It was an event that felt as if it belonged to the whole world. But for astronauts Neil Armstrong and Buzz Aldrin, setting foot on the moon�s surface on July 20, 1969, was an intensely �solitary experience � despite being a hugely public one.

It was an event that felt as if it belonged to the whole world. But for astronauts Neil Armstrong and Buzz Aldrin, setting foot on the moon's surface on July 20, 1969, was an intensely solitary experience - despite being a hugely public one.

The two men walked on a tiny patch of the vast lunar surface, leaving the first human footprints, collecting rocks for analysis and planting an American flag. They did so in the greatest isolation ever experienced by human beings, 236,000 miles from earth.

Reaching the moon took daring and ingenuity, both by Nasa and the men themselves, making them the ultimate pioneers. They were folk heroes, too: three years later, Armstrong was welcomed into the Dumfriesshire town of Langholm, the traditional seat of the clan Armstrong, and made the first freeman of the burgh.

The first moon landing took place just 12 years after man's initial foray into space: the launch of the first artificial satellite, Sputnik I, by the Soviets. It was imagined that, by today, humans would be colonising Mars.

But it was not to be. The Mir Space Station launched in 1986 and was used by astronauts from many countries, but interest in manned space flight began to fade almost as quickly as it had arisen. In the past decade, however, that has begun to change, and manned space exploration has gained new momentum.

The International Space Station (ISS) was begun in 1998, and in 2007 Nasa published a strategy for landing people on Mars in the 2030s. As a first step, though, the plan is for humans to return to the Moon and live there for up to six months.

Any Mars mission will take two and a half years, including six months' travelling each way, and is likely to be an international effort. A Russian-European mission simulation is already under way.

This scenario is all very different from 1969, when Soviet-American competition fuelled progress. The Russians had chalked up most of the firsts, including the first living creature in space (Laika the dog), the first man (Yuri Gagarin), the first woman (Valentina Tereshkova), the first space-walk and the first probe to reach the moon's surface.

Both sides justified the cost by claiming the technology had military applications, but to the watching public the real appeal was man's audacious crossing of a breathtaking new frontier.

Piers Sellers, 54, one of just four British people (three men and one woman) to have been into space, still feels this keenly. To him, it is its own justification. "The relevance of manned space exploration is the same as it's always been - we're humans and we're going to explore the place. It's our own back yard," he tells me from his Houston home. "When people explore Mars and the moon, I think it will be exciting and interesting for everyone on earth."

Sellers was 14 when Apollo 11 landed on the moon. "I had bookshelves of books, big colour diagrams," he says. "I was fascinated."

Sussex-born and an ecological science graduate of Edinburgh University, Sellers worked as a climate scientist for years, before fulfilling his dream of being selected as an astronaut in 1996, for which he became an American citizen. His first mission to the ISS was in October 2002, his second in July 2006, and he is due to return next April.

There is a sense of wonder in his voice when he describes going up in the shuttle to the station. "About two minutes before you go, there's a call to say, Close your visors, turn on your oxygen,'" he says. "The clock goes down - you can see the digits flipping over - and about three seconds before zero, you feel the main engines light. Tremendous noise.

"About a second later the boosters light and they're like two huge bombs going off. It feels like someone has got a gigantic hand under your back and is shoving you up into the sky. You leap off the pad and you're thrust back in your seat.

"There's a lot of noise. Everyone's banging around in their seats, and then the whole stack, all 3000 tonnes of it, twists in the air. You watch the sky rotate and all the light coming through the windows flashes round the walls and you end up on your back.

"You look down in your rear-view mirror and you see Florida getting small. And then all of a sudden the sky goes blue blue blue, blue blue black, just like that, in about a minute and a half. And after eight minutes there's a big, blue, beautiful world and you're doing five miles a second."

Docking with the ISS takes place two or three days later. "It's like a huge great building with wings sticking out of it. It's very strange-looking," says Sellers. Inside, up to six personnel, often of as many different nationalities, are eagerly awaiting the arrival of chocolate and coffee.

According to Sellers, it takes around 20 minutes walking hand over hand to go from end to end - a distance of about 300ft. Cubicles for the crew are large enough for a sleeping bag, a computer and some photos. You can also phone home: "I've called my mum from space and she didn't know it was me so she put the phone down."

The view from space is literally out of this world. "You look down and say, wow, there's Africa. It takes about 10 minutes to go over India. Then you come over the Pacific, the Americas, Britain - I saw Scotland and took a photo. You go around the world every 90 minutes, half in daylight, half in night. It's breathtakingly, unbelievably beautiful."

He regards the ISS as an amazing achievement. "We've gone from having a space race to having cooperation and peace in space. The station's only purpose is science, and we have 16 of the world's developed countries working together up there."

The global economic crisis is not improving the chances of a manned Mars mission. Although President Bush gave the plans his backing, President Obama has set up a panel to review them. Nevertheless, Sellers predicts we'll have a manned moon mission within 10 years and "hopefully" one to Mars 10 or 15 after that. "It will be a great adventure," he says. "I intend to watch it all."