STS-133: Crossfeed flange seal R&R complete – OMS reload in work

by Chris Bergin

Engineers have completed the removal and replacement of the two seals on Discovery’s Right OMS (Orbital Maneuvering System) crossfeed flange on Saturday, after the eduction of the plumbing beat the schedule by over a day. Fuel reloading began at 6:30am local on Sunday, with Interim Problem Report (IPR-47) set to be removed in time to allow managers to press forward with the confirmation of a November 1 launch date target.

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A level of nominal pad flow processing has continued during the IPR-47 troubleshooting, mainly relating to closeouts and work associated with a number of minor problems which have since been resolved – bar a sensor which requires confirmation of a successful retest.

“S1287 orbiter aft closeouts and S0007 launch countdown preps continue,” noted the NASA Test Director (NTD) processing reports (L2). “Pad A GO2 recharge was completed. S1005 LOX Dewpoint/Conditioning performed Friday. PPO2 sensor cal/retest for IPR-0051 (pending).” 

All remaining processing updates have been focused around the changeout of two internal seals on the flange area of the crossfeed line which was originally leaking fuel vapor – prior to a change of pressure in the system, which ‘surprisingly’ causing the primary seal to reseat into position.

For added confidence, given the condition of the secondary seal is unknown, managers decided to changeout both seals, which required the OMS tanks on both sides of the vehicle to be drained of their fuel.

“S0072/IPR-0047 LH/RH (Left Hand/Right Hand) OMS Fuel Offload: QDs (Quick Disconnects) connections for the cross-feed eduction were completed Wednesday evening. Vehicle power-up and call to stations for fuel offload operations was completed at 1620L (Wednesday),” added the NTD.

“Fuel offload in SCAPE (Self-Contained Atmospheric Protection Ensemble (suits used while performing task such as hydrazine loading)) began at 2125L (Thursday), and completed at 0530L (Friday). QD Interface leak checks and demate of the four crossfeed QDs is complete. Securing from hazardous fuel operations is in work. Fuel in the scrubber liquid separator and required to perform a drain prior to opening the pad for controlled work.”

With the tanks drained, the time-consuming “eduction” of the line began – a vacuum-related procedure, used to completely clear the plumbing of the harmful monomethyl hydrazine (MMH) fuel.

“Crossfeed flange eduction begin Friday morning. Seal R&R will be performed following acceptable TVCs (Toxic Vapor Concentrations),” added the NTD. “The first check of the TVC readings will take place at 08:40 local on Saturday, as crews look for values of 250 ppm or less to allow the seal R&R work to begin.

With further readings to be taken after 24 and 48 hours – if necessary – the current plan points to a schedule to proceed with the flange seal R&R task on Sunday, 23:00 local, which would allow for fuel servicing on Monday at 03:00 local. Should all go to plan, the pad will be opened on Tuesday at 11:00 local – allowing for ordnance installation to begin via a nominal pad flow.

However, this timeline is subject to the amount of time it will take to complete the seal R&R, complete Mass Spec leak checks on the seals in the flange, demate the MD 679 QD (Hardline), and temp reinstall the 59-64 access door(doghouse) – all of which need to be completed prior to the re-loading of the OMS tanks.

“Currently, all remaining work in the success-oriented plan forward fits into the remaining calendar days to support the launch attempt on November 1,” added the NTD, although a delay of around 24 hours would place pressure on that opening launch date target, due to the expected lack of contingency days remaining in the flow once the seal R&R operations have been completed.

“Working the IPR 47 on the leak for the RH OMS Pod flange. During the week, the decision was made to R&R the seals. The target is to have the preps wrapped up and get into the draining of the fuel by the second shift tonight,” pre-empted Ground Operations (L2) on Thursday – showing all targets are currently being met as of Friday.

*Click here for articles on IPR-47:

“Once that is complete, they will pick up with the eductions – currently the plan is for a 48-hour duction period. Once they get down to the proper level of fuel, the seals will be R&R’d sometime Saturday night/Sunday morning (now Sunday night). Once that is complete, they will get into refill.

“They hope to have it wrapped up by Sunday night/Monday morning. Once refill is complete, normal prep for launch will pick back up. Right now ordnance installation is scheduled for late Monday/early Tuesday. Still on track for launch November 1.”

UPDATE 1: TVC sample at 12:30 local on Saturday showed 140ppm value – an acceptable level to begin work on the seal R&R, way ahead of schedule on Satuday.

UPDATE 2: Seal R&R operation in SCAPE complete – a day ahead of schedule. Preparing for the critical leak checks on the system with the new seals in place.

UPDATE 3: Mass Spec leak checks all good. S0024 fuel load picked up at 6:30am local on Sunday morning. NTD should withdraw IPR-47 on Monday morning.

UPDATE 4: IPR-47 closed.

All related departments are either providing support for the activities, and/or preparing to bring the vehicle back into a good configuration for continued pad flow operations, once the flange seal work is completed.

“SSME (Pratt & Whitney Rocketdyne/KSC) Working the OMS leak out at the Pad. Doing aft closeouts, working around the clears out there,” noted one example on the latest Shuttle Standup/Integration report (L2). “Once they can get back in Monday they will be able to do their final aft closeout activities and support door installation the end of next week.”

Meanwhile, the STS-133 crew are scheduled to begin their quarantine period on Monday, at the same time managers prepare for the final Flight Readiness Review (FRR) – the Agency FRR – at the Kennedy Space Center (KSC).

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With only a few minor notes of interest – relating to a review of the contents of “a bag and a couple of lockers” – noted at the L-10 day Bench Review, and the “go” polling by the Center FRR during the week, only the crossfeed flange seal R&R is threatening a decision against a green light for the November 1 launch date.

“The JSC Center Director Pre-FRR was conducted on 10/19 and again all orgs polled Go to proceed,” noted an associated memo with the decision. “Primary topics of interest included the SSRMS (Space Station Remote Manipulator System) Latching End Effector (LEE) anomalous signature and the OMS fuel crossfeed flange leak.

“The SSRMS anomalous signature was a caution annunciated during diagnostic tests of the LEE that implied the snare brakes slipped. After further review of the data and discussion among the community, it has been determined that the snare brakes did not slip and the caution was a result of motor movement that occurred when the brakes were released. There is no concern with the ability to support STS-133/ULF5.”

*Please refer to the live update thread for STS-133’s pad flow (linked near the top of the article), L2’s STS-133 Special Section for live engineering updates (already extensive), and this article for summary updates during the weekend.

(Lead Photograph: Larry Sullivan, and MaxQ Entertainment. Graphics and other photos via L2 and

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