Endeavour preparing for SSME installation – RCS test article investigation

by Chris Bergin

Engineers are preparing Endeavour for next week’s installation of her three Space Shuttle Main Engines (SSMEs) for what is likely to be the final time, ahead of STS-134’s mission in February of next year. Meanwhile, an investigation is currently taking place into a failure of a Reaction Control System (RCS) test article, although no inspection of the fleet has been called for at this time.

STS-134 Processing Latest:

Although the youngest orbiter in the fleet is over half a year away from her mission to carry the Alpha Magnetic Spectrometer (AMS-2) and Express Logistics Carrier 3 (ELC-3) to the International Space Station (ISS), Endeavour is enjoying a relatively busy processing flow inside her OPF-2 (Orbiter Processing Facility).

A large element to her recent flow has been related to finalizing Thermal Protection System (TPS) work on the orbiter, following her return from the highly successful STS-130 mission.

“Completed the landing gear functional. The ET (External Tank) door BRI (tile) mod is in work with some prefits. The BLT (Boundary Layer Transition) mod continues,” noted KSC Integration on the Shuttle Standup/Integration report (L2).

“Continuing with the NLG (Nose Landing Gear) TPS evaluations with Mylar pulls. Payload premate testing continues.”

Endeavour and her team have the weekend off, as engineers finalized the installation of the three Flow Control Valves (FCVs)  – which have performed well since the STS-126 incident – into the orbiter’s Main Propulsion System (MPS), ahead of retests next week.

“OV-105 (OPF Bay 2): MPS Flow Control Valve LV58 installation was completed; leak checks worked with electrical retest planned for Monday,” added the NASA Test Director (NTD) processing status (L2).

“Payload pre-mate test was successfully completed. Payload 1553 data bus checkout (complete). Window 7 (ceramic) insert R&R (removal and replacement) has begun. Window 7 installation is scheduled for Tuesday. Weekend Work: None scheduled.”

Endeavour can also look forward to the start of SSME installation operations next week, with Main Engines (MEs) 2059, 2061 and 2057 manifested to aid the orbiter’s ride uphill next year.

It’s been a busy period for the SSMEs, with Discovery’s installation, and subsequent removal – due to an issue with a turbopump on ME-1 – followed by reinstallation, taking place recently, added to the removal of Atlantis’ engines, following her STS-132 mission.

While it is a routine procedure to fully inspect the engines – both before and after removal from the orbiter – engineers will attempt to find the root cause for the hundreds of streaks in Atlantis’ SSME plumes, observed by ground cameras during early first stage flight.

Already, Pratt & Whitney Rocketdyne/KSC (Kennedy Space Center) have confirmed one leak-related observation during initial checks. However, it should be stated that as with the observed streaks, Atlantis’ engines enjoyed no safety or performance issues during powered flight.

“SSME (Pratt & Whitney Rocketdyne/KSC) Last week, removed the engines from OV-104 (Atlantis) post-flight STS-132. Those engines are back in the engine shop, going through nozzle tube leak checks,” added the latest Standup report.

“On Engine 2052, which was in position 1, had some cold wall leaks found after completion of tube leak checks. This explains one of the observations where the film showed a frost area, just above the aft manifold on Engine position 1.”

Over in the Vehicle Assembly Building (VAB), both Endeavour’s External Tank (ET-138) – located in High Bay 2E (HB-2E), and Solid Rocket Boosters (SRBs) – being stacked in High Bay 1 (HB-1), are undergoing the business end of their flows ahead of mating.

ET-138 – the last “new” tank to be shipped from the Michoud Assembly Facility (MAF) – is now undergoing the installation of its Ground Umbilical Carrier Plate (GUCP), which had caused scrubs during both STS-119 and STS-127’s tankings.

Part of the solution involved a new two-piece flight seal being installed into the hardware, which gained a mention for ET-138, as a Problem Report (PR) noted this tank’s GH2 seal is being replaced.

No specifics on what caused the PR to be called have been mentioned in flow documentation, although it appears the issue was spotted during the routine “shakedown” inspections in the VAB’s checkout cell.

“ET-138 (VAB HB-2E): GUCP Installation: PR on seal change out is in work. LO2 & LH2 Preps for checkout are in work,” noted the NTD report, adding status on the early stacking work that has taken place on the boosters. “SRB BI-145 / RSRM 113 (VAB HB-1): Left Aft Center segment stacking is complete. Post Ops & Leak Checks are in work.”

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

RCS Test Article Failure:

The Orbiter Project at the Johnson Space Center (JSC) are continuing evaluations into a failure of a RCS test article at the White Sands Test Facility (WSTF) in New Mexico.

The test article, also known as the “fleet leader”, is one of multiple elements of orbiter hardware, which undergo a large amount of testing, to the level that wouldn’t be possible in an OPF environment. Only part of the RCS fleet leader remains since its debut in 1989, following the retirement of the Forward Reaction Control System (FRCS) element in 2006.

“In June, there was a firing of the RCS fleet leader unit at WSTF that experienced an unplanned controlled shutdown,” noted the opening Standup report note. “Initial troubleshooting of that fleet leader thruster has been completed, and it was discovered that they were not able to maintain pressure in the injector chamber.

“Borescope inspections revealed an apparent breach behind the injector, possibly at the weld. This event is being looked at closely. History data is being gathered on this thruster, and the (Program) is discussing the events of the test to determine what steps to take next.”

The status of the failure was updated on the latest Standup report, following an Orbiter Project Office (OPO) tag up on Wednesday. During the meeting it was confirmed the test article suffered from a large crack in the aforementioned weld.

“The RCS Community provided a status of the investigation into the unexpected controlled shutdown of an RCS test article that was fired in June. The team has completed their initial evaluation of the test article, which led them to identify a large crack in a weld that is between the closeout of a fuel manifold and the injector,” added the update.

As part of the Space Shuttle Program (SSP) due diligence approach, further investigations will take place on the test article, ahead of any decision to inspect the related hardware on all three orbiters in the fleet. In a few weeks, engineers will complete their findings, and decide if there’s any commonality of failure risk related to the orbiters. Until then, inspections on the fleet will not be required.

“The team has pulled in the larger community to define the next step to evaluate that crack. They have defined a plan that includes CT scans as well as destructive evaluation,” added the latest status report. The team has developed an initial thought tree and will be maturing it over the next few weeks.

“They have been evaluating the history of failures that might be similar, as well as the history of this particular part. They will continue to provide a regular status as they let the data lead them through the evaluation. They will also be evaluating whether this instance is applicable to the fleet or just related to what happened to the test facility.”

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