NASA astronaut Terry, Virts Flight Engineer of Expedition 42 is seen working to complete a cable routing task while near the forward facing port of the Harmony module on the International Space Station. February 21, 2015. Image credit: NASA

On Sunday (March 1, 2015) two NASA astronauts aboard the International Space Station (ISS) will perform the last of Expedition 42’s scheduled spacewalks. The spacewalk will begin around 6:10 a.m. Central Time and is expected to last about 6 hours, 45 minutes. NASA Television coverage on Sunday will begin at 5 a.m. Central time. Watch here

NASA astronauts Barry Wilmore and Terry Virts completed the first spacewalk on February 21 and the second on Wednesday (February 25.)

The spacewalks are designed to prepare the orbiting laboratory for future arrivals by U.S. commercial crew spacecraft. The astronauts are laying cables along the forward end of the U.S. segment to bring power and communication to two International Docking Adapters slated to arrive later this year. The new docking ports will welcome U.S. commercial spacecraft launching from Florida beginning in 2017, permitting the standard station crew size to grow from six to seven and potentially double the amount of crew time devoted to research.

When astronaut Terry Virts returned the airlock after Wednesday’s spacewalk, he reported a minor seepage of water in his helmet. The Mission Management Team reviewed the status of spacewalk preparations as well as an analysis of the minor seepage of water and on Friday morning, the team expressed a high degree of confidence was that the suit’s systems are all in good shape and gave approval to proceed with Sunday’s spacewalk as planned.

Spacewalk specialists reported that Virts’ suit — serial number 3005 — has a history of what is called “sublimator water carryover”, a small amount of residual water in the sublimator cooling component that can condense once the environment around the suit is re-pressurized following its exposure to vacuum during a spacewalk, resulting in a tiny amount of water pushing into the helmet.

Spacewalkers Terry Virts and Barry Wilmore work outside Pressurized Mating Adapter-2. Image credit: NASA TV

NASA astronaut Barry Wilmore works outside the International Space Station on the first of three spacewalks preparing the station for future arrivals by U.S. commercial crew spacecraft, Saturday, February 21, 2015. Fellow spacewalker Terry Virts, seen reflected in the visor, shared this photograph on social media.
View larger. | Image credit: NASA

During Sunday’s spacewalk, Virts and Expedition 42 Commander Barry Wilmore will deploy 400 feet of cable along the truss of the station and install antennas as part of the new Common Communications for Visiting Vehicles (C2V2) system that will provide rendezvous and navigational data to visiting vehicles approaching the station, including the new U.S. commercial crew vehicles

NASA astronaut Terry Virts Flight Engineer of Expedition 42 on the International Space Station is seen working to complete a cable routing task while the sun begins to peak over the Earth’s horizon on February 21 2015. Image credit: NASA

All three spacewalks are in support of the long-planned ISS reconfiguration from its current configuration, which was designed to support visiting Space Shuttles, to its new configuration optimived for future visiting commercial crew and cargo vehicles.

While cargo vehicles attach to the ISS using the process of berthing, whereby they are captured with the station’s robotic arm and positioned below a berthing port prior to being bolted into place, commercial crew vehicles will not use this method.

This is because the process of un-berthing takes a long time to complete, since cables and ducting between the visiting spacecraft and the ISS must first be manually disconnected, control boxes installed, hatches closed, and then the visiting spacecraft must be maneuvered away from the station with the robotic arm.

This means that berthing ports cannot support a rapid evacuation of crew from the ISS should it ever be necessary, which will be one of the primary roles of the commercial crew vehicles as they serve as “lifeboats” during their crew’s stay at the ISS.

Instead, crewed vehicles will attach to the ISS via a process of docking, whereby the visiting spacecraft flies itself all the way into its docking port and attaches via a capture ring striking a corresponding attachment mechanism..

The leading end effector of the Canadarm2 (bottom foreground) will be lubricated Wednesday when astronauts Barry Wilmore conduct their second spacewalk. Image credit: NASA TV

Bottom line: NASA astronauts Barry Wilmore and Terry Virts aboard the International Space Station (ISS) completed the first of three spacewalk on February 21, 2105 and the second on February. On Sunday (March 1, 2015) they will perform the last of Expedition 42’s scheduled spacewalks. The astronauts are securing cables to prepare the orbiting laboratory for future arrivals by U.S. commercial crew.

SOURCE::::www.earthsky.org

Natarajan