According to the seller (Beach Parking/eBay), these are from the estate of a Disney animator. It’s a shame we don’t know his/her name or the history of the drawings, because I find them pretty interesting. The basic storyline appears to be in place, but instead of the gorgeously gothic vision we ultimately (and thankfully) got, the artist here presents much cheerier (i.e. typical Disney) fare.
In place of the dreary, massive, cathedral-esque Cygnus, we have the rotund, smiley-faced New Cosmos. And instead of lobotomized zombie slaves, we have a perfectly jovial crew traipsing about the amenity-laden ship like so many Eloi.
The miracle of The Black Hole is that its darker elements were allowed to shine through. That’s a big reason I’m so fond of the film despite the mediocre script.
UPDATE (4/3/13): Please see AcroRay’s comment and link below. These sketches appear to be of prequel stories designed for educational media kits. The kits are, naturally, very rare. If anyone comes across one or has more info, please let me know.