The Ark is being buffeted by some external force, and the hero trio discover that there’s an astronomer on board, the titular Farthing, who has moved the Ark into the path of the titular comet, just so he can observe what they’re like from the inside. So the hero trio are all, “wait, you moved the Ark! Hurrah! Tell us how and we’ll do the same!” and then three-quarters of the episode involves watching them do that, although not enough to get it out of series-motivating peril apparently.
I say “apparently” because this episode seemed more than usually confused about timelines. There seemed to be the implication that Farthing’s comet-chasing was what set the Ark off course, and that the Ark went off course recently, both of which contradict the setup. The episode also featured a lot of what I now think of The Starlost‘s trademark radical personality shifts, with Farthing and his (female, of course, though at least she’s an engineer) assistant seesawing from “the Ark is doomed and there’s nothing we can do about it” to “let’s save everyone with Science!” over and over within a span of minutes.
I don’t know what the record order was, either, but if it was recorded before “The Alien Oro”, it would explain where the hero trio got their spacesuits.
This episode did, surprisingly, have one or two bits of good dialogue, both down to Farthing: “What I say goes, and I say, you go,” and “Can he [Devon] do it?” “I don’t think so, but I got tired of arguing with him.”