In case it isn't universally known around here, I want to recommend Ralph Senensky's online memoir of his experiences directing STAR TREK.
He directed six and a half TOS episodes, plus eps of a slew of other series. I just checked back for the first time in a while, and he has finally written up "Return to Tomorrow."
I don't think I 'm allowed to post links yet. So it's at senensky dot com (no www).