It was Christmas Eve 2013, and NASA astronauts Mike Hopkins and Rick Mastracchio floated in space outside the International Space Station, where they had gone on the second of two spacewalks to fix a failing pump module that was critical to the station’s cooling system.
The repair work was something that on Earth might seem fairly basic—unplugging and removing a refrigerator-sized pump module, moving a replacement into place, and then reconnecting electrical lines and hoses that pumped ammonia into the unit. But in the unforgiving environment of orbital space, astronauts must cope with the rigors of working in a pressurized suit and adjusting one’s movements to microgravity, and they must work with great care and precision, since the slightest mistake can lead to disaster.
The December spacewalks provide an example of the extraordinary physical and mental demands of being a space station astronaut, and the extensive, painstaking training and preparation that allows them to succeed in one of the most difficult professions anyone could imagine.
Only the best of the best even get a shot. Last year, more than 6,000 applicants competed for a slot in the 2013 astronaut candidate class. Ultimately, eight were deemed worthy of entering the rigorous training that qualifies an astronaut to work on the space station, which includes extensive work in flotation tanks that simulate the microgravity environment of space.
Since the first spacewalk in the mid-1960s, astronaut training has become increasingly sophisticated, according to Allison Bolinger, NASA’s lead U.S. spacewalk officer, who has trained astronauts and worked as a controller from Earth. “We’re continually improving the training,” Bolinger says. “After a mission, we have the astronauts sit down and discuss the process with us. What are the things we need to train for, and how to we improve the training? What the things we teach that they don’t need? We’ve also had the benefit of astronauts with a lot of experience, including guys who’ve done six or so spacewalks. They can tell us how things actually are when you’re up there.”
While the basic and pre-mission training builds muscle memory and familiarity with equipment, NASA leaves nothing to chance. In the case of last December’s spacewalks, Hopkins and Mastracchio spent nine days on the station devoted to preparing for the spacewalks, according to Bolinger. They conducted daily video conferences with NASA officials on the ground, in which they planned every detail of the job and virtually every movement they would make in space. They studied slides of the equipment they would be fixing and the tools they would use to do it, and rehearsed the sequence of tasks on DOUG (Dynamic Onboard Ubiquitous Graphics), a virtual-reality trainer on the station. They even practiced one of the trickier tasks, closing and disconnecting four fluid lines on the pump that are filled with pressurized ammonia, by working with a fluid-line trainer device inside the station.
But spacewalks, in a sense, are like running marathons, in that no matter how much preparation, the experience remains a grueling one. Because of the need to accomplish as much as possible in a limited time, astronauts may have to work for six hours or more without any scheduled breaks, or even anything other than drinking water to nourish them. During that time, they’re compelled to concentrate to make sure that untethered tools and parts don’t float away, and they've got to pay attention to a continuous stream of verbal instructions from ground controllers, who are watching a video feed from cameras mounted on the astronauts’ helmets. And while it might seem that the microgravity of space would make movement effortless, in reality astronauts continually must move slowly and methodically, and struggle against the stiffness of the pressurized spacesuits. “You’re in an inflated balloon,” Bolinger explains. “You constantly have to fight the pressure, so that even grasping the handle of a ratchet is difficult.” After spacewalks, she says, astronauts often complain most of extreme fatigue in their hands.
Spacewalks are sufficiently trying physically that controllers on Earth continuously monitor data from sensors in the astronauts’ spacesuits, which enable them to keep tabs on the astronauts’ vital signs. “Mike Hopkins has a higher metabolic rate, so and we saw his CO2 creep up, an indication that he might be working too hard,” Bolinger recalls. “We made him stop for 10 minutes, so that we could try to get his heart rate down.” Additionally, while the astronauts are working in space, they periodically glanced down to check digital displays mounted on their spacesuits, which indicated whether the equipment needed to keep them alive in space was still working. As an additional precaution, each astronaut carried a small piece of paper attached to an elastic band on his wrist, a sort of cheat-sheet that reminded them what to do in the event they saw certain warning codes on those digital displays.
Despite all those challenges, the astronauts and their handlers managed to work so efficiently that they accomplished a task in two spacewalks that had required three walks when it was last performed in 2010. According to an Associated Press account, Hopkins held the bulky pump module with both hands and guided it to the installation spot, where he slid it into place as an astronaut inside the station, Japan’s Koichi Wakata, carefully steered a robotic arm to which the pump was attached. One complication did slow the work—what Mission Control called a “mini blizzard” of frozen chunks of ammonia that leaked from one of the lines, which bounced off the equipment and possibly the astronauts’ spacesuits as well.
But in the end, the work was successful. Six hours into the spacewalk, Hopkins announced, “Houston, you've got yourself a new pump module.”