Endeavour readied for Friday undocking – Thanksgiving on ISS for STS-126

by Chris Bergin
With Flight Day 14 marking the STS-126 crew’s final day onboard the International Space Station (ISS), the performance of Endeavour during her docked mission has been almost issue-free mission, which has allowed the Mission Management Team (MMT) to focus their attentions on other elements of the mission.

Endeavour is being put through the final requirements ahead of undocking, receiving the “Leonardo” Multi-Purpose Logistics Module (MPLM) back into her payload bay, which followed a water dump and a Fuel Cell purge.

“The Orbiter took control of the mated stack at 330/16:11:02 Greenwich Mean Time (GMT) [10/15:15:23 Mission Elapsed Time (MET)] and the 17 degree maneuver to water dump attitude began at 330/16:11:31 GMT (10/15:15:52 MET),” noted MMT status on L2.

“The 17 degree maneuver back to the Torque Equilibrium Attitude (TEA) began at 330/17:04:30 GMT (10/16:08:51 MET) and the ISS assumed control of the mated stack at 330/18:16:00 GMT (10/17:20:21 MET). The Orbiter was in attitude control for approximately 2 hours, 15 minutes.

“The third on-orbit fuel cell purge began at 330/02:06 GMT (10/01:10 MET). During the 120-hour purge interval the approximate voltage decay was 0.13 Vdc for fuel cell 1, 0.12 Vdc for fuel cell 2, and 0.12 Vdc for fuel cell 3.”

Endeavour was also involved in a DTO (Detailed Test Objective) on orbit, relating to a heater modification on the Main Landing Gear (MLG). The results have proven to be positive.

“Results from the MLG tire thermal conditioning test using the MLG brake line heaters B and C were presented to the Mission Management team,” noted the MMT status. “Based upon existing data, the conclusion is that tire temperature response to the operation of the heaters is significant enough to recommend use on upcoming flights when needed.”

A total of 18 MER (Mission Evaluation Room) problems have been listed for this mission – which is extremely low – all of which will be listed in a post flight review article.

On Station, one of the critical elements of hardware that was delivered by Endeavour – the Urine Processing Assembly (UPA) – appears to be working as advertised, following on orbit modifications.

“Previously shutdown due to centrifuge speed and high motor current. Installed 2 additional hard-mount fasteners on FD11, checkout post-IFM delayed due to MTL hose not fully seated,” noted an MMT presentation. 

“First run: UPA successfully operated for 5 hrs w/nominal shutdown. 3.5 hours into the run, crew reported “washing machine’” sound with current increase and motor speed decrease. Event cleared after 30 sec

“Second run: Successfully operated for 4 hr 15 min w/supply tank depletion. Third run: Start-up delayed by a reoccurrence of previously noted check valve failure indication – suspect sticky valve, subsequent start-up nominal.”

As a result, the assembly did not require returning to the MPLM for troubleshooting back on Earth, although managers held open the option to take return it via placement in the middeck, so as not to delay Wednesday’s re-berthing of the MPLM.

“The MMT reviewed the MPLM return option for the UPA and the ISSP reported that they did not require this option to be worked further based on the current status of the UPA,” noted the first MMT status.

“The MMT agreed to continue to review and support development of the option to return the UPA distillate assembly via the Shuttle A/L (Airlock) or middeck with the decision on that option to be at the next MMT.

“Again, based on current status this is considered unlikely to be implemented and there are technical challenges on stowage orientation that are still being worked for this contingency.”

However, later on Wednesday, confidence in the system allowed for the final decision – to leave the assembly on the ISS – to be taken. “The ISS Urine Processing Assembly (UPA) is functioning adequately, and will remain on the ISS. The Middeck/Airlock stowage analysis effort was discontinued.”

STS-126’s crew carried out four EVAs during the docked phase of the mission, highlighted by work conducted on the Station’s Solar Alpha Rotary Joints (SARJs) – which has proved to be successful, according to initial results (follow up will be provided for the undocking article).

The only issue that the MMT have looked into via the EVAs related to increased levels of CO2 – still well within safety limits – inside spacewalker Shane Kimbrough’s EMU suit, which will become part of the mission’s post flight IFA (In Flight Anomaly) review.

“One action was assigned for post-flight to review how EVA training and met(abolic) rate expectations can be more formally understood for the on console team’s management of the EVAs and resource determination (LiOH vs METOX, etc).

“Several points during the EVA had the crew take a break and levels reduced. Managed METOX usage to have crew back in airlock by 6 hrs PET. Officially called for ‘Terminate EVA’ due to a CO2 peak during ingress (resulted in no formal change to ops). Will work this action and report back to a joint program forum.”

The MMT also continued to evaluate the Micrometeoroid Orbital Debris (MMOD) strike to Endeavour’s window 6, which continues to be classed as safe to re-enter with. The discussions on Wednesday related to potential fragment paths, should the thermal pane crack during high pressure loading of the latter stages of re-entry (presentations on L2).

As the docked stage of the mission coming to a close, the STS-126 crew and the ISS crew will share a Thanksgiving meal prior closing the hatches between the two vehicles on Thursday, ahead of Friday’s undocking – which places Endeavour on track for a Sunday landing.

L2 members: All 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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