Endeavour’s heavy STS-126 flight may get heavier – SARJ latest

by Chris Bergin

Shuttle and Station managers are looking into the possibility of adding an extra 1,750 lbs of stowage inside Endeavour’s “Leonardo” Multi-Purpose Logistics Module (MPLM).

November’s STS-126 was already set to be the heaviest logistics flight to the International Space Station (ISS), with Endeavour carrying key equipment for what will be a six man outpost next year – while the mission’s EVAs will involve major repair work to problematic starboard SARJ (Solar Alpha Rotary Joint).

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Heavy Endeavour:

Endeavour’s currently being processed on a timeline that will support rollout to Pad 39B ahead of Atlantis’ launch from Pad 39A. This unique LON (Launch On Need) STS-400 roll will be stood down when Atlantis is cleared for re-entry at the end of her STS-125 mission.

Rolling back off Pad 39B, Endeavour will then roll to Pad 39A to be prepared for her primary STS-126 mission. There she will receive her payload – the MPLM – packed with equipment that even includes a new canteen for the ever-expanding ISS.

‘First flight with all 16 MPLM racks; heaviest MPLM to date,’ noted one of the expansive STS-126 baseline presentations on L2, before listing its contents, making up a staggering 27,585 lbs of payload.

‘Regenerative ECLSS, 6-crew habitability racks/up. two crew quarters (previously three, one moved to STS-128), Treadmill-2 (T2) and T2 Outfitting (now STS-128), Galley h/w (packed in the EXPRESS Rack-6), Water Recovery System (WRS)1, WRS2, WRS 1 and 2 Outfitting, Waste and Hygiene Compartment (WHC),’ listed some of the MPLM’s manifest.

Adding yet more capacity – known as up-mass – to the MPLM, will require a large amount of discussion, with a recent memo outlining both the requirements and the timeline for the potential changes.

‘ISSP (International Space Station Program) trying to put as much up-mass as they can in pressurized volumes,’ noted the information, before noting Endeavour herself has the performance ability to carry an increased load. ‘SSP (Space Shuttle Program) has a healthy APM on STS-126 flight.’

APM (Ascent Performance Margin) is the amount of reserve propellant the External Tank (ET) carries. The amount of APM that the ET carries was recently given a large amount of attention ahead of STS-122, so as to mitigate any potential engine shutdown issues with then-problematic ECO (Engine Cut Off) sensors during ascent.

The additional 1,750 lbs of payload would be ‘squeezed’ in to the MPLM end cone – which would be a first, and thus required a level of assessment. Results are expected next month, which will allow for a decision in September.

‘SSP is concerned it will affect the verification loads assessment (VLA). SSP met with ISSP – and Alenia (who designed the MPLMs) has determined a way to accelerate their model delivery to August, which is a month’s acceleration,’ added the information.

‘Boeing also determined how to surge to do SSP’s part of loads analysis. So, have path on how to do this and can do it in a way where have a decision point around end of September, so can back out of mod if need to.

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‘Working with them on plan. Have to integrate this with SE&I (NASA Systems Engineering and Integration) and Orbiter and ensure not impacting their mission analysis.

‘First decision date will be around end of August when receive sensitivity study from Alenia; Structures Working Group has chance to determine if mod to MPLM end cone would influence existing models much. It would add hopefully about 1,750 lbs of stowage to MPLM.’

No specific reason was mentioned as to why the extra up-mass is desired. However, it is likely to be related to the major work that will be carried out during the mission on the problematic starboard SARJ. Either way, STS-126’s mission will be heavily involved with fixing the joint.

SARJ Latest:

Plans are still being worked on repairing the SARJ, based on information gained over recent flights – since the problem was first observed ahead of STS-120.

While the joint’s Trundle Bearings Assemblies (TBAs) will be replaced during STS-126’s four scheduled EVAs, shuttle managers have also started to talk about the possibility of replacing the race ring – which would be a major undertaking.

The motor-driven race, which rotates outboard solar arrays to track the sun, is held in place by 12 TBAs that grip the race ring on three faces. One of those surfaces – the outer canted surface – has broken down in a condition, termed as ‘spalling’, generating large amounts of metal shavings and debris.

The serious condition of the race was confirmed by Mike Fossum during his EVA to inspect the SARJ, as he observed a depression, or pit – and not a build-up of debris as some had hoped.

A build-up of debris could, in theory, be removed. However, a pit indicates a defect in the surface, possibly a starting point for the same type of spalling that generated the debris on the other face.

‘Considering replacing race ring, but must disconnect S3 from S4 in order to accomplish this,’ noted one recent memo. ‘Starting to talk about techniques for doing race replacement.’

That may become the back-up plan, pending the results of STS-126’s EVAs, with the cleaning of the joint’s surfaces, ahead of the replacement of the TBAs, taking center stage.

‘During ULF2/STS-126, the current plan is to clean up the Stbd SARJ surface as much as we can, and then replace all of the TBA’s so we can return the original TBA’s on the Shuttle and perform in depth inspections and analysis on the ground.’

Thankfully, the port SARJ appears to be unaffected. However, following EVA observations, a further mitigation against damage may call for the lubrication of the port SARJ surface, utilizing the grease gun which was outlined in STS-124 Flight Readiness Review (FRR) documentation.

‘The crew inspected the Port SARJ for any signs of wear. Overall, the Port SARJ was in much better shape then the STBD side. The crew did observe some grease deposits one of the bearing roller surfaces which was not expected. Likely this grease came from one or more of the TBA bearings.

‘Based upon test and analysis of the Stbd SARJ problem, the team believes that this grease is actually helping to ensure that the Port SARJ is rolling on a low friction surface which will likely reduce the likelihood of damage.

‘There was some indication of some very slight indications of wear on another of the three bearing roller surfaces. Because of this, the Program is considering whether it would be prudent to consider lubricating the rest of the Port SARJ surface.’

Launch Date Latest:

STS-126’s actual launch date remains fluid, with the latest CR (Change Request) noting that the originally hoped advancement of the NET (No Earlier Than) target – based on moving STS-125 up a few days to lengthen STS-126’s restricted launch window – is now constrained to just three days.

While the shipping of Endeavour’s tank (ET-129) remains very tight on the timeline to advance the launch dates, the new CR-based NET dates of October 5 for STS-125 and November 7 for STS-126 was driven by Atlantis’ Hubble Space Telescope servicing payload elements.

‘Reason for change: Increase launch opportunities for STS-126 before the Launch Beta angle cut-out in November/December,’ noted the associated presentation on L2. ‘The 10/05 date allows adequate time for HST payload processing prior to installation.’

The final decision is still scheduled to take place in just over two weeks time at the Program Requirements Control Board (PRCB) meeting. At present, STS-125 remains officially scheduled for October 8.

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