Titled Young Sentinels for the first several episodes, Space Sentinels concerned a multi-ethnic trio of young people who were taken from their various homelands on Earth to a far-away planet where they were given super-powers and the gift of eternal youth. Then they were returned to Earth as superheroes, as champions of all that was good and right.
The Space Sentinels consisted of Astraea, who could change her shape; Hercules, who of course had super-strength; and Mercury, who enjoyed super-speed. They were joined by Sentinel One, their mentor, who spoke to them as a sort of hologram; and a small (this was just after Star Wars, remember) cute-ish robot called Mo. The Sentinels made their headquarters out of a hollowed-out volcano. Their main nemesis was Morpheus, a fellow who could have been a fourth Sentinel, but decided to turn to conquest instead.
The Space Sentinels was a pretty pedestrian cartoon, even for being a production of Filmation, which were known to squeeze a budget 'til it squeeked. The plots and characters were pretty much what one would expect, possibly conceived as giving kids a mix of superheroes with the afore-mentioned Star Wars, but apparently nobody's heart was in it. This is one of those cartoons from that era where a shifting eye or flapping mouth could be the only animation the viewer would see for several seconds - again, another Filmation trademark.
In any case, the series only lasted thirteen episodes before disappearing into oblivion - at least until the series was released on DVD in August of 2006.
Morpheus: The Sinister Sentinel
The Time Traveler
The Return of Anubis
The Wizard of Od
The Prime Sentinel
Voyage to the Inner World
The Jupiter Spore
The World Ship