Astronauts tackle one of the most complex spacewalks ever

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After four years of brainstorming, custom tool development and training, two astronauts plan to venture outside the International Space Station Friday for the first of four spacewalks to repair a $2 billion cosmic ray detector. The excursions are considered the most challenging since work to service the Hubble Space Telescope.

“We’re going to perform what could be considered open heart surgery on this amazing experiment,” said Italian astronaut Luca Parmitano, the current space station commander.

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Floating in the station’s Quest airlock, Parmitano and NASA astronaut Drew Morgan plan to begin the first repair spacewalk Friday, switching their suits to battery power around 7:05 a.m. EST. For identification, Parmitano, call sign EV-1, will be wearing a spacesuit with red stripes, while Morgan, EV-2, will be wearing an unmarked suit.

NASA astronaut Drew Morgan, left, and space station commander Luca Parmitano, an Italian astronaut, float in the lab’s Quest airlock with the spacesuits they will wear during four spacewalks to repair the $2 billion Alpha Magnetic Spectrometer. NASA

It will be the 222nd station spacewalk since the lab’s assembly began in 1998, the ninth so far this year, the third for Parmitano and the fourth for Morgan. By all accounts, the four spacewalks needed to repair the Alpha Magnetic Spectrometer’s cooling system are among the most complex ever attempted.

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“It’s definitely towards the top of the list, if not on the top,” said Tara Jochim, the AMS repair manager at the Johnson Space Center in Houston.

During the first spacewalk Friday, Parmitano and Morgan plan to set up tools and equipment before removing a protective debris shield from the AMS, giving them access to the guts of the instrument so a new coolant system pump module can be installed later.

After carefully tossing the debris shield overboard, the spacewalkers plan to attach two handrails to help them move about the device. Parmitano also will snip a half dozen zip ties and cut a cord to fold back insulation blankets.

Actual repair work will begin during the second planned spacewalk next Friday. The third and fourth spacewalks will be officially scheduled after managers assess the results of the first two outings.

Unlike the Hubble Space Telescope, designed from scratch to be serviced by spacewalking astronauts, the Alpha Magnetic Spectrometer was never intended to be worked on in space. As such, it was not equipped with the sorts of fasteners, cables, handrails and internal clearances needed by astronauts working in bulky, pressurized suits.

In the end, it took engineers and astronauts four years to come up with a workable plan, developing some two-dozen custom tools and testing procedures during multiple underwater training runs. Parmitano and Morgan completed seven full-duration training exercises before launching to the station in July.

111419-ams3.jpg The 7.5-ton Alpha Magnetic Spectrometer, lower right, attached to the International Space Station’s solar power truss. Two spacewalking astronauts from an earlier mission provide scale. NASA

“We had to go off and figure out how to create a work site, we had to build new handrails to install on existing hardware, we had to deal with existing sharp edges and in a lot of cases, we’re creating new sharp edges using tools that have sharp edges on them,” said Jochim.

“We did as much as we could to minimize that risk to the crew member and then, of course, to the (repair) of the payload itself,” she said. “But they are certainly very challenging and technically difficult EVAs.”

Launched in 2011 on the next-to-last space shuttle mission, the Alpha Magnetic Spectrometer, is the most expensive science instrument aboard the space station and one of the most expensive ever launched into space.

The 7.5-ton device uses a powerful electromagnet to bend the trajectories of electrically charged cosmic ray particles created in supernova explosions and other extreme-energy events so researchers can characterize their velocities and energies.

The goal is to learn what happened to the antimatter thought to have been created in the big bang birth of the cosmos, to learn more about the unseen dark matter that permeates space and, possibly, gain insights into the nature of dark energy, the mysterious repulsive force that is speeding up the expansion of the universe.

Designed to operate for just three years, the AMS proved longer lived than expected, detecting more than 145 billion cosmic rays during eight-and-a-half years of operation. But the instrument has been hobbled in recent months by the staggered failures of four small pumps needed to circulate carbon dioxide coolant through its sensitive detectors.

To repair the AMS, Parmitano and Morgan will have to cut through eight small coolant lines and splice in, or “swage,” new lines leading to a custom-built replacement pump module launched to the station earlier this month. The pump module will be installed during the third spacewalk.

“We’re going to cut tubes, and then fuse them with other tubes (launched) from Earth and install a completely new pump to help the refrigeration work, keeping the magnet cold so the the Alpha Magnetic Spectrometer can work,” Parmitano said. “This is really the first time any of these actions have been attempted.”

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