EVA-3 terminated due to LiOH concern – DAT present TPS clearance reports

by Chris Gebhardt

Astronauts Dave Wolf and Chris Cassidy have returned to the Quest airlock earlier than scheduled, due to concerns relating to a potentially faulty LiOH canister in Cassidy’s suit during STS-127’s third EVA. Meanwhile, the full findings of the Damage Assessment Team (DAT) have been produced via a series of stunning presentations, confirming Endeavour is an extremely clean vehicle.

EVA-3 Overview:

For EVA-3, Wolf and Cassidy were tasked with the battery Removal and Replacement (R&R) of four of the six batteries on the P6 truss. Due to the early termination, only two were installed.

The LiOH canister is used to control carbon dioxide levels inside the EMUs. The other option, as seen with EVA-2, utilizes the METOX method.

“BREAK, BREAK. Hold what you’re doing,” came over the loop during the EVA as the spacewalkers were talking , as controllers started to notice spikes in Cassidy’s CO2 levels. It is not confirmed – but likely – that the spikes are related to a failing LiOH canister.

However, the rising levels are not a health concern, allowing the EVA to move to some clean up tasks, ahead of transitioning back to the Quest Airlock to end the EVA early. UPDATE: Both Spacewalkers are now safely back into Quest.

EVA-3 Tasks:

According to the extensive Space Shuttle Program Flight Readiness Review (SSP FRR) – available for download on L2 – “JAXA ICS-EF Payload Prep (Multi-Layer Insulation) and P6 Battery R&R – planned completion of 4 batteries – scheduled for EVA-3.”

Overall, the battery R&R are to place over two EVAs (beginning on EVA-3 and concluding on EVA-4). “Batteries R&Red using two EVAs, nominally EVAs 3 (FD8) and 4 (FD10),” notes the SSP FRR EVA overview document.

In preparation for this task, the 2B power channel on the International Space Station (ISS) was taken offline line following the completion of EVA-1 on FD-4 (Flight Day 4). This power channel will remain deactivated until the battery R&R operation is complete.

Currently, the power channel is expected to be brought back online on FD-11. With this power channel offline, however, the power management aspects of the ISS have being effected – mainly in the area of determining the highest priority areas to receive power while this channel is offline.

E3Furthermore, the plan for this mission was designed under the assumption that the Port SARJ (Solar Alpha Rotary Joint) would be able to rotate nominally between the two battery R&R EVAs while the Mobile Transporter platform is stationed and Work Site 8 – just to the inboard side of the Port SARJ.

Nevertheless, a contingency power plan is available should SARJ rotation – for whatever reason – be impossible between the two EVAs.

Additionally, mission planners have noted an area of trouble the EV crew might encounter during the spacewalk today.

The issue, noted in the SSP FRR documents, pertains to a Flight Support Equipment (FSE) bolt that holds the possibility of jamming.

“Issue with the FSE where a bolt can jam when removing the battery from the ICC-VLD (Integrated Cargo Carrier – Vertical Lightweight Deployable); pin must be sheared to finish removal,” notes the EVA section of the SSP FRR document.

If this should occur, the presentation notes that Cassidy and Wolf may lose the ability to properly bolt the battery onto the IEA of the P6 truss – effectively preventing them from completely attachment the new battery to the Station.

TPS Review:

As has become the staple in the post-Columbia era, the Damage Assessment Team (DAT) has poured over thousands of images and videos since Endeavour’s launch one week ago.

E4As a result of all their hard work (and the careful and skillful dedication of the MAF workers who assembled ET-131), Endeavour has received a sparkling report from the DAT in regard to the condition of her TPS (Thermal Protection System).

In fact, the DAT only noted 14 areas of damage or TPS “softgoods” (areas of protruding gap fillers, raised thermal blankets, or embedded External Tank foam that did not cause damage to the TPS tiles or blankets).

“Imagery review complete. External Tank (ET) doors verified closed. DAT unanimously recommends clearing TPS for entry,” note several DAT review presentations available for download on L2.

In all, the 14 areas of damage or softgoods included: eight gap filler/thermal barrier protrusions, 10 tile anomalies located in six clusters on Right Hand chine, two lower surface protrusions, and one area of embedded ET foam.

For Endeavour’s OMS (Orbital Maneuvering System) Pods, only the Port-side Pod gained any attention from the DAT.

E5Two gap fillers were noted to be protruding (4.1” x 0.38” and 4.2” x 0.25”) from the Port-side Pod as well as one lifted Leading Edge Blanket (1.1” x 0.2”).

Gap filler “Protrusion localized to outer layer of sleeving. Bond integrity of gap fillers remains intact,” notes the DAT assessment.

Similarly, the DAT presentations note that the protruding Thermal Blanket is still bonded to its surrounding tiles and is of no concern for liberation during entry as “Ascent flight loads bounds entry” – mean that this area of the vehicle experiences more aerodynamic loads during ascent than it does during entry.

All analyses and assessments of the OMS Pods were conducted via the hand-held camera images taken by Endeavour’s Flight Crew from the aft Flight Deck of the Orbiter.

The next minor area of interest to gain note in the DAT summaries relates to two areas near the Forward Reaction Control System (FRCS) pod.

E6“Fabric protrusion at tile to blanket interface (2.0” x 0.47” x 0.4”),” notes the presentation.

The area only contains a fabric fray and all insulation qualities around the area are not affected. Likewise, there are no heating or structural concerns should this area of fabric liberate during entry.

The other area near the FRCS pod is a protruding Thermal Barrier fabric that is lifted by approximately 0.55” at its maximum height.

As with the frayed fabric, this area poses not concerns for abnormal heating, nor does it pose a risk of liberating during entry.

Transitioning to the underside of the Endeavour, the DAT assessment notes only nine areas of damage or softgoods – six damage sites on the Right Hand Chine, two softgoods on or near the Nose Land Gear Door (NLGD), and one softgood on the Left Hand outboard elevon.

On the elevon, “0.25” +/- 0.15” pillow gap filler protrusion noted on the port outboard elevon edge.”

E8The gap filler, however, is still providing “sidewall compression” on the surrounding tiles. Therefore, there is sufficient bond area remaining to preclude the possibility of liberation during entry.

Furthermore, as the elevon is at the aft end of the vehicle, there will not (nor could there be) any downstream affects on Endeavour.

The two remaining softgoods on the underside of Endeavour are toward the front of the vehicle.

The first of these remaining softgoods is located on the NLGD door.

“Debris was identified on NLGD centerline,” notes a DAT presentation. The debris, which can clearly be seen on the RPM photographs, is most likely a piece of ET foam which liberated from the External Tank during ascent and became wedged between the two NLGDs.

The identification of the wedged debris is based on the debris’ color, location, and potential transport paths during ascent. With all those factors, the DAT has concluded that this is, in fact, a piece of ET foam.

E7Nevertheless, since the Thermal Barrier cords that seal the two NLGDs together for entry (as well as the adjacent TPS tiles) are undamaged and intact, there is no entry or heating concerns regarding the wedged piece of foam.

The final softgood area on Endeavour is a protruding TPS blanket at the Arrowhead (the place on the underside of the Orbiter where the forward attachment strut for the External Tank is bolted to the vehicle).

The presentation notes that there is a “0.32” +/- 0.15” protrusion of arrowhead blanket sleeving at the 6 o’clock position.”

This protrusion is expected to transition the Boundary Layer at Mach 18.7, creating an early transitional area of influence on the downstream protruding gap filler on the Left Hand outboard elevon.

However, thermal limits and constraints will not be violated by the transition. Thus, this area is of no concern for entry.

E9Finally, the DAT presentation notes the six distinct TPS tile damage sites on the Right Hand chine area of Endeavour.

Of these six damage sites, a total of 10 TPS tiles are damaged with a maximum damage depth observed at 0.35” – well within the thermal and structural capabilities of the underbelly TPS tiles.

In the end, all the TPS chine damage areas were cleared by comparing the specific damage locations and depths with previous analyses, flight histories, and certified analytical tools.
See also:

STS-125 DAT Overview Article:
STS-126 DAT Overview Article:
STS-124 DAT Overview Article:

Further updates will follow. Refer to live update pages – linked above – for up-to-the-second live coverage.

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.

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