STS-131: Discovery in final preps for countdown – T-RAD debated

by Chris Bergin

Discovery is enjoying a nominal pad flow towards the start of the STS-131 countdown on Friday morning. Composite Overwrap Pressure Vessels (COPV) pressurization is currently being finalized, ahead of the closure of the orbiter’s Payload Bay Doors (PLBDs) for flight. The only discussion that has taken place at the Program level this week related to an issue with the T-RAD tile repair dispenser.

STS-131 Processing Latest:

With processing on track, only one “non standard” item of work has been conducted on Discovery at Pad 39A, as two cracked tiles – which were observed after window insert inspections last week – underwent repair.

“Got the aft of the orbiter closed out. The SRB aft skirts are closed out for flight. Getting ready to close PLBDs this week on Thursday. The crew has to do a walkdown and then the doors will be closed,” noted KSC Integration (L2).

“One piece of non-standard work being done is Window 6, the carrier panel. Did complete the repairs on the two tile damages. Installed the carrier panel, and the plugs. The rest of the week, will be picking up with COPV pressurization (through to) third shift Wednesday. Will pick up with the count Friday morning at 2:30 a.m. ET.”

All appears well with the Right Reaction Control System (RRCS) during the pressurization of the system, which is providing another test on the condition of the two downstream regulators – following the problem with the helium isolation valve, which has failed open.

“OV-103 / ET-135 / SRB BI-142 / RSRM 110 (Pad A): IPR 0033: The right Reaction Control System (RCS) fuel helium tank was vented down and the manual isolation valve was opened to put the vehicle back in a normal configuration. Quick Disconnect flight cap installation and leak checks have been completed,” added the latest NASA Test Director (NTD) report on the status of the STS-131 flow (L2).

“OMS/RCS/MPS (Main Propulsion System) helium system pressurization for flight was delayed 12 hours to allow for left RCS oxidizer temperature to increase to nominal temperature with the aid of a heated purge. Pressurization started at 0240 EDT Wednesday morning.”

Following the flood damage to the Launch Control Center (LCC) ahead of STS-130, another water leak was reported by the NTD. However, the latest leak is being classed as minor, and no LCC operations or hardware have been affected.

“Launch Control Center: Tuesday night a water leak was reported on the 4th floor of the Launch Control Center (LCC). Personnel reported on station and isolated the leak to the steam humidifier that increases the humidity in the LCC Control Rooms on the 3rd floor.

“The humidifier manual valves were closed to secure the water leak. No water leaked into critical equipment areas or into the Control Rooms. There was no impact to operations in the LCC.”

STS-131 Specific Articles:

Orbiter Repair Equipment – T-RAD:

With the STS-131 Prebrief/STS-130 MMT (Mission Management Team) Debrief the latest meeting to be completed, only one item of interest – other than final closure evaluations of Flight Readiness Review (FRR) materials – was debated.

This related to the Tile Repair Ablator Dispenser (T-RAD), an item of EVA hardware with origins in the smaller STA-5 applicator, which was part of a scrapped CIPAA (cure in place ablator applicator) back pack system.

T-RAD – as the name suggests – rides uphill with the orbiters in case an on orbit repair is required on the Thermal Protection System (TPS). It was successfully demonstrated during STS-123’s EVA-4.

The problem discussed this week pointed to an issue with the one of the dispenser’s relief valves.

“There was a question regarding flying a second set of repair hardware, so a second TRAD dispenser was being processed to ship to KSC. One of the relief valves opened at a lower pressure than it should have,” noted the Orbiter Project Office on the latest Shuttle Standup/Integration report (L2). “The replacement relief valve opened up at an even lower pressure.

“A little troubleshooting indicates that the jam nut that is supposed to keep the adjustment nut in place is not adequately functioning. Ascent vibe testing was performed over the weekend, which indicates that ascent environment itself will not cause the setting to change.

“The plan is to test the unit at KSC this week to make sure that the relief valve opens at the correct pressure. If necessary, a second Class I unit is being prepared to ship to KSC. The team is also looking at modifications to the relief valve, which might be implementable before launch, and hopefully would eliminate this problem.”

While a second unit available, it currently appears the original dispenser will be in a good condition to fly.

“The TRAD unit at KSC passed all the functional testing, so there is high confidence in that unit. However, with this particular internal failure, it cannot be said that it could not happen. The vibe testing done this weekend gives us confidence that the unit at KSC is okay,” added the EVA office on the Standup report.

“In the meantime, there is another unit up. Leak testing is done. Have vibe tested the relief valve, and got it ready to ship out. In addition, have some relief valves that have put staking on, that they will be vibe testing. It could be possible to change out the relief valve at the Cape. Will see how testing goes to see if that is something we would want to do.”

The ability for the EVA and Orbiter departments to spend time on this minor issue also shows the large scale debates about the RRCS and Ceramic Inserts at last week’s Agency FRR have been managed extremely well, allowing for the full concentration of engineers to focus towards the start of the countdown.

Deserved praise for the team’s work on the FRR items was noted by SSP (Space Shuttle Program) manager John Shannon on the Standup report.

“Mr. Shannon congratulated everyone on the great job at FRR last Friday. The team was extremely well prepared to talk about all the issues since the SSP FRR. It is flight week at the end of this week. Most of the people that are going to KSC will fly out on Friday; therefore, we do not have any plans to change any normal Program meetings during the week. Have a great week.”

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