External Tank ET-138 under investigation after washer is found in feedline

by Chris Bergin

Currently set to fly with Endeavour, External Tank ET-138 is under investigation – after engineers found a washer inside the LO2 Feedline. The investigation will follow a similar route to that undertaken on ET-129 – when a noise was heard inside that tank during processing inside the Vehicle Assembly Building (VAB) – in order to be completely satisfied with tank’s configuration.

STS-134 Processing Latest:

Endeavour is in a smooth flow insider her Orbiter Processing Facility (OPF-2), with all three of her Space Shuttle Main Engines (SSMEs) installed and undergoing integrated testing with the Main Propulsion System (MPS).

The Orbiter Boom Sensor System (OBSS) has also undergone simulated thermistor testing, in preparation for being left on the International Space Station (ISS) at the conclusion of STS-134’s docked phase of the mission.

“OV-105 (STS-134): Engines were installed last week, continuing with engine securing. In the midbody, are routing the payload harnesses. Completed testing this week on Window 7, and are scheduled to install it on the vehicle next Monday,” noted KSC Integration on the latest Shuttle Standup/Integration report (L2).

With the Space-to-Space Orbiter Radio (SSOR) SCAN retest completed, along with Endeavour’s Nose Landing Gear (NLG) strut GN2 decay check showing positive results, processing on the youngest orbiter in the fleet will standdown over the weekend.

“OV-105 (OPF Bay 2): SSME/MPS integrated testing is scheduled for Monday and Tuesday pending resolution of a galled bolt hole on Engine #3 GOX interface documented in the PR (Problem Report),” added the NASA Test Director (NTD) processing report (L2) on Friday morning, noting the only issue (minor) reported in Endeavour’s OPF flow.

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

“Window #7 Installation is scheduled for Friday. The KU-Band pre-mate testing is scheduled to begin Monday. Weekend work: none currently scheduled.”

Endeavour is also closing in on the business end of payload operations, with the installation of the Detailed/Development Test Objective (DTO) known as STORRM (Sensor Test for Orion RelNav Risk Mitigation) due next week.

The primary payload of the Alpha Magnetic Spectrometer (AMS-02) is currently undergoing its latest review at the time of this article’s publication.

The AMS Capability Review (Delta CIR) is Friday,” added Flight Operations and Integration (NASA/JSC) on the Standup report. “On STS-134, the STORRM (DTO) hardware is supposed to be at KSC this week, with installation next week.”

SRB Milestone:

Although STS-135 is likely to be approved within weeks, STS-134 remains the final scheduled shuttle mission on the official manifest. As such, numerous milestones are being met as STS-134’s stack builds up inside the VAB – the latest of which relates to the Solid Rocket Boosters (SRBs).

Friday marked the final major piece of SRB hardware to depart the Kennedy Space Center’s Assembly and Refurbishment Facility. It joined with the other segments, which are currently being stacked in High Bay 1 (HB-1).

“SRB BI-145 / RSRM 113 (VAB HB-1): Right Aft Center segment stacking is complete and post ops are complete. Right Aft Joint leak check is in work. Left Forward Center segment stacking is scheduled for next Monday and Tuesday,” added the NTD.

“Friday morning, transferred the right forward assembly for STS-134 over to the VAB. That is the final for the February flight.”

The transfer of the final segment was marked by a ceremony for the related workforce, hosted by United Space Alliance (USA) Director of Manufacturing Operations Greg Henry and Astronaut Kay Hire.

ET-138 Investigation:

The last “new” tank to be shipped from the Michoud Assembly Facility (MAF) – ET-138 – has been located in High Bay 2E’s checkout cell since its arrival in Florida, where it has undergone numerous checks and preparations for its mating with the SRBs.

It was during the evaluations on the LO2/LOX 17 inch feedline – which involves the removal of a cover plate to allow for inspections of the inner workings of the lines – that a washer was found.

“On ET-138, removed the LOX 17” cover plate to perform angle and tip load measurements; a loose washer was found in the feedline. The washer was removed and sent to MAF for analysis,” noted the Standup report, and also noted by the NTD.

“ET-138 (VAB HB-2E): A washer was found in the LO2 feed line during inspections and was removed. The washer has been sent and received at MAF for further engineering evaluations. Wipe samples were completed and routed to Wiltech for analysis.”

ET contractor Lockheed Martin are also part of the investigation both at MAF and KSC, where they will use lessons learned from ET-129 – relating to when a handful of engineers heard a metallic noise coming from inside the tank during its transition into the checkout cell ahead of STS-126.

Even though most of the engineers present didn’t hear the noise, managers immediately called for a full investigation – one which would reach as far as the Flight Readiness Review (FRR) and the Space Shuttle Program (SSP) management. A similar Foreign Object Debris (FOD) investigation will be used to confirm the tank is in a good condition to continue processing.

“Are going back to the ET-129 noise investigation assessment and looking for what was done during that to form any possible forward work for ET-138 to assure are satisfied with tank configuration,” added ET/Lockheed Martin.

“ET-138 On the washer observed in the feedline, the washer was removed, bagged, and returned to MAF. MAF is kicking off an investigation. In the photographs, it appears to be a cad-plated fastener. Cad-plated fasteners are used for flight, not for tooling at MAF. Looking for possible sources.”

Had Endeavour launched with an undiscovered FOD in such a location, it wouldn’t of been ingested into a critical system, due to the prevalve screens in the MPS.

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