NASA updates requirements for STS-129 mission – window still under evaluation

by Chris Gebhardt

With Atlantis deep in processing for STS-129 – and damage evaluations continuing on window 5’s pressure pane – engineers in OPF-1 (Orbiter Processing Facility 1) continue to prepare Atlantis for her scheduled November 12, 2009 launch to deliver the Express Logistic Carriers 1 and 2 (ELC-1 and ELC-2) to the International Space Station.

Vehicle Hardware and Flow Updates:

According to the Delta Launch Site Flow Review (DLSFR), which was held at the end of June for STS-129, Atlantis remains on track to meet all of her processing goals.

The main constraint relates to the health of Atlantis’ Window 5 (pilot window) pressure pane, with evaluations still ongoing into potentially unacceptable damage – following the removal of a work light knob that embedded itself between the window and the dashboard in the flight deck.

A second set of mold impressions on Atlantis’ Window 5 have been ordered for Monday, which are currently “in cure” – per morning processing information on L2.

Evaluations may not be complete until later in the week, with the hope any damage is within acceptable levels for flight. Otherwise the pressure pane may require replacement, resulting in up to a six month schedule impact for Atlantis.

Currently, Atlantis is scheduled to use External Tank 133, Left OMS Pod 04, Right OMS Pod 01, Reusable Solid Rocket Motor set 108, as well as Space Shuttle Main Engines 2048, 2044, and 2058 in the number one, two, and three positions, respectively.

Engines 2048 and 2058 last flew on Discovery during STS-119 while engine 2044 few with Atlantis in May during STS-125.

Currently, Atlantis is tracking toward a rollover to VAB on October 7 for mating to her External Tank. This will be followed by rollout to Pad-A on October 14 ahead of a launch No Earlier Than November 12th at approximately 4:30pm EST.

at2This mission will mark the first time in nearly two years that Atlantis will visit the International Space Station (ISS), carrying vital upmass to the Station ahead of the retirement of the fleet. 

The last time Atlantis was docked to the Station was during STS-122 (which delivered the Columbus research module for the European Space Agency) in February 2008.

Furthermore, as part of the ever evolving nature of every Shuttle mission, Atlantis’ total launch weight has changed slightly since the Launch Site Flow Review held in April of this year.

As a result of the changing nature of Atlantis’ payload, the vehicle and mission are now expected to have an Ascent Performance Marin of ~625 lbs at launch.

Changes to Atlantis and Flow Processing Turnaround:

Furthermore, since Atlantis’ return to KSC following a landing at Edwards Air Force Base, CA on STS-125, engineers and mission planners have conducted a thorough review of Atlantis and all the work items that were baselined/scheduled for the OPF flow leading to STS-129.

As a result, the DLSFR noted several additional modifications that will be made to Atlantis as well as modifications and deferrals of some work items until the Orbiter’s next OPF flow later this year.

at3The first such modification listed in the DLSFR is the partial deferral of the Air Duct Clamp and Cushion inspection and modification.

“Program approval is requested to partially defer baselined modification record until access is available for implementation,” notes the 122 page STS-129 DLSFR document available for download on L2.

The three issues leading to this modification were the observance of a missing clamp form a flex duct, “two cushions installed but not shown on the drawing, and two cushions installed per drawing, but installation documentation not located.”

The first two issues were noted during return to flight processing on Atlantis for STS-115. However, after evaluations showed that the discrepancies would not affect flight performance, a form was written to “correct the engineering discrepancies” and defer work on the area to the next available period of access.

Originally, this access would have come during Atlantis’ flow between STS-125 and STS-129. However, the OPF flow for STS-129 was shortened considerably when STS-125 was delayed from October 2008 to May 2009.

The extra time in the OPF before STS-125 in May 2009 allowed engineers to perform several get ahead tasks on Atlantis – thereby shortening the amount of time she would have to spend in the OPF before STS-129.

Currently, the access engineers do have to the area is not enough to verify the part numbers of the cushions that are installed. As a result, flight rationale is being worked on at this time to, once again, defer work on these discrepancies.

The second item noted by the DLSFR is for two technical order changes: one to a GN2 (gaseous nitrogen) Purge Line Installation and the second to a Mission Kit associated with the SSPTS (Station to Shuttle Power Transfer System).

For the GN2 Purge Line, the presentation notes that the line was “required for STS-125 HST mission to provide GN2 purge line to the Super Lightweight Interchangeable Carrier (SLIC) and the Orbital Replacement Unit Carrier (ORUC).”

The tech order change notes that the purge line will remain installed on Atlantis because it is located below the payload bay liner and will not interfere with vehicle or payload operations during STS-129.

Secondly, a tech order change was also initiated to remove a mission kit and its associated hardware from Atlantis.

The mission kit was originally designed to support the installation of SSPTS onto Atlantis. However, since Atlantis will no longer be receiving a SSPTS, the mission kit is not applicable anymore.

at4The next major modification for Atlantis is the development of a new Tyvek Rain Cover for FRCS (Forward Reaction Control System) thruster positions F3D and F4D.

This redesign is expected to “prevent tearing/partial cover release” during the initial seconds of liftoff.

The partial release of several FRCS thruster covers has occurred on a handful of Shuttle missions.

“During STS-119, the remnant (FRCS thruster cover) was estimated from imagery to be 6-10 grams which was larger than remnants from previous flights,” notes the DLSFR.

The new design, dubbed a Rain Cover Plug (RCP), will be smaller and installed deeper in the thruster.

Final approval for this new thruster cover is still pending. However, the review document notes that the final presentation on risk mitigation via the new design was to be presented to the Orbiter Project Office around June 26th.

In addition to these modifications, several other enhancements are being made to Atlantis this flow.

As previously reported by this site, these modifications include: Middeck ISS Payload Cooling Requirements, Rudder Speed Brake Inconel Thermal Barrier Redesign, Oxygen Crossover Valve Signal Talkback Modification, Relocation of D-Hatch Actuator Handle Position Decal, External Airlock Ducting Configuration Change, OMS Pod Micro-WIS Strain Recorder Removal, and Acreage Doublers Addition to Avionics Bays 4, 5 and 6.

Additional Work:

In addition to modifying Atlantis, engineers are also conducting a series of Wing Leading Edge (WLE) spar inspections.

at5Structural inspections of the Wing Leading Edge spars are due prior to the last manifested flight of OV-104 (due date January 22, 2010 with final flight currently manifested for May 2010).

However, the performance of these inspections (a total of 22 WLE panels per wing on Atlantis) is a very intrusive process and a “significant flow impact” that is necessary to maintaining the safety of the Orbiter fleet.

In order to accommodate both the spar inspections and the desire to fly Atlantis past January 22, 2010, engineers have developed a series of mini spar inspections that can be performed within the standard OPF flows.

In fact, during Atlantis’ second stay in the OPF before STS-125, engineers began these spar inspections – leaving only 16 panels on each wing remaining.

However, the Program Design/Director’s Review Resources Team has determined that, for safety matters, all of Atlantis’ spars have to be inspected by January 22, 2010.

Currently, the plan is to inspect the spars of four panels per wing – down from the originally planned six panels per wing – during this current flow.

Following the results of the spar inspections from this flow and the flow prior to STS-125 in May 2009, the Orbiter Project Office will determine if “an exception to the requirement to complete the spar inspection before January 22, 2010 can be created without compromising vehicle and crew safety.”

The presentation did not mention whether this exception would include the option of not inspecting some of the spars or simply allowing the final spar inspections to take place in February and/or March 2010.

Furthermore, engineers and program officials are also waiting on post-flight measurements of “prevailing torque on Endeavour’s multi-flight windows” before clearing a potential issue with Atlantis’ multi-flight windows.

Windows one and six on Endeavour were torqued at Pad-B (during STS-400 processing) before their first flight, notes the DLSFR document.

An adverse finding on post-flight measurements could raise concern for Atlantis# multi-flight windows modification locations and could lead to a request to retorque the windows.

Based on a mid-July launch date of Endeavour on STS-127, post-flight measurements would be expected sometime in the August timeframe – well within the “need date” for STS-129.

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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