Space junk—the bits and pieces of failed rockets and broken-down satellites—is becoming an increasing headache for NASA. This past weekend, the Shuttle Discovery had to move the International Space Station out of the way of an approaching piece of metal, just four inches across. It was the third such incident in recent weeks, and a big deal given that even the smallest collision could lead to a catastrophic hull breach. “Space debris is becoming an ever-increasing challenge,” NASA flight director Kwatsi Alibaruho says. When it comes to dodging junk, “it’s a big deal. It’s very tiring. Sometimes it’s exhausting.”