Diligent to the end – Endeavour’s engineers spot 0.005 inch FCV defect

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Space Shuttle Program (SSP) manager John Shannon has praised the team responsible for installing the Flow Control Valves (FCVs) on Endeavour, after they spotted a 0.005 inch shim was missing from one of the three valves. Endeavour – processing for next year’s STS-134 – wouldn’t of suffered from any ill effects, had she launched with the since-replaced FCV.

STS-134 Processing Latest:

Endeavour is being processed inside her OPF-2 (Orbiter Processing Facility), ahead of her February, 2011 mission to carry the Alpha Magnetic Spectrometer (AMS-2) and Express Logistics Carrier 3 (ELC-3) to the International Space Station (ISS).

The 15,300lbs AMS-02 unit will undergo a milestone review next week, based on the changes made since engineers decided to replace the cryogenic super-fluid helium superconducting magnet with a permanent alternative – the reason the launch date slipped down the manifest.

“There will be a Delta Compatibility Review on August 6 for the AMS payload to ensure that all the changes made are still consistent with our engineering and their mission profile,” noted Flight Operations and Integration on the latest Shuttle Standup/Integration report (L2).

All three of her Space Shuttle Main Engines (SSMEs) were installed by Thursday of last week, and are now being put through closeout and interface procedures. Endeavour is currently enjoying the weekend off.

“OV-105 (OPF Bay 2): OIU (Orbiter Interface Unit) verification was successfully completed. SSME #2 was installed; all three engines are now installed. Closeouts continue,” noted the NASA Test Director (NTD) processing report (L2), which mentioned ongoing testing on the Orbiter Boom Sensor System (OBSS), which will remain with the ISS after Endeavour undocks.

“OBSS keep alive test was completed. SPEE premate testing was started and will resume once adapter cables are routed from Bay 3. Weekend work: None scheduled.”

Over in the Vehicle Assembly Building (VAB), engineers are stacking the twin Solid Rocket Boosters (SRBs) in High Bay 1 (HB-1), while External Tank (ET-138) continues it’s “shakedown” operations in HB-2E’s checkout cell.

“SRB BI-145 / RSRM 113 (VAB HB-1): L/R (Left/Right) Stud Tensioning; Need RT-455 pull test results. ETAR foam repair; PDL repair complete less closure. LA Joint Closeout; Cork pull test complete, on hold for PR (Problem Report) on ‘D’ dimension tool,” added the NTD report.

“ET-138 (VAB HB-2E): Bond Adhesion test repairs PDL (foam) application, trim and sand and final acceptance are complete, to engineering pre scaffold removal walkdown.”

STS-134 Specific Articles: http://www.nasaspaceflight.com/tag/sts-134/

Flow Control Valve Spot:

Most Shuttle followers will be only too aware of how the Flow Control Valves (FCVs) became an item of great interest, following the liberation of part of a valve’s poppet during Endeavour’s STS-126 launch in November 2008.

The finding led to the immediate inspection of the FCVs throughout the fleet, highlighted by Special Program Requirements Control Board (SPRCB) meetings and Flight Readiness Review (FRR) debates ahead of Discovery’s STS-119 mission.

The GH2 FCVs – of which there is one per SSME – are designed to provide the proper amount of pressurized GH2, while maintaining the ET LH2 tank flight pressurization limits.

However, one of the main concerns related to the potential of a large enough piece of the poppet liberating from the valve and impacting the downstream 90 degree elbow in the Main Propulsion System (MPS), which may cause an undesirable GH2 leak into the aft compartment.

FCV Specific Articles (Extensive): http://www.nasaspaceflight.com/tag/FCV/

Subsequent reviews of all FCV flight history and risk information revealed that the overall likelihood of a FCV poppet failure in flight is low. All the FCVs that have flown since have also undergone Non Destructive Evaluation (NDE) eddy current inspections, in order to spot any potential cracks forming in the valves prior to installation.

With no notable issues recorded by the valves since STS-126, the SPRCB and FRR conclusions and mitigation plans have again been proved to be correct. However, they are backed by highly experienced hands-on engineering teams at the Kennedy Space Center (KSC), who need to keep their eye on the ball at all times, and not just on areas of recent interest.

An example of their diligence was noted when one FCV on Endeavour was rejected via a tolerance problem, a five thousands-of-an-inch deviation from nominal, about the width of a sheet of paper.

“During installation of FCVs on OV-105 (Endeavour), one of the units failed an installation dimension requirement check,” noted the Orbiter Project Office (OPO) on the latest Standup report, noting the valve was sent back to its fabricator in California, who found the valve was missing one of its numerous – yet tiny – shims.

“That unit was sent back to the vendor where it was discovered that a 0.005 inch shim was missing. Orbiter is in the process of evaluating all the remaining units coming out of the vendor that have the proper configuration, and are confident that the units on the vehicle are in the proper configuration because they all passed the same installation dimension requirement check.”

A replacement valve has since been installed into Endeavour over the past few days and passed “mass spec” checks, confirming the new valve isn’t suffering from the same issue.

The spot earned praise from Mr Shannon on the Standup report, showing the teams are remaining extremely focused during what is a difficult time for the Program, with continuing lay-offs and uncertainty about the future after the fleet retires.

“Mr. Shannon said it was a good catch by the team installing the FCVs finding the tolerance problem; that is the way we want to do business,” he was noted as saying at the Standup meeting, before adding a message about the recent notices that informed nearly 1,500 workers they would lose their jobs in October.

“Please be compassionate and understanding as people’s lives are going to change, and we must still concentrate on getting the mission ahead of us done. It is vitally important that we do that, but it is a tough time for a lot of our team members. Please be aware of that and be compassionate about that.”

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