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Watch live: Spacewalkers work to prep space station for future upgrades

STORY WRITTEN FOR CBS NEWS & USED WITH PERMISSION

Space station commander Chris Cassidy and Robert Behnken floated back outside Tuesday for their fourth spacewalk in less than a month, this one to complete preparations for future upgrades including the eventual installation of an airlock that will allow commercial experiments to be moved into and out of vacuum as required.

The astronauts originally planned four spacewalks to install replacement batteries in the station’s solar power system, but that work was completed ahead of schedule during three excursions on June 26, July 1 and July 16. The fourth spacewalk was replanned as a result and now includes a variety of unrelated tasks.

Floating in the Quest airlock, Cassidy and Behnken switched their spacesuits to battery power at 7:12 a.m. EDT to officially kick off a planned six-and-a-half-hour spacewalk, the 231st in station history, the seventh so far this year and the 10th for both astronauts.

The first item on the agenda was to install a robotics tool box on a rail-mounted carrier used to move the station’s robot arm from one worksite to another.

After that, Behnken planned to move to the lab’s right-side inboard set of solar arrays to remove a no-longer-needed handling, or “H,” fixtures, one of several that were used to lift and move the stowed arrays before launch. Cassidy planned to detach a second fixture on the far right side of the power truss.

All of them must be removed to make way for future power system upgrades. Behnken attempted to remove the first fixture during the July 16 spacewalk, but he was unable to pull it free. Engineers then developed new procedures and tools, including a 3D-printed wedge, that were expected to help the crew pull off the two fixtures.

Cassidy and Behnken then planned to make their way to the left side of the power truss to prepare the outer hatch of the Tranquility module — the same compartment that features the station’s multi-window cupola — for the later attachment of a commercial airlock.

The Bishop Airlock, designed by Nanoracks as a commercial venture, is scheduled for launch later this year aboard a SpaceX Dragon cargo ship. Once in place, the airlock will enable research payloads and equipment to be robotically moved into and out of the space station, exposing them to the space environment as required.

The airlock will be attached to the Tranquility module’s currently unoccupied outboard port. To make way for installation, Cassidy and Behnken planned to remove a thermal cover and protective shields, reposition a variety of cables and clean the common berthing mechanism’s attachment fittings.

Once the airlock preps are complete, Cassidy and Behnken will wrap up the day’s work by routing camera power and data cables and removing a damaged lens filter from an external camera assembly.

Assuming the spacewalk runs the full six-and-a-half hours, Behnken will move up to No. 3 on the list of most-experienced spacewalkers with more than 62 hours of EVA time 10 excursions. Cassidy’s mark will stand at nearly 56 hours, moving him up to eighth on the list.

With the spacewalk complete, the station crew will turn its attention to the launch and docking of a Russian Progress supply ship Thursday. The next major task after that will be preparations for Behnken and Douglas Hurley to return to Earth aboard the SpaceX Crew Dragon spaceship that carried them into orbit May 30.

The Crew Dragon, developed as a commercial venture, is the first piloted U.S. orbital since the final shuttle flight in 2011. Hurley and Behnken plan to undock from the station’s forward port the evening of Aug. 1 and to splash down in the Gulf of Mexico or the Atlantic Ocean off Florida’s east coast on Aug. 2 to close out a 64-day flight.