Harrison Schmitt and Eugene Cernan blasted off from the Taurus-Littrow valley on the moon in their lunar module Challenger on December 14 1972. Five days later, they splashed down safely in the Pacific, closing the Apollo 17 mission and becoming the last humans to visit the lunar surface or venture anywhere beyond low-Earth orbit.

Now the international Artemis program, lead by Nasa, is aiming to put humans back on the moon by 2024. But it is looking increasingly likely that this goal could be missed.

History shows just how vulnerable space programs, which require years of planning and development spanning several administrations, are. After Apollo 17, Nasa had plans for several further lunar Apollo missions, even including a possible flyby of Venus. But budget cuts in the early 1970s and a reprioritising of human spaceflight to focus on the Skylab project precluded any further lunar missions at that time.

It was not until July 20 1989, the 20th anniversary of the Apollo 11 landing, that President George H.W.