Season three of Lost in Space features relatively few spacecraft (although it does introduce the very cool space pod). In fact, ships are referred to that are never actually shown. It might be interesting to do an actual count of these ships left parked just off camera in the final season.
The first alien ship is seen in “Kidnapped in Space.” It is the same ship as in “The Derelict.” The set dressing of the interior is of course completely different, but otherwise, we are left to wonder why this particular ship appeared so often (and did the same trick of swallowing the Jupiter 2 the two times it did appear as a ship). “Two Weeks in Space” and "Deadliest of the species both uses slightly different versions of the same ship. Rather than land (it does seem rather large), the passengers of the ship in "Two Weeks in Space" arrive planet-side in a golf-cart that appears and disappears in a flaming puff of smoke.
Perhaps the most intriguing spacecraft portrayed in this season were the choppers ridden by the space hippies in “Collision of the Planets.” They are never seen in flight (more flaming puffs of smoke) and you really have to wonder how the passengers survived in space on them.
When Farnam B. reappears in “Space Beauty” we see mainly the interior of his ship in numerous scenes. Where these scenes do not occur in the specific cabin where he communicates with his sponsor, the interiors shown are most notable for their lack of detail—the foreground contains set dressing, but the background is pitch black.
The same situation applied with his ship in his first appearance in “A Day at the Zoo.” The action of “Princess of Space” takes place in what might be taken to be a sister ship of Farnum B.’s—a number of locations in the ship are notable for have black backgrounds around a furnished foreground, although the exterior of the ship is seen near the beginning of the episode in an establishing shot. Different elements of the set dressing seem to come from “Mutiny in Space,” not surprisingly, given the Treasure Island-like elements in both episodes.