"Space:1999" was a British space-fantasy TV show that was aired ~1976..~1977, famous for its Eagle space-ship models.
After USA's moon missions, the next advance was expected to be constructing a moon-base (people really believed that would happen). Viewers hoped Space:1999 would show what a moon-base might resemble, what types of space-ships would be flying there.
Space:1999 brought new wonderful fx into a TV show. Eagle space-ship model, the true star of the show, had a realistic modular design.
But Space:1999 proved to be absurd space-fantasy, rather than realistic science-fiction. Its premise, explosion blasted moon out of solar system, was beyond belief. Almost every script was bad, beginning-to-end. Stories were regurgitated, strange-blob-approaching, humans-vs-magical-alien, unstoppable-machine. (Yet this author still loves Space:1999.)
First and second series were very different. Many viewers love the first and hate the second, or vv. Yet others (this author included) just accept or like both series were different.
First series: was eerie, sort of "Twilight Zone: Moonbase", with subtext of philosophical and meta-physical questions. Show suffered with a revolving crowd of characters with no personalities, at whom the dislikable dictator Koenig was always shouting "I WANT YOU TO..! I WANT YOU TO..!".
Second series: had improvements, some character development, moments of fun and humor. Koenig had become a mellow approachable character like Captain Picard. But was worse in some ways, those silly monster costumes, those dumbed-down action-oriented scripts.
Eagle space-ship was notable for being a space-ship that seemed (in 1970s) possible to construct (in 1990s). Eagle was a modular space-ship built for utility, it could carry passenger and cargo pods.