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Will man ever walk on Mars?

Neil Armstrong's 1969 walk on the moon was a milestone in space exploration. But in the last 37 years, despite advances in technology, no astronaut has returned to the moon, let alone another planet.

Critics of the Constellation programme have said the proposal is unrealistic given the programme's technical problems and multi-billion dollar price tag - both of which are closely under review by a panel appointed by Barack Obama, the US president.

And although a global effort has made projects like the International Space Station possible, some still feel that the promise of Nasa's famed Apollo space programme has not yet been realised.

On the 40th anniversary of the first manned space walk, we look at the future of manned space exploration and ask: What are the merits of returning to the moon and what do we stand to gain from manned space exploration?