According to the Orbiter 155 page SSP FRR presentation, “Prior to STS-130, a zero spares balance for MADS instrumentation low pass filter resulted in a study to determine which existing lower priority filters could be deactivated/removed and used for higher priority locations.”

This resulted in the deactivation of seven (7) low priority OV-105 MADS measurements. Three were removed prior to STS-130 to support Discovery and Endeavour spare requirements. A further four filters were removed during the STS-134 flow to support the new OMS pod MEI instrumentation mods on Discovery and Endeavour.

Moreover, Endeavour’s Orbiter Boom Sensor System (OBSS) Integrated Boom Assembly has been updated to reflect the fact that the OBSS will be left on the ISS at the end of the STS-134 mission.

“IBA will be upgraded to EIBA (enhanced IBA) on-orbit at a later stage EVA to be more compatible with ISS RMS (Remote Manipulator System).

Lastly, Endeavour received 43 new BRI-18 (Boeing Reinforced Insulation 18) TPS tiles around critical areas of the vehicle. This brought the total number of BRI tiles on Endeavour to 267 – making her the fleet leader for BRI tiles and enhanced TPS safety.

Moreover, 29 putty-repaired tiles were completely replaced on Endeavour during her STS-134 OPF flow – 12 based on chit approvals and 17 because of degradation concerns.

Endeavour’s Rudder Speed Brake was also inspected and the tile gaps shaved to achieve minimum desired gap configuration.

TPS gap filler work was also performed upstream of the BLT DTO modification to reduce the possibility of adverse BLT effects.

Finally, Endeavour’s 10L WLE RCC panel and associated T-seal was replaced due to thermography signatures and tactile inspections that raised some minor safety concerns.

(Numerous articles will follow. L2 members refer to STS-134 coverage sections for internal coverage, presentations, images and and updates from engineers and managers. Images used: Larry Sullivan MaxQ Entertainment/, and the 155 page Orbiter FRR presentation – one of over 50 FRR presentations for STS-134 on L2).

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