Stephen Cass in Spectrum:

“Houston, we’ve had a problem.”

Thirty-five years ago today, these words marked the start of a crisis that nearly killed three astronauts in outer space. In the four days that followed, the world was transfixed as the crew of Apollo 13–Jim Lovell, Fred Haise, and Jack Swigert–fought cold, fatigue, and uncertainty to bring their crippled spacecraft home.

But the crew had an angel on their shoulders–in fact thousands of them–in the form of the flight controllers of NASA’s mission control and supporting engineers scattered across the United States.