CHICAGO – Surviving Apollo 13 astronauts and several flight directors reunited Monday to remember a failed moon mission 40 years ago this week that they managed to turn into one of the greatest triumphs in the history of space exploration.

Those on hand included Apollo 13 commander James Lovell, fellow crew member Fred Haise and NASA’s legendary flight director, Gene Kranz — all three of whom were immortalized in the 1995 movie “Apollo 13,” which starred Tom Hanks as Lovell and Ed Harris as Kranz.

The Adler Planetarium, where the reunion took place, is holding a series of events this month commemorating the Apollo 13 flight.

On April 13, 1970, an oxygen tank exploded as the spaceship was four-fifths of the way to the moon. The crew, which included Jack Swigert, who died in 1982, was forced to scrap the moon mission and focus solely on getting back to Earth alive.

Lovell’s calm if unsettling words to Mission Control following the explosion that, “Houston, we’ve had a problem” — now widely recited as, “Houston, we have a problem” — belied his quick internal calculation that their chances of survival were slim.

“But you don’t put that in your mind,” he said. “You don’t say how slim they are but rather how you can improve the odds.”

In Houston, Kranz led hundreds of flight controllers and engineers in a furious rescue plan. He insisted Monday that he never allowed himself to believe that the plan could fail.

Still, he added, “there is some point when you do the best you can and then it’s up to a higher authority to steer this mission to its ultimate conclusion.”

The plan involved the crew moving from the command module into the cramped, frigid lunar lander while they rationed their dwindling oxygen and electricity. Using the lunar module as a lifeboat, they swung around the moon and aimed for Earth. In the process, they created one of NASA’s finest moments.

In 1994, Lovell and Jeff Kluger wrote “Lost Moon,” the story of the Apollo 13 mission and the basis for the movie. The movie, Lovell and Kranz concede, helped renew the public’s interest in Apollo 13 at a time when it had started to fade.

Kranz said Hollywood provided a largely accurate account of what happened. The one thing he took issue with was his character sometimes raising his voice in the control room.

“The fact is, controllers very seldom raise their voices, not in that control room,” he said. “If you lose your temper, people recognize it and they start (thinking) that you are closer to the edge than you really are.”