The Partridge Family had ended its run on ABC after 4 seasons, but someone at Columbia Pictures Television (formerly Screen Gems, now Sony Pictures Television) decided there was potential in converting the series to cartoon form. Apparently, that nameless executive, and counterparts at CBS, were the only ones interested, because Partridge Family 2200 AD , one of two Hanna-Barbera freshman series sold to CBS in 1974 (Valley of the Dinosaurs was the other), was cancelled after 1 season, only to return, rechristened The Partridge Family in Outer Space when reruns aired 3 years later on Fred Flintstone & Friends.
Not all of the cast returned for the cartoon. In fact, Susan Dey (Laurie) left the show after 2 weeks, forcing the producers to call on Sherry Alberoni (Super Friends, ex-Josie & the Pussycats) to take her place, while Suzanne Crough, Brian Forster, & Danny Bonaduce soldiered on for the full run. Those three, along with Dey, had joiued the cast of Goober & the Ghost Chasers over on ABC the previous season when ABC decided that series needed a boost. Didn't work.
Chuck McClendon took over for David Cassidy as Keith, and also sings lead on "Gypsy Girl", the only musical number from the series currently available on YouTube. Judge for yourselves, kids.