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How Neil Armstrong practiced that 'One Small Step' line for the moon

Astronaut Neil Armstrong claimed that his famous quote "This is one small step for man…" was spontaneous, but his brother Dean Armstrong says in a new BBC documentary that the quote was dreamed up months before the lunar landing.

The brother of first moonwalker Neil Armstrong says in a new BBC documentary that the phrase accompanying humanity's first footprint on the moon — "that's one small step for (a) man, one giant leap for mankind" — was not a spur-of-the-moment improvisation but a speech that was written out and practiced in advance.

In a rare interview, Dean Armstrong recalled that his brother slipped him the words — including the long-disputed reference to "a man" — on a piece of paper as they played a game of Risk, weeks before the Apollo 11 launch in July 1969.

"He says, 'What do you think about that?' I said 'fabulous.' He said 'I thought you might like that, but I wanted you to read it,'" Dean Armstrong is quoted as saying in a Telegraph report on the documentary, titled "Neil Armstrong: First Man on the Moon." The show premiered tonight on BBC Two.

The genesis of one of history's most famous phrases has long been shrouded in mystery: In his definitive history of the Apollo moon effort, "A Man on the Moon," Andrew Chaikin noted that as the mission neared, Neil Armstrong was inundated with suggestions for his speech, including passages from the Bible and from Shakespeare.

Chaikin implied that Armstrong was undecided about what he'd say until after Apollo 11's Eagle lunar lander had set down on Tranquility Base: "Now, on the moon, Armstrong knew he could delay no longer. As he thought about the first step he would take from Eagle's footpad he pondered the inherent paradox — a small step, yet a significant one — and he knew what he would say."

See images from the career of astronaut and American hero Neil Armstrong.

Dean Armstrong's recollection suggests that his astronaut brother, who died in August at the age of 82, scripted the words early on but held them close to the vest. The BBC documentary's director, Christopher Riley, speculated that Armstrong let people think the words came to him spontaneously to head off any outside tinkering in advance, or any second-guessing in retrospect.

The interview also confirms that Neil Armstrong meant to say "one small step for a man" — even though the "a" wasn't audible in the transmission from the moon. That's an important stylistic point, because the "a" draws a contrast between the physical length of a human's footstep and Apollo 11's "giant leap" for human exploration.

After the flight, Armstrong insisted that he intended to say "a man." Some experts say that the "a" was dropped because of a glitch in the radio signal, but most assume that Armstrong just left out the word. As the years went on, Armstrong's comments on the mystery took on an air of ambiguity. "We'll never know," Neil Armstrong told an interviewer in 1971.

If he did leave out the word, it's a natural slip to make: Dean Armstrong omitted the "a" himself the first time he quoted the phrase, and had to correct himself a moment later. "It was 'that is one small step for A man,'" he said.

Update for 5:30 p.m. ET Dec. 30: A commenter points out that Dean's recollection runs counter to what his brother Neil told James Hansen about the speech for his authorized biography, "First Man: The Life of Neil A. Armstrong," published in 2005:

"Once on the surface and realizing that the moment was at hand, fortunately I had some hours to think about it after getting there. My own view was that it was a very simplistic statement: what can you say when you step off of something? Well, something about a step. It just sort of evolved during the period that I was doing the procedures of the practice takeoff and the EVA prep and all the other activities that were on our flight schedule at the time. I didn't think it was particularly important, but other people obviously did. Even so, I have never thought that I picked a particularly enlightening statement. It was a very simple statement."

So maybe the controversy over those first words from the lunar surface will continue after all. ...

Update for 4:50 p.m. ET Jan. 4: Over the past few days, there's been a lot of back and forth over Neil and Dean Armstrong's intentions. Was Neil lying when he said that the words "just sort of evolved" after the moon landing? Was Dean lying when he said Neil had the words in mind before liftoff? In a Space.com commentary, Andrew Chaikin suggests that both men could be right. He says Neil Armstrong wasn't the kind of guy to let the matter of his moon speech go unconsidered until the last minute:

"... Nothing in Neil’s post-flight statements rules out the possibility that he thought up the 'one small step' line before leaving Earth. He didn’t say 'I thought up the quote after we landed'; he said, 'I decided what I would say after we landed.'

"Dean Armstrong's story just adds a little ambiguity. Maybe Neil had more than one quote in mind at that point, and only shared one of them with his brother. Or maybe the quote he showed his brother was an early draft, but after all these years, Dean remembers seeing the final version.

"We'll probably never know the answer.

"What it does not mean is that somehow Armstrong 'fibbed' or 'lied' to the public for 40 years. Everyone who knew Neil well has described him as extraordinarily principled. That was certainly the man I saw when I interviewed him, and in the years that followed, as we became friends. ..."

More about the first moonwalker:

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.