Chris Cassidy woke on his 43rd morning in space, a Friday, and before even switching on the light in his tiny sleeping quarters, opened his laptop to read the daily report. When he and the five other astronauts on the International Space Station had gone to bed, mission control was pondering a problem: a leak outside the station the astronauts had discovered earlier that day. Russian cosmonaut Pavel Vinogradov had noticed little ammonia snowflakes outside the window sputtering from the cooling system, the space equivalent of a slow drip. Not an emergency, but it would have to be fixed.
Over dinner that night, the astronauts and cosmonauts had discussed their options. Cassidy was of the opinion that NASA would probably wait until he and Italian astronaut Luca Parmitano, who was scheduled to arrive in a couple of weeks, could do an extravehicular activity—NASA parlance for a spacewalk—to assess the problem. Houston ordinarily didn’t like to rush into anything, let alone an EVA. Plus, half the crew was packing up to return to Earth in just four days. That’s why Cassidy couldn’t believe what he now saw on his laptop screen in big red letters: “Welcome to EVA prep day.” He and fellow NASA astronaut Tom Marshburn were going outside—tomorrow.
Rubbing the sleep from his eyes and still in his boxers, Cassidy floated down the dark passage toward the U.S. lab, where Marshburn was already up, having just read the same news. “All I could see was his white teeth smiling,” recalls Cassidy, “and I think he saw the same thing on me. And without saying a word, we high-fived.” They were more than happy to squeeze in another EVA, absolutely. What astronaut wouldn’t be? In a job full of unforgettable experiences, spacewalking ranks among the most desirable.
As it turned out, the astronauts were able to replace a suspect part on the ammonia pump and in just a few hours were back inside. But spacewalks don’t always run that smoothly, and one was coming that would test two astronauts—and their colleagues on the station and in mission control—with some of the tensest moments in EVA history.
There was a time, not long ago, when spacewalks were considered risky business, almost feared. When NASA was preparing to build the space station in the mid-1990s, some experts didn’t think the agency could safely pull off three or four assembly spacewalks on every shuttle mission, several times a year, for a decade. They called the station’s demanding EVA schedule The Wall, and thought it was insurmountable.
But the wall came down. In the first decade of this century, spacewalks became, if not routine, at least a well-practiced art. Perhaps the most amazing thing about NASA’s EVA record (more than 1,100 hours in the space station era alone) is that there has never been a serious accident. About the worst that astronauts suffer are aching hands, bruises, and the occasional discomfort from some part of the suit digging into their bodies. No spacesuit has ever ruptured in the vacuum. On shuttle mission STS-37 in 1991, a metal rod poked a tiny hole in Jay Apt’s glove, but he didn’t even notice until he came back inside.
Even though spacesickness is a common ailment in orbit, no astronaut has ever vomited in his or her helmet, which would pose a serious risk of choking. Spacewalkers have been known to cough on the water they sip from a drink bag located inside their suits at chest level, but that’s about it. Carlos Noriega was closing out an EVA in 2000 when a sip of water went down the wrong way and he sputtered. A single drop hit his helmet visor, which was coated with a soapy material to prevent fogging, and bounced back into his eye. The soapy droplet stung like crazy, blinding that eye until he could get back inside and remove his helmet. Canadian astronaut Chris Hadfield had the same thing happen on an EVA in 2001, except that it happened to both eyes, and he couldn’t see at all. It took more than half an hour for the tears to evaporate (they don’t fall in zero-G) and the stinging to go away. Hadfield’s vision improved, and he was able to finish the spacewalk.
None of these mishaps turned into full-blown emergencies, though. Even Hollywood’s favorite space disaster scenario—the astronaut drifting off alone, like Sandra Bullock in last year’s Gravity—isn’t much of a risk, thanks to well-drilled procedures in which everything is checked, double-checked, and checked again by your buddy. Spacewalking astronauts are as careful as mountain climbers when it comes to tethering themselves to the station. They have one long safety tether on a spring-loaded reel, plus smaller, supplemental ones, as well as a mini-jetpack called SAFER—the astronaut’s equivalent of a life vest—that can bring them back if the tethers fail. Joe Tanner, a seven-time spacewalker who used to head the astronaut office’s EVA branch and now teaches aerospace engineering at the University of Colorado, can think of only one instance in which somebody—he’d rather not say who—was completely untethered on a spacewalk, and that was just for a few seconds, a momentary lapse in safety so rare he still remembers it years later.
What happened on July 16 therefore came as a surprise, and some participants think it could have ended up worse. “In some ways we got lucky,” says Shane Kimbrough, the astronaut who was in mission control that day talking to spacewalkers Parmitano and Cassidy. Tanner, the veteran EVA chief, says, “I would rank the level of stress for crew members and ground team right up there” with the first space U.S. spacewalk in 1965. Parmitano, he says, “had every right to be fearful for his life.”