A year or more back, I shared a rare TV spot for 1979's Kenneth Johnson-produced NBC genre oddity, Cliffhangers!, but that vid has since been removed from YouTube (and thus this site, as well). Fortunately, I stumbled across a different, one-minute network promo today, and here it is - for as long as it stays available.
Cliffhangers! was a modern "take" on the theatrical movie serials of the 30s and 40s, composed of three, 15-minute chapters of three different ongoing stories in each episode.
The one that most fit in with the Space: 1970 aesthetic was "The Secret Empire," an update/rip-off of the 1935 Gene Autry vehicle, The Phantom Empire. Both dealt with cowboys battling the inhabitants of secret underground scientific super-cities. In the Cliffhangers! version, the leader of the villains was portrayed by none other than Mark Lenard of Star Trek and the Planet Of the Apes television series, and the cowboy hero didn't sing a song in each installment.