As the world marks the 40th anniversary of the first lunar landing, astronauts have called for the US to take inspiration from the Apollo program and go back to the moon and beyond, to Mars.
'We need to go back to the moon,' said Eugene Cernan, who was the last man to walk on the moon as part of the Apollo 17 mission in 1972.
At a news conference held with half a dozen other astronauts from the Apollo programme, he stressed that the 'ultimate goal' had to be Mars.
James Lovell, who flew on Apollo 8 and Apollo 13, called Mars 'the other moon,' and claimed Mars was 'a tangible goal that could rekindle public enthusiasm for manned space flight.'
'When we get there, if we don't find any life on Mars, from that point on there will be life on Mars because we'll bring it there, whether it's germs and leftover urine bags, whatever it is,' said Buzz Aldrin.
An estimated 500m people crowded round televisions and radios to watch Neil Armstrong step out of the Apollo 11 lunar lander on 20 July 1969.
Events were held today to mark that moment.
Celebrations were held at all space centres involved in the Apollo mission in 1969, including Cape Canaveral in Florida where Apollo 11 blasted off.
Neil Armstrong, Buzz Aldrin and Michael Collins set off from Earth on NASA’s Apollo 11 mission on 16 July, 1969, and the Eagle module landed on the moon’s surface four days later.
The three astronauts met US President Barack Obama at the White House this evening.
In addition to the White House reception, there was also a news conference and a simulcast to science centres across the US about the Apollo legacy and the future of space exploration.
The lunar landing was a huge morale boost for a country mired in the Vietnam war and on edge because of the Cold War.
'That was a proud moment, to be a military person and to salute that flag on the surface of the moon,' said astronaut Buzz Aldrin yesterday.
Mr Aldrin, second to Armstrong to step onto the moon, said what stays with him most about his rendezvous with history was a realization, upon touchdown, of the scope of what he and the rest of NASA had achieved.
However NASA's ambitious plans to put US astronauts back on the moon by 2020 to establish manned lunar bases for further exploration to Mars under the Constellation Project are increasingly in doubt.
Other nations such as Russia, China and even India and Japan are increasingly honing and expanding their own space programs.
The cost of the Constellation Project is put at about $150bn, but estimates for the Ares I launcher to put the project into orbit have skyrocketed from $26bn in 2006 to $44bn last year.
Only 12 men, all US citizens, have ever walked on the moon, and the last to set foot there were in 1972, at the end of the Apollo missions.
Currently NASA's budget is too small to pay for Constellation's Orion capsule, a more advanced and spacious version of the Apollo lunar module, as well as the Ares I and Ares V launchers needed to put the craft in orbit.
With a space exploration budget of $6bn in 2009, Senator Bill Nelson of Florida, a former astronaut, said: 'NASA simply can't do the job it's been given.'
