Even before the dream of a lunar landing had been realised, the Apollo project's funding was cut. But what is Nasa had continued its lunar project and eventually been able to establish a human settlement on the Moon?
One giant step after another
It is December 14, 1972. Eugene Cernan and Harrison Schmitt climb back aboard Apollo 17's lunar module. Just three years after Neil Armstrong's historic step, human exploration of the Moon is coming to an end. The die had been cast years before Apollo 11 had even reached the Moon. In the late 1960s, the Vietnam war was straining US finances. A fatal fire on the Apollo launch pad in January 1967 had blotted Nasa's copybook. The Soviet Moon effort seemed to be going nowhere. In the budget debates during the summer of 1967, Congress refused Nasa's request to fund an extended moon programme.
What if things had been different that summer? Suppose Congress had granted Nasa's wish, then fast-forward 40-odd years ? It is July 2009, and in Johnson City, America's permanent colony on the Moon - named after Lyndon B Johnson, the president who authorised it - they are celebrating the third generation of lunar Americans: the first child born to parents themselves born on the Moon. With just 5,000 inhabitants, "city" is perhaps too grandiose a term. Those who had anticipated a domed city of the kind that once graced science fiction comics had also been disappointed. That idea never stood up to the harsh lunar reality of cosmic rays and meteorite bombardment.
Fortunately, there was a ready-made alternative: subsurface lava tubes carved by extinct volcanic flows. The early Apollo missions had seen evidence for partly collapsed tubes in the form of intermittent surface trenches. The extreme dryness of the rock and the Moon's weak gravity meant tubes a kilometre or more in diameter could remain stable, and it proved a straightforward task to seal off and pressurise one of these in the late 1970s.
In the beginning, the government had run almost everything in Johnson City. These days, though, lunar exploration increasingly depends on the colony's independent businesses. Shipping costs of material from Earth are still astronomical, and local extraction of water and oxygen is a boom business. There's talk of a trade in mined helium-3 for use in fusion reactors on Earth - if fusion technology ever gets established on the mother planet.
There are thriving schools for the colony's children, but more advanced education is beamed up from Earth. Forty years on from Apollo, passenger flights into space are routine, but travelling to Earth is still expensive, and lunar inhabitants can't easily adapt to its higher gravity. Even if, like 90 per cent of the population, you were born on Earth, you can't easily go back. These problems are not shared by space tourists, who pay a pretty penny for a week or so's stay in orbit - and soon in the first hotel in Johnson City.
There's a Russian lunar colony too, a legacy of Nikita Khrushchev's desire to establish a permanent moon presence for the Soviet Union. In fact, the Moon in 2009 is more multinational than ever: European and Japanese voices fill Johnson City, and China and India are considering starting their own colonies. Exploring beyond the Moon has been less of a success. In 1980, three US astronauts landed on Mars for a stay of a week, but that was a hastily conceived "flags and footprints" effort to keep ahead of the Soviet competition. A Soviet landing and a couple more US missions followed, but by the late 1980s manned missions to Mars had stopped. Nasa's fixed budget was strained by cost overruns in establishing Johnson City, and the tottering Soviet economy was unable to match even that.
So apart from a visit to two near-Earth asteroids using leftover Mars hardware in the early 1990s, exploration beyond the Moon stopped until the turn of the millennium. Technological improvements then inspired a cautious revival. Not least of these was the ability to supply rocket fuel extracted from the Moon's unexpectedly rich polar ice deposits, meaning long-distance missions could be launched far more cheaply from the Moon than from Earth.
In January 2004, a team of four Americans and two Europeans made it back to Mars, spending 14 months on the first extended surface exploration. They found spectacular scenery, and the odd hint of past riches: traces of organic compounds, tiny rock features that might be microfossils. But life on Mars was clearly never common. If it is still around, it probably only inhabits niches such as the neighbourhood of geothermal vents - if they exist.
Analysing geology from orbit is always tricky, and the one hoped-for geothermal area within reach of the 2004 Mars explorers turned out to be a damp squib. It didn't help that their deep-drilling rig didn't work well in the unexpectedly hard and abrasive Martian permafrost. Still, hopes are high that the next multinational mission, to be launched in 2011, will be followed by a new base and perhaps even a colony.
All in all, humanity's engagement with space has been a positive affair. Launching and repairing communications satellites has become routine. High-speed computer networking and applications such as remote learning and telemedicine - developed for the early Mars expeditions - have brought spin-off benefits back on Earth. The scarce resources that characterise space exploration and colonisation have boosted green technologies such as waste water recycling, which is finding Earthly use as we try to cool our warming world. The same goes for a prototype orbiting solar power station currently under construction. Its use of a microwave beam to transmit power to Earth was controversial, but such worries have been trumped by the prospect of abundant clean energy.
Progress in space has been slower than in the dreams of the pioneers of the early 1960s. But with a permanent presence on the Moon, and plans for bases further afield, in 2009 the idea is firmly entrenched that, for humanity, the sky is no limit. Henry Spencer is a computer scientist, satellite engineer and space historian in Toronto, Canada www.newscientist.com