For eight days they were squeezed together on a 500,000-mile voyage of a lifetime. They deposited a plaque on the Moon noting that they “came in peace for all mankind” and a gold ornament in the shape of an olive branch — and with the 40th anniversary of the launch of that flight yesterday, the eyes of the world were once more on the trio who made the historic journey.

The crew of Apollo 11, however, have not shared the cosy friendship one might have expected since they splashed back to Earth on July 24, 1969. “Amiable strangers” is how Michael Collins — the third astronaut, who remained aboard the command module orbiting the Moon while Neil Armstrong and Buzz Aldrin landed and took a walk — once described their relationship.

On Sunday, the eve of the 40th anniversary of their return to Earth, the three will be reunited in public for what is likely to be the last time. With all of them nearing their 80th birthdays, they will deliver a joint lecture on space history at the Smithsonian Institution’s National Air and Space Museum in Washington.

In recent days, however, Mr Armstrong has been agonising over how to present his views on space flight. Given the infrequency of his public appearances, he is wary that the world will be hanging on his words — but his opinion about whether Man should go back to the Moon is at odds with that of his former crewmates.

Times Archive 1969 Man takes first steps on the moon

The spectacular moment came at 3.56 am: "That's one small step for man but one giant leap for mankind"

• Topic: Men on the Moon

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“Neil’s not sure — hasn’t been sure in the last couple of weeks — of what to do or say in response to Aldrin’s positions,” explained Mr Armstrong’s friend and biographer, James Hansen. “Buzz is suggesting that we need to skip over going back to the Moon and start moving towards Mars, and the Nasa position has been somewhat different to that. I think Neil really believes that the Moon is very important — not that he doesn’t want to go on to Mars, but maybe that going back to the Moon is the right thing to do first, and then use the Moon as a staging post for a Mars mission.

“He does not really feel the same way about some of these current policy issues that Aldrin does, and here’s Buzz out there hawking his book and being the one that everyone’s interviewing, and he’s making these comments. Neil doesn’t quite agree with them, but how does he handle that?”

Mr Aldrin’s policy has been to evangelise about space at every opportunity — signing autographs, endorsing commercial products, writing three books and famously punching a conspiracy theorist who approached him outside a Los Angeles hotel and accused him of faking the Moon landing — but Mr Armstrong has been more reticent. “Neil was not really looking for the first-man role in terms of the icon that he now is. He’s embarrassed by it a little bit,” said Professor Hansen, a history expert at Auburn University, Alabama, and the author of the 2006 biography First Man.

So if Mr Armstrong were to contradict Mr Aldrin on Sunday night, he added, he would be very difficult to spot. “You’d really have to be listening for it to know that this is what Neil’s up to,” he said. In turn, Mr Aldrin was unlikely to pick an argument — for a reason that many would find surprising. “Buzz is still very unsure — and this is ironic for those who don’t understand the relationship within that Apollo 11 crew — but I don’t think Buzz, to this day, really understands Armstrong very well.”

The three men see or speak to each other rarely. “From time to time Neil might get a call from Buzz or Mike, but I don’t see Neil calling them unless something specific had come up. Collins called the three of them ‘amiable strangers’ and I think they’re still that,” said Professor Hansen.

“The kind of male bonding that you definitely found on the Apollo 12 crew and many other crews, I just don’t think it ever happened with these guys.”

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