The planet Mars may be around 250 million miles away, but getting there is the easy part, according to astronaut Edwin "Buzz" Aldrin.
The American, who in 1969 became the second man to set foot on the moon, believes that mankind could touch down on the red planet by 2040 and thinks the generation born around the year 2000 will be the first to make the journey.
Dr Aldrin, 86, believes that through international collaboration and the input of big businesses a human colony could be established on Mars.
Such an outpost would need people willing to stay there for long periods to set up a base that could become self-sufficient, he said, and suggested it would be necessary to use Earth's own moon and that of Mars as staging posts.
It would also require a constant "cyclical" transportation to get people and supplies from the Earth to Mars.
But getting to the planet would not be so difficult, he believes.
"That is the easy part", Dr Aldrin said. "We know how to do that, we know how to get people there. It is being able to sustain yourself.
"(Getting there) is very realistic, in my mind."
Speaking at the Science Museum in London, Dr Aldrin said that focusing man's attentions on the moon would be to regress 50 years, to when he and Neil Armstrong first stepped on the moon as part of the Apollo 11 mission.
But a journey to Mars would break new ground. He said: "I look at where we were 47 years ago leading the world in space exploration, having six landings on the moon, no one has done anything like that ever since ...
"To take the step (to Mars), to take the movement, to take the action to begin to occupy ... is there anything bigger that humans could do on Earth than to leave and begin to occupy?"
Dr Aldrin told the Press Association and BBC World News that it would be wrong to just send people to the planet and tell them "you're on your own".
He said: "It is estimated that people on Mars initially could only produce 15% or 20% of what they need to eat. We would need to supply them continually."
There would be little to be gained from just sending people to the planet and bringing them back, as Nasa did with the moon landings, but instead it would be more worthwhile to establish a series of bases which subsequent visitors could develop.
He added: "I feel that we need to concentrate our efforts on one major base (on Mars), to make that as close to being self-sufficient.
"If we try and be at many places the scientists may be happy but we'll have to bring people back, as we haven't built up a self-sustaining system and when people start to stay they will still need to be supplied (with things from Earth).
"We have to acknowledge that they can't grow everything they need. We are doing a lot of research on how to use the water that we can find there and the soil to grow from seeds enough to feed the people who are there.
"I don't think that you just put people there and that's it, you want to be building that up, and in order to do that you have to keep supplying more and more people and learning here how we can create the conditions on Mars to learn how to provide the people there with the means, whether it's some kind of fertiliser that we can discover and find some of it there."
One of the great challenges would be the mental impact of the prospect for someone of having to spend a huge amount of time - possibly the rest of their life - on Mars, Dr Aldrin suggested.
But he said: "I can see people making that decision. That's the most important thing. I can see many (making the decision) to get there, but I can also see things getting a little tough and they regret the decision and their functioning going down and that being disruptive to people."
Dr Aldrin has a vision of seeing a population of "several hundred" on Mars, a number that would be grown.
But he said economics and issues destabilising peace on Earth could hinder projects, and that a great amount of international collaboration would be required.
He said: "It is very difficult for one nation to do everything, even at the moon, and a plan that brings people together and builds things at the moon that can be used at Mars, that becomes very, very helpful.
"For the US, we have already been to the moon, so to start off where we left off would be wasteful.
"We should build on that and move ahead and not compete with other nations, especially China, but help them join all the rest." He added: "I am very optimistic, we just need to get Europe and Japan enthusiastic about going to the moon."
But for the current generation of children and teenagers to have the prospect of reaching the red planet, plans need to be put into action.
Dr Aldrin said: "I think we need a starting point, and in about two years or so it will be 50 years since we landed on the moon.
"That is a time to celebrate, sort of - we can look back and see where we've been, where we are, and where we should go."
:: An interview with Buzz Aldrin will be shown on the Horizons programme for BBC World News in May.