When the astronauts and engineers of the Apollo programme were in the frenzy of their moonshot in the 1960s, it is hard to believe that they knew they were engaged in a one-off exercise. The moon landings should have been the start of an epic age of space travel, moon bases and trips to Mars. But Nasa somehow lost its way after the pinnacle of Apollo, its ambition hobbled by drastic funding cuts and a muddled sense of identity over the past four decades.
The first decade of the 21st century, however, has brought with it a new space race: a mixture of private companies battling to make space travel cheaper and a series of big national space programmes in the east that could finally propel explorers to build on the legacy of Neil Armstrong's first step on the moon in 1969.
Since the crew of Apollo 17 came back from the moon in December 1972, humans have not left low Earth orbit. More than 450 men and women have been into space since Apollo, but all of them have stayed within a few hundred miles of the Earth's surface. "I don't think the Apollo astronauts realised they were doing something that would stand alone for the next four or five decades," said the astronomer and author Stuart Clark.
A flurry of robotic probes was sent out by Nasa to all parts of the solar system in the decades after the Apollo programme – the Mariners, Pioneers and Voyagers were the first step in realising Apollo's wider legacy. They would survey the planets, space enthusiasts believed, while the space shuttle of the 1980s would help to build, in Earth orbit, the rockets and space stations needed to send humans to new places.
One problem was that Apollo was crushingly expensive and no government could spend that amount of money over the long term. At its height in the 1960s, Nasa's budget took up 3.45% of US federal government spending. After 1975, the budget dropped below 1% of federal spending and in the past decade it has fallen further to around 0.5%.
The Apollo missions had developed a culture inside Nasa that could relentlessly focus on a single goal in a specified time limit, but that culture was not quite right for carrying out a long-term programme of exploring the solar system.
The space shuttle programme, though successful as an engineering exercise, did little for Nasa's image in Congress. Politicians had been promised by Nasa chiefs that the reusable space plane would fly 50 times a year and drastically reduce the costs of a space mission to millions, rather than billions, of dollars.
"They believed they could make low Earth orbit commercially sustainable because of the massive launch rate of shuttles but, of course, it never achieved it," said Kevin Fong, an expert in space medicine at University College London. The shuttle was an engineering success but the commercial promises made by Nasa chiefs were orders of magnitude out of line with what the programme eventually delivered.
There was a brief flicker of ambition in 2004 when the then president, George Bush, called on Nasa for a return to the moon followed by Mars expeditions. The space agency's response was the Constellation programme, composed of a new exploration vehicle called Orion, shaped like the Apollo space capsules last used in 1972 but three times larger, which could replace the space shuttle. Two new rockets, known as Ares I and Ares V, would blast the astronauts and equipment separately into space. Plans followed for a permanent moon base and for scientific experiments to measure cosmic rays, hunt for exotic subatomic particles in space and look for asteroids on a collision course with Earth.
But Bush's challenge was never met with the increase in funding for Nasa needed to develop the required technology. In 2010, Barack Obama cancelled Constellation's funding. With the retirement of the space shuttle in 2010, the lack of priority for human spaceflight has left Nasa in the doldrums.
But not all hope is lost for would-be space adventurers. In May, the PayPal entrepreneur Elon Musk's company, SpaceX, made history when his Dragon craft carried out a successful mission to dock with the International Space Station.
Clark said that this rejuvenation of the space programme – led by private companies – rested on learning from many of the mistakes of Nasa's wilderness years. "It's better to use a cheap launch vehicle to get the equipment into space and then put humans up separately," said Clark. "That's the way we're going now. Perhaps the space shuttle tried to be all things to all people and ended up being the jack of all trades and master of none."
Nasa's collaborations with private companies might lack the national prestige of the big-ticket space adventures. And there is the spectre of commercialism entering the pure idealism of space travel, but Clark said it was an exciting time. "It's possibly the opening of the door we need to realise the dreams of Apollo."
Nasa and its collaborators are not the only player in the future of space. The same year that Bush challenged Nasa with the 21st-century moonshot, Yang Liwei became China's first astronaut. The country wants to build its own space station and land robots and rovers on the Moon – and by 2020 there is a good chance it could send a person there too. The former Nasa administrator Mike Griffin has said that he believed China had the capability to get to the moon and he wouldn't be surprised if the next person to walk on the moon was Chinese.
India has also sent a probe to the moon and is investing large amounts – reportedly more than £500m a year – on its space ambitions, which include human spaceflight.
This year, in what would turn out to be his last public interview, Armstrong lamented the wasted years since the end of the Apollo programme. "Nasa has been one of the most successful public investments in motivating students to do well and achieve all they can achieve," he said. "It's sad that we are turning the programme in a direction where it will reduce the amount of motivation and stimulation it provides to young people."
He said he was concerned about Nasa's policy direction, which was was uncertain because of tensions between the White House and Congress. "They're playing a game and Nasa is the shuttlecock they're hitting back and forth as both sides try to get Nasa on the proper path."
In 2010, Armstrong wrote to NPR's science correspondent, Robert Krulwich, and spoke of the need for humans to return to the moon. "Some question why Americans should return to the moon. After all,' they say, 'we have already been there.' I find that mystifying. It would be as if 16th-century monarchs proclaimed that 'we need not go to the New World, we have already been there.' Or as if President Thomas Jefferson announced in 1803 that Americans 'need not go west of the Mississippi, the Lewis and Clark expedition has already been there.' Americans have visited and examined six locations on Luna, varying in size from a suburban lot to a small township. That leaves more than 14m square miles yet to explore."
