It's not hard to figure out where L. Ron Hubbard came up with Scientology's space cooties - 2019-07-16
After Ron Hubbard had sold the rights to Dianetics to Don Purcell in 1952, he had to create a new subject from whole cloth. Much of the "new" material that he now called "Scientology" came from Aleister Crowley — including the notion of "entities." But entities proved unpopular, and would only re-emerge in 1967 with the release of the secret Section Three of the Operating Thetan Course (more commonly known as OT III).
In OT III, Hubbard would call the entities "body thetans," but a much earlier encounter with this material is recorded in Monitors, the biography of Hubbard's mentor Major Arthur J Burks. Thirteen years Hubbard's senior, Burks was hailed by The New Yorker as "the King of Pulps." He had resigned from the US Marines in 1928, because he was making a living from his pulp fiction. But, even at 200,000 words a month, it was a scant living.
Burks first met Hubbard before the US entry into WWII, when he offered to publish Hubbard's Excalibur. His associates, however, refused to publish this "squirmy, self-revealing book," which "seemed to open queer windows in the bodies of everyone one thereafter met."