In the summer of 1969, two weeks after Neil Armstrong became the first man to walk on the Moon, rocket scientist Wernher von Braun delivered to Nasa a detailed, fully costed plan for landing humans on Mars.

Dr von Braun, who had masterminded America's lunar programme, intended to send astronauts on an initial excursion to the Red Planet lasting two years, with a fly-by of Venus on the journey home.