Just a few weeks shy of the 50th anniversary of humanity’s first spacewalk, Expedition 42 astronauts Barry “Butch” Wilmore and Terry Virts are scheduled to venture outside the International Space Station (ISS) in mid-February, embarking on no fewer than three EVAs to install and configure cables and umbilicals in readiness for the arrival of two International Docking Adapters (IDAs), later this year. Wilmore and Virts will also lube the Ball Screws and Linear Bearings of the “sticky” Latching End Effector (LEE) of the 57.7-foot-long (17.6-meter) Canadarm2 robotic arm and install the booms, antennas and Laser Retro-Reflector (LRR) hardware for the Common Communications for Visiting Vehicles (C2V2) architecture. Much of this new hardware will support not only unpiloted visiting vehicles, but also NASA’s future Commercial Crew aspirations.
Already, during U.S. EVA-28 last 15 October—which also featured Wilmore on his first career spacewalk—the initial steps were taken to move hardware in readiness for 2015’s major reconfiguration of the U.S. “side” of the station. As outlined in a recent AmericaSpace article, the need for this reconfiguration centers on the requirement for two Pressurized Mating Adapters (PMAs 2 and 3) to be equipped with IDAs, thereby converting them from the shuttle-era Androgynous Peripheral Attach System (APAS)-95 docking interface into the new Soft Impact Mating and Attenuation Concept (SIMAC), for use by Boeing’s CST-100 and SpaceX’s Dragon V-2 Commercial Crew vehicles.
PMA-2 resides at the forward port of the Harmony node—at the extreme “front end” of the space station—and will be fitted with IDA-1. Meanwhile, PMA-3 is presently situated at the forward port of the Tranquility node, but will be moved to Harmony’s space-facing (or “zenith”) port in the October timeframe, to accept IDA-2 in December. Part of this process also requires the movement of the Leonardo Permanent Multipurpose Module (PMM) to a new position, in order to “open up” a Common Berthing Mechanism (CBM) interface at the nadir port of the Unity node for unpiloted visiting vehicles, as well as ensuring that sufficient clearance is available for the arrival of future craft. All tasks are expected to be completed by year’s end and will require at least seven U.S. EVAs.
During last October’s EVA-28, Wilmore and Expedition 41 crewmate Reid Wiseman prepared for this major reconfiguration by removing television cameras and equipment from Camera Port (CP)-7 on the Earth-facing (or “nadir”) inboard side of the station’s P-1 truss and repositioning them further outboard at the CP-8 location. They also moved a Wireless External Transceiver Assembly (WETA) to a new site and transferred an Articulating Portable Foot Restraint (APFR) and tool stanchion from the nadir side of P-1 to the central S-0 truss. All of these movements will help to ensure sufficient clearance when the 22-foot-long (6.7-meter) Leonardo PMM is robotically moved in late July from its current position on the nadir port of Unity to the forward port of Tranquility.
According to NASA’s most recent Flight Planning Integration Panel (FPIP) documentation, published last month, the three EVAs by Wilmore and Virts were originally planned to occur between 28 January and 6 February, but AmericaSpace understands that these succumbed to a slippage of around two weeks, caused by delays to SpaceX’s CRS-5 Dragon mission. Originally targeted for December, the cargo flight—which carries 51 pounds (23 kg) of tools and equipment for the EVAs—was postponed until the New Year and finally launched on 10 January, as captured in a stunning AmericaSpace folio of images. Two days later, the Dragon was captured by the Expedition 42 crew and berthed at the nadir port of the Harmony node, allowing its payloads and the EVA tools to be accessed.
Last week, as the crew awaited Dragon, Wilmore and Virts assembled a pair of specialized tools for the upcoming EVAs. The Ballscrew Lube Tool (BLT) and a Grease Gun will be used during the second spacewalk—designated “EVA-30”—to tend to the “sticky” LEE on Canadarm2. “Additional tool-gathering and tool build-up will be completed after SpaceX CRS-5 arrival,” NASA explained in a 7 January On-Orbit Status. Current estimates are that Wilmore and Virts will perform their first spacewalk (EVA-29) on 16 February, followed by the second (EVA-30) on 20 February and the third (EVA-31) on 25 February. All three excursions are expected to last around 6.5 hours.
Assuming that this schedule holds, final preparations will get underway early on the morning of each EVA, when the two spacewalkers—with Wilmore designated “EV1” and sporting red stripes on the legs of his space suit and Virts clad in a pure white ensemble—will be assisted by their “Intravehicular” (IV) crewmate, Italian astronaut Samantha Cristoforetti. They will conduct 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 down to 10.2 psi. Upon completion of this protocol, Wilmore and Virts will don and purge their bulky suits and the airlock’s atmosphere will be repressurized to 14.7 psi.
This will permit them to enter a nominal pre-breathing regime, lasting about 50 minutes, followed by another 50 minutes of In-Suit Light Exercise (ISLE). The latter was first trialed on the STS-134 shuttle mission in May 2011 and involves the spacewalkers flexing their knees for about four minutes, resting for 60 seconds, then repeating over and over until the 50 minutes are up. This technique serves to rapidly remove nitrogen from their bloodstreams, thereby preventing an attack of the “bends.”
At length, the fully-suited pair and their equipment—including the Simplified Aid for EVA Rescue (SAFER) units, affixed to the lower section of their life-sustaining backpacks—will be transferred by Cristoforetti from the equipment lock into Quest’s outer “crew lock.” Hatches between the two locks will be closed and depressurization will get underway. When it reaches 5 psi, the process will come to a halt for standard leak checks, after which depressurization will continue until the crew lock reaches a condition of near-vacuum. The EVA will officially begin when Wilmore and Virts transfer their suits’ critical life-support utilities over to internal battery power.
The exact steps of the two spacewalkers will be more precisely defined in a NASA TV press conference, presently scheduled for 2:00 p.m. EST on 12 February, but it is expected that Wilmore will be the first crewman to exit the hatch. When both spacewalkers are outside, they will close the thermal cover of Quest and press immediately into critical “buddy checks” to ensure that their suits and safety tethers were properly configured for EVA operations, as well as carrying out an inventory of their tools. Although EVA-29 is Wilmore’s second spacewalk, it will be the first for Virts, who will be granted a short period of time to acclimatize to his new environment, before heading to his first work site.
EVA-29 is dedicated to “IDA Prep” and is part of the “Critical Pathway to IDA-1.” At a pre-flight press conference in July 2014, Wilmore explained that during the trio of EVAs he and Virts will be “the cable guys,” responsible for routing power and other utilities in readiness for the arrival of IDA-1 aboard SpaceX’s CRS-7 Dragon in June 2015 and IDA-2 aboard the CRS-9 Dragon in December 2015. Kicking off EVA-29, the two spacewalkers’ focus will be upon PMA-2, which resides at the forward port of the Harmony node, and their work will thus take place at the extreme “front end” of the space station. They will firstly stow PMA-2 umbilical cables, then begin to route 10 IDA Preparation ISS Mod (IPIM) cables along the port and starboard sides of the adapter and fasten them underneath the micrometeoroid shield. These cables are for Heater Power & Data, as well as for use during the installation of IDA-1 and for the future docking of visiting piloted vehicles. This will set the stage for a joint robotics/EVA operation in June-July—featuring Expedition 44 astronauts Scott Kelly and Kjell Lindgren of NASA, together with Japan’s Kimiya Yui—to install IDA-1. If time permits in the final stages of EVA-29, Wilmore and Virts will continue routing the IPIM cables and may lay cable “branches” to the IDA-2 temp-stow location.
Four days later, on 20 February, the two spacewalkers will return outside for EVA-30. Although this spacewalk is also part of the Critical IDA-1 Pathway, it will also play an important role in the Leonardo PMM Relocation and September’s scheduled arrival of the Bigelow Expandable Activity Module (BEAM) aboard the CRS-8 Dragon. During the first three hours of the EVA, the spacewalkers will work together to remove the PMA-2 cover and complete the routing of IDA-1 keep-alive, latching and operational cables, before parting for separate tasks. Wilmore will spend the second half of EVA-30 on the “LEE Lube” activity, tending to the Ball Screws and Linear Bearings of Canadarm2’s Latching End Effector. Launched to the ISS by the STS-100 shuttle crew, way back in April 2001, after more than a decade in orbit, elements of the Canadian-built arm are becoming “kinda sticky,” in Virts’ words, and require lubrication. Meanwhile, Virts will move to the Tranquility node, where his activities include preparing the forward and aft CBMs for their future roles hosting Leonardo and BEAM. It will be akin to coming home for Virts, who previously served as pilot on the STS-130 shuttle mission in February 2010, which delivered Tranquility to the ISS. He will remove Launch Locks from the forward and aft CBMs, open window flaps, and remove the Non-Propulsive Vent Valve (NPV) and a handrail.
The third and final spacewalk, EVA-31, is scheduled for 25 February and is devoted entirely to the installation of hardware for the Common Communications for Visiting Vehicles (C2V2) architecture. Developed under contract between NASA and Mason, Ohio-based L-3 Cincinnati Electronics, C2V2 “provides standardized communications between the International Space Station and docked vehicles by using a standard data link for exchanging audio, video and telemetry data at varying data rates and communications ranges.” For unpiloted Visiting Vehicles (VVs), this includes trajectory and overall spacecraft health data, whilst for the crewed vehicles it will also feature a two-way audio capability. When its hardware is fully installed and activated, C2V2 will operate for up to 13 years—throughout the remaining lifetime of the space station—and consolidate station-based communications, save weight and volume, and greatly simplify logistics for co-ordinating the arrival and departure of all VVs.
In September 2012, L-3 was awarded a $24 million contract by NASA to deliver four S-band flight units and associated equipment for C2V2. This hardware will “provide coverage to all ISS docking ports” and will occur “throughout the VV trajectory,” with locations for the antennas, supporting booms and Laser Retro-Reflectors (LRRs) on the forward and aft faces of the starboard-side S-3 and port-side P-3 trusses, together with three of the Express Logistics Carriers (ELCs), the space-facing (or “zenith”) face of the central S-0 truss and the nadir sides of the Quest airlock and the Tranquility node. Under the terms of the contract, the integrated C2V2 hardware should be ready “to support on-orbit operation by March 2015.” Documentation pertaining to the technical requirements and constraints of the system notes that the number of C2V2-related EVAs should be minimized and restricted only to the physical installation of the hardware.
Although classified as “Non-Critical with regard to ISS Reconfig,” the installation of the C2V2 hardware by Wilmore and Virts will allow for an all-up demonstration of the architecture during the rendezvous and berthing of SpaceX’s CRS-9 Dragon cargo ship in December. According to planning slides, the first 4.5 hours of EVA-31 will see the astronauts routing C2V2 cables from the junction between the Unity node and Destiny laboratory module, across the S-0 truss and outboard along the starboard and port trusses to the antenna installation locations. Wilmore will focus on the S-3 side, whilst Virts does likewise at the P-3 side, with both spacewalkers expected to have completed the installation of antennas and their reflectors by about 5.5 hours into the EVA. They will then clean up their respective work sites and return to the Quest airlock.
With all three EVAs expected to run to about 6.5 hours apiece, this will bring Wilmore’s cumulative spacewalking time to about 26 hours, spread across a total of four excursions. This will elevate from his current status as the world’s 166th most experienced spacewalker—on a list which currently totals 201 members—into the Top Seventy and will push Virts, with about 19.5 hours overall, directly into the Top Ninety, as well as making him the 202nd human being to embark on an EVA.
The author would like to express thanks to Rob Navias of NASA Public Affairs and Robert Pearlman of collectSPACE.com for their assistance in the preparation of this article.