Streaks from Atlantis’ SSMEs noted as Discovery gains engines back

by Chris Bergin

An In Flight Anomaly (IFA) Review into STS-132’s ascent has noted an observation of over 200 streaks from Atlantis’ Space Shuttle Main Engine (SSME) plumes during ascent. While the number of streaks is twice the amount of the previous “record” no loss of performance or safety margins were breached. Meanwhile, Discovery has received all of her SSMEs back, following the removal of the engines last week.

STS-133 Processing Latest:

Discovery continues to enjoy a busy processing flow, despite her STS-133 launch target moving out to the end of October (now confirmed as Nov 1), with her two latest Interim Problem Reports (IPRs) in the process of being closed.

“OV-103 (OPF Bay 3): Payload pre-mate and load testing for IPR-0025 (Remotely Operated Electrical Umbilical (ROEU) System) was completed, disposition is in work. IPR-0026 (ARPCS) update: Atmospheric Revitalization and Pressure Control System testing is complete,” noted the NASA Test Director (NTD) processing report (L2).

Work is being conducted throughout Discovery, including testing of her Orbiter Boom Sensor System (OBSS), which began on Wednesday.

“PRSD (Power Reactant Storage and Distributation) system testing was completed. Main landing gear seal R&R was completed. OBSS testing has begun.

“Additional WSB 3 (Water Spray Boiler) decay checks and WSB 1, 2, & 3 core fill is scheduled. WCS installation was completed Wednesday morning; functionality testing is scheduled for Thursday.”

Discovery’s three SSMEs were uninstalled last week – in order to allow ME-1 to be removed after its Low Pressure Oxidizer Turbo Pump (LPOTP) failed torque checks.

While work was ongoing to install a replacement LPOTP on ME-1, the Program Requirements Control Board (PRCB) approved a Change Request (CR) to swap the positions of two engines, allowing for their reinstallation without being delayed by the work on ME-1.

“Engine relief valve checks were completed Tuesday; post-ops are scheduled to complete Wednesday,” added the NTD. “LH/RH (Left Hand/Right Hand) translators were opened Tuesday in support of SSME installation which began on Wednesday.”

UPDATE: However, on Thursday – according to the NTD – the last of the three SSMEs was already being installed. Due to the new positions, only ME-1 would need to be removed, if the same issue repeats itself during testing. Previously, all three engines had to be uninstalled to allow for ME-1’s removal from its center position, due to interferences.

Meanwhile, in the Vehicle Assembly Building (VAB) High Bay 3 (HB-3), final torque and leak checks between the mated External Tank (ET-137) and the twin Solid Rocket Boosters (SRBs) are in the process of being completed this week.

“SRB BI-144 / RSRM 112 / ET-137 (VAB HB-3): Installations; complete less final torque. Perform final torque after leak checks are completed Thursday,” added the NTD report. “L/R SRB NSI Ordnance Installations are complete, closeouts are in work. L/R Heater Cable closeouts; L/R Heater Cables complete less RT-455 pull test results. Camera cable RT-455 in cure.”

STS-133 Specific Articles:

STS-132 SSME Streaks:

Streaks in the engine plumes are not uncommon. However, the number of observations seen during Atlantis’ first stage ascent earned a mention in three presentations at the STS-132 IFA review – primarily on the Pratt and Whitney SSME presentation to PRCB-level managers.

“Numerous plume streaks between 23 – 54 seconds MET (Mission Elapsed Time). Do not correspond to any anomalous engine events,” noted the SSME IFA presentation for STS-132 – all 15 presentations available on L2.

The observations are not a safety issue, nor was there any loss of performance – backed up by the Mission Management Team (MMT) review of Atlantis’ ascent performance, which was deemed to be excellent. However, a root cause for the events are still being investigated.

“Photo Analysis of SSME Plume Streaks: Engine performance as predicted. No indication of event that would cause engine debris,” added the SSME IFA presentation. “MSFC (Marshall Space Flight Center) photographic analysis group reviewed video to determine most likely source of debris.

“11 of 217 events identified as possibly engine related (streaks appear to initiate at the nozzle rim). No streaks believed to be internal to the plume boundary.”

The source of the streaks – a number classed as twice as much as the previous record’ – may be found once Atlantis’ SSMEs undergo a detailed inspection later this month (July).

“Multiple Streaks Observed in SSME Plume Description: 217 streaks were observed in the SSME plumes. Normally get 20-40 streaks per flight, have seen up to 94 streaks,” added the Integration IFA review presentation (L2). “Engine detailed visual inspections will begin in July.”

Atlantis’ SSMEs are due to be removed shortly, with engineers currently working on uninstalling the SSME dome heat shields.

Atlantis continues to be processed as the STS-335 vehicle – Launch On Need (LON) support for STS-134. With the possibility STS-135 may be approved in the next 4-8 weeks, Atlantis – providing managers approve OV-104 for the mission – may still receive one more flight.

STS-132 Specific Articles:

The performance of Atlantis’ engines – E2052, E2051 and E2047 – during what is currently her final mission was classed as nominal at the SSME IFA Review, with only a frayed Flow Recirculation Inhibitor (FRI) note added to the aforementioned observation of streaks in the SSME plumes.

“Issue: Degraded FRI found on Nozzle 5007 / E2051 post STS-132. Approximate 6” (25 degree) section frayed and extending into the flow path.”

FRI is filled ceramic fiber tube installed in the space between nozzle tubes and MCC wall at the G15 joint. The fact such a small observation was even listed in the IFA review is a testament to the inspection process, and historical performance of the engines.

“FRI protects G15 Bellows Seal from overheating by reducing recirculation of hot gas into G15 cavity. FRI degradation is a normal wear issue with hot fire exposure. Function is maintained with fraying,” added the presentation, before noting hot fire experience for added confidence the issue held no safety concerns.

“Nozzle 2027 E0423 showed FRI damage after 1023 sec hot fire. FRI continued to provide protection and engine tested successfully to 4367 sec without damage to seal.”

FRI was only added to the SSMEs after STS-34, and a bellow seal will not fail during one flight – thus the issue was closed as no concern for safety of flight or performance.

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