The ship is lost in space due to sabotage by an enemy agent, Dr. Zachary Smith, who is trapped aboard the ship at launch. Hurtling on into deep space, the Jupiter 2 crash lands on an unknown planet.
Although remote, this lost world soon becomes a stopping-off point for practically every space-traveling alien or monster in the galaxy, each episode seeing the arrival of some new visitor.[4]"
https://en.wikipedia.org/wiki/Alpha_Centauri_in_fiction#Film_and_television
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I remember watching the premiere, and intermittently some of the episodes (it was one I had to sneak to watch). Poor substitute for Star Trek. :') When the 'reboot' movie didn't result in sequels or a new TV series, I was pretty glad about it.