The commander of NASA's Artemis II mission briefly feared that he and his crew would never return home from their trip around the moon after overshooting their turn-back point.

Commander Reid Wiseman and his three crewmates were supposed to reach 219,667 nautical miles (252,788 standard miles, or 406,823 kilometers) — farther than any humans have ever traveled from their home planet — before turning back toward Earth on the sixth day of their 10-day mission to the moon.

But the odometer on the Integrity spacecraft continued to tick upward as they shot past their intended point of return, leading the astronaut to fear that something had gone terribly wrong, he told an audience here at the Starmus VIII festival earlier this week. (This semi-annual event is held to celebrate achievements in science, exploration, and creativity.)

"Mission control in Houston had told us our maximum distance would be 219,667 nautical miles and that was the furthest we were supposed to be from Earth," Wiseman said. "I was watching this number, and I saw it hit 219,667, and I thought, 'Great, this is the farthest we will be from Earth, and the next number I will see will be 219,666 ‪—‬ we'll be going home.' But about three minutes later, I didn't see 219,666; I saw 219,668. It went up. I was like. 'Huh? That's weird.'