US President Donald Trump welcomed surviving Apollo 11 crew members Buzz Aldrin and Michael Collins to the White House on Friday, on the eve of the 50th anniversary of the first Moon landing.
"Tomorrow is a very big day... 50 years from the time we planted a beautiful American flag on the moon," Trump said in the Oval Office.
Relatives of the late Neil Armstrong, the first man to step on the Moon on July 20, 1969, were also present, and Trump asked them to raise their hands.
The president hailed his administration's efforts to relaunch crewed space flights with planned missions to the Moon and Mars. "We are bringing the glamour back to it," he said.
Aldrin later tweeted: "Just had an excellent meeting with President Donald Trump! We discussed America's future in space, ways to address space challenges, and the need to keep exploring beyond the horizon.
"Keep America Great in Space!!"
With the Apollo 11 Moon landing, the US achieved the ultimate victory in the Space Race after losing the initial heats to the Soviet Union, which was first to put a satellite and then a man in space.
The undertaking, announced by president John F Kennedy in 1961 and partly spurred by the Bay of Pigs crisis, involved enormous spending rivaled in scope only by the construction of the Panama Canal and the Manhattan Project.
It was a resounding achievement not just from a technical perspective but also diplomatic, as the two super powers jostled for global prestige in the Cold War.
Trump has relaunched the race to re-conquer the Moon -- this time with the first woman -- and to journey onwards to the Red Planet.
But the deadlines -- 2024 and 2033 respectively -- appear unrealistic and have caused turbulence within the space agency.