Fluff
A reason why the moon isn't an option. Solar flare? Radiation? Grey goo infestation? Furry colony? I'd just like to hear from you guys on this.
Well... how about the basis of operations being a space station? Just think of ISS MK-4, the frontier of humanities space-research and space-related technological advances! Such stations are not really meant to be moved, only making some correctures to their orbit, and maybe some emergency boosters to get out of collision courses.
The "landers" might also not be constructed for leaving the inner spheres of the earths magnetic field, which could make flying to the moon hazardous and far more complicated. Making it completely impossible might be a stretch though, but them needing a complicated retrofitting, plus "heavy" spacesuits for the crew to withstand the radiation and such is more than in. As in, making it very unviable.
The players also might have been kinda left behind, with ships that could handle longer flights either lost in the last desperate struggles, or gone with those that tried to get to mars. As for their fates, hey, maybe in a very hypothetical sequel, no? ;3
Crunch
In XCOM, players have to wait at the base for missions before they can send their troops out. It's the same in this game, except I don't know how to decide how long before the players can go on a mission beyond arbitrarily choosing so. Any ideas?
Well.... there are these often cube-shaped things, with optical worth indicators on their sides. Each worth is normally unique to one of the sides, the later which can number up to 100 in special designs.
You... you kinda throw them, and depending on which side shows itself on the top, some rules fall into place. In the best case, said rules are made before you throw these things.
Hum... that might sound far more snide than it actually should sound like, really. That aside, how about the obvious choice - how about throwing some dice? 3D6 whereas each number represents anything between 1 hour, or a quarter day, your call. Now just add some random minute thingy, so that it doesn't look too clean-cut "staged" as it actually is, and you are ready to rumble. In this regard, at least.
Kinda Both
In XCOM, the player actually plays as the Commander who sends out troops on the battlefield. I was wondering if I should give a single player control of what to build and who to send on missions and stuff. This can let more than 6 players play at once (they're characters get rotated through missions) and if we go the YAK route they can serve as a second GM so that more than 6 players can actively play at once. That's the crunch. The fluff part comes from whether I should have the commander chosen by the council (myself) or the highest-ranking player. Thoughts?
Truth be told, I am not sure if this would make the game easier for you, or even harder to manage. Either way.
Player rotation might be a good idea to not be fixed - make it first come first served, no sense in waiting for those that only play twice a week.
Same actually goes for the commander. By all means, choose him yourself. In the best case, he is the most active, and has "good" rp skills. I leave the worst case up to your imagination, but I would think that a "bad" commander could easily ruin the game for the other players.