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.”...