Now you know something about Afrofuturism.
I think Robert Springett may be sometimes confused with Mati Klarwein. Klarwein did the cover art used for Bitches Brew and This Is Madness shown in this post. Sextant is credited to the mysterious Springett along with Crossings (also by Herbie Hancock) and a small handful of other albums, but they are sometimes mis-attributed to Klarwein (on wikipedia for instance). Because of the stylistic similarities, the matching time frame, and the fact that both are featured on these fairly narrow-genre jazz album covers, I've wondered if they're the same person. More specifically, Klarwein using the name Springett maybe for artistic, but more likely legal/contractual reasons.
Robert Springett is my cousin and yes he did these albums. He was 19 for the first Herbie Hancock album cover. He lives in California.
Rob also also painted covers for Van Morrison.