— Two astronauts have completed "surgery" outside of the International Space Station, slicing small metal tubes as part of the efforts to repair a state-of-the-art cosmic ray detector.

Expedition 61 crewmates Luca Parmitano of the European Space Agency (ESA) and Drew Morgan with NASA ventured outside of the space station on Friday (Nov. 22) for a 6 hour and 33 minute extravehicular activity (EVA, or spacewalk). The excursion continued the work they began one week ago to replace the failing cooling system for the $2 billion Alpha Magnetic Spectrometer (AMS).

The science instrument, which was installed on the space station in 2011, needs new coolant pumps so it can continue capturing high-energy cosmic rays in order to reveal the nature of antimatter, "dark matter" and "dark energy."

During their first spacewalk on Nov. 15, Parmitano and Morgan removed and jettisoned a debris shield cover and carbon fiber composite insulation cover from the AMS, exposing the lines to the degraded cooling system, and prepared their work area by installing temporary handrails and maneuvering aids. The AMS was not designed to be worked on in space and is positioned high atop the station's backbone truss.

Friday's spacewalk, which began at 7:02 a.m. EST (1202 GMT), had the two astronauts pick up where they left off, connecting new power and data cables that will lead to the upgraded coolant pump module to be installed on the next EVA. As they had last week, Parmitano worked from at a foot restraint attached to the end of the Canadarm2 robotic arm, while Morgan free floated near him.

"And I have a good mate," reported Parmitano, as he secured the second of two power cable connectors about an hour and 40 minutes into the EVA.

"Nicely done," replied Morgan.

"You made that look easy today, Luca. That was way different than I was expecting to see. Nice work there," radioed Canadian astronaut Jeremy Hansen, who as capcom, or spacecraft communicator, guided the spacewalkers through their work from Mission Control in Houston.

Parmitano and Morgan next installed a mechanical attachment device to which the upgraded thermal tracker pump system will be mounted on the third spacewalk.

NASA astronaut Jessica Meir, working at a robotics control station inside the station's U.S. Destiny laboratory, then repositioned Parmitano on the Canadarm2 to begin the next task, cutting a 0.2-inch-wide (6 millimeter) line to vent the carbon dioxide that fed into the AMS's failing pumps. This cut permanently disabled the instrument's original cooling system, which began having problems in 2014.

Parmitano's first snip with the "rough cutter" — one of 20 specially-designed tools for this series of AMS spacewalks — was confirmed by Mission Control to begin depressurizing the line. The rate of venting, though, was slower than expected and so Parmitano was directed to cut another line, resulting in a brief visible release of carbon dioxide into space.

Once the purging of the fill line was complete, Parmitano turned to a different series of eight stainless steel tubes, which will be used to splice in the new pumps. After cutting each, he installed a labeled cap on the end of the tube to protect from the sharp edge he created and to help with identifying the tubes as the new lines are connected.

"Luca, pop quiz, I've got a warning here. What's the rule of thumb for the rough cutters? What can you not put in them?" asked Hansen.

"My fingers?" replied Parmitano as he prepared to cut more of the coolant lines.

"Exactly, you pass," said Hansen, as laughter from the other flight controllers could be heard in the background of Mission Control.

Six of the lines were cut at the worksite from the first spacewalk, where the debris shield was removed. Another two were then severed from the opposite side of the AMS, wrapping up the work for this second of at least four planned spacewalks.

On the next EVA, currently scheduled for Dec. 2, Parmitano and Morgan will use another tool to smooth the end of the cut coolant lines in preparation for their being swaged, or spliced, with the lines leading to the new coolant pump module.

Friday's spacewalk, which ended at 1:35 p.m. EST (1835 GMT), was the 223rd EVA in support of space station assembly and maintenance since 1998 and the tenth this year. It was the fourth career spacewalk for Parmitano and the fifth for Morgan.