For the second time in 2017, a pair of astronauts will depart the International Space Station (ISS) on Friday, in support of an ambitious, multi-year campaign to remove 48 aging nickel-hydrogen batteries on the Integrated Truss Structure (ITS) and install 24 lithium-ion replacements. Tomorrow’s 6.5-hour EVA-39 will be performed by Expedition 50 Commander Shane Kimbrough—a veteran spacewalker, with three excursions, totaling 19.5 hours, to his credit—and Flight Engineer Thomas Pesquet. As well as making his first career EVA, Pesquet will also become the fourth Frenchman to perform a spacewalk. Just a few weeks shy of his 39th birthday, he will also be the youngest of his countrymen to do so.
As outlined in last week’s EVA-38 article, all of the nickel-hydrogen batteries on the U.S. Orbital Segment (USOS) are either approaching—or have long exceeded—their original 6.5-year design life. The batteries are located in the Integrated Equipment Assemblies (IEAs) on the station’s port-side P-4 and P-6 truss segments and starboard-side S-4 and S-6 truss segments. Each of these trusses was launched with 12 nickel-hydrogen batteries, with P-6 delivered to orbit in November 2000, followed by P-4 in September 2006, S-4 in June 2007, and, most recently, S-6 in March 2009. Although spacewalkers on the STS-127 and STS-132 shuttle missions in July 2009 and May 2010 changed out nickel-hydrogen batteries on the P-6 truss, the remainder are all the original units.
The new lithium-ion batteries, as well as being smaller than their nickel-hydrogen counterparts, have a capacity roughly equivalent to two of the older units and can handle at least a decade of operational service. All told, four sets of six new batteries will arrive at the station, via Japanese H-II Transfer Vehicles (HTVs) over the next few years. Their integration requires no changes to existing IEA interfaces or hardware, and they can handle upwards of 60,000 charge/discharge cycles, routing power to ISS systems during periods of orbital darkness.
The first set of six batteries were delivered last month aboard HTV-6, housed inside the ship’s External Pallet. This was robotically removed from HTV-6 and relocated to a Payloads Orbital Replacement Unit (ORU) Accommodation (POA), close to the S-4 worksite. The new batteries were then robotically installed into the Power Channel 3A IEA over the Christmas and New Year period. In a remarkable juggling of incoming and outgoing hardware, four of the six nickel-hydrogen batteries on the 3A IEA were removed, with three of them loaded directly aboard HTV-6 for disposal and the other one temporarily accommodated on one of the station’s Dextre robotic manipulator “hands.”
Last Friday, Expedition 50 Commander Shane Kimbrough and Flight Engineer Peggy Whitson—the latter of whom became the world’s oldest female spacewalker, as well as tying the record for the greatest number of EVAs ever performed by a woman—ventured outside the ISS for EVA-38. The duo spent six hours and 32 minutes working to install three adapter plates and hook up electrical connections for the three new batteries. They also repositioned the other two nickel-hydrogen batteries atop adapter plates to serve as dormant, on-orbit spares. So successful were their efforts that the astronauts completed a number of “get-ahead” tasks previously allocated to EVA-39, including a photographic survey of the Alpha Magnetic Spectrometer (AMS)-2 and the removal of a failed external light.
The Removal & Replacement (R&R) task has thus far required a carefully choreographed period of EVA and robotics. Following EVA-38, the Expedition 50 crew—which, in addition to Kimbrough, Whitson, and Pesquet, also includes Russian cosmonauts Sergei Ryzhikov, Andrei Borisenko, and Oleg Novitsky—enjoyed a period of light duty. They debriefed from the spacewalk and performed standard post-EVA work on the Extravehicular Mobility Units (EMUs), including water recharging. The same EMUs, #3006 and #3008, will be utilized on EVA-39, with one of the suits resized for Pesquet.
Meanwhile, last Sunday, the robotics effort to remove the remaining nickel-hydrogen batteries from the Power Channel 1A IEA on the S-4 truss got underway. Over the course of the next four days, ground controllers pulled out the old batteries, placing three aboard HTV-6 for disposal and temporarily accommodating two others on Dextre. By Wednesday morning, the three new batteries for Channel 1A had been installed. “All six new lithium-ion batteries are now installed on the S-4 truss IEA,” NASA’s Rob Navias told AmericaSpace. “The 3A power channel is fully operational. The 1A power channel will be activated on Friday, during the EVA, after adapter plates are moved into place on the 1A IEA.” Additionally, Dextre has been employed to tighten bolts on two of the previously-moved lithium-ion batteries.
Kimbrough and Pesquet’s pre-EVA regime tomorrow morning will follow a similar profile to last week’s activities. As before, Kimbrough will serve as “EV1,” sporting red stripes on the legs of his suit for identification, whilst Pesque (“EV2”) will wear a pure white EMU. Assisted by Whitson and Novitsky, the duo will perform 60 minutes of pre-breathing on masks, during which time the inner “equipment lock” of the station’s Quest airlock will be depressed from its ambient 14.7 psi to 10.2 psi. Kimbrough and Pesquet will purge their suits, after which the atmosphere will be repressurized back up to 14.7 psi, allowing them to head into a nominal pre-breathing regime of around 50 minutes in duration. They will then perform 50 minutes of In-Suit Light Exercise (ISLE) to rapidly remove nitrogen from their blood and avoid a potentially fatal attack of the “bends.”
With all tasks completed, the spacewalkers and their tools will be maneuvered into the outer “crew lock” by Whitson and Novitsky. Hatches between the two locks will be closed and the process of depressurization will commence, leading to the opening of the outer hatch at about 7 a.m. EST. Embarking on his first career spacewalk, Pesquet will be only the fourth Frenchman in history to perform an EVA. He follows in the footsteps of Jean-Loup Chrétien—who also became the first non-Russian and non-U.S. spacewalker, when he ventured outside the Mir space station in December 1988—and, more recently, Jean-Pierre Haigneré and Philippe Perrin. To date, Perrin holds the record for the greatest number of EVA hours ever attained by a French national. Just a few weeks before his 39th birthday, Pesquet will become the youngest Frenchman to make a spacewalk.
After customary “buddy checks” of each other’s suits, they will head for the Power Channel 1A IEA on the S-4 truss, following a similar translation path to that adopted by Kimbrough and Whitson last week. During the course of EVA-39, the astronauts will install the three remaining adapter plates onto the Power Channel 1A side of the IEA and mount one of the old nickel-hydrogen batteries to serve as a third dormant, on-orbit spare. Three old batteries will be removed and transferred directly over to HTV-6’s External Pallet, with another pair temporarily stowed on Dextre. “The three temp-stowed on Dextre are being done because of the space limitation on the HTV External Pallet right now,” Mr. Navias explained. “They will be moved to the EP after the second EVA.”
Should Kimbrough and Pesquet complete all of their primary tasks in good time, a number of get-ahead activities are expected. The list in the “jobs jar” includes changing out a camera pan and tilt assembly on the Mobile Transporter (MT) reel assembly, retrieving a handrail, photographing the “Rat’s Nest”—an area of the Z-1 truss, so named because of the jumble of cables and umbilicals snaking through its vicinity—and swapping a worksite interface adapter on Canadarm2. All of these get-aheads are dependent upon the satisfactory progress of the EVA and consumables usage.
By the time they return inside the ISS, Kimbrough and Pesquet will have left the S-4 truss with six fully functioning lithium-ion batteries, together with three old nickel-hydrogen units as dormant spares, for potential future use. Meanwhile, the three old batteries temp-stowed in the grasp of Dextre will be robotically transferred to the HTV-6 External Pallet over the weekend and finally the pallet itself will be inserted back inside the HTV-6 spacecraft itself on Tuesday, 17 January. This will leave the Japanese cargo craft with a full load of nine old batteries for disposal in the upper atmosphere at the end of its mission.
Assuming all goes to plan, HTV-6 will be robotically detached from its berth at the Earth-facing (or “nadir”) port of the Harmony node on 27 January. At the controls of the 57.7-foot-long (17.6-meter) Canadarm2 for the unberthing and 10:30 a.m. EST release will be Shane Kimbrough, backed-up by Thomas Pesquet. Current plans are for HTV-7 to launch in “early 2018,” with HTV-8 and HTV-9 following in 2019 and 2020 to deliver the remaining lithium-ion batteries.