A mad or eccentric person, esp one who seems stuporous or out of touch with reality as if intoxicated by narcotics; nut,spaced-out: Alda presents her as such a space cadet that the agony of divorce is tempered/ meant to convince the jury that he is an unreliable space-out, that perhaps he was hallucinating
[1980s+; probably fr the 1950s TV program Tom Corbett, Space Cadet, which followed the adventures of a group of teenage cadets at a 24th-century space academy, thought of humorously as being far out, way out, etc]