Neil Armstrong: “One small step for man” or “one small step for a man”?

Question

Today on Facebook the Science Museum (London) posted:

#OTD in 1930 American astronaut and aeronautical engineer Neil Armstrong was born.

In July 1969, Armstrong and Apollo 11 pilot Buzz Aldrin performed the first manned Moon landing. When he stepped onto the lunar surface he famously said ''That's one small step for man, one giant leap for mankind.''

I though it was “one small step for a man”. That seems to make more sense.

Which is correct?

Clarification at mod request: please don’t answer with what you think the audio sounds like, because that’s a matter of opinion. There is professional audio analysis to cite (although a good answer would evaluate the strength, or not, of that evidence) as well as Armstrong’s reports of what he intended to say and what he believed he said.

Answer 1

It seems that he fluffed his line. He meant to say "a man", but inadvertently missed out the "a". It is also possible that the "a" was masked by static.

What did Neil Armstrong really say when he stepped on to the moon?

According to the authors of the 1986 book Chariots for Fire, the astronaut tried to argue it omitted the word "a" but after hearing a recording of the flight he admitted:

"Damn I really did it. I blew the first words on the moon, didn't I?"

Neil Armstrong’s family reveal origins of 'one small step' line

It is the most famous and disputed quote in history.

Now, three months after Neil Armstrong’s death, it has emerged that the first man on the Moon wrote the words to mark the moment he stepped onto the lunar surface months in advance and had always intended to include the notorious missing “a” in the speech.

Answer 2

More grist for the mill:

Despite his initial adamance that he got the grammar right by including the indefinite article, Armstrong acknowledged at a 30-year anniversary event in 1999 that he couldn't hear himself utter the "a" in the audio recording of his moonwalk transmission, according to the Associated Press.

But then, in 2006, computer programmer Peter Shann Ford might have vindicated Armstrong.

Ford downloaded the audio recording of the moon man's words from a NASA website and analyzed the statement with software that allows disabled people to communicate via computers using their nerve impulses.

In a graphical representation of sound waves of the famous sentence, Ford said he found evidence that the missing "a" had been spoken after all: It was a 35-millisecond-long bump of sound between "for" and "man" that would have been too brief for human ears to hear.

"I have reviewed the data and Peter Ford's analysis of it, and I find the technology interesting and useful," Armstrong said in a statement. ''I also find his conclusion persuasive. Persuasive is the appropriate word."

And so was "a," whether spoken or not.

This corresponds with my familiarity with spoken English: The word "a", in a context such as Armstrong's utterance, is easily "swallowed" -- if you really listen for it you can sort of hear it, but many people will insist it's not present.