NASA previews spacewalk to install IDA-2
Two members of the International Space Station’s (ISS) Expedition 48 crew will be performing a spacewalk this Friday to install an International Docking Adapter (IDA) on the forward end of the station. The docking ring was brought up on SpaceX’s CRS-9 Dragon mission and has been sitting inside the spacecraft’s trunk since arriving at the orbiting outpost one month ago.
Extravehicular Activity (EVA) 36 will be performed by Commander Jeff Williams and Flight Engineer Kate Rubins. This is a spacewalk that has been in the planning stages for a number of years. It was supposed to occur last summer with members of Expedition 44. However, due to a launch mishap in June 2015 that resulted in the loss of both the Falcon 9 and CRS-7 Dragon, IDA-1 was lost.
This adapter, IDA-2, is the second to be built. A third is currently being manufactured by Boeing as a replacement for IDA-1 utilizing spare parts. Both will be used to support SpaceX’s Crew Dragon and Boeing’s CST-100 Starliner in the coming years.
“This EVA that we’re going to be doing on Friday represents a very significant milestone on the path to establishing a commercial crew capability on board the ISS, so we’re very excited,” said Kenny Todd, ISS Operations Integration manager. “We’ve had this in the queue for quite a while. We were going to try to do this last summer, but things didn’t go our way, so here we are back again in August of 2016. We’re staring at the IDA daily in the SpaceX trunk and we’re ready to go put it on board.”
An adapter for the adapter
The reason these adapters are being sent to orbit is that a new docking standard has been developed for use by spacecraft. The International Docking System Standard (IDSS) was created by the ISS Multilateral Coordination Board, which includes NASA, Roscosmos, the Japanese Aerospace Exploration Agency (JAXA), the European Space Agency (ESA), and the Canadian Space Agency (CSA).
The design uses low-impact technology and allows for both docking and berthing. It can also support autonomous or piloted dockings. Additionally, the design allows for the transfer of power, data, commands, and communication.
Boeing, SpaceX, and Sierra Nevada Corporation (with their Dream Chaser Cargo System) plan to utilize the IDSS for their crew and cargo vehicles.
Currently, on the U.S. side of the station, the Pressurized Mating Adapters (PMA) utilize the APAS-95 docking system, which was Russian-designed. It was selected for the Space Shuttle to allow for dockings with the Mir space station in the mid-1990s. The design remained unchanged for the ISS program.
PMAs themselves convert the Common Berthing Mechanism (the main ports between U.S. Orbital Segment space station modules) to the APAS-95
The IDSS is not compatible with the APAS-95 system. The IDA converts the Russian design to the NASA docking standard, which is the agency’s implementation of the IDSS.
On Wednesday, the ground robotics team will command the robotic Canadarm2 with the Special Purpose Dexterous Manipulator (Dextre) robotic “hand” attached to the end of the arm. The arm will use Dextre to grab the IDA-2 inside the trunk and move it to the forward end of the Harmony node, where PMA-2 is located.
PMA-2 was used by almost all Space Shuttle missions to the ISS. Its last use was during the final shuttle flight, STS-135.
Canadarm2, with Dextre, will position IDA-2 to within a few feet (about a meter) in front of PMA-2 and hold until Friday morning. Then, before the EVA is set to begin, ground teams will move it in closer to make contact with the older adapter.
The spacewalk will start at 7:10 a.m. CDT (12:10 GMT) August 19. Williams and Rubins will leave the airlock and traverse to the work area. Williams will be the lead spacewalker, EV-1, and sport red stripes on his suit. Rubins will be EV-2 and have white stripes.
This will be Williams fourth EVA, his first being during the STS-101 mission in May 2000. That mission to the ISS was to help prepare the outpost for its first crew, which would arrive some five months later in November 2000.
Rubins will be conducting her first spacewalk.
Williams and Rubins will translate over to PMA-2 and connect adjustable equipment tethers with IDA-2. After that, Dextre will then be commanded to unlatch to allow extra movement for the crew to cinch the tethers down.
At this point, the two spacewalkers will begin to attach power and data cables that have been run across the station over the last year or so during four spacewalks and multiple station expeditions.
After that task is complete, inside the ISS, Flight Engineer and JAXA astronaut Takuya Onishi will support the spacewalkers. He will reside in the Harmony module where a special IDA control panel will command the hooks of the adapter to engage into PMA-2.
After a firm connection is established, the crew will mate a few more remaining cables. Additionally, the will start covering up old reflectors and installing new reflectors that will guide incoming commercial crew vehicles. Finally, the cover on the front of IDA-2 will be removed and stowed in a bag for storage.
Ready to receive commercial vehicles
After all of that is complete, the docking adapter will officially be ready to receive commercial crew vehicles. The first one is currently expected late next year.
Afterward, the crew will begin routing more cables for the next adapter, IDA-3. Sometime next year, PMA-3 will be moved to the space-facing side of Harmony. It is currently in a storage location on the port side of the Tranquility module.
Then, likely in 2018, another SpaceX Dragon cargo ship, CRS-16, will bring IDA-3 to the outpost. The process that took place for IDA-2 will be done again, only in front of PMA-3.
A second IDA is not required for commercial crew vehicles to begin visiting the ISS. It will be used primarily for redundancy as well as for direct handovers between commercial crew vehicles.
“The last time a vehicle undocked from this area of the space station where we’ll do the EVA was the Space Shuttle Atlantis five years ago, closing the door on that chapter of the incredible Space Shuttle program,” said Steve Stich, deputy manager for the Commercial Crew Program. “We very much look forward to getting this docking adapter installed [as well as] the second docking adapter. It will really be that gateway, or [a] new door, to open up the space station to these new commercial vehicles and enhancing the science with an additional crew member.
Video courtesy of NASA
Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a website about human spaceflight called Orbital Velocity.