In lieu of the spaceship book that is far down the pipeline, GURPS Spaceships offers a self-contained and realistic ship construction system, easily able to accommodate the Eclipse Phase setting. In separating turns into distinct crew member phases, it also keeps the action and drama at the character level rather than subsuming them in a seemingly unrelated strategy game. Finally, the decile values allow easy conversion between base Eclipse Phase and a scaled up ship combat system.
A full layout of all the rules in GURPS Spaceships is beyond the scope of this document, which lists only converted figures and the rules amended specifically for compatibility. For a full walk through, refer to GURPS Spaceships and the tactical game in GURPS Spaceships 3: Warships and Space Pirates.
For an illustration of the system being applied to similar setting and tech level, see GURPS Spaceships 8: Transhuman Spacecraft.
Conversion Notes from GURPS Spaceships
- All d6 rolls converted to a d10 system
- Modifiers reduced by a factor of 1.5 to represent the 1-10 1d10 range, instead of the 3-18 3d6 range. Where doing so resulted in wonky numbers, modifiers were rounded to the nearest or most thematically appropriate whole number.
- Ship Size Modifier divided by 2 (rounded down) for the purpose of sensor detection and attack roll modifiers. This helps align size categories to the ones already present in Eclipse Phase. The smallest SM +4 ships, which include fighters, interceptors and weapon platforms have a size modifier of +2, and are thus Very Large Targets in the base game.
- Hex scales, weapon ranges and delta-V budgets all changed to metric units. Tables modified to reflect this.
- Dodging no longer requires acceleration by one hex during the Piloting phase. Anything with a functioning engine can dodge, modified by its handling.
- Gun (kinetic) shots altered to reflect that in Eclipse Phase they cannot course correct. They suffer no penalty to hit from high relative velocity. Instead, their targets get a bonus to dodge them, modified downward by relative velocity and up by turn length. This is to solve the problem in standard GURPS whereby kinetics suffered enormous base accuracy penalties even against stationary targets. Probabilities to hit remain the same, but ponderous targets more vulnerable than maneuverable ones.
- Removed recoil effects from weapons, which made no sense for beams anyway. Salvo tables handle large numbers of attacks with fewer dice rolls.
- Precision Attacks now follow the same rules as Called Shots in Eclipse Phase.
- Some specific system alterations described in detail.
For deep space battles a hex size of 1,000 km and 3-minute or 10-minute turn lengths is appropriate. Orbital combat might use smaller hex sizes. 100 km hex size will work for bodies up to Cerean diameter; anything larger works better with 1,000 km hexes. Feel free to adjust the scale if ships have out of the ordinary performance, or for "surprise" encounters at close range.
Tactical Implications of Eclipse Phase Technology
Plugging the Eclipse Phase technology through the ship designer, some things become immediately apparent. The thrust rating of fusion and antimatter plasma rockets is much lower than that of the Eclipse Phase spacecraft descriptions, while chemical and metallic hydrogen rockets are mostly the same. The tradeoff between Isp and thrust is huge. This limits tactical maneuver by interplanetary vessels and prefigures a kind of carrier warfare in which these craft deploy swarms of high-thrust assets.
Armor can be much stronger than the core Eclipse Phase rules indicate, but a direct hit by a nuke or high velocity kinetic impactor will still one-shot even something as large as a destroyer. Ships that want a rounded survivability will have to invest just as heavily in point defense and manuever.
Railguns are slow and inaccurate but can be deadlier than nukes at high velocities. The choice of relative velocity is itself a tactical decision with its own tradeoffs, with kinetic-happy and risk-prone combatants seeking a fast approach.
Lasers (even UV) have weak damage, limiting their offensive utility to precision strikes on small targets and exposed systems. Their most valuable effect is to deter opponents from deploying their radiators within a certain range.
Nanofactories allow ships to alter their assets and capabilities on the fly, allowing them a great degree of adaptation. Strategy centers on correctly guessing your enemy's capabilities while concealing your own, and in correctly timing the deployment of scarce resources. Do you bet on a long-range missile strike, or wait to knock out their point defenses with beam weapons? Do you keep your radiators extended, risking them in the hopes of outlasting a more cautious enemy? Place more drones in forward deployment, or reserve them as a trump card?
There is also a neat rock-paper-scissors dynamic between the different types of weapons and their ideal countermeasures, with armor countering lasers, point defense countering missiles and maneuver countering railguns. Particle beams have all the speed of lasers with much higher damage; the counter to them is stay outside their short range.
A full description of the rules for character actions can be found in GURPS Spaceships and GURPS Spaceships 3: Warships and Space Pirates. The rules regarding these roles are detailed here only when they have been changed.
This modified system uses 1d10 for skill rolls rather than 1d100. For converting base Eclipse Phase skills, divide by 10 and round to the nearest number (eg a skill of 63 becomes 6, 37 becomes 4 etc).