So today's game showed that I'm not up to adjudicating a very complicated ad-hoc skill system.
Classic Traveller has what appears at first to be a pretty arbitrary system for assigning difficulty to various task related throws. This is compounded by the fact that the rules essentially tell the GM to "make something up" if it's not in the rules.
The system I'd been using is based on the concept of "Throw less than STAT, with DMs for skills and situation", combined with the standard skill "Throw X+ to succeed".
However, throwing low sometimes and high other times is just confusing, so instead, I'm going with a very slightly tweaked version of "Rule 68A". The name comes from the hexadecimal values 6+, 8+ and 10+, which are the target throws for Easy, Average, Hard under this system.
The one tweak I'm making, which I might decide to not bother with, relates to UPP statistics. If a character's stat is relevant to the task AND it is equal to the task's target or better, then DM+1. If the stat is less than half the target, then DM-1. This nicely echoes the weapon "advantageous stat" system, and I think meshes with the flavor of CT nicely.
And that's pretty much it.
There's also the matter of CT's combat system conflating armor with ease of being hit. I think I'll leave that one alone for now, even though it means that in many cases a shot can't miss. I do like the idea of making two attack rolls, one with the range DM and one with the armor DM, and both have to hit to cause damage, but I'm not sure if people would go for it. Though it would solve some problems, and would reduce the "can't miss" cases to "if you hit, they're gonna feel it" cases. That's a thought for another day.