Mr Armstrong and Mr Aldrin were the first men to go to the Moon in 1969, exactly 50 years and one day ago. A third astronaut, Michael Collins, remained in the control module and picked up his colleagues later. Mr Armstrong died in 2012 aged 82 and Mr Aldrin made a heartbreaking statement.
He said he was disappointed that they would not be able to celebrate the 50th anniversary of the Moon landing together in 2019.
In an official statement, he wrote: “I am deeply saddened by the passing of my good friend, and space exploration companion, Neil Armstrong today.”
He added: “I had truly hoped that on July 20th, 2019, Neil, Mike and I would be standing together commemorate the 50th anniversary of our moon landing, as we also anticipated the continued expansion of humanity into space, that our small mission helped make possible.
“Regrettably, this is not to be. Neil will most certainly be there with us in spirit.”
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He added on Twitter: “I know I am joined by millions of others in mourning Neil’s passing – a true American hero and the best pilot I ever knew.”
Mr Armstrong, Mr Aldrin and Mr Collins had just six frantic months to get to know each other before their mission and apparently “felt the weight of the world” upon them, Mr Collins later admitted.
Mr Collins is the least well-known of the three and on previous anniversaries was content to be forgotten.
However, with the “huge gap” left by Mr Armstrong’s death, Mr Collins said he felt compelled to speak up even though “my first inclination for celebrating the 50th anniversary is to go hide under a rock somewhere.”
His two daughters have helped the 88-year-old’s avalanche of requests.
The extraordinary Apollo 11 mission 50 years ago was the culmination of decades of work by hundreds of thousands of people in science, technology and engineering.
It cost around $25billion – which is £20billion or £323billion in today’s money.
They achieved the incredible feat using technology developed far before modern computers.
In fact, it has been calculated that an i-Phone has around 100,000 times the processing power of the computers used in the 1969 Moon landings.
When they eventually reached the moon, Mr Armstrong’s famous words appropriately marked the century-defining moment.
He of course said: “One small step for man, one giant leap for mankind.”