Cepheus Quantum

Stellagama Publishing

Posted: 2023-06-09
Last Modified: 2023-09-15
Word Count: 1459
Tags: cepheus rpg srd

Table of Contents

Editor’s Note

This document attempts to preserve the text of “Cepheus Quantum Revised Edition” but with necessary formatting changes for Markdown and some small spelling and punctuation differences. Any divergences from the original text that change the meaning are the fault of the editor.

Frank Mitchell

The following text is published under the Creative Commons Attribution-ShareAlike International License (CC BY-SA 4.0) by Stellagama Publishing. See LEGAL, below.

Cepheus Quantum

Revised Edition by Stellagama Publishing

One-sheet sci-fi RPG rules

Starships riding fire across the sky. Heroes and villains exchanging laser fire. Desperate spacers struggling against an alien monstrosity. Vast alien vistas, flying cities, moonscapes, mad robots, and first encounters. High-action science-fiction adventure that stimulates your sense of wonder. Now – on a single two-sided sheet!

All you need to play this game are this sheet, two or more six-sided dice, writing instruments and supplies, and an active imagination.

The Basic Game Mechanic

Throw 2d6: throw two six-sided dice and add the results together, add the skill modifier, and compare to difficulty. If the total equals or exceeds the difficulty number, you succeed. Otherwise, you fail. Skill notation: “throw Technical 6+” = throw two dice, add them together and add the Technical skill, and if the total equals or exceeds 6, you succeed. If you lack a skill, throw at -1 penalty (i.e., subtract 1 from the throw).

Task Difficulties

Difficulty Description Difficulty Number
Easy 4+
Average 6+
Difficult 8+
Formidable 10+


There are 6 skills:

Character creation

  1. Distribute 5 points among your six skills. You may not exceed 3 in any one skill.
  2. Your Stamina is equal to 12 plus twice times your Physical skill. This represents your resistance to injury.
  3. Your equipment is at the Referee’s discretion.
  4. You may carry up to 10 Items plus two items per point in your Physical skill.
  5. Think of a description and a personality for your character.



Armor Protection
Leather 2
Bulletproof vest 3
Ballistic Cloth 6
Space Suit 6
Combat Armor 11


Weapon DMG Range
Dagger 1d6 -
Axe or Machete 2d6 -
Two-handed sword or battleaxe 4d6 -
Sword or Cutlass 3d6 -
Handgun 2d6 10/50
Shotgun 4d6 20/40
SMG (Auto) 2d6 30/100
Assault Rifle (Auto) 3d6 50/200
Laser Rifle 5d6 300/500
Pulse Rifle (Auto) 4d6 300/600
Blaster 4d6 50/200
Hand Grenade (3m radius) 5d6 5/15


Vehicle Agility Armor
Ground Car +0 Unarmored
APC -1 Light
Helicopter +1 Unarmored
ATV -1 Light
Aircar +0 Unarmored
Grav Gunship +0 Heavy
Tank -2 Heavy
Motorcycle +2 Unarmored

Personnel Combat

There is no initiative – everything happens simultaneously, and the results of combat actions (e.g. wounds) are applied after all combat actions are resolved.

In a combat round, you may move up to 10m and attack or move 20m without attacking.

Throw Combat 8+ to hit a target in melee or in ranged Effective range; Combat 10+ to hit beyond Effective range. Apply the target’s Combat skill as a penalty to hit. Shotguns can hit two adjacent targets at once (throw to-hit for each). Automatic weapons can attack twice a round (any target).

Upon a hit, throw the weapon’s damage dice, subtract any armor, and apply to the target’s Stamina. As long as Stamina is positive, the character is not wounded, only bruised. However, if Stamina runs out, the character is Wounded and typically is out of combat. Characters may attempt to keep fighting even when Wounded; throw Physical 6+ to keep fighting when receiving a wound.

Any further damage caused to a Wounded character causes additional Wounds. The character may throw Physical 6+ to keep fighting every time they receive a wound. However, every Wound the character suffers incurs a -1 penalty on the Triage roll, as well as to the roll to keep fighting when wounded.

When combat is over, characters with a positive Stamina recover their full Stamina within 10 minutes of catching their breath and resting. For each Wounded character, roll on the Triage table after combat. Apply -1 per Wound the character suffers; -2 if the character is attempting to recover on their own (without first aid); +2 if another character uses a medical kit on them.


2d6 Result
5 or lower Death
6-7 Severe injury; character will recover after 3d6 weeks of medical care.
8-10 Moderate injury; character will recover after 1d6 days of rest
11 or higher Flesh wound; character will recover within 1 day of rest or immediately with a medical kit.

Vehicle Combat

Vehicle combat is a chase and is played in turns. Each side throws 1d6 + Technical + Agility; the vehicle with the higher throw has Position. The Pursuer wins on ties. A vehicle with Position may attack normally (Combat 8+). A vehicle without Advantage can attack at a -4 penalty. Chase lasts until one side is disabled or 5 turns pass without either being destroyed.

Armor penetration depends on weapon and armor. Upon a successful hit, compare the vehicle’s armor to the weapon type on the following table. Then, refer to the appropriate Vehicle Damage Table.

Vehicle Penetration

Armor/Weapon Small Arms Support/Laser Gunnery
Unarmored Regular Regular Critical
Light - Regular Critical
Heavy - - Regular

A hit component is disabled or destroyed (Referee’s discretion). Knocked Out is out of combat; a Crew hit causes 3d6 damage to all crew and passengers; Destroyed is destroyed and causes 5d6 damage to all crew and passengers unless they throw Physical 8+ to bail out.

Vehicle Damage

2D Regular Critical
4- Breach Knocked Out
5 Cargo Knocked Out
6 Crew Knocked Out
7 Weapon Crew
8-9 Locomotion Crew
10 Electronics Destroyed
11 Power Plant Destroyed
12 Critical Destroyed

Spaceship Combat

Spaceships have Agility, armor, and weapons.


Spaceship Agility Armor Weapons
Fighter +2 Unarmored 1x Pulse Laser (Light)
Corsair +1 Armored 2x Missiles (Heavy, 2 rolls per hit)
Frigate +0 Armored 2x Particle Beams (Heavy)
Merchant or Scout -1 Unarmored 2x Pulse Lasers (Light)

Spaceship combat is a chase and is played in turns. Each side’s pilot throws 1d6 + Technical + Agility; the spaceship with the higher throw has Position. The Pursuer wins on ties. A spaceship with Position may attack normally (Combat 8+; one gunner per weapon). A spaceship without Position can attack at a -4 penalty. Chase lasts until one side is disabled or 5 turns pass without either being destroyed.

Upon a successful hit, consult the following table, comparing the weapon power to the ship’s armor.

Armor/Weapon Light Heavy
Unarmored Regular Critical
Armored Regular on 4+ on 1d6 Regular

Missiles are limited in number (Referee’s discretion); the defender, in lieu of an attack on the enemy, may attack a missile, destroying it on a successful hit. A hit component is disabled or destroyed (Referee’s discretion). Knocked Out is out of combat; a Crew hit causes 3D damage to all crew and passengers. Destroyed ships usually take some time to explode dramatically, so crews often have time to race to the life-pods.

Spaceship Damage

2D Regular Critical
2 Hull Breach Knocked Out
3 Power Plant Knocked Out
4 Jump Drive Knocked Out
5 Weapons Knocked Out
6 Maneuver Drive Crew
7 Fuel Crew
8 Cargo Hold Crew
9 Crew Crew
10 Computer Destroyed
11 Bridge Destroyed
12 Critical Destroyed

Star Travel

When travelling between planets or stars, the pilot rolls Technical 6+, modified by the ship’s Agility. On success, the ship arrives just one time. On failure, the ship arrives a short bit too late for the intended purpose.

Alternatively, for more elaborate travel using a hexagon grid, any ship may travel 2 hexagons per week, and requires refueling and recalibration (Referee’s discretion) after each such Jump, typically taking one week.


Heroic and determined characters may develop their talents quickly and become living legends. To represent this, Cepheus Quantum offers an experience system.

Characters gain 1 XP per adventure. Every 5 XP, the character rises in Rank. When they gain a new Rank, they may choose one of the following:

A player character may advance up to four times in Rank (up to Rank 5). Most NPCs do not rise above the Rank 2; higher Ranked NPCs are rare and unique.

This Product is published under the Creative Commons Attribution-ShareAlike 4.0 International License (CC BY-SA 4.0). In summary, you may distribute and modify this text, even publish it commercially, provided you credit Stellagama Publishing and permit others to do the same.