STS-133: Discovery on track for February 24 launch thanks to IPR resolutions

by Chris Bergin

After what was an eventful pad flow for Discovery last week, STS-133 is enjoying a relatively trouble-free final week ahead of S0007 (Launch Countdown) operations. Despite the one day delay to Ariane 5’s successful launch of ATV-2, shuttle managers remain focused on a February 24 launch date, pending Flight Readiness Review (FRR) approval.

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Discovery’s preparations at Pad 39A are now fully focused on the start of S0007 operations – the complex ballet of tasks which will be carried out during the three day countdown. As to when the countdown will begin remains an open question due to the one day delay of ATV-2’s ride on an Ariane 5 ES launch vehicle.

It was understood that one day delays to ATV-2 launch – through to Friday – would be mirrored by one day delays to STS-133’s launch date. However, managers have been evaluating the options, ranging from the ISS’ sleep shifting requirements, communication satellite resources, rendezvous timelines, through to the pad flow schedule – given ATV-2 would be due to dock with the International Space Station (ISS) around the time ET-137 would begin tanking.

The latter would be an item of interest in the event of a problem with ATV-2 docking – especially in relation to what caused the issue, should it potentially impact on Discovery’s arrival at the orbital outpost.

Should managers opt for the 24th as the launch date, only for ATV-2 to suffer a problem during docking that would hold an impact to Discovery’s own docking, a scrub would likely be called, resulting in an additional cryo cycle on the tank. However, a scenario of a such a serious issue during ATV-2 docking is highly unlikely.

The final decision on the launch date will be made at the Kennedy Space Center (KSC) on Friday, when managers meet for the Agency-level Delta Flight Readiness Review (FRR). The Mission Management Team (MMT) will then meet on L-2 and on launch day ahead of tanking.

UPDATE: FRR approves ATV-2 docking on the same day as Discovery’s launch day.

“The team continues to target Thursday, 2/24 for the launch of STS-133,” noted the NASA Test Director (NTD) on Friday morning’s report (L2). “The ISS program is working options to preserve the 24th, and the official launch date will be set at the FRR on Friday.”

Sources note that February 24 is the current launch date they are working towards, pending any change of plan via the FRR.

Following the eventful flow last week – highlighted by several new Interim Problem Reports (IPRs) – engineers have successfully resolved the reported issues and continue to hold contingency time in the flow heading into the launch countdown next week.

“ET LH2 GUCP (Ground Umbilical Carrier Plate) 7” Disconnect Seal Checks were successfully completed,” noted the NTD on two of the more notable IPR resolutions. “SSME (Space Shuttle Main Engine) dome heat shield (DHS) splice lines update: Torque checks on Main Engines 1, 2, and 3 were successfully verified within specification.”

Recent pad flow tasks include checks on the orbiter’s flight computers, PPO2 sensor calibration, LOX/LH2 system dew point testing and S1287 aft closeout operations – including the closure of ET-137’s Intertank, which was finalized by the flight door being installed on the tank.

Only one outstanding IPR made it into this week, relating to a transducer harness on Discovery’s Main Propulsion System (MPS), which required replacing out at the pad.

“IPR 0086, Engine 3 LO2 temperature transducer, update: MPS LO2 transducer repair continues with wire harness splicing complete. The circuit was validated on Friday. Channelization validated using test equipment. Wiggle test and resistance checks are complete with no anomalies noted.”

The update to the work carried out on the harness allowed for the Engineering Review Board (ERB) to close the Problem Report (PR).

“An ERB met and determined that no further work is required on the PR,” added the NTD reports this week. “All suspect harness components have been replaced and satisfactorily tested. The PR will close.”

The MPS transducers on Discovery were also an item of interest for the Delta FRR, albeit unrelated to the recent IPR. Due to the amount of cryo cycles on the MPS – given its use during the tanking process – some of the temperature transducers were beginning to approach their cycle limits.

“A total of five MPS cryogenic temperature transducers located at the LOX/LH2 manifolds and in the LOX feedlines (two of three affected) are approaching limits on cryo cycles,” noted the Delta FRR presentation – available in the collection of 50 STS-133 FRR presentations.

“OV-103 (Discovery) has five transducers with only two remaining cryo cycles. Limit was the result of a cracked LH2 feedline transducer mandrel weld found during the 1990 hydrogen leak investigation. Non-mandatory LH2 feedline temp probes (one per line) located downstream of the prevalve screen were removed and plugged.

“Six total cryogenic transducers remain in the MPS LO2/LH2 systems. Mandatory LO2 feedline probes (one per line) required for engine start box temperature verification (LCC – Launch Commit Criteria – MPS-24 and MPS-25) as well as LOX anti-geyser monitoring.

“Two temp probes located at the LO2 17″ disconnect for LOX antigeyser monitoring during loading. One temp probe located at LH2 17″ disconnect for propellant quality verification (LCC MPS-11). Sufficient spares exist to support replacement of the transducers. After transducer removal, they are X-ray and visually inspected, and if acceptable returned to stock with a reset ‘counter’.”

As per the FRR, KSC Vertical Ops were brought up to date with the requirement to carry out replacement work (ducer R&R, mass spec leak checks, and re-foaming) into the pad flow – which was successfully completed earlier in the flow.

A few minor processing issues were charged against Discovery this week, including the observation of a crack found on a hydraulic line support bracket during aft closeout inspections – requiring Structures and Hydraulics engineering to evaluate potential repair options.

Following meetings it was decided the fabrication of a Z-bracket for installation over the existing damaged bracket – since completed – would be the forward plan.

“Cracked hydraulic hose bracket update: Fabrication of the Z-bracket was completed, and the bracket was installed,” added the NTD. “Based on successful installation, completion of S1287 and closure of the aft for flight is expected Friday night or Saturday morning.”

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After the work was completed on the line, engineers then noticed a scratch on its surface. While the defect remains under investigation, it is understood engineers are likely to clear it via a Material Review (MR) report before the end of the week.

“After removal of insulation on hydraulic line involved in STR-9992 (Crack), a scratch was noticed on the hydraulic line,” listed the NTD report. “Mold impressions have been performed and are under engineering evaluation. Engineering evaluation continues; a decision on whether the condition is acceptable to MR as-is is expected (this week).”

The only other issue listed by the NTD was also resolved within a day, relating to a problem with one of the EVA Mobility Units (EMU) which will be used during STS-133’s spacewalks.

“New IPR 0091 was picked up during V1103 EMU functional checkout: Unable to establish water flow in the Hard Upper Torso (HUT) of EMU 2. Troubleshooting confirmed the problem was internal to the EMU,” noted the NTD report.

A decision was taken to replace the Hard Upper Torso of EMU 2, before testing showed EMU functional checkouts were successfully completed, allowing the airlock to be closed out for flight. The late change will require flight rationale at the FRR.

The FRR – which will obviously tie up the flight rationale for the modifications on ET-137’s stringers – will also cover the ISS’ status, with water management evaluations set to be overviewed due to a repeat of last week’s hiccup with the Water Processing Assembly (WPA) on the Station.

(Further updates and articles will follow. Refer to live coverage threads linked above. L2 members refer to STS-133 live coverage sections for internal coverage, presentations, images and and updates from engineers and managers – which will ramp up into full Flight Day coverage during the mission. Images used, via L2 and acquired PRCB presentations).

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