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Very vague on the details. I would have read these books in the late 80s, possibly around '87-'88. They were in my school library, which had students from age 6 to 10, so would have been age appropriate.
You could also say the ship was shaped like a nautilus, I guess. I'm pretty sure there were diagrams of the ships layout in the cover.
There may have been a robot sidekick. I have an inkling of a mining/industrial element or aesthetic.