STS-129: Atlantis arrives in VAB for mating – SSME mystery

by Chris Bergin

Atlantis is preparing to mate with her External Tank (ET-133) and twin Solid Rocket Boosters (SRBs), following rollover to the Vehicle Assembly Building (VAB) on Tuesday morning. Meanwhile, engineers are finaling plans to protect the Space Shuttle Main Engine (SSME) nozzles at the pad, following leaks on the last two missions, and an observation of a mystery organic rubber material on Discovery’s Engine 3.

STS-129 Latest:

Atlantis’ roll to the VAB came after one late engineering item of interest was noted, relating to the changeout of the onboard Waste Collection System (WCS).

All associated mechanical work was completed in the Orbiter Processing Facility (OPF), while retests will take place at Pad 39A – when Atlantis as the STS-129 stack rolls out of the VAB in a week’s time.

“WCS R&R work is complete, and retest will be done vertically at the pad,” noted Tuesday processing information on L2.

Atlantis took less than an hour to be rolled into the VAB on top of the Orbiter Transporter System (OTS). Engineers will begin mating the orbiter to the stack on Wednesday morning.

“S0004 Orbiter/ET mate CTS (Call To Stations) is scheduled for 0600L this morning. Sling attachment is scheduled for after lunch. Orbiter rotate to vertical and lift over transom is scheduled for 2nd shift. Orbiter/ET hard mate is scheduled to be completed tomorrow (Wednesday) morning.”

“ET/SRB Aft Fairing installation is complete. Foam closeouts to be performed after S0004. Forward & Aft Skirt Firing Line Checks will be performed after S0004.”

Out at the Pad, truckloads of LOX and LH2 are arriving at the giant spheres that store the propellant ahead of launch day’s tanking into the ET.

“Pad A: 4 waves of LOX tankers were offloaded yesterday. 2 waves of LH2 tankers are scheduled for today,” added Tuesday processing information. “N2O4 tanker offload (in SCAPE) is scheduled today at Ox Farm.”

Work is also picking up behind the scenes, as managers prepare to head into STS-129’s Flight Readiness Review (FRR) season. The STS-129 L-30 (Days) Bench Review is scheduled for Thursday, while the opening bulk of mission documentation will be presented at the MOD FRR – due on October 15.

This will be followed by the Space Shuttle Program (SSP) and Agency level FRRs, which will discuss not only the mission in hand, but also items of interest from recent missions. One such item up for discussion will be the recent leaks observed on the SSME nozzles.

As previously reported by this site, engineers have found the application of an adhesive tape – used to seal the throat plugs on the SSMEs since the 1990s – was the initial root cause of 340 leaks on Endeavour’s number one engine (STS-127), and likely with the leaks seen on Discovery’s Engine 3 (STS-128).

A2Sulfur in the tape has been found to interact with the nozzle’s nickel finish under the extreme temperatures endured during their ascent role, causing embrittlement and then tiny cracks and corrosion of the A286 iron which the SSME nozzle tubes are made from.

However, additional protection out at the Pad may be able to mitigate against these symptoms.

“SSME (Pratt & Whitney Rocketdyne/KSC): On OV-104 (Atlantis), there was a meeting Friday to discuss potential options on how to protect the nozzles from environment out at the launch pad – it looks like will have an opportunity to try three different methods to keep an inert atmosphere in the nozzles,” noted the latest Shuttle Standup/Integration report on L2.

“One is to redirect the current trickle purge that runs through the engine. The second is the use ECS (Environmental Control System) air, and the third is the use a 743 panel (a direct to nitrogen purge). Will work details of that test activity this week and execute it Friday. Whichever one meets our criteria would then be available for us to use once we get out to the pad.”

With Endeavour’s Engine 1 nozzle now undergoing repairs in California, engineers at the Kennedy Space Center (KSC) have switched their attention to Engine 3 that has now been removed from the aft of Discovery.

Once in the engine shop, the nozzle will be mapped for the exact number of leaks, currently estimated to be around 200.

“Of interest to SSME/PWR (Pratt & Whitney Rocketdyne) will be to get Engine #3 to the Engine Shop to do a detailed mapping of the nozzle tube leaks to compare to those of STS-127,” notes the Standup report, adding one area of interest will require further evaluations, as engineers aren’t sure what they are looking at.

“One interesting note was when the orbiter (OV-103) got back to KSC from Dryden, Logistics was able to thoroughly inspect the exterior surfaces of the nozzle. On Engine #3 hatband styben #6, which is halfway up the nozzle at the 8:00 position (when standing on runway looking at it), there was a black material adhered to those two hatbands.

“Initially it was thought to be some SRB residual. Took a sample of that material to the KSC lab, and it appears to be some kind of organic rubber compound with a neutral pH. It looks like it was heated.

“If anyone has any ideas of where the rubber came from, SSME/PWR would appreciate being contacted. Will get the official KSC material report out.”

L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

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