Apollo 11's surviving astronauts are returning to the exact spot from where they flew to the moon 50 years ago.
NASA has invited Buzz Aldrin and Michael Collins to Kennedy Space Centre's Launch Complex 39A on Tuesday.
They will mark the precise moment - 9:32 am on July 16, 1969 - that their Saturn V rocket departed on humanity's first moon landing.
It kicks off eight days of golden anniversary celebrations for each day of Apollo 11's voyage.
Mission commander Neil Armstrong - who took the first lunar footsteps on July 20, 1969 died in 2012.
Also Tuesday morning, 5,000 model rockets are set to launch simultaneously at the US Space and Rocket Centre in Huntsville, Alabama.
A full scale image of the Saturn V rocket will be projected on to the Washington monument.
Australian Associated Press