International Space Station (ISS) astronauts Doug Wheelock and Tracy Caldwell-Dyson have completed their third specialized spacewalk to kick off a week that will hopefully result in the return of Loop A cooling on the External Thermal Control System (ETCS) for the first time since its failure at the end of last month. ISS EVA-17’s prime aim of installing the replacement Pump Module (PM) was a huge success.
The NASA duo already have two epic EVAs under their belts, as they put into work a complex set of plans created by ground engineers – aided by simulation runs in the NBL (Neutral Buoyancy Laboratory) at the Johnson Space Center (JSC) – with an aim of returning the ETCS Loop A.
The ETCS provides cooling to the entire United States On-Orbit Segment (USOS). The ETCS consists of two independent loops, designated Loop A and Loop B – the latter of which is currently working without issue. With Loop A down, ISS crewmembers were forced to deactive various station systems and experiments to prevent overheating.
The system is designed to collect heat from the Internal Thermal Control Systems in the US Lab, Node-2, COL, JEM, and Node-3, via IFHXs (Interface Heat Exchanger). The PM provides the motive force to transport the ammonia around the loop.
The main task of EVA-1 was to remove the current PM – which suffered from a power spike which tripped a circuit breaker on July 31 – and replace it with a spare during the second EVA next week. However, issues with one of the Quick Disconnect (QD) lines resulted in a re-arranged timeline, and the potential for four EVAs to complete the entire task.
EVA-2 was highly successful, with the troublesome M3 QD literally forced off the faulty PM via the brute force of Wheelock – after ground controllers gave him permission to “violently” shake the QD – allowing for its removal from the S1 truss.
Caldwell-Dyson also played her part, aiding the next EVA tasks by releasing the non-functional PM electrical and data cables as well preparing similar tasks for the translation of the new PM on ESP-2 (External Stowage Platform) into its new home on the S1 Truss.
ISS EVA-17/EVA-3 for ETCS Troubleshooting:
On what was the 150th EVA devoted to space station assembly and maintenance since ISS construction began, the main aim was to install the new PM, bolting into place, with electrical and fluid connections attached – eventually allowing the process to bring back ETCS Loop A back to life.
“Install spare PM (Pump Module) mechanically. Mate & open spare PM fluid QDs (Quick Disconnects). Perform electrical & data continuity checks plus bump-start test (by MCC-H, to check pump functionality). Re-couple stbd & port CETA carts,” NASA noted the tasks for the EVA.
“Clean up spare PM/S1/CETA (Crew & Equipment Translation Aid) cart. Clean up SSRMS (remove APRF for walkoff). Install J612 extension cable for ULF5/PMM (Pressurized Multipurpose Module). Clean up tethers at S1 truss segment. Configure CETA cart to allow for WS8 (Worksite 8 ) ops. Move old PM to ESP-2/mate min electrical connectors (if time allows). Cleanup/Ingress.”
Should all go to plan, the ISS may be back into its nominal cooling configuration by Thursday.
Detailed EVA Events:
Eager to get out of the door, the spacewalkers were over 30 minutes ahead of the timeline for Quest Airlock, for what is expected to be a six hour, 30 minute EVA that officially began at 5:20am Central Time.
Both spacewalkers egressed from the Quest Airlock and began to set up tethers and tools, as the Space Station Remote Manipulator System (SSRMS) was placed into position to assist with the EVA.
With both spacewalkers in position, Wheelock used the Pistol Grip Tool – with torque multiplier installed – to break the torque on the bolts holding the replacement PM into its home on ESP-2.
Meanwhile, Caldwell-Dyson removed insulation and worked electrical and fluid line connection caps in preparation for the PM’s removal for the platform.
Next, Wheelock started to fully release the bolts on the PM, starting with Bolt 1 – which proved to be troublesome. While Bolt 2 released without issue, use of the torque multiplier was required on the sticky bolt.
“Come on now, Bolt,” Wheelock exclaimed, as the bolt finally started to release. With the Scoop installed on to Bolt 2, Wheelock then moved to work on Bolt 4, which released without issue. Bolt 3 – the final bolt holding the PM into position on ESP-2 – also released.
With 780lbs of mass in his hands, Wheelock was translated on the end of the SSRMS with the replacement PM, over to the S1 truss, where he waited for Caldwell-Dyson to aid in the careful placement of the hardware into the vacated slot.
With fine-tuned SSRMS operations, Wheelock eased the PM into position on S1, wasting no time in securing the replacement into place by using his PGT to start work on the four associated bolts, while Caldwell-Dyson worked on mating several electrical connections, “waking up” the PM.
With the Thermal Systems officer Shaun Robinson standing by in the ISS Flight Control Room in Houston, the key moment arrived for the orbiting outpost, as preparations for a “bump test” were readied on the PM – which proved to be successful, confirming they have a good PM installed, following its four year stay on ESP-2.
Next up was the closing and demating of the M4 fluid line from the jumper box, allowing for nitrogen to be vented through the new PM ahead of the flow of ammonia. M2 followed, allowing the jumper box to be handed over to Caldwell-Dyson for her task to install it on the CETA cart.
Key events followed, with the go to fill the PM with ammonia for the first time, as the troublesome M3 QD was installed – following some difficulty.
Once completed, Wheelock moved on to the mating of M2 and M1, which provided no issues, while ground controllers noted that the ammonia fill – a three minute process – was completed without a hitch.
On completion of the QD tasks, Wheelock held up his checklist, attached to his left arm, which had a special message for Tim Bond, a fluids engineer on the ground – reading: “Tim Bond 1-0 M3 QD – Game Over!! Thanks Tim.”
Wheelock then closed the thermal cover over the newly installed PM, while Caldwell-Dyson moved the two nearby CETA carts into a position that would best assist the STS-133 mission.
Also related to the upcoming mission for Discovery, a get-ahead task of installing a 10 foot long J612 cable between the Quest and Destiny modules was being worked, taking the EVA well past 7 hours PET. Managers continued to evaluate if to complete the task, which would have taken another 45 minutes.
With Wheelock only having 50 minutes of consumables remaining, Caldwell-Dyson would have been left to complete the task, and potentially breach the record time for an ISS EVA – depending on completion time. The ultimate decision was to cancel the get-ahead, clean up and ingress the Quest airlock – completing a superb EVA – ending after 7 hours and 20 minutes.
“The Pump is looking good,” noted MCC-H. “Aww, sweet! We got our Station back”, responded Wheelock.
Praise for the ETCS troubleshooting on the ISS has been noted throughout NASA, with Space Shuttle Program (SSP) manager John Shannon taking time to note how impressed he has been with the efforts.
“Flight Crew has been supporting the EVA and robotics development for the spacewalk. EVA is learning a lot from this Increment EVA,” noted the latest Shuttle Standup/Integration report (L2).
“Congratulations to the team on the great EVA,” added Mr Shannon. “It was impressive to see how they worked around all the problems.”