OOC: Very fun start to the campaign! Will you (Rob) be posting up an AAR? I'm guessing that we could've made some sort of roll to find out things about the power station, such as the fact that it had point defenses or was likely to explode upon destruction? If so, what skills would've been useful for such rolls?
I'll post AARs when possible.
As for skill rolls, generally speaking, several possible skill rolls can apply to any check for knowledge. The trick is justifying which one does what, and then I figure out how closely they're related. For example, the cooling tower was a high-pressure container suddenly exposed to a low-pressure/low-temperature environment. Several skills, including some science-related skills (physics) or technicial (cooling systems) could have applied. Some would apply more than others, and the ones that applied less would have a higher difficulty modifier to figure it out. Technician/cooling systems would end up probably being a straight-up roll with no difficulty modifiers (since that directly applies), while a Tactics/Mech roll to extrapolate that since Mech heat sinks "explode" slightly when hit as the pressure is released, a system 5000 times bigger might also produce a similar "explosion" big enough to damage a Mech at a significant distance would be a real reach, and thus have a Very or even Extremely Difficult modifier, as well as requiring a higher Margin of Success. Technician/fusion engines would have had a difficulty modifier somewhere in the middle. There isn't a clear-cut system of "this situation requires X skill" when it comes to knowledge skills, and setting the details and TNs requires a high level of GM fiat and finesse (usually on the fly, since there's no way a GM can account for every way in which every skill might be useful).
The hidden point-defenses around the cooling tower would have required a Sensor Operations or Perception skill check, both with very high difficulty modifiers representing the deliberate concealment. Mechs with advanced sensor suites would have helped, but not guaranteed it, as would taking a turn of not moving or shooting to concentrate on the skill check. Be aware that there are, very rarely, things that are straight-up "impossible". It doesn't matter how good your piloting skill modifier is - you can't use your jump jets to attain orbit on a 1G world. Most of the time, you'll get a roll, but be aware that making said rolls can take time away in-game; it is possible to lose a TW turn making lots of rolls to try to get a high result. Likewise, there's some things that there's just no way to know from the results of briefings and sundry. The satellite images of the cooling tower, for example, would not reveal the type of coolant being used, no matter how high your Perception skill check was.
And for full disclosure and a taste of how I stat things, the full rules for the cooling station, c/p'd from my notes:
Cooling station: 7 hexes, 3 levels high across all hexes.
-160-point damage capacity (reinforced construction cancels partial building collapse rules)
-6 surrounding hexes each mount a point-defense Machine Gun under a hidden panel (Perception TN 14, Sensor Ops TN 11 to notice; not moving or shooting that turn grants a +3 bonus to the check). MGs use Gunnery 2, infinite ammo. MGs cannot fire across hexes containing cooling tower. Must declare whether they are using Point-defense or anti-personnel/Mech fire. Pop out at end of movement phase (only have to move 4 feet).
-High-pressure coolant: When cooling tower is destroyed, the system may detonate (combination of a "steam boiler"-style explosion and actual detonation). On a straight 2d6 roll of 10+, the failsafes fail, and the tower explodes for 2d6x10 damage to immediate surrounding hexes, dropping by 10 points per hex of radius. If any Mechs are ON the tower, they take 3d6x10 damage to front hit location table and are displaced to the nearest hex adjacent to the building. They must make a PSR at +5 penalty (incl. low gravity) or take a 4 level fall. If PSR succeeds, they take mass/10 x0.4 to each leg and are still displaced, but remain standing. Technical skills (cooling systems, fusion engines) may allow for warning (MoS 1+). Sensor Ops checks (TN 10+) on the tower as it takes damage may reveal brewing detonation, but require a turn to stand still and scan (range 15 hexes-ish?) unless Mech has good sensors (beagle, quirk of some sort).
-When tower is destroyed, all turrets and doors lock down as they lose power during the End Phase of that turn. Mechs and tanks may still operate, but become receptive to surrender offers.