Usually, when you're talking about a TV show, differences between different seasons are not so important. Maybe you can find one or two different characters, or different ideas in the scripts.
But "Space: 1999" had very big differences.
First of all, three main characters (Prof. Bergman, Paul Morrow, David Kano) disappeared without any explanation.
Some others did not appear in all episodes (Alan Carter, who was about to be discarded as the previous three, and Sandra Benes).
Another one disappeared after two episodes without any explanation (Dr. Mathias).
New characters came in (Maya, Tony Verdeschi, Bill Fraser, Yasko, Dr. Vincent), but only Maya had her own episode enter.
Not only the cast, but also clothing changed (more or less similar, but with a number of jackets of various colors added), and the control room changed too.
Another change was the score composer: the touching orchestral music composed by Barry Gray (who had worked with Gerry Anderson since the first Supermarionations) left place for the electric guitar of Derek Wadsworth.
Too many changes, so I thougt it was better to give the second season its own space.
So you can see also the most important change, the scripts quality.
The first season was often disturbing, with psichological or horror stories; in the second season all was terribly lighter, any doubt or worry vanished in the final laugh and they were all happy to go on wandering in space.
Everybody is quite sure about the real responsibilities of all that: guilty of all those crimes is "the man who killed Star Trek", Fred Freiberger. His duty was to make the necessary changes to have better sellings in the USA, but he made too much and the serie totally changed.
The worst result is that he gave good arguments to all people who don't like "Space: 1999", forgetting that it had born as a very better serie and, anyway, not so silly.
I chose this episode for two reasons. The first is that the script is signed by a certain Charles Woodgrove, who is, by chance, Fred Freiberger's nickname... and this gives us an idea about american producers'ideas about the scripts.
Then there is a (very inappropriate) confrontation with "Dragon's domain", the first season episode I have already shown.
The story was written for the supporting cast, Maya, Tony Verdeschi, Bill Fraser and San. Because during filming Martin Landau (Cmdr. Koenig) and Barbara Bain (Dr. Russell) had even took an holiday...
This assumed, the story is just a continue run to chase the alien creature walking through Alpha's corridors, or, on the contrary, to escape from it.
This is all the confrontation with "Dragon's domain": the horrible monster which had appeared in that episode had become very popular, so that Freiberger simply thought that "monsters do work", and scattered a lot of them in the second season. But too many monsters don't scare any more, and anyway there's no contest: the first season "dragon" was nightmarish and horrifying (and had a quite good story anyway), the second season monsters are simple stand-ins dressed as bug-eyed-monsters, the most stereotyped ones possible. More than "monsters", we should say "the monster": because this episodes' creature was also modified and recycled for other two...
There's a curiosity about this. In this episode it is portrayed by a famous stand-in: David Prowse, better known (if we can say this...) as Star Wars' Darth Vader.
Finally a note about two characters. Tony Verdeschi (Tony Anholt), is Koenig's number two, and also security chief (why the red colored sleeve instead of the purple one?), and I always thougt it was the only positive change in the second season: his predecessor Paul Morrow (Prentis Hancock) was not so charismatic and seemed always angry...
Probably Bill Fraser (John Hug) should have been substitute for Alan Carter (Nick Tate): but Carter was too popular and regained his role, so they sometimes alternated or appeared together like in this episode. Fraser should be an astronaut, so he should have a golden sleeve instead of a red one... anyway, Fraser is too very popular between fans, and is still surprised to be invited at "Space: 1999"conventions.
Now the story. A mysterious cloud appears above Alpha, and in the same time most of the personnel passes out and is confined in the sick bay. A monstrous alien creature lands on Alpha with a particular mission: to steal the Moonbase life support system...