EVA-41 spacewalkers outfit relocated docking module

Astronauts Shane Kimbrough and Peggy Whitson work to remove the cover on PMA-3 during EVA-41 to prepare it for next year's arrival of IDA-3. Photo Credit: NASA TV

An astronaut duo stepped outside the International Space Station in the second spacewalk in less than a week. Expedition 50 Commander Shane Kimbrough and Flight Engineer Peggy Whitson ventured outside on a 7-hour long spacewalk to outfit a recently relocated docking module to ready it for commercial crew spacecraft sometime in 2018.

During the March 30, 2017, spacewalk, the two astronauts worked to upgrade a computer relay box, connected power and data cables to Pressurized Mating Adapter 3, and covered the Common Berthing Mechanism port PMA-3 recently vacated. However, one of the four shields used to cover the CBM ended up floating away causing ground teams in Houston to come up with a makeshift plan to replace the cover.

Extravehicular activity 41 came four days after PMA-3 was relocated from the port-side CBM of the Tranquility module to the space-facing CBM of the Harmony module. A spacewalk before that, EVA-40 on March 24, had disconnected power and data cables to allow for ground-based robotics teams to move the docking adapter.

PMA-3 after arriving in the Space Station Processing Facility before being integrated into the payload bay of Space Shuttle Discovery's STS-92 mission in 2000. Photo Credit: NASA

Pressurized Mating Adapters

PMA-3 was a docking module used during the early days of space station construction. It allowed two Space Shuttle missions to dock below the fledgling outpost in order to attach the the P6 truss and Destiny laboratory in 2000 and 2001 respectively.

After that, PMA-3 was no longer needed for construction. It remained attached to various CBMs over the course of station expansion to make way for newer modules. It was at its previous location for seven years.

There are actually three PMAs at the station. PMA-1 connects the Unity module with the Russian Zarya functional cargo block module. PMA-2 was the primary docking module used for the Space Shuttle program during ISS construction and is located on Harmony’s forward CBM.

Built by Boeing, all three are identical. They converted the 127-centimeter CBM hatches to the 80-centimeter Russian-designed APAS-95 docking hatch used by the Space Shuttles and Zarya. The small, 1,200-kilogram docking module is 1.9 meters wide at its widest and is 1.9 meters long.

PMA-3 will be getting International Docking Adapter 3 placed on it sometime in 2018 to convert it from APAS-95 to the new NASA Docking System that the two Commercial Crew Program spacecraft will be using. PMA-2 already got IDA-2 attached to it in mid-2016.

The more modern system follows the International Docking System Standard, which uses low-impact technology and can be used for both docking and berthing, and autonomous or piloted dockings.

EVA-41

EVA-41 began at 7:29 a.m. EDT (11:29 GMT) when the Quest airlock was depressurized and the two astronauts’ spacesuits switched to battery power.

Once outside the airlock, the two went separate ways. Kimbrough, the lead spacewalker, translated hand-over-hand to the front of the S0 truss to work on installing an upgraded computer relay box.

Meanwhile, Whitson moved all the way forward to the location of PMA-3. There she started to work to connect power and data cables stored there on previous spacewalks over the years in preparation for the docking module’s relocation. After that was completed, she started taking off the cover on the APAS-95 docking fixture, which has been attached to the front of the docking adapter since 2010.

At S0, Kimbrough worked to replace a computer processor box called the External Control Zone 1 Multiplexer-Demultiplexer. The task was essentially the same one he did during EVA-40 less than a week ago, but with a box on the zenith side of the truss instead. There was nothing wrong with the device, it was just being replaced with a more capable version.

Unlike last week, however, this device put up a fight. Some of the bolts did not release properly and required extra work. Additionally, the new device in didn’t stay in its place when inserted and Kimbrough had to physically hold it while he used the pistol grip tool – a space-grade power drill – to tighten the central bolt.

Once it was secure, the rest went by fast. He finished driving bolts and reconnected the Ethernet cable to integrate it back into ISS systems. After cleaning his area, he moved over to PMA-3 to help Whitson finish putting the docking module cover into a storage bag.

The two together went back to the airlock to drop off the cover and other items not needed for the rest of EVA-41. They then grabbed new items to assist with attaching the CBM shields on Tranquility.

Spacewalk support engineers work to come up with a solution to finish covering Tranquility's port after one of its shields floated away. Photo Credit: NASA

Shield Lost

Axial CBMs, like the one PMA-3 vacated, do not have retractable petals like those around the circumference of node modules. These petals are essentially shields to protect the berthing mechanics from debris and thermal variations. If a CBM is expected be vacant for an extended period of time, it needs shields attached.

Unfortunately, one of these shields somehow became untethered while the two spacewalkers were preparing the work area. It could be seen floating away on camera.

Mission Control in Houston determined the shield posed no threat of striking the station on subsequent orbits. It will eventually fall back into the atmosphere to burn up.

However, that left the problem of one quarter of the CBM being exposed. Engineers in Houston worked to figure out how to cover it, at least temporarily.

While Kimbrough and Whitson finished installing the other three shields as well as a cover for the porthole window, engineers on the ground devised a solution to use the cover from PMA-3 that was just stored inside the airlock.

While the plan was being finalized the two astronauts translated back to the airlock to grab it and bring it over to the Tranquility work space. It was ultimately strapped down in such a way that it covered the shield hole to the satisfaction of engineers on the ground.

The port-side CBM of Tranquility is expected to be unoccupied for at least a couple years before NanoRacks finishes its commercial CubeSat airlock. It will be launched aboard a future SpaceX Dragon capsule.

Final Tasks

With that task finished, one more primary task needed to be completed: the attachment of three small shields around the base of PMA-3. Three of these cumberbunds, as they are called, were placed on the two sides of the PMA and one in the forward section.

After completing that, the crew moved on to one get-ahead task. They translated to the bottom of Harmony to inspect the Earth-facing CBM. Robotic surveys showed a buildup of foreign object debris, known as FOD. They inspected it, took pictures for ground teams to inspect, and then attempted to scrap off some of the debris with a scraper with only partial success.

Kimbrough and Whitson, nearing the seven-hour mark, then translated back to Quest to end EVA-41. A minor bit of drama struck when Whitson’s Helmet Camera Group, which houses cameras and lights, came loose. Kimbrough was able to secure it before it floated away to join the lost CBM shield.

Finally back inside the airlock, and re-pressurization beginning, EVA-41 officially ended at 2:33 p.m. EDT (18:33 GMT). The total time spent in space by the duo was 7 hours, 4 minutes.

New Record

This brought Kimbrough’s cumulative spacewalk time over six EVAs to a solid 39 hours. Whitson, having completed her eighth EVA, is at 53 hours, 22 minutes. She is now the most experienced female spacewalker, surpassing Sunita Williams record of 50 hours, 40 minutes.

Whitson is scheduled for one more spacewalk before returning to Earth in June. That spacewalk, EVA-42, was originally scheduled for April 6. However, it requires a piece of equipment that is inside the Cygnus spacecraft awaiting launch. It was scheduled for a March 27 launch, but has since been delayed due to a hydraulic issue on the Atlas V rocket that will be flying it to orbit.

When EVA-42 does occur, and it lasts at least 5 hours, 10 minutes, Whitson will be the third most experienced spacewalker, just behind retired astronaut Michael Lopez-Alegria’s 67 hours, 40 minutes.

The world leader in spacewalking time is retired cosmonaut Anatoly Solovyev. He has 82 hours, 22 minutes over 16 EVAs in time spent in a spacesuit in the vacuum of space.

EVA-41 was the 199th spacewalk in support of space station assembly and maintenance for a total of 1,243 hours, 42 minutes.

A time lapse of EVA-41, video courtesy of Julian Danzer

NOTE: While this article was written by Derek Richardson, it was originally published at SpaceFlight Insider. Feel free to head over there to read all the stuff they write about!