Filmation's Space Sentinels had one strike against it when it debuted in 1977. The studio had sold the series to NBC, which had bombed out with the last offering from Filmation, The Secret Lives of Waldo Kitty. Unfortunately, if NBC was hoping to recapture the sci-fi audience that had helped make the animated Star Trek so successful for 2 years, they were disappointed.
Alternately known as the Young Sentinels, the series focused on a trio of Earthlings transported to a distant world for training. Hercules (George DiCenzo) and Mercury (Evan Kim) took their names from the gods of myth. Astria, an African-American (or was she just African?) shape-shifter, rounded out the team. Apparently, Filmation didn't learn anything from the last team that relied on a computer as its leader (Butch Cassidy, a 1973 Hanna-Barbera entry for----wait for it----NBC), either. Most of the action fans opted to tune to ABC.
Here's the intro:
Had the Sentinels been on another network, like maybe, CBS, there may have been a better chance at renewal, but we'll never know for sure. The series was cancelled after 1 season, just like Waldo Kitty, and would be replaced by The Fabulous Funnies on NBC's schedule the next year.