“Set The Controls For The Heart Of The Sun” is a hypnotic paean to the sun which, despite its sci-fi-resounding title, actually borrows a lot from ancient Chinese poetry as its main inspiration. The lyrics to this song, written by Roger Waters, are remarkably elusive and delivered in a murmur, almost unintelligible.

Ref:

Allusions to Classical Chinese Poetry in Pink Floyd — Cjvlang

Poems Roger Waters alluded to in 'Set the Controls for the Heart of the Sun' and 'Cirrus Minor'. Great poetry in English and the original Chinese (pronunciation and meaning shown)

The studio version of the song is faster-paced than the live one, and while the latter uses the Farfisa organ’s sound heavily to give it an oriental feel, the album version features Richard Wright playing the vibraphone, giving it an ambience more inclined to evoke buddhist prayers. According to David Gilmour, it’s also the only Pink Floyd studio recording to feature all five members – though ironically, both Gilmour’s and Barrett’s guitar parts are rather buried in the mix.

The studio version of the song being on A Saucerful of Secrets (1968), a live version was also included on their album Ummagumma (1969). It was one of the band’s most performed songs in concert up until about 1972/1973.