STS-135: Final shuttle mission preparing for SRB stacking – Mission tweaking

by Chris Bergin

Preparations for Atlantis’ honor of rounding off the 30 year long Space Shuttle program are proceeding to plan, with processing about to enter the latest milestone of Solid Rocket Booster (SRB) stacking inside the Vehicle Assembly Building (VAB). Minor alterations to the mission content – as is normal for this stage in the planning – are also taking place at the Program level.

STS-135 Processing Latest:

Atlantis is currently in the final stages of her final Orbiter Processing Facility (OPF) flow for flight, with preparations taking place for rollover. This includes closeouts and pre-mate testing for Atlantis’ Multi-Purpose Logistics Module (MPLM) payload.

“OV-104 (STS-135): In OPF Bay 1, completed payload pre-mate testing this week. Next week will be performing payload IVTs (Interface Verification Tests). Continuing to work aft closeouts,” noted Ground Operations on the latest Shuttle Standup/Integration report (L2).

No firm date for rollover has been set, although Atlantis’ trip the VAB is expected to take place in the first half of May.

“OV-104 (OPF Bay 1): Closeouts and disconnects of various systems continue as the orbiter is configured for rollover. Potable water servicing is complete less sample results. Aerosurface positioning for rollover completed. Payload electrical Assembly Power Converter Unit (APCU) IVT completed,” added the NASA Test Director (NTD) processing update (L2).

“Aft hydraulic leak checks are planned in work. TRIDAR (relative navigation vision system) payload mates will be performed. Weekend work: None.”

The Orbiter Project Office (OPO) also noted that Atlantis will fly with Discovery’s three Flow Control Valves (FCVs) used for STS-133, providing the poppets pass post flight inspections at the vendor (Vacco) in California.

The valves – and specifically the poppets – have not suffered from any major issues since a crack was observed on one of STS-126’s poppets – leading to a large Program Requirements Control Board (PRCB) and Flight Readiness Review (FRR) mitigation plan.

“On OV-104 (Atlantis)/STS-135, Vacco has removed the poppets from the three FCVs that were flown on OV-103 (Discovery)/STS-133,” noted the OPO on the latest Standup report. “These are at Huntington Beach, and inspections will pick up.”

FCV Specific Articles (Extensive):

Most of the hardware processing is taking place in the VAB, with the Mobile Launch Platform (MLP) inside High Bay 1 (HB-1) for the start of SRB stacking, which is scheduled to begin on Tuesday, March 29.

Currently, the Left and Right Aft Boosters have been lifted from the build-up stands in the Rotation Processing and Surge Facility (RPSF) to pallets in preparation for transfer to the VAB for stacking. The D Platform has been extended to support SRB stacking optics, with the operation scheduled to begin with the Left Aft Booster buildup.

Over in High Bay 2E (HB-2E) checkout cell, ET-138 is continuing to undergo radius block modifications to its LO2 flange intertank stringers, a mitigation procedure used to avoid cracks forming in the stringers during the cryo cycle of tanking, pressurization and ascent environments.

This modification successfully debuted with ET-137 on STS-133, after that tank suffered from cracks during the scrubbed launch attempt back in November.

“On ET-138 in the Checkout Cell, the ET stringer modification is in work with Lockheed-Martin,” added KSC Ground Operations. “All the structural work is being completed, and it is into the foam closeouts.”

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At present, engineers have successfully installed all of the radius blocks around the circumference of the intertank, with Thermal Protection System (TPS) foam spraying and trimming currently in work. This is expected to be completed sometime next week.

“ET (LMSS/MAF): ET-138 mods are going well. All the mechanicals, radius block installations are complete all the way around. All the foam is in on the +Z side, and is in trims right now. Right now, the -Z side is in work. They will transition over to the other two panels and work into spray.”

“SRB BI-146/RSRM 114 (RPSF)/ET-138 (VAB HB-2E)/MLP-3 (VAB HB-1): TPS ET-138 Stringer Mod: Foam trims continue on panels 1-3,” added the associated NTD status. “Foam application on panel 6 was completed. Final foam application on panel 7 in work.”

ET-138 will undergo a Tanking Test shortly after arrival at launch pad 39A, although it is unlikely the stack will then be rolled back to the VAB for Non Destructive Evaluations (NDE) of stringers unless driven by data from the test itself.

“ET-138 for STS-135 will probably have a tanking test following the radius block modifications; decision needs to be made whether to roll back following a tanking test to perform full NDE testing or accept the limited NDE that can be done at the pad,” noted a managerial memo (L2) last week, prior to Space Shuttle Program (SSP) manager John Shannon noting a rollback is not being planned, unless they saw something unexpected via the test.
While processing on the hardware continues, program managers are continuing to refine the mission’s finer details, with the Flight Operations Review (FOR) team evaluating the mission timeline and some of the smaller payloads set to fly with Atlantis.

“The FOR for STS-135 is going on this week. One of the big topics is getting the timeline back in the box; transfer is still broken a little,” noted United Space Alliance (USA) Logistics on the Standup report. “Station is worried about some of the commercial flights not getting there as soon as they thought they would, and not getting delta V. They want to go up to 215 nm, currently at 205 nm.

“Looking at pulling the TSA (Tool Storage Assembly) off and pull all the UFK (Unique flight Kit) out of the TSA and round trip it in the MPLM. They are also looking at multi-stage deorbit. Also considering a 3-minute window.”

STS-135 Specific Articles: 

It is also understood that some unique views of the International Space Station (ISS) will be observed during Atlantis’ undocking from the orbital outpost, given the Station will be in a different attitude than normal during the flyaround.

The ISS’ attitude will be under a yaw of 90 degrees, placing the Y-axis in the Velocity Vector (+/-YVV). As a result, this will provide some unique side-on views of ISS during Atlantis’ post-undocking manuever.

(Numerous articles will follow. L2 members refer to STS-135 coverage sections for internal coverage, presentations, images and and updates from engineers and managers. Images used: All via L2).

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