ISS cooling configuration returning to normal confirming ETCS PM success
After three epic EVAs, International Space Station (ISS) managers are celebrating their orbital outpost’s staged return to a nominal condition, as the replacement Pump Module on the External Thermal Control System (ETCS) Loop A provides the required cooling to the numerous systems that were forced to shut down after the July 31 failure.
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A dual effort, on the ground and on Station, has paid dividends – following the incident that was heard live over the flight loop on July 31, resulting in immediate contingency planning for an issue that is tagged as one of the “Big 14” issues that can hit the ISS.
Two EVAs were initially set up for the changeout of the Pump Module on the S1 truss, prior to challenges during EVA-1’s task to remove the Quick Disconnects (QDs) from the old module. QD M3 was the main cause of the hold up, as it decided to make life hard on spacewalkers Doug Wheelock and Tracy Caldwell-Dyson, by leaking ammonia and initially refusing to bid farewell to its home on the to-be-replaced hardware.
Pushing the task into three EVAs, the second spacewalk was a large success, as the duo removed the old PM from S1, whilst they prepared the translation of it replacement PM from the External Stowage Platform (ESP-2).
EVA-3 couldn’t have gone smoother, with the new PM eased into place, prior to the connection of electrical and fluid lines, with only a minor protest from QD M3 – as the Thermal Systems Officer on the ground initiated the flow of ammonia through the replacement, confirming all appeared to be well.
“Wheels (Wheelock) mated and opened the M4 QD. This allows the ground to vent the N2 from the new PM through the ATA (Ammonia Tank Assembly). Next the crew will mate the M1, M2 and M3 QDs. In parallel with this work, the ground will fill the PM with ammonia from the ATA and then the crew will open the remaining QDs,” noted the Mission Evaluation Room (MER) during the EVA (L2).
“M3 has been mated and the PM has been filled with NH3 from the ATA. The crew had a tough time getting M3 aligned, but after a bit of QD manipulation, they managed to get the QD properly seated. Both crew and ground teams are doing an excellent job. All QDs have been mated and valves are open. There were no indications of a leak and the system appears to be solid.”
With the EVA tasks complete, controllers on the ground wasted no time in giving the new PM a quick “spin” to test its status via what is known as a bump test. This short test provided the positive data they had hoped for.
“Pump has been started… looks good. Loop A has been repressurized and the pump is up and running. Pump performance from a quick data review looks nominal. We’ll leave the pump running overnight to watch the system and then step into the power reconfiguration and final loop activation.”
It was noted during the EVA that a full return to life for the PM and the Loop A cooling on the ETCS would be completed no later than Thursday.
ISS Flight Director Courtenay McMillan updated her team on Wednesday (memo acquired by L2) with news of a major milestone in the comeback from the initial failure.
“We’re not done with the reconfigurations & power-ups yet – the team is working to bring JEM and Columbus up right now – but here’s an awesome milestone: the Caution & Warning display up on the big screen in FCR1 (Flight Control Room) is clean – no more red & yellow – for the first time since the pump failed. WOW!!!
“We had our final post-EVA debrief conference with the crew this morning (Wednesday). MCC has been keeping them up to date as work progresses to bring all the systems back online in their nominal configuration, which they’re happy to hear. They asked us to pass along their thanks and congratulations again to the whole team – and they’re looking forward to celebrating with everyone when they get back.”
Bringing the ISS back to a nominal configuration has taken a huge amount of work behind the scenes, from engineers to controllers, from managers to astronauts running simulated EVAs in the NBL (Neutral Buoyancy Laboratory) at the Johnson Space Center (JSC).
Deserved thanks were passed on from FD McMillan, along with a note that further work will be conducted via the NASA tradition of “Lessons Learned” – potentially with evaluations into the potential root cause.
“THANK YOU for all your long hours and hard work. It took the dedication and determination of every person on the team to get this job done, and that is surely recognized. I hope everyone gets a chance to rest and recuperate,” noted the FD.
“In true NASA tradition, we’ll have some Lessons Learned discussions mixed in with the celebratory ‘debriefs’ over the next couple weeks. Until then – thank you again, and enjoy the clear view on the big board!!!”
With FD McMillan also receiving praise for her leadership during the troubleshooting, the “Lessons Learned” effort is already being set up into the timeline of the failed module, with notes that the PM was already showing signs of problems month’s prior to the eventual Loop A failure on the ETCS.
“Great job to the entire team on the Loop A pump R&R. Special Kudos to Courtenay McMillan for all the work she did to get these EVAs completed,” noted a separate ISS memo (L2).
“There was data on the pump module back in February to show that this pump was going south, but this was not seen by the folks looking at the trending pump data. (Manager) has asked for an assessment of what data the MER folks are looking at to ensure that we can see failures like this in the future.”
Bringing the failed PM back to Earth has been openly noted as desirable, allowing engineers to take the module apart to find out priceless engineering data that will be used in relation to the replacement now providing the cooling, and other spare PMs on Station.
Such a return is not possible on STS-133 or STS-134 – although the notional STS-135 could be used to bring the hardware back to Earth.
The decision on whether to proceed with STS-135, by way of NASA approval, is expected as soon as next week – along with preliminary plans for Atlantis’ payload bay configuration, and a potential return slot for the old PM.