Watch live: Astronauts begin third spacewalk to fix cosmic ray detector


After prepping their patient — a $2 billion cosmic ray detector — during two earlier spacewalks, two space station astronauts ventured back outside for a third outing Monday to perform what amounts to transplant surgery, installing replacement coolant pumps to revive the costly instrument and extend its life.

The work requires European Space Agency astronaut Luca Parmitano and NASA crewmate Drew Morgan to attach an intricate pump module to the 7.5-ton Alpha Magnetic Spectrometer and then to splice it into eight thin coolant lines. A fourth spacewalk will be needed later to check for leaks and to re-attach insulation.

The equipment was not designed to be serviced in orbit and the work is considered the most challenging since spacewalks to repair and upgrade the Hubble Space Telescope.

Floating in the Quest airlock compartment, Parmitano and Morgan switched their spacesuits to battery power at 6:31 a.m. EST to officially kick off the 11th spacewalk so far this year, the 224th devoted to station assembly and maintenance and the third of four needed to repair the Alpha Magnetic Spectrometer.

For identification, Parmitano, call sign EV-1, is wearing a suit with red stripes and using helmet camera No. 11 while Morgan, EV-2, is wearing an unmarked suit equipped with “helmetcam” 18.

Launched to the space station in 2011, the AMS was built to study high-energy cosmic rays to glean clues about what happened to the antimatter presumably created during the big bang in equal measure with normal matter. Matter and antimatter annihilate on contact and it’s not clear why the universe is dominated by normal matter today.

The AMS also may shed light on the nature of the unseen dark matter permeating the universe and the mysterious dark energy that appears to be speeding up the expansion of the cosmos.

NASA astronaut Drew Morgan pictured during a Nov. 22 spacewalk. Credit: NASA

To achieve the required sensitivity, the AMS detectors must be chilled using carbon dioxide coolant pushed through the instrument in thin lines the width of a pencil. Originally designed to operate for just three years, the AMS chalked up eight years of operation before being hobbled by coolant pump failures.

To fix the system, engineers came up with a four-spacewalk plan to install a custom-built module containing four powerful pumps and a reservoir of fresh carbon dioxide coolant. Because the AMS was not designed to be serviced, engineers had to come up with a variety of innovative tools and techniques, requiring years of planning, development and training.

“Something that is really really cool for an astronaut is to actually be part of the development of an EVA,” Parmitano said during pre-flight training. “I’ve been lucky enough to have been part of the development team from the beginning, initially just as a consultant and then … as a test subject for some of the tools.

“We’re going to perform what could be considered open heart surgery on this amazing experiment. We’re going to cut tubes, and install a completely new pump to help the refrigeration work, keeping the magnet cold so the the Alpha Magnetic Spectrometer can work. This is really the first time any of these actions have been attempted.”

During spacewalks Nov. 15 and 22, Parmitano and Morgan removed a protective panel from the AMS, exposing the thermal control system. Then they cut zip ties and pulled back insulation, cut through a line to vent residual coolant overboard and then cut eight coolant circulation lines, setting the stage for Monday’s spacewalk.

“The third EVA is when we bring out the new pump system, we install that, and then we’ve got … eight tubes that we’re connecting,” said Brian Mader, an engineer at the Johnson Space Center who helped design the repair work. “It’s a piece of art. It’s really amazing how … the engineers figured out how to coil these tubes on the box.”

To pump module contains four small pumps, a spherical carbon dioxide tank, data and power cables. To splice it into the AMS thermal control system, Parmitano and Morgan will connect the eight previously cut cables, one by one, effectively splicing, or “swaging,” them together using custom tools.

A fourth spacewalk will be required to carry out leak checks, make any adjustments that might be needed and then to re-install insulation. The final excursion is not yet scheduled and may be put on hold in the near term because of crew time needed for unloading cargo ships and other higher-priority tasks.

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