Expedition 38 astronauts Rick Mastracchio and Mike “Hopper” Hopkins have begun a complex and challenging series of up to three EVAs to remove and replace the International Space Station’s failed S-1 pump module. The two spacewalkers—with Mastracchio designated “EV1,” sporting red stripes on the legs of his space suit, and Hopkins as “EV2,” with a pure white suit—opened the outer hatch of the station’s Quest airlock at 7:01 a.m. EST Saturday, 21 December, kicking off a scheduled 6.5-hour EVA to start the process of disconnecting the faulty pump module. Working ahead of the timeline, and with exceptional smoothness, the astronauts completed all of the EVA-24 tasks and jumped into several get-ahead tasks originally timelined for EVA-25 on Monday. The spacewalk ended after five hours and 28 minutes. This raises the likelihood that a third EVA on Christmas Day may be unnecessary.
As noted in an earlier AmericaSpace article, the need for these EVAs became acute following the automatic shutdown of the starboard pump module on one the station’s external ammonia coolant loops back on 11 December. The shutdown was effected when pre-set temperature limits were reached. NASA flight controllers worked tirelessly to get the loop back up and running, and suspicion quickly centered on the improper functionality of a regulating flow control valve inside the pump module. By regulating the temperature of ammonia in the coolant loop, the valve ensures that when it is re-introduced into the heat exchanger of the station’s Harmony module, it does not freeze the water also passing through the exchanger. Although NASA stressed that the six-man Expedition 38 crew—consisting of Mastracchio and Hopkins, together with Japan’s Koichi Wakata and Russian cosmonauts Oleg Kotov, Sergei Ryazansky, and Mikhail Tyurin—was in no danger, engineers worked to move certain critical systems over to the second coolant loop, and a number of non-critical elements were powered down inside Harmony, together with Japan’s Kibo and Europe’s Columbus laboratory modules.
Replacing the valve itself is not an option, since its location within the pump module is inaccessible to the hands of spacewalkers. Only the removal and replacement of the entire pump module—of which three “spares” were delivered to the ISS by the shuttle—is a realistic possibility. At 3:10 a.m. EST Saturday, after post-sleep and personal hygiene activities, the astronauts jumped onto a well-trodden path of 60 minutes of pre-breathing on masks, during which time the Quest airlock’s inner “equipment lock” was depressed from its ambient 14.7 psi down to 10.2 psi. Their next step was to don and begin purging their bulky Extravehicular Mobility Units (EMUs), after which the atmosphere was repressurized to 14.7 psi. Assisted by Wakata and Expedition 38 Commander Kotov, the spacewalkers then entered a nominal pre-breathing period, lasting about 50 minutes, followed by another 50 minutes of In-Suit Light Exercise (ISLE) beginning at 4:35 a.m. EST. This protocol required Mastracchio and Hopkins to flex their knees for four minutes, rest for one minute, then repeat over and over until the 50 minutes were up, in order to remove nitrogen from their bloodstreams in a shorter time span.
Just under an hour before the scheduled 7:10 a.m. EST start time of EVA-24, the fully-suited pair and their equipment were transferred into Quest’s outer “crew lock,” and Wakata and Kotov confirmed the closure of hatches between the two locks at 6:26 a.m. Depressurization was briefly halted at 5 psi for leak checks, after which the process resumed until the crew lock had reached a condition of near-vacuum.
Key personnel in Mission Control today included astronauts Doug Wheelock and Tracy Caldwell-Dyson, who performed three EVAs back in August 2010 to remove and replace the failed pump module on the starboard loop. Wheelock, together with Japanese astronaut and veteran spacewalker Aki Hoshide, served as Capcoms for EVA-24. Meanwhile, Caldwell-Dyson provided live commentary for NASA TV. Speaking at 6:50 a.m. EST, she noted that Wakata’s responsibilities as the only U.S. Orbital Segment (USOS) crew member encompassed not only monitoring the progress of the EVA and controlling the station’s 57.7-foot (17.4-meter) Canadarm2 robotic arm, but also keeping track of station systems. She quipped that he has exceptional time-management skills, but that his workload would mean that the opportunity for bathroom breaks would be “seldom.”
By 6:58 a.m. EST, the pressure of the crew lock was down to 0.5 psi, and shortly thereafter Mastracchio and Hopkins were given the go-ahead to open the outer hatch. The spacewalk officially began at 7:01 a.m., when the astronauts transferred their suits’ life-support utilities over to internal battery power. Mastracchio, making his fourth space mission on Expedition 38, is already a veteran of six prior EVAs, whilst first-timer Hopkins was savoring his first experience of spacewalking today. Yet as Tracy Caldwell-Dyson explained, despite the presence of Wakata and Mission Control in their earpieces, watching their every move, the spacewalkers depended upon each other. “You realize you are the only two people in space,” she said, “so your partner is very important to you. They’re your lifeline.”
Their first few minutes outside were spent checking each other’s suits and tethers. “The enormity of the station is not lost on you,” said Caldwell-Dyson, as NASA TV relayed impressive external views of the Quest airlock and other ISS structures. “You do get the sense that you are alone.” At 7:10 a.m., the spacewalkers were advised that they were passing over western Africa, specifically Liberia and the Ivory Coast, and after checking their suits and tethers they split up to begin their respective first tasks. Mastracchio began moving to collect an Articulated Portable Foot Restraint (APFR), which he would subsequently install at the end of Canadarm2 for today’s work, whilst Hopkins translated, hand-over-hand, to the Crew and Equipment Translation Aid (CETA) cart to collect the pump module jumper box and attach it to his Body Restraint Tether (BRT) for subsequent use.
Retrieving the foot restraint proved initially troublesome for Mastracchio, who was advised by Wheelock that its securing paddles are sometimes sticky and temperamental, but by 7:31 a.m. he reported the APFR was released and was given a go to proceed to the S-1 worksite. By this stage, the spacewalkers were already 15 minutes ahead of schedule, although Caldwell-Dyson cautioned to NASA Public Affairs Officer Josh Byerly that getting too far ahead is not always desirable, due to the need to pause and take the occasional breather in order for the in-suit scrubbers to reduce carbon dioxide levels. Finally, at 7:40 a.m., under Koichi Wakata’s deft control, Canadarm2 began movement and Mastracchio set to work installing the APFR. His task was completed by 7:52 a.m., after which he transferred his safety tether to the arm’s Latching End Effector (LEE) handrail. Shortly after the top of the hour, Wakata gave Mastracchio a go-ahead to ingress the APFR. At this stage, EVA-24 was 30 minutes ahead of the timeline.
In order to remove the pump module, the spacewalkers needed to demate four ammonia fluid quick disconnects (QDs)—three of which measure 1.5 inches (3.8 cm) and one which measures 0.25 inches (0.6 cm)—after which they would work to detach five electrical connectors and four fasteners. Last week, in the Partial Gravity Simulator (POGO) test area of the Space Vehicle Mockup Facility at the Johnson Space Center in Houston, Texas, Wheelock and Caldwell-Dyson completed a training run to guide Mastracchio and Hopkins. Three years ago they experienced difficulty when removing the QDs, and Caldwell-Dyson told Byerly that they were at a pressure of about 300 psi back in August 2010, but that lessons were subsequently learned and they are now at about 180 psi.
On Twitter last week, Doug Wheelock was asked what advice he would offer Mastracchio and Hopkins for the demating of the pump module’s four ammonia QDs—which proved troublesome back in August 2010—and he replied: “Slow, methodical, challenge & response,” with “50% force, 50% finesse.” Unlike the experience of Wheelock and Caldwell-Dyson, today’s effort passed with exceptional smoothness. Periodically checking their gloves and reporting that the backs of their helmets remained free of water, following Luca Parmitano’s unfortunate water intrusion incident during EVA-23 in July, Mastracchio and Hopkins stepped smartly through their tasks. Hopkins removed the multi-layer insulation cover from the failed pump module and wire-tied it out of the way, and by 8:47 a.m. the first of the four QDs had been successfully disconnected.
Although the astronauts reported some evidence of ammonia “snow,” several flakes of which appeared to strike Mastracchio’s suit, it was considered of limited seriousness. Next came the task of installing the ammonia lines to the pump module jumper box. As the men worked, the only issue appeared to be the cold, and at 9:30 a.m. Lead U.S. Spacewalk Officer Allison Bolinger, seated in Mission Control, reported that they were one full hour ahead of schedule. At this rate, it appeared probable that several “get-ahead” tasks originally timelined for EVA-25 on Monday, 23 December, would be incorporated into today’s EVA-24 schedule, possibly including the physical removal of the failed pump module and the venting of nitrogen from the replacement spare.
By 9:50 a.m., the last of the four QDs were successfully demated and their valves confirmed closed by the Station Power, Articulation and Thermal Control (SPARTAN) console in Mission Control. Shortly afterward, still working briskly, it was reported that Mastracchio and Hopkins were a full 90 minutes ahead of the timeline and were given the go-ahead to begin the key EVA-25 task of moving the failed pump module over to its temporary-stow location at the Payload Orbital Replacement Unit (ORU) Accommodation (POA) on the Mobile Base System (MBS). “That was due to be the first major task of Monday’s spacewalk,” explained Josh Byerly, adding that the progress was such that the entire pump module changeout might be accomplished in just two EVAs and that Christmas Day’s planned EVA-26 might be unnecessary.
In the following quiet time, the spacewalkers were asked to assess each other’s suits for the presence of ammonia contaminants, although both men acquiesced that any flakes would likely be too small to be visible to the naked eye. Mastracchio’s sole concern was coldness in his suit, possibly from being on the end of Canadarm2 for so long, and he reported good airflow into his boots. Asked for his consideration of extending the EVA from 6.5 hours to as long as 7.5 hours, he replied in the affirmative. In readiness for this extension, Hopkins was directed to return to the Quest airlock to recharge his oxygen supply.
The next task was to remove electrical connectors from the failed pump module, and Hopkins removed the Adjustable Grapple Bar (AGB) from its stowage location on the Flex Hose Rotary Coupler (FHRC) on the station’s External Stowage Platform (ESP)-2. The bar would provide a grapple fixture for the failed pump module and enable it to be held by the POA. By 10:40 a.m., all three electrical connectors had been removed, and a few minutes afterward NASA reported that Mastracchio and Hopkins were entering into the tasks originally scheduled for Monday’s EVA-25. By 11:10 a.m., the astronauts began the process of removing the failed pump module, with Mastracchio guiding it out and Hopkins attaching the AGB by means of the Pistol Grip Tool (PGT).
By now, EVA-24 was a little over 4.5 hours old and had already completed all of its pre-planned objectives, as well as shaving at least an hour off the tasks originally baselined for Monday’s EVA-25. At 11:30 a.m., Mission Control requested Mastracchio and Hopkins’ approval to begin movement over to the External Stowage Platform (ESP)-3—where the replacement pump module is located—to get started on preparing it for movement. However, Byerly noted that it was being considered more prudent to wrap up the EVA-24 tasks and secure the failed pump module. This option gained Mastracchio’s approval. After cleaning up the worksite, Hopkins was back inside the Quest airlock by 12:17 p.m., followed by Mastracchio a few minutes later at 12:20 p.m. The hatch was closed and EVA-24 officially ended at 12:29 p.m., after five hours and 28 minutes.
At the time of writing, it was becoming increasingly likely that no spacewalk on Christmas Day will be required, which will give the crew some well-deserved quiet time, ahead of a planned EVA from Russian segment by Oleg Kotov and Sergei Ryazansky on Friday, 27 December. If a Christmas Day spacewalk is declared unnecessary, it will mark out the final Skylab crew as the only human beings to have ever performed an EVA on the traditional date of Christ’s birth. On 25 December 1973, astronauts Gerry Carr and Bill Pogue spent several hours outside Skylab, photographing Comet Kohoutek and replacing film in the station’s Apollo Telescope Mount. Others have since spacewalked close to the big day, and on Christmas Eve 1999 astronauts Steve Smith and John Grunsfeld made their final EVA of STS-103 to service the Hubble Space Telescope, but Carr and Pogue’s accomplishment has never been repeated.
The author would like to express his thanks to AmericaSpace’s Leonidas Papadopoulos for providing screen captures in support of this article.