Next week will mark 51 years since the incredible NASA achievement which saw Neil Armstrong and Buzz Aldrin touch the lunar lander Eagle down at Tranquility base on July 20, 1969. Six hours later, Armstrong jumped off the spacecraft and delivered his one small step speech to the millions watching anxiously back on Earth, before he was joined by Aldrin 19 minutes later. The pair would spend two-and-a-quarter hours exploring what would become Tranquility Base, collecting more than 20kg of rock samples before they buried the US flag into the surface to signify the end of the Space Race.

But in Mission Control, in the tense moments before the celebration, there was also confusion and finger-pointing, with questions asked of Professor El-Baz the leading geologist on the Apollo programme who was responsible for the selection of the landing site.

The 82-year-old recalled in an exclusive interview with Express.co.uk how he believed his team had calculated everything every minute detail to ensure the astronauts had the perfect landing on flat ground, but what was being relayed back did not match the photos of the zone selected.

Remembering the day, he said: It was absolutely stunning when Armstrong looked at the Moon and he saw very large rocks that his spacecraft was heading to because we worked it so beautifully that there was absolutely no question of mine that he would go there and see flat land like it was a carpet.

He was supposed to land beautifully, there should have been absolutely no rocks, we made sure that there would be no big rocks.

As the descent began, Armstrong and Aldrin found themselves passing landmarks on the surface two or three seconds early, and reported that they were "long" Eagle was travelling too fast and the consequences could have been unspeakable.

Five minutes into the descent burn, and 6,000 feet above the surface of the Moon, the guidance computer distracted the crew with the first of several unexpected 1201 and 1202 programme alarms.

Inside Mission Control, computer engineer Jack Garman told Guidance Officer Steve Bales it was safe to continue, and this was relayed to the crew.

But when Armstrong looked outside, he saw that the computer's landing target was heading for a huge crater and so he was forced to take over control.

The former test pilot cleared the crater and found a patch of level ground with just seconds of fuel remaining, but, what later became Tranquility Base, was actually miles from where they should have been.

Professor El-Baz explained: We were at a loss for a very long time where they were on the surface of the Moon, we could not figure exactly what crosshair they had landed at because all of our calculations said this is it and all the pictures that we saw from the landing were not it.

So something happened and it turned out that none of us were wrong, but actually, as the lander separated from the mothership in orbit of the Moon, there was a little bit of extra velocity a push.

So it actually sent the spacecraft, not to the place where we had all calculated, but four kilometres downstream.

We were still safe because we had an ellipse of 11 kilometres long because before the mission we did not know if they would land exactly in that spot or somewhere else.

It transpired that the issue had nothing to do with Professor El-Baz's team, but instead calculations made over the separation from the command module.

Luckily, his team's contingencies meant the area was still safe and everything worked out fine, but Professor El-Baz said the mood in Mission Control was tense.

He added: We made sure that spot where they were supposed to land had an ellipse of 11 kilometres long that was clean of rocks, clean of bad craters.

So the landing was fine, except the exact spot where he was supposed to put the Eagle was not because he had an excess velocity that was not calculated in the system.

I felt personally responsible, at that point, for any mistakes.

We were the ones that selected the landing site, we were the ones that said it was clear and its free of rocks, we were the ones that assured everyone that it was safe.

Then here he comes saying what he said and it was like what the hell happened (in Mission Control).

Professor El-Baz remembers a furious Deke Slayton who was in charge of the crew asking where Apollo 11 had landed.

He continued: Of course we felt responsible for the mess, people looked at us immediately the flight planners and the engineers.

Deke Slayton, the head of the astronauts, came to me and said where the heck did they land? And I had to say it was not where I thought they would.

I did not know, at that time, that the spacecraft had acquired this extra velocity to make it go beyond the landing point.

That is the whole reason why Neil had to take over manual control because he simulated the landing in the place we selected for him and he knew from the pictures in the simulator hed used a thousand times that he was seeing something different.

There were rocks the size of a car, so he immediately took control of the spacecraft and moved away from that location and thats why we had no idea why he was doing it because we couldnt see what he saw."

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NASA directors confusion over Moon landing footage: Where the heck did they land? - Daily Express