This is a pre-production 10" playback metal lacquer (also known as an acetate) most probably produced in just a handful of copies!
According to Chinese whispers from the time Set The Controls For The Heart Of The Sun was intended to be the group's follow up single to the flop 45 It Would Be So Nice. Whether or not that rumor was true, needless to say, this was never released commercially as a single by the group!! I guess John Peel would have played it but I doubt very much that this would have cracked the top 20 either!
The Pink Floyd Set The Controls for the Heart of the Sun 10" EMIDISC ACETATE 1-sided acetate (flip side is blank - no label or grooves), approximate playing time is around 5:15. It seems to play for about 7 or 8 seconds longer than the version on A Saucerful of Secrets.
Obviously.....a mega serious Pink Floyd rarity: as was the case with these studio acetate discs there would have only been a handful of copies produced, probably five or less, usually for group members, studio engineers and high level record company personnel etc.. etc..