It's effectively just the same to personal-scale conflict, except the ships add their one die to everyone's tests.
Shields are Stress. Breaches are Injuries. The players still get one action per turn. Other ships get one action per Scale, and get an additional penalty of +1 difficulty for each action they take in the same department after the first in a round (so if a Klingon cruiser wants to just fire five times in a round, it's at a progressively-tougher stacking +1 difficulty for each additional shot). Take a look at what each crew position can do in the ship chapters; those are the ship-specific actions each station on the players' ship can do. Otherwise, they're still spending Momentum to generate Advantages, giving stirring speeches, and etc. just like any other scene.
Ok I'm going to try to cook up a quick example. Since it would get confusing to bring PC talents into the mix, I'm going to run two NPC vessels against one another: a Romulan D'deridex against a Cardassian Galor cruiser. Not exactly a fair battle but whatever.
The two meet in space over some issue and hold at the edge of weapons' range (Long range) and communicate for a few minutes, which essentially boils down to a lot of "No, fuck you!" back and forth. The Cardassion Gul realizes that he's outclassed so he decides that a first strike is his best chance. Mid-sentence, he subtly signals his crew to open fire.
Turn 1: C
His crew rolls for their disruptor banks (costing 1 power) with 9/2 skill and assisted by the ship's 9/3. The difficulty is 2 (standard 2 + 1 for Long range but we'll give - 1 for the dastardly ambush on a sitting duck).
They roll: 10 14 + 12. Two successes. Barely enough, no extra Momentum generated though.
Damage roll: 10 successes! Vicious 1 really does do wonders.
The warbird has Resistance 6 so it ends up taking only 4 damage to its shields.
Turn 1: R
The Romulan commander is incensed and orders his crew to immediately return fire. This costs 1 power again and the difficulty is 3 (2 standard + 1 range).
They roll but get only two successes. Green beams of energy scythe through space but the Galor is already on the move and they narrowly evade.
Turn 2: C
Ok, problem. The Romulan's shields are holding. Getting closer would be better for their accuracy... but it would help the Romulans as well! Better to make some easy rolls and generate Momentum. They decide to take Evasive Action, costing 1 power (they're at 7 now). They roll: 1 20 + 7.
Three successes is nice because it nets them 2 Momentum. The 20 is not as nice, however, as it represents a Complication. It turns out the Romulans quickly figure out the limits of the Galor's engines and any future attempts to take Evasive Action will take +1 difficulty.
Turn 2: R
The Romulans aren't scared and Maneuver closer by one zone. This costs no power but it does take a roll, another chance to earn Momentum.
Roll: 9 11 + 7. Three successes at a difficulty of 0 is three Momentum. (We'll say the Cardassians use Momentum and the Romulans use Threat from now on, to avoid mixing up their pools.)
Turn 3: C
It's now or never, fire! Difficulty is 3 (standard 2 + 1 for having already used a Tactical action in the same round). They will spend 1 Momentum for another die, leaving them with 1 stored. Naturally this also costs power, leaving them with 6.
Roll: 1 3 14 + 2. Whoo boy! That's five successes! So they hit, with two extra Momentum.
Damage roll: only 6 damage though, that's disappointing. But the Cardassians are growing desperate so they will blow all three of their Momentum to ignore 6 points of Resistance. All 6 damage gets through so the Romulans are left with 4 shields but they also suffer a Breach (5+ damage taken in one blow) in section... *roll* 15, the general Structure. Next round the warbird has one fewer turn.
Turn 3: R
Sparks fly from consoles and some random background crew gets injured, green blood spattering all over the bridge. The commander yells, get me back those shields!
The crew rolls: 3 3 +18. Four successes at a difficulty 1 task means another 3 Threat, for a total of 6. The Romulans get back 2 Shields, plus another 2 per Threat spent. They decide to spend 2 Threat so their Shields go from 4 back up to 10, leaving them with 4 Threat stored.
Turn 4: C
Well shit this isn't working out after all. All hands, brace for impact! Modulate those shields!
They roll to Modulate shields and get an extra die by adding 1 Threat to the Romulans, giving them 5 in total. The difficulty is at 3 though: 1 standard + 2 for the two earlier Tactical actions.
Roll: 7 6 9 + 7. Well hey, it worked! With a Momentum to spare! They spend this to give themselves +2 Resistance for now.
Turn 4 + 5 + 6: R
Hey, want to know something cool? The Cardassians only had four turns this round, but the Romulans get six.
So let's make this count.
First, scan for weaknesses: they succeed.
Second, an Attack Pattern: they succeed.
By now, the Cardassians can do nothing but keep their fingers crossed.
Third and finally, attack! Buying two extra dice for three Threat, difficulty is 2 standard, plus 1 Evasive, minus 1 Pattern, plus 1 for the earlier Tactical move: three in total.
Roll is 2 11 15 18 + 1: five successes.
The Romulans roll a whopping 12 damage dice which have Vicious 1 and Piercing 2 (10 dice standard +2 because Scan for Weakness helps out) and get: twenty-one damage!
Oh good lord, these dice are on fire! Needless to say, a ton of 5s and 6s in there, so the Galor's armor might as well not exist and those modulated shields don't do jack shit either. Its shields are instantly depleted and it takes two Breaches on... *rolls* 6, the Engines. Those are immediately damaged so the Galor suffers a +2 difficulty to all Engine-related Tasks and loses 1 power at the end of each round. Which is right now, by the way. They also lose two Power from suffering a hit on the Engines in the first place.
As round two starts, the Romulans go first, having literally seized the initiative and more actions (albeit five instead of six due to that one solid hit earlier). The Galor has damaged engines, is low on Power, out of Shields, out of Momentum, and the Romulan looks like it's about to fire again. Looks like today is a good day to die...
This was made up and rolled on the spot. I'm sure I made some tactical mistake here or there, but let's be honest: opening fire on a D'deridex is in itself the biggest blunder the Gul could've made. Now if this had been a wing of three Galors however, things might look very different. We might see tag-team tactics, the Romulans trying to cloak and use their persistent plasma torpedo's damage, creating Advantages to represent outflanking the target, and so forth. Good stuff.
In STA starship combat it's very easy to get in trouble, but much harder to get annihilated. The Galor suffered an unbelievable amount of damage but in the end it was just two Breaches. Troublesome but not fatal. I like this because it adds tension and drives home that idea that you're getting all shot up but you still have a fighting chance.
Scale 4 is pretty weak. It's pretty easy to inflict two Breaches with a single attack and for a Scale 4 vessel that means something just got Damaged. On a scale 5 vessel it would take three Breaches rather than two, so that's noticeably tougher.
I'd just like to add that while all of these points are true when two NPC ships fire at each other like that, things get more complicated with PC crews as Talents, Advantage Creation and Supporting Actions come into play. If the PCs all coordinate fully and have characters with suitable Talents they can actually take on far greater odds than they should and win. Momentum is accurately named here- it can roll over and build to create situations where anything is overcome. As nasty as Vicious can be, you'll soon learn that the bonus Momentum that Phasers generate is far more deadly.
Player knowledge matters. There's a vast gap in how well a starship performs when the players don't understand the system and just roll dice each round and how well a starship performs if everyone wrings the maximum possible number of bonus dice, momentum points and Advantages they can out of each round.
Secondly, if shields go down then insta-kill actually becomes possible. A full spread of Photon Torpedoes to an unshielded starship of any size should at least cripple it- which is actually pretty accurate to the lore, shields going down is universally seen as a bad thing. (Please consult the rulebook on how Spread and High Yield work if you haven't already.) So if your shields are failing consider a tactical retreat because this is probably the last round of combat one way or the other.
In my experience, the hardest thing for player groups to come to grips with about starship combat is getting into a rhythm where probably only one or maybe two of them is going to actually make an attack roll each round. There's plenty to be done by every PC on a starship - damage control, evasive maneuvers, scanning your target, etc - but I've had several players kind of vapor-lock, confused about what they should be doing if they're not the person rolling phaser checks.
Larry DiTillio, co-author of Masks of Nyarlathothep, one of the best RPG campaigns ever written, has passed. In addition to his role-playing work, Larry was also the author of the story bible for he-Man and the Masters of the Universe, and the executive story editor for Babylon 5. The thread on his loss can be found here.