STS-133: Structural defect/cracks found under foam damage on ET-137

by Chris Bergin

While troubleshooting on the Ground Umbilical Carrier Plate (GUCP) saw the flight seal removed on Wednesday, engineers have been removing the cracked foam from Discovery’s damaged Thermal Protection System (TPS) area on the flange between the intertank and LOX tank. Two cracks has been found on the structural stringer, which is undergoing an immediate investigation.

STS-133 Latest:

Discovery has completed full safing operations, following last Friday’s scrub, with the disconnection of ordnance on her Solid Rocket Boosters (SRBs) and depressurization of her numerous Composite Overwrap Pressure Vessels (COPVs) used by her Main Propulsion System (MPS) and Reaction Control Systems (RCS).

“MPS/SSME and OMS/RCS COPV Depress: COPV depressurization complete. The 59-1/2 and 28-1/2 doors were removed and the QDs (Quick Disconnects) will be mated,” noted the NASA Test Director (NTD) processing report (L2). “Work to disconnect the SRB ordnance in the forward skirts and the aft IEAs completed.” 

The delay, to an interim launch date of November 30, is focusing on the GUCP troubleshooting, along with the repair to cracks found on the flange area of the ET – between the LOX tank and the Intertank – with work progressing to plan on both issues.

“IPR 68: GH2 Ground Umbilical Carrier Plate (GUCP) leak: The ET/IT Arm was extended and the extendable platform was partially deployed providing access. The GUCP and T-0 lock bolt ordnance disconnects are complete,” added the NTD.

“The team disconnected the QD from the GUCP, recording measurements as they go for engineering analysis once the hardware removal is complete.”

Measurements were taken – with an aim to check for any potential misalignment of the hardware – prior to the removal of the flight seal, the two leading candidates for the gaseous hydrogen leak observed during the fast fill process of Friday’s tanking.

“More GUCP alignment measurements were taken with the vent line lifted and lowered. The measurements are under engineering evaluation. The 7” QD will be de-mated this morning and the flight seal will be inspected and removed,” the NTD added on Wednesday. “Axial and concentricity measurements will also be taken.”

Given the size of the leak is being claimed as the largest engineers have ever seen from the GUCP, it is hoped that an obvious fault will soon be apparent, allowing for a speedy root cause to undergo mitigation.

The other major problem being worked on is the repair on the crack on the flange area of the tank – consisting of one large crack and several smaller, associated cracks – with the aim to confirm engineers can access the area, and then create the required environmental conditions to carry out the reapplication of new foam to the flange.

Access options appear to be positive, with the Engineering Review Board (ERB) giving the go for engineering to carry out the dissection of the damaged foam, which has begun.

“ET LO2 IT foam crack: The ERB concluded that there is adequate access at the Pad on the -Y ET access platform to inspect and repair the crack,” confirmed the NTD. “MAF (Michoud Assembly Facility) will perform NDE (Non Destructive Evaluation and then develop a dissection plan for defect analysis. At this time, the team is not clear exactly when work will be complete.

“Four strips were cut out of the foam for dissection analysis. Engineering is evaluating to determine failure root cause. ET Mechanical will perform an ET LO2 Feedline inspection using the +Y access platform.”

However, once some of the damaged foam was removed from the tank, two cracks were observed on the actual structure of one of the stringers.

Managers are evaluating how serious the defects are, along with a forward plan – which includes the continued effort to bring the tank back to flight status without a rollback.

UPDATE 1: Initial plans noted by NASA include the potential to repair the area via the use of Doublers, which would cover what is now being described as two nine inch cracks in the aluminum, prior to the reapplication of foam.

As of the latest update, managers were set to make a final decision on being able to reapply foam over the dissected area by Friday, potentially utilizing a hood structure over the area in order to provide the environmental needs for the spraying of foam and its stable cure whilst out at the pad.

ET-138, the last “new” tank to be produced by MAF also suffered from a cracked stringer during production, prior to undergoing a repair.

“In cell J.  Had an intertank cracked stringer,” noted a Shuttle Standup/Integration report (L2) a year ago. “That mechanical repair is complete, less the TPS closeout.”

Further updates will follow.
(Images all from L2’s STS-133 Coverage)

Related Articles