Their moon-bound spacecraft wrecked by an oxygen tank explosion on April 13, 1970, the astronauts urgently radioed, "Houston, we've had a problem here."

Screenwriters for the 1995 film Apollo 13 wanted to punch that up. Thus was born "Houston, we have a problem."

Even more artistic licence was taken with NASA flight director Gene Kranz' mobilising speech to his team in Houston.

Kranz never declared, "Failure is not an option."

Ask Kranz what he actually told flight controllers, and he rattles it off without a moment's hesitation a half-century later.

"I have never lost an American in space, sure as hell aren't going to lose one now. This crew is coming home. You got to believe it. Your team must believe it. And we must make it happen."

Kranz said the moviemakers came up with "Failure is not an option."

Does he wish he'd said it? "No - I'm satisfied with what I said."

Kranz constantly finds himself setting the record straight - "in fact, every time I speak."

"I try not to plagiarise," he said with a laugh.

He did borrow the phrase for the title of his 2000 autobiography.

Director Ron Howard's film starring Ed Harris as Kranz and Tom Hanks as mission commander Jim Lovell was based on Lovell's 1994 autobiography, "Lost Moon." Actors Bill Paxton and Kevin Bacon portrayed Apollo 13 astronauts Fred Haise and Jack Swigert.

Australian Associated Press