STS-133: Engine placement order altered for Discovery

by Chris Bergin

Two of Discovery’s Space Shuttle Main Engines (SSMEs) will be re-installed in opposite positions, following their removal to allow for work to take place on Main Engine #1 (ME-1). The change to the engine order will allow for two SSMEs to return to Discovery’s aft next week, after the troublesome ME-1 turbo pump is sent back to California for engineers to investigate its first reported issue in 13 years.

STS-133 Processing Latest:

With internal schedules now adhering to the newly aligned October 29 launch date for STS-133 – which will become official at the end of the month – contingency in the flow has allowed for this unrelated issue to avoid causing any impact to the realigned schedule.

Based on the October 29 NET, the updated Integrated Operations Assessment Summary (L2) has Discovery leaving her Orbiter Processing Facility (OPF-3) on September 13 for mating with her awaiting External Tank (ET-137) and Solid Rocket Boosters (SRBs), before rolling out as the STS-133 stack to Pad 39A on September 23.

Mating of ET-137 and the SRBs in the Vehicle Assembly Building (VAB) continues to proceed to plan, with work being conducted on the upper and diagonal strut closeouts in High Bay 3 (HB-3), bar evaluations into minor damage to a fairing support plate.

“L/R (Left/Right) Heater Cable routing and connections are complete less snapshot. RH OI cable testing in work. L/R Ordnance preps are work complete,” noted the NASA Test Director (NTD) flow report (L2). “L/R heater cable closeout complete less RT-455 pull test results.

“Left upper strut fairing installation complete less RT-455 pull tests. Right RT-455 complete less pull tests. RTV-133 in cure. L/R lower strut closeout complete less RT-455 pull tests. Problem Report (PR) on damage to Fairing Support Plate, photos and measurements taken. More disposition to follow.”

In OPF-3, nominal processing is continuing on the orbiter, which is currently without all three of her engines and her Right Hand OMS (Orbital Maneuvering System) Pod – the latter of which is due back next month, following the changeout of a faulty helium isolation valve on the Right Reaction Control System (RRCS).

“OV-103 (STS-133) Continuing work in the midbody with payload premate testing activities. Closing the PLBDs (Payload Bay Doors) for the hinge line post plug rework; will be in-work next week,” noted KSC Ground Operations (L2). “Will reopen the PLBDs next week.

“Continuing with TPS (Thermal Protection System) processing, to date have 88 cavities remaining. At the HMF (Hypergolic Maintenance Facility), a new valve is going into the RH (Right Hand) pod; back on schedule there.”

Thursday’s Program Requirements Control Board (PRCB) also approved the increase to a 0.5” protuberance for Discovery’s Boundary Layer Transition (BLT) Detailed Test Objective (DTO). The approval also applies to Endeavour’s debut BLT DTO on STS-134.

Meanwhile, the latest NTD report noted the 26th Interim Problem Report (IPR) to be charged to the flow, relating to the testing of the Atmospheric Revitalization and Pressure Control System (ARPCS) – which keeps the crew compartment at the correct cabin pressure (nominally 14.7 psia) and maintains the correct ratio of GN2 and GO2 (80 percent and 20 percent respectively).

“OV-103 (OPF Bay 3): Main Landing Gear brake installation is scheduled. PRSD (Power Reactant Storage and Distributation) system testing is scheduled to continue Monday on 1st shift,” added the NTD report.

“New 0026: During ARPCS interval testing, system 2 N2 200 psi system relief valve reseat pressure was 195 psig should be 220 psig. Under engineering evaluation. Side hatch closure is scheduled in support of tile installation. Weekend Work: TPS payload bay door plug installation and carrier panel installations are scheduled to be completed this weekend.”

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On the latest Shuttle Standup/Integration report (L2), Pratt & Whitney Rocketdyne/KSC posted an overview of the situation that caused the removal of all three engines this week, due to the problem with ME-1’s Low Pressure Oxidizer Turbo Pump (LPOTP).

“Put engines in OV-103 (Discovery) on Monday and Tuesday of last week. On Friday afternoon they were performing torque checks on the low pressure (LP) pumps, and the LP LOX turbo pump on Engine #1 started causing problems. It couldn’t make the complete revolution,” noted the report. “The Technical Team worked the issue over the weekend.

“By Monday, no other troubleshooting or investigative work could be found with the pump left in place on the engine, so the decision was made to replace the LP LOX turbo pump. It was in Position #1, requiring the removal of Engines #2 and #3 to get it out.”

ME-1’s LPOTP will be sent on a journey back to Pratt & Whitney Rocketdyne’s Canoga facility in California next week, and is scheduled to arrive late on Wednesday.

“(Have) Engine #1 back into the Engine Shop, the pump off the engine (Friday) and will work the weekend to get it packaged. A FedEx Custom Critical truck is coming Monday afternoon and should deliver the LP LOX Turbo pump back to the Canoga pump room late Wednesday night. They are planning and are ready start the investigation on that pump.

“This is the first time for a problem with a LP LOX turbo pump since putting in the Block-2 pump thirteen years ago. There should be some preliminary data available by the end of next week.”

ME-2 and ME-3 will be reinstalled into Discovery next Wednesday, following the PRCB-level approval to change the position for two of the engines – mitigating the interference issues that caused the removal of all three engines, due to ME-1 center position.

“A replacement LP LOX turbo pump has been selected for Engine #1. Will start reinstalling engines next Wednesday. For a schedule relief, a CR (Change Request) was put in the system to swap Engines #1 and #2. Swapping these engines will give more time work the pump change out in the Engine Shop,” added P&W – with the official CR instructions listed in the PRCB presentation (L2).

“Re-baseline engine assignments for STS-133 in FDRD (Flight Definition and Requirements Directive),” noted the presentation. “Swap engines between position 1 and position 2. ME-1 (Engine 2048) failed LPOTP torque check after engine installation to engine LPOTP. Plan remove engine, replace LPOTP, and reinstall.

“SSME Position 1 must be removed last and re-installed first. Install Engine 2044 into Position 1 allows additional time for LPOTP replacement.”

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