Earthsearch (1981) by James Follett?
Three crew-generations previously, the starship Challenger - a vast ten-mile-long survey vessel – was launched from Earth on an interstellar mission to search the universe for an Earth-type planet to colonise. This has been unsuccessful, and the ship's once enormous crew-count has now been reduced to four. Telson (the ship's Commander), Sharna (Science officer), Darv and Astra are the third-generation crew- the only survivors of the disastrous Great Meteoroid Strike which seriously damaged the ship two decades previously, killing the entire second-generation crew and rendering large areas of the ship "uncontrolled" and inaccessible to its electronic systems. [...]
With no suitably colonisable planet found after over a hundred years of searching, a crew-vote is taken and the Challenger sets a course for the return to Earth. Darv and Astra, while exploring one of the uncontrolled zones, find a survey recording of an Earth-type planet called Paradise. (In the accompanying novelisation, Darv is alone when he makes the discovery.) As is standard procedure, the crew enter suspended animation in order to prevent ageing and possible death during the many years of journey time. [...]
Reaching the Earth's solar system, the Challenger's crew are horrified to discover that Earth has vanished altogether, with the Moon now occupying Earth's former orbit. Although the crew locate a large city on the Moon, they are unable to receive any answers to their communications and are unable to leave the ship to explore. This situation is changed when Darv and Astra enter an uncontrolled zone within the Challenger and locate a space shuttle previously unknown to the Angels. Using this, they visit the city, named "first Footprint City", and discover the Moon Sentinel, a computerised guardian and archive whom they can question.
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scifi radio drama spaceship ai earth missing.