Only seven episodes? Guess it was like "The Prisoner", where it establishes its premise and then wraps everything up.
I wonder if the series ended when the spaceship achieved a victory -- or peace -- with the Frogs. (See Star Trek VI...) Surely it's just a coincidence that "frogs" is also a derogatory slang word for French people...
Actually, it ended because it was too expensive to produce - especially the special effects. They are not great, but then it was 1966, and Orion showed a lot more space action than Star Trek, where the redshirts beam down to whatever stage setting was available from the latest western or mobster movie.
You'd blow your budget too if you had to land your spaceship on a new planet every week. The parking meter fees alone will drive you into bankruptcy.