Discovery’s SSMEs to be removed on Thursday due to LPOTP issue

by Chris Bergin

Engineers are preparing to remove Discovery’s three Space Shuttle Main Engines (SSMEs) on Thursday, after SSME 1’s Low Pressure Oxidizer Turbo Pump (LPOTP) failed torque checks. No schedule impact will be suffered as a result of back-stepping in the flow, due to the six week slip to STS-133’s launch date caused by payload requirements.

STS-133 Latest:

Discovery is being prepared for her mission to deliver the Permanent Multi-Purpose Module (PMM) – the converted Multi-Purpose Logistics Module (MPLM) Leonardo – and ELC-4 (ExPRESS Logistics Carrier -4) to the International Space Station (ISS).

Due to constraints relating to the PMM’s payload, the original launch date of September 16 was slipped to the end of October via internal planning, with a Change Request (CR) in the system to officially slip the NET (No Earlier Than) target at a meeting next week.

STS-134 – with Endeavour – is due to follow on February 24-28, with the notional STS-135 placed on a provisional June 24 launch date – although manifest evaluations are taking place, both at a program and political level, with the latter considering a position of negotiating STS-135 to launch “up to the end” of FY2011, whilst evaluating the costs of adding STS-136 in 2012 (evaluation content in L2 – specific article will follow when appropriate).

With a mini-manifest stretch already in effect by proxy, engineers have at least two missions to support either side of the New Year, with Discovery’s flow enjoying a large amount of contingency inside her Orbiter Processing Facility (OPF-3).

“Nose Landing Gear and forward ET (External Tank) separation assembly connector mates as well as forward NASA Standard Initiator (NSI) resistance tests were successfully completed on 3rd shift Tuesday morning,” noted the NASA Test Director’s overview of the list of processing tasks that have either been recently completed, or in work (L2).

“The TACAN turnaround system test was completed Tuesday. The drag chute door installation and checkout for flight was completed Tuesday night. The NLG (Nose Landing Gear) strut pressurization for flight was completed Tuesday night. The payload pre-mate test was worked Tuesday and is scheduled to finish today.

“PRSD (Power Reactant Storage and Distributation) system testing continues. The payload bay doors will be closed today in support of TPS Thermal Protection System) work payload bay door plug installation which begins Thursday.”

The plug reference relates to the modifications that are being implemented on the small ceramic plugs that are located on the Payload Bay Door Hinge Line. Similar work is also taking place on Endeavour, as engineers work on mitigating potential debris hazards – after the issue was raised at recent Flight Readiness Reviews (FRRs).

STS-133 Specific Articles:

The issue with the LPOTP on Main Engine 1 was reported by the NTD earlier this week, not long after they had been installed, resulting in preparations for all three engines to be removed – due to interferences with the removal of ME-1 (ME2048) – being worked.

“PR (Problem Report): SSME 1 Low Pressure Oxidizer Turbo Pump (LPOTP) failed toque checks. All three SSME’s must be removed to allow replacement of the turbo pump,” noted the report (L2). Pre-ops for engine removal began Monday with engine removals scheduled to begin on Thursday.”

The LPOTP is an axial-flow pump driven by a six-stage turbine powered by liquid oxygen. The flow from the LPOTP is supplied to the High-Pressure Oxidizer Turbopump (HPOTP).

During engine operation, the pressure boost permits the High Pressure Oxidizer Turbine to operate at high speeds without cavitating. The LPOTP operates at approximately 5,150 rpm.

Discovery’s flow has been relatively trouble-free up to this point, with only 25 Interim Problem Reports (IPRs) noted since arriving back from her highly successful STS-131 mission. The latest two issues have been resolved, bar engineering reviews into a potential need for further troubleshooting.

“IPR 0024: A GSE (Ground Support Equipment) panel was replaced and the pressure relief valve A check out was successfully completed,” added the NTD. “Cabin positive pressure relief valve A troubleshooting will continue Wednesday. ARPCS (Atmospheric Revitalization & Pressure Control System) testing is scheduled to continue all week.

“IPR 0025: Remotely Operated Electrical Umbilical (ROEU) System 1 Release talkback is blank. The problem was picked up while moving the ROEU from the deployed position to the stowed position. System 2 reading was nominal. Continuity checks through the ROEU and connector upstream exhibited nominal values. Engineering is evaluating further troubleshooting.”

Over in the Vehicle Assembly (VAB), Discovery’s External Tank (ET-137) and twin Solid Rocket Boosters (SRBs) are mated and undergoing electrical work to connect the hardware that will be tested during the inferface test later in the flow.

The only issue noted from High Bay 3 (HB-3) related to a damaged sensor wire, which required a replacement to be shipped from Utah.

“SRB BI-144 / RSRM 112 / ET-137 (VAB HB-3): RFJ Sensor Wire Damaged. Parts arrived from Utah. Need Engineering release,” noted the opening report from the NTD, followed by its closure. “RFJ sensor wire repair complete close and out in work.

“Right Heater cable routing and connections complete. Right OI Cable routing to go in work when above referenced sensor PR complete. Left ETA Ring cover RT-455 in cure. Left Forward Crossover cover installations complete. Left and Right Upper Strut electrical connections complete. Left and Right Lower Strut Closeout complete and in cure.”

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