From Starfleet Commander
Combat occurs when one fleet encounters another as the result of an Attack. The attacker's ships immediately fire on the defender's ships and defenses, if there are any. If the attacker destroys all ships and defenses, and still has cargo space available, plunder will occur.
Note: Only ships, defenses and unspent resources are affected by combat. Buildings and droids are not vulnerable to combat losses.
How it Works
Combat lasts until either the attacker's or defender's forces are completely destroyed or six rounds of combat take place. In each of the rounds, all of the attacker's and defender's units fire randomly at the opposing fleet's units simultaneously. If any unit strikes a unit against which it has Rapid Fire, that unit will get a chance at firing an extra shot, also randomly. This will repeat until all units fail on their random Rapid Fire chance or hit a unit against which they do not have Rapid Fire.
The damage dealt from each shot is equal to the shooting ship's Weapons Rating. So for instance an Artemis Class has a Weapons Rating of 50. If it hits an Atlas Class it will deal that Atlas 50 damage.
Shield and Hull
Damage done to a ship in each round is first absorbed by that ship's Shield Rating and then the remaining damage subtracts from the ship's Hull Rating. An Atlas Class has a Shield Rating of 10 and a Hull Rating of 400, so if it were shot by an Artemis Class, which deals 50 damage, the first 10 would be absorbed by the shield and the remaining 40 would reduce the Atlas's hull to 360.
Shields replenish between rounds but Hull does not repair until the end of battle. So in our example above, in round 2 the Atlas would start with 10 Shield again and only 360 Hull. After round 2, if it survived, it would have a Hull of 320.
Any strike from a ship with a weapon rating that is less than or equal to 1% of the shielding capacity of the target is absorbed with no effect on the target. As an example, suppose a player with a Weapons Tech of 12 attacks a player with a Shield Tech of 9, and in the battle one of the attacker's Artemis Fighters targets the defender's Large Decoy. The fighter would have a weapon rating of 110 (50 + 5 * 12). The Large Decoy would have shield rating of 19,000 (10,000 + 1,000 * 9). Since 110 is less than 190 (1% of 19,000), the Artemis Fighter would do no damage; that shot is ineffective. Furthermore, it is essentially impossible that an attacker could research their Weapons Tech high enough that an Artemis would ever damage a Large Decoy. However, some units have base weapons ratings that are equal to 1% of other units' base shield ratings; in these cases the respective weapon and shield tech levels come into play.
Note: The following rules (including the table) presume reasonable AWS numbers. Hired Guns Eradeon modification and Alien techs may violate this presumption.
Shots by the following ships are always effective (base weapon greater than 1500): Prometheus, Thanatos, Zeus. Also, shots by Moros and Erebus are always effective because they bypass shields entirely.
Shots against the following units are always effective (base shield less than 100): Missile Battery, Laser Cannon, Space Mine, Hermes Probe, Helios Solar Satellite, Atlas Cargo, Zagreus, Dionysus Recycler, Hercules Cargo, Charon Transport, Empusa, Artemis Fighter, Apollo Fighter, and Poseidon Cruiser.
Defenses have relatively high weapons ratings; their shots are effective against all attack ships, with the exception that “fodder” defenses (Missile Battery, Laser Cannon, Pulse Cannon, and Particle Cannon) are ineffective against Zeus. Also, against Thanatos, Missile Battery is ineffective and Laser Cannon may be ineffective.
On attack, the Empusa is highly idiosyncratic. It is ineffective against defenses and when defending. It is effective against most ships (when sent to attack), with the exception of the Hephaestus.
For other pairings, consult the following table:
At the end of each round, when all ships are done firing, any ship that has less than 70% of its initial Hull Rating has a chance to explode equal to the total hull reduction.
So in our above example after round 4 the Atlas class will have suffered 160 total Hull damage and have 240 Hull (out of its starting 400) left. That means it has lost 40% of its Hull ((160/400)*100) and will therefore have a 40% chance of being destroyed.
If it survives, at the end of round 5 it will have suffered another 40 Hull damage for a total of 200, giving it a 50% chance of destruction. At the end of round 6 it will have suffered 240 Hull damage and have a 60% chance of destruction. Thus it is actually possible for an Atlas Class to not be destroyed by an Artemis.
At the end of combat if all of the defender's ships and defenses have been destroyed, and the attacker has ships remaining, the attacker will have won the battle and will Plunder the defender's planet.
At the end of combat if all of the attacker's ships are destroyed, and the defender has ships or defense remaining, the defender will have won combat. No Plunder will be received by the attacker.
If at the end of combat both sides have ships left, or all ships have been destroyed, the battle will have been a draw and no Plunder will be received by the attacker.
Special Rules for SFC Nova
In Starfleet Commander Nova, the amount of DSP awarded to each side for a battle is adjusted according to the RSP of each side and then distributed proportionally to the value of the ships each player has committed to the battle. DSP is calculated based on pre-attack RSP values. The DSP awarded is [(1 DSP per 1,000 Resources destroyed) × 0.5 × (Total Opponent's RSP ÷ Total Allied RSP)], with a range of 0.1 to 1.0. (“Allied” ships and defenses are those on the same side of the battle as yours.) This means that attacking a player of equal size to you will result in 1 DSP per 2,000 resources destroyed, but attack a player twice your size will result in 1 DSP per 1,000 resources destroyed. Then, when part of a group, DSP awarded to you is (The RSP Value of your Ships and defenders ÷ RSP Value of all allied Ships and defenses). This ensures that the player that commits the most ships and defenses to the attack or defense will receive the largest share of total DSP.
Note that the above formula for DSP adjustment has changed; DSP is still adjusted but the above is no longer correct.
If a defender is more than 100 RSP ranks lower than the attacker and the RSP value of the attacking fleet is more than 5x the RSP value (3x if the Defender has an Admiral) of the defending fleet, then the defending fleet, except for Hermes Probes, Shadow Probes, Helios Satellites, Genesis Satellites, Zeus, and an undeployed Hephaestus, will escape from combat if hydrogen is available on the planet. When calculating the RSP value of the defending fleet probes count for .25RSP and Satellites count for 0RSP. If the player is group defended, no fleet escape will be possible. No fleet escapes are possible after the player has 100,000RSP.
A spreadsheet to determine both DSP and whether a fleet escape is possible is available at http://bit.ly/HaJnoG.