The Black Sun
As it was actually the 3rd episode produced it should have at least been shown as no 3 or better still episode no 2 to explain how the moon got so far away.
Perhaps even incorporate it into the opening episode.
The execs who decided on the running order in both the UK and America probably had no understanding of the distances involved.
Clearly when the moon encountered its first exoplanet it must have been several light years from Earth. As to how it reached other planets around different stars is anyone's guess unless there was a group of tightly clustered stars with large groups of planets around them.
By the way if you want to see model making at it very best get the DVD Blueray. I've got season one and the special effects are beautiful. It's just a pity that they didn't have motion control cameras a few years earlier so that some of the shots of the Eagles didn't look so static.
Regarding Space 2099 I don't think it's going to happen given by the lack of activity.