Yes, it's another of the mystical/fantasy episodes that tends not to make a lot of sense in the first season. As with several first season episodes, the impression is given is that there is some god-like force at work, but it functions in a dubious and sometimes cruel/sadistic way.
The basic premise is rather vague. Apparently the Moon hits a space phenomena that causes it to split into timelines, and one of those timelines to jump five years into the future. Okay, that's clearer than the show (and the rather mystical-sounding Bergman) puts it. That has some possibilities. And the idea of a sensitive who can detect both timelines and is slowly being driven insane by them isn't bad. Stephen King used it in the third Gunslinger/Dark Tower book.
But then it goes rather pear-shaped. What sends the Moon back to Earth? Why do both Moons go to the alternate Earth? Shouldn't the "real" Moon go to the "real" Earth, not the alternate? How does Regina not only get two sets of memories, but two brains?!? If she has a counterpart on the other Earth, did that counterpart lose her brain? Or did the counterpart have two brains too? If so, where did all the brains come from?
The idea of the Alphans seeing a future for themselves where Earth is all but destroyed isn't bad either. Even if the alternate Bergman's speech undermines that by saying, "Well this might not really be any Earth at all." But again, weird stuff intervenes. With Regina, both versions died simultaneously. But here, the "real" Dr. Russell is fine and her counterpart dies. Did her counterpart have two brains? Did the real Dr. Russell temporarily lose her brain? Shouldn't bother Russells die, just like both Reginas died? And what is causing the alternate Moon to accelerate? Again, there seems to be indications that someone or something is directing all these events. But why? How? To what purpose?
There's nothing wrong with a mystical episode, or a mystical approach to the series. But Space 1999 always worked best when it stuck with the hard science, or hard science with a mystic tinge (Dragon's Domain, Earthbound). Here writer Johnny Byrne invokes mysto-babble the way Trek writers invoke techno-babble. Nothing is learned, no moral is passed on.
Judy Geeson as guest artist doesn't have much to do other than scream convincingly, wear fake sunburn flakes (they like like eyeglass nosepads glued to her face), and have a very underplayed death scene. Landau isn't bad confronting the future, Morse always does portentous mystic disguised as a scientist, and Nick Tate is his usual jumpy self. Bain underplays and underacts as usual, and can't deliver the mumbo-jumbo worth a darn.
Overall, okay and kinda spooky when it stick to science and an element of horror. Forgettable mystic claptrap otherwise.