The landing sites of four of the other five Apollo missions that landed on the moon between 1969 and 1972 reveal similar scenes - abandoned spaceship remnants, scientific instruments and, in the case of the Apollo 14 landing site, even the footprints left by astronauts Alan Shepard and Edgar Mitchell 38 years ago, along with the track marks created as they pushed a wheelbarrow full of moon rocks through the dust. 'Though in a lot of ways we are looking back in time today, the LRO and all these terrific instruments it has on board are really about the future, creating the kinds of maps and images that are going to allow us to return safely to the moon and explore interesting, useful and compelling places,' Michael Wargo, the US space agency's chief lunar scientist, said.

Mark Robinson of Arizona State University, the expert responsible for LRO's camera, said: 'It was fantastic to see the hardware sitting on the surface. Of course it was just as we thought it would be ... waiting for us to come back and waiting for humans to come and visit again.'

But the question of when, how and if Nasa can get astronauts back to the moon is surrounded by uncertainty and controversy. Whereas president John F. Kennedy captivated America with his 1962 'moon speech' setting out his vision for 'the most hazardous and dangerous and greatest adventure on which man has ever embarked', the nation's plans for human space flight 47 years later arguably lack the same energy.

With its shuttle fleet due to retire by the end of next year, once construction of the International Space Station is complete, Nasa is working on a new generation of spacecraft to send astronauts out beyond the lower earth orbit onto more ambitious exploits - like going back to the moon by 2020 and, by 2037, on the 400-million-kilometre voyage to Mars.

But US President Barack Obama has ordered a review of the new manned space programme, known as Constellation, due to increasing unease over its cost, timeline and safety. Among the concerns is that the newly designed Ares rocket that will launch astronauts into space - due for its first unmanned test launch this September - may have technical flaws that would result in the crew being literally shaken to death.

Some of Nasa's own engineers are so concerned that they are moonlighting on a rival design project, codenamed Jupiter, convinced that they have a blueprint that would get man back to the moon and beyond quicker, safer and more cheaply than the apparently troubled Ares.

The White House-ordered reappraisal of Constellation, set up to hear from all sides and consider all options, could recommend radical changes to Nasa's plans. Not only will the panel review the hardware, it must also consider whether the moon is the right destination - or whether to skip Nasa's lunar ambitions and strike out directly for Mars.

Coupled with news of budget cuts, the move has raised fears that America's space plans could be sent back to the drawing board, a move that may compromise American space dominance as China, India and Russia mull lunar ambitions of their own.

'If we do a review every four or five years to see if Nasa is on the right path, we're never going to get a product,' Michael Griffin, the former head of Nasa who quit in January when Mr Obama took over the presidency, said. 'You can't grow carrots by pulling them up out of the ground to see how they are going.'

Norman Augustine, the head of the review panel, has indicated that he will be putting forward 'more than one option' to the White House when he makes his final report next month - suggesting that the status quo at Nasa is unlikely to get his seal of approval though also indicating that he does not yet consider Ares 'dead in the water'.

But he also warned that the president and Congress may need to start digging deeper into their pockets if America is to return to the golden era of space flight it enjoyed during the Apollo era, complaining that while Kennedy was so firmly and financially committed to space, the presidents who have followed since have not been. 'That puts Nasa in a terrible position,' he said.

In a Gallup poll conducted to coincide with Apollo 11's anniversary weekend, a majority of Americans indicated they believe Nasa's space programme is still worthy of the hundreds of billions spent on it each year.

But even the three Apollo 11 astronauts - Mr Armstrong, Mr Aldrin and their colleague Michael Collins - are divided as to where Nasa should next set its sights.

While Mr Armstrong was set to voice his support for a return to the moon - at what could well be the trio's final public reunion at the National Air and Space Museum in Washington today - Mr Aldrin and Mr Collins favour Mars.

Wherever Nasa plots its next course, space advocates agree that man's long-term future on earth has its limits.

John Logsdon, a space policy expert at the National Air and Space Museum, said: 'Apollo showed us that we don't have to stay on this planet forever. It was the first step in a centuries-long process of moving humanity into the solar system. Apollo, when you look back, will be the first step in the evolution of humanity to a multi-planetary species.'

A space odyssey

Forty years ago today, millions of people sat glued to television screens watching a man walking on an alien world for the first time. The Apollo 11 mission fulfilled John F. Kennedy's 1961 pledge to land a man on the moon before the end of the 1960s - here's how they got there

The spacecraft and Saturn V rocket

July 16, 1969

Apollo 11 - carrying Neil Armstrong, Edwin 'Buzz' Aldrin and Michael Collins - blasts off atop a Saturn V rocket from Kennedy Space Centre

1 First stage

Five F-1 engines powered by refined kerosene and liquid oxygen lift Apollo spacecraft to height of 67.6km in 158 seconds

2 Second stage

Five J-2 engines burn for six minutes, lifting craft to 176km at 25,182km/h, powered by liquid hydrogen and liquid oxygen

3 Third stage

Single J-2 engine boosts craft into earth orbit, where trans-lunar injection (TLI) propulsive manoeuvre sets it on course for the moon

4 Trans-lunar voyage

About 40 minutes after TLI, the command service module (Columbia) separates from third stage, rotates to dock with lunar module and starts 385,000km journey to moon

July 19

Apollo 11passes behind moon and fires engine to enter lunar orbit. Craft makes 30 orbits

July 20

Columbia pilot Collins remains in lunar orbit while Armstrong and Aldrin descend in lunar module

I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to earth

US president John F. Kennedy, May 1961

Sources: NASA, Smithsonian Institution National Air and Space Museum