Master of Orion — Rules Summary

Setup

Economy

Each colony's production (BC) splits across five ratio sliders that must sum to 100%: Ship, Def, Ind, Eco, Tech. Total production = colonist output (0.5 BC/colonist, rising to 2 BC/colonist at Planetology 50) + factory output (1 BC/factory) + trade/tribute/reserve transfers, minus maintenance/trade/tribute/espionage/security/transport upkeep.

Allocation effects

• Ship: builds the one design queued at that colony (or a Star Gate, once researched).
• Def: upgrades existing bases → builds planetary shields → builds new missile bases, in that priority order.
• Ind: builds factories. Base cost 10 BC each; overflow beyond what your population can operate goes to the Planetary Reserve instead.
• Eco: cleans waste → terraforms/converts atmosphere → enriches soil → boosts growth rate, in that priority order.
• Tech: converts to research points, pooled empire-wide, split across the six fields per your ratios on the tech screen. Spread investment over turns — lump-sum "crash funding" is less efficient (see the interest rule under Technology).

Factories & waste

• Base factory control: 2 per colonist, risable to 7 with Robotic Controls (Computer tech). Each robotic level above the first adds +50% to factory build cost; refitting existing factories to a new control level costs the price difference.
• Each factory generates ~1 unit of industrial waste (modified by waste already present); waste shrinks max population and can kill colonists outright. Never let it build past 10.
• Improved Industrial Tech (Construction) drops factory cost to as low as 2 BC; Ecological Restoration (Planetology) lifts waste-cleanup rate from 2 units/BC up to 20/BC at the top tier.

Planetary Reserve

Tax up to 20% of each planet's production into the Reserve (1 BC banked per 2 BC collected). Transfer to any colony; a colony can only use up to its own total production per year from a transfer (effectively doubling that year's budget), with the rest carried over.

Planets & Colonization

Environment types (14)

Hostile worlds are also the ones most likely to roll Mineral Rich/Ultra Rich. Yellow primary stars roll the most habitable planets; purple neutron stars roll more mineral-rich ones. Controlled-environment tech unlocks in a ladder — researching one hostile type also unlocks every environment less hostile than it.

Planetary specials

Population growth

Surplus Eco spending beyond waste cleanup buys extra growth directly: 20 BC/colonist baseline, 10 BC with Cloning, 5 BC with Advanced Cloning. Bonus growth from this is capped at ¼ of current population per year.

Colonization & invasion

• New colony: build a ship with a Colony Base special device, fly it to an uncolonized world you can survive on, then confirm — the ship is scrapped to found the colony.
• Transports move at (best known warp speed − 1); at most half a planet's population can transport in one turn, one destination per turn.
• Invasion: clear orbital ships/missile bases first (space combat resolves before landing), then ground combat resolves in repeated rolls (1–100 + tech bonuses for armour/shields/weapons; Bulrathi +20) until one side is wiped; ties kill one unit each side.
• Taking an enemy colony beats colonizing empty space: no colony-base ship needed, you inherit (and can refit) their factories, and there's a chance of grabbing tech you didn't have.

Movement & Scanners

• Ship range starts at 3 parsecs from a colony; Increased Ship Range tech (Propulsion) eventually removes the cap. Reserve Fuel Tanks add +3 parsecs.
• Nebulas: ships inside are capped at warp 1, and deflector/planetary shields stop working entirely — but planets inside roll mineral-rich more often.
• Scanner range starts at 3 parsecs (colonies), stepping to 5 (Deep Space), 7 (Improved — also reveals destinations), 9 (Advanced — also reveals planet types). Ship scanning range itself starts at 0, reaching 3 parsecs with Advanced Scanners.
• Relocate orders let a colony redirect its newly built ships straight to another owned system without manual piloting.

Ship Design

Hull sizes

+1% available space per level of Construction tech. Defense modifier applies to both beam and missile defense.

Cost & miniaturization

Components

• Computers: set attack level and add to maneuverability for initiative.
• Shields (Class I–X…): flat damage reduction per hit equal to class. Dead inside nebulas.
• ECM: adds to missile defense on top of beam defense.
• Armour: +50% base hits per level; double hull (shown as "II") costs 2× space for another +50% hits on top.
• Engines: warp rating = parsecs/turn on the map; also generates 10 power/level for other systems. Combat speed = +1 per 2 levels of maneuverability; larger hulls need more engine units to hit the same combat speed.
• Up to 4 weapon types and 3 special devices per ship (one of each device type).

Weapons & Special Devices

Weapon categories

• Beam: range 1 (unless extended), instant hit resolution, damage scales with margin of the to-hit roll.
• Heavy Cannon: bigger beam variant — more damage/range, more power/space.
• Missile: tracks over multiple turns, adds targeting bonus to attack, always deals full damage on hit; limited magazine, replenished after combat.
• Torpedo: unlimited ammo but fires every other round; half damage vs. planets (atmosphere).
• Bomb: ground targets only, ~10 shots per ship, no power required.
• Biological: kills population outright and permanently lowers habitability — tanks relations with everyone when used.
• Autofire (Gatling-type): multiple shots/round, splittable across targets.
• Continuous fire (Graviton-type): overkill damage carries to the next target in the group.
• Projectile (Mass Driver-type): halves defender's shield class before applying.
• Enveloping (Hellfire-type): one hit = four attacks from all sides, shield applied each time.
• Wide beam: +3 to hit.

Special devices (max 3, one of each)

• Cloaking: +5 defense while unfired; decloak-to-fire always goes first; 1 full turn cooldown before recloaking.
• Battle Scanner: reveals enemy specs, +3 initiative, +1 attack level.
• Stasis Field: traps a target group — can't fire or be fired on — for one turn.
• Black Hole Generator: 1-space range, kills 25–100% of crews in target space; shields cut the kill rate 2%/class.
• Subspace Teleporter: move anywhere on the combat map, always fires first; nullified near planets with a Sub Space Interdictor.
• Repulsor Beam: knocks adjacent enemies back 1 space/turn.
• Warp Dissipator: −1 combat speed per hit, restored after battle.
• Technology Nullifier: range 4, drops enemy computer/ECM 1–3 classes (rolled separately), cumulative, auto-repairs post-battle.
• Ion / Neutron Stream Projector: hits a whole group; strips armour 20% (+0.5%/attacker, cap 50%) or 40% (+1%/attacker, cap 75%) respectively.
• Pulsar (Energy/Ionic): damages everything adjacent, 5–10 base + scaling per ship firing.
• Oracle Interface: focuses all beams to one point — halves target shielding for those hits.
• High Energy Focus: +3 range to all beam weapons.
• Zyro / Lightning Shield: intercepts incoming missiles 75%/100% of the time, reduced 1%/missile tech level.
• Inertial Stabilizer / Nullifier: +2 maneuverability/+1 combat speed, or +4/+2 for the Nullifier.
• Automated / Advanced Damage Control: auto-repairs 25%/50% of max hits per round.
• Anti-Missile Rockets: 35% intercept, −1%/missile tech level.
• Colony Base: required to found a new colony (ship is consumed).

Combat

Triggers whenever hostile fleets share a system; resolves immediately, ends on annihilation, retreat, or a 50-turn cap (forces attacker retreat). A defender with no fleet can still fight via ground missile bases.

Initiative & to-hit

Missiles/torpedoes use the same math but ignore range, add the missile's targeting value to attack, add the defender's ECM to defense, and always deal full listed damage on a hit (no interpolation). Shields subtract flat from whatever damage got through. A ship dies once accumulated damage exceeds its hit points; one huge weapon can still only kill one target per shot (continuous-fire weapons are the exception — leftover damage carries over).

Attacking planets

• Missile bases: 50 hits to kill, unlimited ammo, base defense 1, add the planet's shield to their own force field.
• Beam weapons and torpedoes do half damage through a planetary atmosphere.
• Bombardment vs. population/industry: 400 damage kills 1M colonists, 100 damage destroys 1 factory — while bases still stand. Once every base is down, both kill rates double.
• Biological weapons kill outright and permanently cut habitability — plus tank relations with everyone, every time.

Transports & ground combat

• Colony transport: 15 base hits (modified by best armour), no shields, speed = best warp − 1 (combat speed is half that). Combat Transporters give a 50% chance to land troops before the transport fights in orbit at all.
• Ground combat: repeated 1–100 rolls + tech bonuses (armour/shield/weapon) per side each round; high roll kills one enemy population unit, ties kill one from each side. A +10 tech-bonus edge already yields roughly a 3:2 kill ratio. Bulrathi get a flat +20.

Diplomacy

15-step relations scale, feud ↔ harmony, drifting back toward each race's fixed starting disposition if you take no action. Humans are broadly liked; everyone distrusts the Darlok.

Pacts/alliances don't move the needle immediately but keep relations propped up for as long as they hold; trade helps too, just less. Declaring war breaks all treaties and pulls ambassadors — they won't even discuss peace until relations stabilize, which requires a lull in attacks from both sides. Winning fights and taking colonies pressures the loser toward suing for peace.

Trade & Tribute

Upsizing an existing treaty resets the rate to the average of (current rate, −30%), applied to the new amount — so a treaty at 50% return jumping to a bigger deal restarts around 10%. Breaking a treaty drops the rate straight back to −30% and you rebuild from scratch.

Tribute: donate from the Planetary Reserve to buy relations, roughly half a diplomacy level per 10% of the rival's production donated — or offer technology for a bigger, one-time swing. Doesn't work once an AI has committed to eliminating you.

Espionage & Sabotage

Your base security = your Computer Tech level, +2% security bonus per 1% of production spent on Internal Security. Each year, per enemy spy network, security rolls 1–100 + your security bonus + (your Computer Tech − theirs, if positive); hiding spies subtract 30 from that roll. Darlok security gets +20. On a confession, all other spy attempts that year stop cold. Surviving spies then roll once to infiltrate (+ their Computer-tech edge, Darlok +30 to the roll).

Missions (successful infiltration required)

• Espionage: steal the highest tech your infiltrators roll (1 to target's level) in a chosen field.
• Sabotage bases: 50% chance per spy per 10 levels of your Weapons tech.
• Sabotage factories: 1–5 factories destroyed per spy per 10 levels of your Weapons tech.
• Incite rebellion: up to 10% of population turned per spy; the colony revolts once the total passes 50%.

Technology

Six fields: Computer, Construction, Force Field, Planetology, Propulsion, Weapons. Only the first 50 levels add new devices — beyond that you're paying to refine/miniaturize what you already have.

Artifact planets double research output; Orion quadruples it. Each race has field-specific cost multipliers (some cheaper, some at ~125% "Poor" cost) — check the Races screen for your race's spread.

Field highlights

• Computer: battle computers (attack level + initiative), ECM jammers, Robotic Controls (factories/colonist, +50% factory cost per level above 1st), Space Scanners, Technology Nullifier, Battle Scanner, Hyperspace Comms (redirect in-flight fleets).
• Construction: Starship Armour (+50% hits/level), factory cost reduction, waste reduction, Powered Armour line for ground troops (+10/+20/+30), +1% ship space per level, Reserve Fuel Tanks (+3 parsecs).
• Force Field: Deflector Shields (absorb = class), Planetary Defense Shields (100 BC/class, auto-built), Black Hole Generator, Cloaking, Stasis Field, Repulsor Beam, Lightning/Personal Shields.
• Planetology: waste cleanup rate, Atmospheric Terraforming (200 BC, hostile→standard), Soil Enrichment (150 BC standard→fertile) / Advanced (300 BC →gaia), size-increasing Terraforming (5 BC/unit, later 2 BC), Controlled Hostile Environments (unlocks ladder + needed for hostile-world invasion), colonist output ½→2 BC by level 50, Biological Weapons/Antidotes.
• Propulsion: warp engines (10 power/level), range extension, Inertial Stabilizer/Nullifier, Subspace Teleporter, Star Gate (2000 BC build, 100 BC/yr upkeep, instant travel between gated systems), High Energy Focus (+3 beam range), Combat Transporters (50% pre-combat troop landing), Warp Dissipator, Pulsars.
• Weapons: beams/missiles/bombs/hand weapons across the categories in Weapons & Devices; Anti-Missile Rockets (35% − 1%/missile level); Hand Weapons for ground combat (+5 to +30 by tier).

Races

Leaders

Every leader (initial and revolt-replacement) gets one personality and one objective, which drive AI diplomacy/resource-allocation behavior. Poorly-performing empires are more likely to suffer a revolt; a revolt breaks all trade/treaties and resets relations toward neutral. New leaders after a revolt tend to address whatever the empire's weak point was (e.g., a tech-poor empire gets a Technologist).

Personalities

• Ruthless: attacks with little provocation.
• Erratic: unpredictable, can flip to war with no real cause.
• Aggressive: attacks whenever the odds favor them.
• Pacifistic: seeks peace even after being attacked.
• Honourable: won't attack allies, but doubles retaliation for betrayal.
• Xenophobic: halves positive diplomacy, doubles hostile-action effects.

Objectives

• Diplomat: trade with allies, espionage on enemies, otherwise balanced.
• Militarist: weapons tech, standing fleet.
• Technologist: broad tech spend, no single focus.
• Ecologist: planetology/construction focus.
• Industrialist: maximizes factories and industry tech.
• Expansionist: propulsion/planetology, colonizes aggressively.

Racial tendencies

Crises & Disasters

Random per-colony events; likelihood rises the longer it's been since your last one. Mostly need direct intervention.

• Ancient Derelict: free force-field/weapons tech.
• Climate Change: +50% population growth.
• Comet: destroys the colony unless your fleet destroys it first (more ships = faster).
• Computer Virus: erases research progress on one tech (not devices already owned).
• Diplomatic Blunder: tanks relations with one race, possibly to the brink of war.
• Donation: free BC into the Planetary Reserve.
• Earthquake: kills colonists, damages factories.
• Industrial Accident: waste maxed on that planet — clean up fast.
• Mineral Discovery / Depletion: planet becomes Mineral Rich / Poor.
• Piracy: drains trade income until you clear the pirate system with enough ships.
• Plague: colonists die until cured; colony's research auto-redirects to a cure; transports quarantined.
• Rebellion: production stops; send colonists to fight the rebels; population doesn't count for High Council votes until resolved.
• Space Monster: roams destroying colonies until your fleet kills it (tough fight).
• Super Nova: mass casualties/industry loss unless research (auto-redirected) finds a fix in time.

Victory

Strategy notes from the manual

• Scout aggressively at the start; invest in Propulsion range early if nothing habitable is nearby.
• Don't over-expand — let colonies build up factories/defense first.
• Defend mineral-rich colonies hard; they're prime targets.
• Never let waste exceed 10.
• Don't fall behind in tech — a small force with superior tech can beat a large obsolete fleet.
• Steal missing key tech (robotic controls, waste reduction) via espionage; raise security if you're the one ahead.
• Keep ship maintenance under ~30% of budget; scrap obsolete hulls.
• Ground assaults net factories and possible tech finds, not just territory.
• Keep a Planetary Reserve for emergencies and new colonies.
• Fight one enemy at a time — multi-front wars are much harder to win.
• Trade with allies for both economy and relations.
• Periodically max security to flush out hidden spies.