Space Thing is a softcore nudie-cutie/roughie from 1968, produced by David F. Friedman.
A guy (Steve Vincent) falls asleep after reading sci-fi magazines (which he prefers over his horny wife), and dreams he is an alien in human form, in a space ship commanded by Captain Mother, a sadistic lesbian (LA nude model Cara Peters).
Captain Mother is a tyrannical commander who has two lesbian scenes with Playmate Mercy Rooney (a.k.a. Merci Montello), the last one ending with a brutal whipping by Captain Mother when the girl admits to being attracted to the hero/alien (Vincent).
The space ship lands on an alien planet (which looks oddly like the California desert) which allows the crew to stretch their legs and "let their hair down".
Captain Mother and the rest are supposedly killed when the landed space ship explodes (a model with a firecracker).... but then it's all a dream anyway, and our hero wakes up.
Space Thing is available from Something Weird video.