1540s, "to make of a certain extent;" 1680s in typography; 1703 as "to arrange at set intervals," from space (n.). Meaning "to be in a state of drug-induced euphoria" is recorded from 1968. Space cadet "eccentric person disconnected with reality" (often implying an intimacy with hallucinogenic drugs) is a 1960s phrase, probably traceable to 1950s U.S. sci-fi television program "Tom Corbett, Space Cadet," which was watched by many children who dreamed of growing up to be one and succeeded. Related: Spaced; spacing.
<a href="https://www.etymonline.com/word/spacer">Etymology of spacer by etymonline</a>
Harper, D. (n.d.). Etymology of spacer. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/spacer