STS-133: Agency FRR approval for Nov. 1 launch date – SRB review

by Chris Bergin

The Agency Flight Readiness Review (FRR) has concluded by approving November 1 as the launch date for STS-133. The decision came after a smooth review process, aided by the resolution of the OMS (Orbital Maneuvering System) crossfeed flange leak and the clearance of one “action item” from the Space Shuttle Program (SSP) FRR, relating to the Solid Rocket Boosters (SRBs).

STS-133 Processing Latest:

Discovery is now back into a nominal pad flow, thanks to the excellent work by engineers and technicians who successfully worked through the weekend to clear the Interim Problem Report (IPR-47) relating to requirement to changeout two internal seals on the right OMS crossfeed flange plumbing.

*Click here for articles on IPR-47:

The work was conducted ahead of schedule, thanks to the sooner-than-expected eduction of the system after the fuel was offloaded, with acceptable Toxic Vapor Check (TVC) sample readings recorded a full day ahead of schedule. 

With no issues relating to the changeout of the seals, good mass spec leak checks and the timely reloading of fuel into the OMS tanks, the issue was officially cleared as a constraint early on Monday.

“OV-103 / SRB BI-144 / RSRM 112 / ET-137 (Pad-A): S0072 LH/RH OMS/RCS Fuel Offload was completed Friday morning. IPR-47 cross-feed flange leak: Cross-feed flange eduction was completed Saturday morning with acceptable TVC sample readings. Seal R&R was completed Saturday evening along with the cross-feed flange reassembly,” noted the NASA Test Director (NTD) report on Monday (L2).

“TVCs post-S0024 and prior to cross-feed line heater insulation re-installation were acceptable. The 59-64 ‘doghouse’ door is installed for flight. Carrier Panels are in work.  S0024 OMS/RCS (Reaction Control System) Hyper Fuel Load: OMS/RCS fuel load was completed on Sunday.

“Pad A was opened for controlled work at 22:00 EDT Sunday night. Aft Propulsion System (APS) quick disconnects have been removed and the flight caps installed.”

With the issue cleared – along with the successful resolution of a sensor which required a retest – Discovery can look forward to closeouts for flight, along with Monday night’s ordnance installation and connection tasks. Although most – if not all – of the remaining contingency days in the flow have been used up on IPR-47, Discovery is already closing in on S0007 Launch Countdown operations, set to begin on Friday.

“S1005 LOX Dewpoint/Conditioning was completed on Friday. PPO2 sensor cal/retest for IPR-0051 was completed on Friday,” added the NTD report. “S5009 Ordnance Installation/Connection is scheduled for tonight. S1287 orbiter aft closeouts and S0007 launch countdown preps continue.”

STS-133 Agency FRR:

The FRR was completed in just over half a day – shortly than a number of recent FRRs – a sign of a smooth review by the numerous presenting departments and managers.

STS-133 Specific Articles:

“All orgs polled go to proceed toward launch on November 1st. Great job by Royce Renfrew and Bryan Lunney representing MOD’s excellent preparation. ISSP summarized consumables, ECLSS (Environmental Control and Life Support System) status and the status of some 24S (Soyuz) anomalies none of which have a constraint to STS-133/ULF5,” noted a post-FRR overview to managers (L2).

“SSP reviewed previous anomalies, configuration changes, and first flight items. The primary and secondary seals in the leaking crossfeed flange have been replaced. The crossfeed line pressure was increased and toxic vapor check performed with no further leakage detected. Shuttle processing is on schedule.”

Despite a “late breaking Orbiter item – Pyro shock numbers computed incorrectly. They looked at everything in the payload bay and all are okay so no issue,” the Agency FRR confirmed a “Go to proceed toward November 1st launch.”

As always, the Agency FRR is aided by a large amount of work that was conducted at numerous center and departmental FRRs over the past month or two, which led into the SSP FRR earlier this month.

At the SSP FRR, only one “action item” was noted, relating to the two boosters which will aid Discovery’s first stage ascent next Monday. Specifically, the FRR managers reviewed a test failure on a frangible nut – part of the SRB Hold Down Posts (HDPs) which release the vehicle during launch.

“Problem: Lot AAY Frangible Nut S/N 3000444 failed 110 percent web margin test during Destructive Lot Acceptance Testing (DLAT). 110 percent web thickness configuration with single crossover booster assembly. Failed to sever completely into two pieces (minimum) and release from test stud as required,” noted the SRB FRR presentation (all FRR presentations available on L2).

“Discussion: Observations noted after booster cartridge firing. Frangible nut stayed attached to test stud. Preload relieved during firing. Minimal force required to dislodge stud. Visual inspection after nut removal found one outer web intact. No thread anomalies noted during test stud inspection.

“Lot AAY frangible nut data pack review found no anomalies. Fabrication, inspection and testing met requirements. Nut material strongest produced to date.

Although such a failure during a launch would result in a LOV/C (Loss Of Vehicle/Crew) scenario, the action item gained the expected Flight Rationale in time for the Agency FRR at the Kennedy Space Center, given STS-133’s boosters are using nuts from a lot that has already passed its related testing.

“Flight Rationale: Frangible nut installed on STS-133/BI144 from Lot AAW successfully passed Lot Acceptance Testing (LAT) and flown since STS-125/BI137,” added FRR materials. “Failure isolated to Lot AAY. Booster cartridge installed on STS-133/BI144 from Lot AAU successfully passed qualification tests and LAT and flown since STS-126/BI136.”

“The SSP FRR action to review the frangible nut Destructive Lot Acceptance Testing (DLAT) was closed,” added the post-Agency FRR notes. “This nut came from Lot AAY, which is currently slated for STS-335. Lot AAW frangible nuts are installed on STS-133 and STS-134 so this anomaly has no impact to these flights.”

The FRR presentations also covered other items of interest, from the SRB recovery/disassembly operations, which are “ready to support pending completion of open work – includes repair of Hangar AF slip concrete apron,” and the minor In Flight Anomaly (IFA) items from STS-132.

“IFA STS-132-B-001 for the Forward Booster Separation Motor (BSM) exit cone closeout RTV-133 debond and liberation is no constraint to STS-133/ULF5,” noted the post-Agency FRR notes. “The RTV-133 seal is an environmental seal and not for thermal protection. Most likely cause considered water impact or retrieval based on lack of loads or environments to liberate during flight and drogue parachute suspension line entanglement likely contributor.”

The boosters will also be sporting a redesign to the SRB Thrust Vector Control (TVC) Auxiliary Power Unit (APU) fuel pump, which was initially set to debut with STS-134, prior to the manifest alignment which placed Endeavour’s flight behind STS-133.

The redesign, which was covered in depth via Program Requirement Control Board (PRCB) documentation (L2) and the resulting article on this site, will eliminate the highest – although extremely unlikely to occur – ‘critical 1’ failure scenario, which holds the potential of a LOV/C (Loss of Vehicle/Crew) event.

“Background: Current SRB fuel pump carbon seal prevents hydrazine leakage from fuel pump drive shaft to overboard drain line. Loss of carbon seal results in metal-to-metal contact (between rotating drive shaft and seal adapter) leading to fire or explosion, loss of APU with possible loss of mission under worst case conditions (Criticality 1). Represents highest SRB risk per current Shuttle Probability Risk Assessment (PRA),” noted the FRR materials.

“Discussion: Implemented Phase II fuel pump as alternate configuration. Redesigned pump based on Orbiter fuel pump design and eliminates carbon seal Criticality 1 failure scenario. No new failure modes introduced with Phase II fuel pump. Potential to eliminate one accepted risk hazard cause with full implementation.

“Currently no change in cause counts as alternate design. Full implementation planned for STS-134/BI145 and STS-335/BI146. Represents decrease in risk.”

In conclusion, the FRR – as would be expected – certified the use of the new pump, passing on the qualification reports and proven commonality with flown-hardware.

“Basis for Certification: Test, analysis and similarity. SRB APU Phase II Fuel Pump Qualification Report: All functional, vibration, shock, acceptance and five mission duty cycle tests successfully completed.

“Analysis shows affected components meet requirements for margins and safe-life as applicable. Similarity to current SRB and Orbiter fuel pumps used for qualification.”

(All images and graphics via L2).

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