US EVA-20 Updates (ISS Exp. 33)
Expedition 33 Updates, Expedition 33 Section
Photo Gallery: US EVA-20
ISS Spacewalkers deploy Thermal Control Radiator to bypass Ammonia Leak
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November 1, 2012
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Photo: NASA
Photo: NASA
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International Space Station Crew Members Suni Williams and Aki Hoshide successfully completed US EVA-20 on Thursday, reconfiguring one of the Space Station’s Photovoltaic Thermal Control System Channels to take care of an ammonia leak.
The ammonia leak on the P6 Integrated Equipment Assembly 2B Channel Photovoltaic Thermal Control System has been known since December 2006. The leak was rather small and the system lost about 0.7 Kilograms per year requiring periodic refills of the system to keep the total amount of NH3 above the critical limit to keep the system up and running. During Space Shuttle Mission STS-134 in May 2011, the 2B PVTCS system was refilled and teams assumed that another refill would be needed 4 years after that, assuming leakage remained constant. Recently, leakage started trending up to about 2.5kg per year and the system was approaching its limit much quicker than expected with quick-look assessments indicating that this threshold would be hit in late December 2012 or early January 2013. Each PVTCS channel holds about 25 Kilograms of ammonia in its nominal condition and channel 2B had been trending down until being replenished in 2011, followed by an increase in leak rate in 2012. ISS Mission Managers decided to perform the EVA as soon as possible to take advantage of the current spacewalking crew of Suni Williams and Aki Hoshide as long as they are still aboard ISS. This EVA featured a very experienced spacewalking team, both, inside Mission Control and aboard the Station. Suni Williams started this EVA as the leading female spacewalker with six EVAs and 44 hours and 2 minutes of total EVA time. |
More importantly, Suni Williams had past experience working on the P6 Truss and its PVTCS System. She and Michael Lopez-Alegria performed three spacewalks in 2007 to work on an Early Ammonia Servicer on P6 and associated cooling lines. She performed the stowage of the EETCS Radiator that was deployed on this EVA, so she already has hands-on experience with the actual hardware in orbit. Aki Hoshide started this ISS Expedition as Spacewalking Rookie, but performed two challenging EVAs with Williams in August and September to remove and replace a failed Main Bus Switching Unit on the Station’s power system, so he has had the opportunity of gaining extensive EVA experience, becoming the leading Japanese Spacewalker with 14 hours and 45 minutes of EVA time.
The spacewalking team was supported by fellow ISS resident Kevin Ford who was in charge of EMU configuration and airlock operations. The IV-Crew Member choreographing this EVA from Mission Control was Mike Fincke, a very experienced spacewalker with previous experience working with the PVTCS 2B System on STS-134 to re-fill the loop. Behind him was an experienced EVA team with EVA-Lead Allison Bolinger who was supported by MCC Backroom Personnel and hardware specialists.
ISS Photovoltaic Thermal Control System Background
The spacewalking team was supported by fellow ISS resident Kevin Ford who was in charge of EMU configuration and airlock operations. The IV-Crew Member choreographing this EVA from Mission Control was Mike Fincke, a very experienced spacewalker with previous experience working with the PVTCS 2B System on STS-134 to re-fill the loop. Behind him was an experienced EVA team with EVA-Lead Allison Bolinger who was supported by MCC Backroom Personnel and hardware specialists.
ISS Photovoltaic Thermal Control System Background
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The eight individual Power Channels of the International Space Station are cooled by the Photovoltaic Thermal Control System (PVTCS) that circulates ammonia through Photovoltaic Radiators (PVRs) to dissipate excess heat generated by solar power generation in the Solar Arrays Wings and keep the EPS (Electrical Power System) at a stable temperature. There are four PVRs on ISS, one on each Truss Segment that features Solar Array Wings. Each PVR has two Decks, each supporting an individual PVTCS channel corresponding to the two power channels fed by the two SAWs. In case of the P6 PVR, channels 2B and 4B share one radiator. The other ISS Systems are thermally controlled by the External Thermal Control System (ETCS) that uses Heat Rejection Subsystem Radiators (HRSRs) that cool all other electronics that are not part of the Photovoltaic System. The systems are strictly separated to reduce the overall operating temperature of the ETCS Loops and to avoid technical challenges coming with cooling fluid being transferred through the rotating SARJs (Solar Alpha Rotary Joint). HRSRs and PVRs are not compatible due to a different cooling loop architecture.
The P6 Truss Segment is also outfitted with two EETCS Radiators (Early External Thermal Control System) that were used from 2000 to 2007 when the P6 Truss was located on top of the Z1 Segment as part of the early Space Station configuration. P6 has a TTCR (Trailing Thermal Control Radiator) and a STCR (Starboard TCR). These names are coming from the system’s past life, back when they were deployed in position on top of Z1. The EETCS provided thermal control to the ISS Modules while the assembly phase of ISS was still underway and the HRS was still under construction. |
Image: NASA
Image: NASA
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Back in 2007, on Space Shuttle Mission STS-120, the two EETCS radiators were stowed and the P6 Truss took its spot next to P5. At that time the HRS was in place and the EETCS was no longer needed.
Now, with one of the PVTCS Radiators showing a growing leak, it pays off to have the option of bringing the old system back online which was completed on EVA-20, converting an EETCS Radiator to a PVTCS radiator, which is not really a conversion because the design of the two systems is identical. Refilling the system was not a good option for the long-term as replenishing the ammonia would lead to it being lost once again.
Now, with one of the PVTCS Radiators showing a growing leak, it pays off to have the option of bringing the old system back online which was completed on EVA-20, converting an EETCS Radiator to a PVTCS radiator, which is not really a conversion because the design of the two systems is identical. Refilling the system was not a good option for the long-term as replenishing the ammonia would lead to it being lost once again.
Image: NASA
EVA Preparations aboard the Space Station started several weeks ago. Since the EVA equipment & space suits were still configured for Suni Williams and Aki Hoshide, hardware preparations did not require as much time as before the first EVA that the two crew members performed. This gave teams more time for procedure reviews and tagups with ground teams which are important for EVAs that were not rehearsed by the crew members back on Earth, but they still have to understand all procedures to get ready for the EVA – making these unplanned spacewalks more challenging. Suni and Aki performed several procedures review sessions over the past few weeks and they spent time inside the Quest Airlock to get the two Extravehicular Mobility Units configured for the spacewalk.
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On Thursday, the day of the Spacewalk, the USOS Crew had a nominal breakfast to get their day started before pressing into EVA Preparations. The two EV crew members put on their EMUs and completed normal checkouts and activation before utilizing the ISLE Pre-Breathe Protocol. ISLE is a relatively new pre-breathe technique. The acronym stands for In-Suit Light Exercise.
Spacewalkers need to pre-breathe to flush Nitrogen out of their blood stream that could cause decompression sickness when the crew members are subjected to the lower pressure inside the EMUs. The 'bends' as this problem is also called, could lead to major complications during the spacewalk which is undesirable for obvious reasons. For ISLE, the two crew members pre-breathe pure Oxygen for 50 minutes and start the exercise protocol which required crew members to perform ten cycles of four minutes of exercise and one minute of rest. The exercise is essentially light flexing of the knees and arm movements that are sufficient to remove Nitrogen from the blood streams. ISLE had its debut on Space Shuttle Mission STS-134 and passed its evaluation and is now part of NASA's EVA repertoire. With ISLE complete, ISS crew members Yuri Malenchenko and Kevin Ford installed the two SAFER Units on the EMUs before moving the crew members to the crew lock portion of the Quest Airlock. Once the crew lock was isolated, depressurization was started. Thirty minutes of depressurization followed to set the stage for hatch opening. During Airlock Depress, final leak checks were performed before Mission Controllers gave to GO to start the EVA. Hatch Opening occurred at 12:28 UTC and the two Crew Members switched their Spacesuits to battery power at 12:29 – marking the official beginning of the EVA. After verifying the initial Tether Configuration on the two EMUs, Suni Williams was clear to egress the Airlock. |
Photo: NASA
File Image - Photo: NASA
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Once outside, Suni received a tool bag from Aki Hoshide before he stepped outside himself to get started on this third EVA. After the usual ‘buddy checks’ during which the two EV crew members check each others suits, Suni Williams and Aki Hoshide parted ways with Suni heading for P6, stopping at P1 to anchor the Safety Tethers of both crew members. Aki had to wait at the Airlock until all tethers were in place so that he could remove the first tether from the Airlock, close the thermal cover and go to the Z1 truss segment to retrieve a Pistol Grip Tool Socket for later use in the EVA. Once retrieving the socket from the toolbox, Aki headed back to the Airlock, removed his safety tether and started to translate to P6, taking the same path that Williams took earlier. Once arriving at P6, Aki took advantage of a few minutes of daylight that were left to acquire engineering images of the P6 Integrated Equipment Assembly and Photovoltaic Radiator.
Photo: NASA
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While Aki was busy at Z1 and with the images, Suni Williams set up shop at the P6 truss location starting with a visual inspection of the EAS Jumpers that she was working on later. She configured the work site and put tools and tethers in place to start working on the 2B tasks. Once moving herself into the proper position, she started the EAS Jumper Reconfiguration task, beginning by removing the protective cap from the M2 socket on the P6 IEA Fill&Drain Box.
Suni then moved on to the Quick Disconnect interface on M3, made a visual inspection and mated the FH-02 jumper to M2 and installed the cap on M3. She had some trouble with the FH-02 Jumper and its QD-Filter and QD-Extender and needed some time to get it engaged before confirming a good installation. These Fluid Quick Disconnects have shown on numerous previous occasions that they are not as ‘quick’ as advertised, giving crew members some trouble when working with these QDs. Luckily, Suni Williams had past experience with these systems and was able to properly adjust her body position to get the QD engaged. There were a total of 3 QD reconfigurations during the EVA: FH-02 from M3 to M2, FH-01 from M9 to M10 and FH-02 from its wire-tied position to M9. Suni and Aki joined forces again to work on the M9 interface and the FH-01 jumper, removing the thermal bootie and getting started to install an SPD (Subject Positioning Device). Unfortunately, the two spacewalkers were unable to install the device and teams on the ground could not come up with a quick solution. It was suspected that the issue was related to the SPD used and the crew member tried a different one, but that was also not engaging properly and teams decided to get started with the FQDC Demate Task while the back room in Mission Control assessed the problem. |
Image: NASA
Image: NASA
OD/SPD Design
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They moved on to the FQDC (Fluid Quick Disconnect Coupling) Demate Task, starting with the removal of the protective cover by driving four bolts to release the cover to set the stage for a very delicate operation. Under the cover, the crew found two FQDCs, the left one being for PVTCS Channel 2B and the right one for the 4B channel. Suni Williams started to drive the H18 bolts on the 2B side to close all valves that are leading to the 2B section of the P6 radiator.
There were some concerns of possible leaks and teams had procedures ready in case a flowing ammonia leak. Williams started to drive the H18 Bolt for total of 7 turns while Hoshide was monitoring for any possible leaks. A small amount of leakage was expected and the astronauts reported five to ten flakes of ammonia being released. This small amount was not of concern to teams and the crew got the green light to re-install the cover to finish the task. The FQDC Demate was completed faster than expected and the 2B portion of the radiator was isolated from the PVTCS loop, setting the stage to bring the EETCS Radiator back online.
There were some concerns of possible leaks and teams had procedures ready in case a flowing ammonia leak. Williams started to drive the H18 Bolt for total of 7 turns while Hoshide was monitoring for any possible leaks. A small amount of leakage was expected and the astronauts reported five to ten flakes of ammonia being released. This small amount was not of concern to teams and the crew got the green light to re-install the cover to finish the task. The FQDC Demate was completed faster than expected and the 2B portion of the radiator was isolated from the PVTCS loop, setting the stage to bring the EETCS Radiator back online.
Image: NASA
*File Image* - Photo: NASA TV
ISS Ammonia Quick Disconnects
Photo: NASA
P6 Work Site
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Once the FQDC task was complete, the spacewalkers started to work on different tasks: Suni went back to the EAS Jumper reconfiguration task while Aki moved to the inboard side of the TTCR to remove the cover of the radiator.
Suni removed the FH-01 Jumper from the M9 Socket on the P6 Long Spacer and connected it to a Nitrogen Vent Tool to release N2 that was inside the jumper. She installed the jumper on M10 and made sure the installation was successful by performing a pull test. FH-02 was not installed anywhere prior to the EVA, being wire-tied next to FH-01. Suni Williams installed it on M9 to complete Wet Quick Disconnect Operations with time to spare. There was a 3-hour 55-minute limit for QD operations to be completed for decontamination requirements – allowing sufficient time for an ammonia bake-out in the event of ammonia contamination of either of the two space suits. With all QDs installed, Suni Williams started to open the valves on M9, M2, M1 and M10 in that particular order while SPARTAN Flight Controllers inside Mission Control were monitoring the ammonia flow, looking for possible leaks. All was good and Suni Williams went back to the troublesome SPDs. These devices are not required for the system to work, but their installation is desirable since they rigidify the Quick Disconnect Connection. Mike Fincke instructed Suni to use long wire ties to attach the SPDs which took some additional time, but teams were able to afford that after working efficiently throughout the EVA. Suni had trouble getting the thermal insulation booties installed around the QDs and QD Extenders and teams inside mission control scratched their heads as none of their plans worked very well. Finally, the crew members managed to get three of the SPDs and all thermal booties installed to be able to move on to the next task. The booties were secured on a best-efforts basis, making sure no metal of the QD components was exposed. Meanwhile, Aki Hoshide started a two-hour task to get the protective shroud removed to expose the stowed TTCR. |
The cover was released and Hoshide folded it next to the radiator where it was secured in place. After all jumpers were properly configured, the crew started by securing the shroud in place before removing six cinches and two PIP Pins to free the radiator. Once all tools, tethers and crew members were clear of the work site, the SPARTAN Mission Controller inside MCC commanded the radiator to deploy. First motion occurred at 17:34 UTC and the deployment sequence was nominal and concluded at 17:41. Afterwards, Aki Hoshide stowed a TTCR winch and Suni Williams went back to the EAS Jumper site to have another attempt to install the SPD on the M10 QD and place the bootie around it. They succeeded and crossed the final item on the EVA objective list off.
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"Suni and Aki, our heartfelt congratulations to you and the entire team," Fincke said. "We've accomplished just about everything we set out to do today."
"And a big huge congratulations to you guys on the ground for putting this together. It's nice to see it deployed again," Williams replied from Orbit. After all operations were successfully completed, Suni Williams and Aki Hoshide departed the P6 work site. Aki was first to reach the Airlock where he installed a safety tether to give Suni a GO to remove the anchor hooks from P1 and make her way back to Quest. Once both were back outside the Airlock, they completed a final tool inventory and buddy check before going back inside, hooking their suits up to ISS power and cooling, and starting A/L Repressurization – marking the official end of the EVA at 19:07 UTC for a total EVA time of 6 hours and 38 minutes. This marked the 166th spacewalk dedicated to ISS Assembly and Maintenance. It was Suni Williams’ 7th spacewalk for a new total of 50 hours and 40 minutes. Aki Hoshide now has 21 hours and 23 minutes of EVA time under his belt that he completed on his three spacewalks performed during ISS Expedition 32 and 33. With this EVA successfully completed, the big question is whether this reconfiguration will take care of the leak or not. Teams believe that the leak is within the 2B Segment of the P6 PVR, but with a leak that small, there is no chance of isolating it and pinning down its exact location. Should the leak not be on the PVR side, the system will continue to lose ammonia after the EVA and teams would need to re-evaluate the issue and plan new repair operations. Other possible locations for the leak include a number of other Thermal Control System components out on the P6 truss segment, but the radiator is the most likely location as it is vulnerable to MMOD (Micrometeoroid and Orbital Debris) strikes. |
*File Image* - Photo: NASA
*File Image* - Photo: NASA
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The theory that was developed by Mission Controllers is that the original leak was caused by an MMOD strike and was followed by a second strike on 2012 that caused the increase in leakage – as opposed to the first leak getting bigger by itself.
Should the leak(s) still be present, teams have now gained more time to work out new procedures as the EETCS system was filled with ammonia that was re-filled during the 2011 spacewalk along with the rest of the 2B system, so connecting the system to the full EETCS led to an automatic ammonia refill. Should the leak still be present and leakage be as before, the lower ammonia limit would be hit in the Fall of 2013. It will take several days or weeks to determine whether the system is sill losing ammonia or not.
Should the leak(s) still be present, teams have now gained more time to work out new procedures as the EETCS system was filled with ammonia that was re-filled during the 2011 spacewalk along with the rest of the 2B system, so connecting the system to the full EETCS led to an automatic ammonia refill. Should the leak still be present and leakage be as before, the lower ammonia limit would be hit in the Fall of 2013. It will take several days or weeks to determine whether the system is sill losing ammonia or not.
ISS Spacewalkers set for busy EVA to restore ISS Cooling System |
October 26, 2012 |
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The International Space Station Program and ISS Expedition 33 crew members in orbit are gearing up for a Spacewalk on November 1, 2012 to perform required maintenance on the outside of the orbiting complex. This Spacewalk, US EVA-20, was not planned ahead of the increment, but over the course of the previous months, it became clear that a known ammonia leak on the outside of the Station will require attention in 2012.
The ammonia leak on the P6 Integrated Equipment Assembly 2B Channel Photovoltaic Thermal Control System has been known since December 2006. The leak was rather small and the system lost about 0.7 Kilograms per year requiring periodic refills of the system to keep the total amount of NH3 above the critical limit to keep the system up and running. During Space Shuttle Mission STS-134 in May 2011, the 2B PVTCS system was refilled and teams assumed that another refill would be needed 4 years after that, assuming leakage remained constant. Recently, leakage started trending up to about 2.5kg per year and the system is currently approaching its limit much quicker than expected with quick-look assessments indicating that this threshold would be hit in late December 2012 or early January 2013. Each PVTCS channel holds about 25 Kilograms of ammonia in its nominal condition and channel 2B had been trending down until being replenished in 2011, followed by an increase in leak rate in 2012 as the chart to the right clearly shows. When the cooling loop shuts down and down no longer provides thermal control to PVTCS Channel 2B which would in turn be powered down, the International Space Station would experience serious consequence as a Shutdown of 2B would be problematic since the system carries a number of crucial systems that would have to be reconfigured to other power channels, causing a loss in science operations aboard the complex. |
Photo: NASA
Image: NASA
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The International Space Station Mission Management therefore decided to perform the EVA as early as possible, with the current spacewalking crew currently on ISS. Suni Williams and Aki Hoshide are planned to depart the Station aboard their Soyuz on November 19, 2012 which would only leave a single US Segment Crew Member aboard ISS, Kevin Ford, member of the Soyuz TMA-06M crew. With Soyuz TMA-05M gone, teams would have to wait for the arrival of Soyuz TMA-07M in December to bring up the next two USOS crew members that could support an EVA. And with December close to the margin and no guarantee that the leak would stay at its current rate of leakage, teams pressed into EVA preparations for Increment 33.
Image: NASA
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Image: NASA
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The eight individual Power Channels of the International Space Station are cooled by the Photovoltaic Thermal Control System (PVTCS) that circulates ammonia through Photo Voltaic Radiators (PVRs) to dissipate excess heat and keep the EPS (Electrical Power System) at a stable temperature. There are four PVRs on ISS, one on each Truss Segment that features Solar Array Wings. Each PVR has two Decks, each supporting an individual PVTCS channel. In case of the P6 PVR, channels 2B and 4B share one radiator. The other ISS Systems are thermally controlled by the External Thermal Control System (ETCS) that uses Heat Rejection Subsystem Radiators (HRSRs) that cool all other electronics that are not part of the Photovoltaic System.
Photo: NASA
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The P6 Truss Segment is also outfitted with two EETCS Radiators (Early External Thermal Control System) that were used from 2000 to 2007 when the P6 Truss was located on top of the Z1 Segment as part of the early Space Station configuration.
The EETCS provided thermal control to the ISS Modules while the assembly phase of ISS was still underway and the HRS was still under construction. Back in 2007, on Space Shuttle Mission STS-120, the two EETCS radiators were stowed and the P6 Truss took its spot next to P5. At that time the HRS was in place and the EETCS was no longer needed. Now, with one of the PVTCS Radiators showing a growing leak, it pays off to have the option of bringing the old system back online which will be done during EVA-20, converting an EETCS Radiator to a PVTCS radiator. Refilling the system is not a good option for the long-term as replenishing the ammonia would lead to it being lost once again. |
The big question is whether this reconfiguration will take care of the leak or not. Teams believe that the leak is within the 2B Segment of the P6 PVR, but with a leak that small, there is no chance of isolating it and pinning down its exact location. Should the leak not be on the PVR side, the system would continue to lose ammonia after the EVA and teams would need to re-evaluate the issue and plan new repair operations. Other possible locations for the leak include a number of other Thermal Control System components out on the P6 truss segment, but the radiator is most liekly location as it is vulnerable to MMOD (Micrometeoroid and Orbital Debris) strikes. Should the leak still be present, teams will have gained more time to work out new procedures as the EETCS system is filled with ammonia that was re-filled during the 2011 spacewalk along with the rest of the 2B system, so connecting the system to the full EETCS will lead to an automatic ammonia refill.
Image: NASA
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Suni Williams and Aki Hoshide will be stepping outside on November 1, to take care of the issue by connecting an EETCS radiator to PVTCS Channel 2B. Luckily, both Astronauts are now experienced spacewalkers. Suni Williams had already performed four EVAs prior to ISS Expedition 32/33. Aki Hoshide started Expedition 32/33 as a spacewalking rookie, but he was able to gain spacewalking experience during the challenging US EVAs 18 and 19 that he performed with Williams to remove and replace a failed Main Bus Switching Unit to restore two of the Station's power channels.
In addition, Suni Williams has previous experience working on the Space Station's P6 Truss Segment. She and Michael Lopez-Alegria performed three spacewalks in 2007 to work on an Early Ammonia Servicer on P6 and associated cooling lines. |
Image: NASA
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She performed the stowage of the EETCS Radiator that will be deployed on this EVA, so she already has hands-on experience with the actual hardware in orbit which, in spaceflight, is an important factor. Also, Williams already worked with the Fluid Quick Disconnects that have presented large challenges to other spacewalking Astronauts, familiarizing herself with the system in orbit under real EVA conditions.
Both spacewalkers have started preparations for the EVA earlier in October and they have performed a number of procedure reviews and tagups with EVA specialists on the ground to make sure they understand all procedures and are ready to perform them during the spacewalk. Also, they started equipment and tool preparations inside the Quest Airlock from where they will begin this six-and-a-half hour EVA on November 1 at about 12:15 UTC.
Both spacewalkers have started preparations for the EVA earlier in October and they have performed a number of procedure reviews and tagups with EVA specialists on the ground to make sure they understand all procedures and are ready to perform them during the spacewalk. Also, they started equipment and tool preparations inside the Quest Airlock from where they will begin this six-and-a-half hour EVA on November 1 at about 12:15 UTC.
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To begin the EVA, the two Astronauts will use the ISLE Pre-Breathe Protocol to prepare themselves for the spacewalk. Kevin Ford will be supporting the crew during Extravehicular Mobility Unit ingress and preparation before taking care of Airlock Depressurization to get the spacewalk started. Veteran Astronaut and Spacewalker Mike Fincke will be taking over the IV-Crew Member Role once the crew members are outside. He will be watching over the EVA from Mission Control and choreograph the EVA. Fincke also has previous experience working with the PVTCS 2B System on STS-134 to re-fill the loop.
With all this experience, both, in orbit and Mission Control, the two spacewalkers will step outside via Quest and get started with EVA set-up procedures, taking out tools and configuring tethers. |
Image: NASA
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Suni Williams will be departing the Airlock first, heading outboard on the Port side of the truss segment, stopping at P1 to set up the Safety Tethers that will be used by both spacewalkers. She will then translate out to P6 where she will prepare the work site. Aki Hoshide's first task will be the retrieval of a Pistol Grip Tool Socket before he can also translate to P6. The Pistol Grip Tool will be used once Aki arrives at P6 to remove four fasteners that are holding a cover in place before the crew can access the work site for the PVTCS 2B Fluid Quick Disconnect Coupling demating task. They will reconfigure the system by driving a bolt with the PGT in order to close all valves leading to the 2B Radiator to isolate it. Afterwards, the shroud will be re-installed.
Image: NASA
Aki will spent some time taking pictures of the P6 PVTCS equipment for engineering assessments. Suni Williams will get started on the Early Ammonia System Jumper Reconfiguration. To connect the EETCS radiator, also called Trailing Thermal Control Radiator (TTCR), to the loop 2B, two jumpers have to be reconfigured. She will work with a Nitrogen Vent Tool to vent the FH-01 jumper before installing FH-01 between the M1 and M10 Quick Disconnect and FH-02 between the M2 and M9 QDs. Once the system is back up and running, FH-02 will be feeding cooled ammonia from the radiator to the 2B channel while FH-01 will feed heated ammonia from the loop back to the radiator. Aki Hoshide will be working with the TTCR Cover that was put in place in2007 to protect the stowed radiator. The cover will be removed and installed on the inboard side of the TTCR.
Image: NASA
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Once the radiator is exposed, the crew members have to remove equipment that is securing the radiator in its stowed configuration. When that is complete, the crew members clear the work site and make sure that no equipment is in the TTCR envelope before giving the GO for radiator deployment. The TTCR will be deployed automatically after being commanded to unfurl from the ground. This would take a bit less than 10 minutes.
A manual deployment by the crew using the Pistol Grip Tool is also possible should the automatic deploy fail at some point in the sequence. With that, the EVA tasks would be complete and Suni and Aki would clean up the work site and go back to the Airlock. Aki would go first and set up a safety tether at Quest to allow Suni to remove the safety system from P1 before translating to the Airlock herself. The crew will perform tool reconfigurations to head back into the Airlock to call it an EVA. |
Photo: NASA
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After the EVA, it will take several days or weeks of monitoring the 2B PVTCS Channel before teams will know whether bypassing the Upper Deck of the PVR corrected the problem. Should the leak be still present at its most recent rate, teams would have to come up with a new plan by Fall of 2013 before the replenished ammonia would run out once again.
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