CAPE CANAVERAL (CBSMiami/AP) – For the second week in a row, a pair of astronauts aboard the International Space Station ventured outside to continue repairs on a cosmic ray detector.

Luca Parmitano and Andrew Morgan needed to slice through eight stainless steel tubes, using hardware store-type bolt cutters. That will set the stage to install new coolant pumps during the third spacewalk on December 2nd.

NASA likens the repair work to heart bypass surgery. At least four spacewalks are needed to fix the $2 billion spectrometer, on the hunt for elusive dark matter and antimatter for 8 ½ years. Without a new cooling system, the experiment — led by a Nobel laureate — would end.

NASA considers these the most complicated spacewalks since the Hubble Space Telescope repair missions a few decades ago. The spectrometer was not designed to be operated on in orbit.

A zip tie got away from Parmitano, floating harmlessly into space, as he struggled to free power cables buried in the spectrometer. Mission Control told him not to worry about it.

Parmitano, an Italian, and Morgan, an American, began the repair work last week. They spent years training for the operation before launching in July.

The 7 ½-ton spectrometer rode to the space station during shuttle Endeavour’s final mission in 2011. If successful, the repairs will keep the device working throughout the life of the station, or another five to 10 years.

(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)