Island in the sky.
Just watched this recently and you know for the time and type of show this episode was pretty dark.
Smith at one point won't let Don land the ship orders the robot to crush a space helmet, as a warning, and the way they did that with the props they had was pretty good. His threat being that the next time he'll make sure his head is inside the helmet when the robot crushes it..
For a family show of that time period it never occurred to me that this was meant to be that dark. I just took Smith's threat as bluster.
I do wonder if he would have gone through with it if pushed.