By Chris Riley
BBC series producer on Space Odyssey - Voyage To The Planets
The BBC's new science series Space Odyssey: Voyage To The Planets is part drama - the gripping story of five astronaut-explorers on the ultimate expedition to the planets.
People are once again talking about going to Mars with astronauts
It is a tale of fiction, of course, but there was a time when a mission like this looked as though it might happen for real.
I grew up at a time when men explored the Moon, and sophisticated robots hunted for life on the surface of Mars.
Even as Armstrong, Collins and Aldrin were setting out to make the first lunar landing in 1969, the then US vice-president Spiro Agnew had declared that Nasa would have a man on Mars by 1980.
The image of astronauts bounding across ochre landscapes in one-third gravity, under butterscotch Martian skies, was surely just around the corner.
Even the oppressive acid streaked skies and super-heated landscapes of Venus, depicted inside my National Geographic magazine, seemed a place worth trying to land a human, if only to marvel at its hell.
But as I entered my teens, this dream seemed to fade. We left our last footprints on another world in 1972.
A new age
Astronauts and cosmonauts were confined in Earth orbit. And by 1982, the Russian Venus exploration programme had been scrapped, leaving just four tantalising vistas from the surface of our nearest planet.
Mission failures and politics ensured that it would be 15 years before another spacecraft made a successful landing on a planet.
The stuff of imagination: On the surface of Venus
One of President John F Kennedy's reasons to explore the Moon and planets in the 1960s - "not because they are easy, but because they are hard" - had become exactly the reason not to go anymore.
We will never know the lost landscapes and discoveries that those cancelled and failed missions might have written into our history.
We will never get back these lost years of exploration. But, thankfully, that barren time is now behind us. A boom in computing power and the commercialisation of spaceflight have propelled us once more into a golden age of Solar System exploration.
Our robotic explorers returned to the surface of Mars in 1997 when Nasa's revolutionary Pathfinder spacecraft, cocooned in air bags, bounced on to an ancient Martian flood plain.
It's in the human species to reach out
Its 2004 descendents, Spirit and Opportunity, have just completed their tenth successive month rolling across the surface of Mars, bringing our total cumulative experience of "living" on the Martian surface to almost 12 years.
Today we have a better idea of what a walk on Mars would be like than any other planet. So are we any closer to Spiro Agnew's rather optimistic pledge to land a human there?
The immense and sustained commitment that such a task would demand remains the same; and the original Cold War drive to embark on such a mission no longer exists. But some of the desire of that earlier time hangs on.
As Kennedy put it, "such goals serve to best organise and measure our energies and skills. The Moon and the planets are there - and new hopes for knowledge and peace are there as well".
Such prizes still characterise space exploration - a rare global endeavour we could rise to do together as a species.
In striving to send humans to new worlds, we might just unite our own in a peaceful quest that transcends national interests and ideological obsessions.
To quote JFK once more, such a voyage could be "the most hazardous and dangerous and greatest adventure on which man has ever embarked". Perhaps it should still be a challenge we take up.
Space Odyssey: Voyage To The Planets is broadcast on BBC One at 2100GMT on Tuesdays.
Digital viewers can press their red button to access the science behind the scenes.
The book of the series, co-written by Chris Riley, is available through BBC Books.