Commonly Referenced Rules

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Wounding Modifiers and Injury

Any damage left over after subtracting DR from basic damage is “penetrating damage.” If there is any penetrating damage, multiply it by the attack’s “wounding modifier.” This is a multiplier that depends on damage type:
• Small piercing (pi-): x0.5.
• Burning (burn), corrosion (cor), crushing (cr), fatigue (fat), piercing (pi), and toxic (tox): x1 (damage is unchanged).
• Cutting (cut) and large piercing (pi+): x1.5.
• Impaling (imp) and huge piercing (pi++): x2.

The damage after this multiplier determines the injury – the HP lost by the target. Round fractions down, but the minimum injury is 1 HP for any attack that penetrates DR at all.

Flexible Armor and Blunt Trauma

Flexible armor is much lighter than rigid armor, but it doesn’t absorb the full force of the blows it stops. An attack that does crushing (cr), cutting (cut), impaling (imp), or piercing (pi-, pi, pi+, pi++) damage may inflict “blunt trauma” if it fails to penetrate flexible DR. For every full 10 points of cutting, impaling, or piercing damage or 5 points of crushing damage stopped by your DR, you suffer 1 HP of injury due to blunt trauma. This is actual injury, not basic damage. There is no wounding multiplier. If even one point of damage penetrates your flexible DR, however, you do not suffer blunt trauma. If you layer other DR over flexible DR, only damage that penetrates the outer layer can inflict blunt trauma.

Injury to Unliving, Homogenous, and Diffuse Targets

Unliving: Machines and anyone with Injury Tolerance (Unliving) (p. 60), such as most corporeal undead, are less vulnerable to impaling and piercing damage. This gives impaling and huge piercing a wounding modifier of x1; large piercing, x1/2; piercing, x1/3; and small piercing, x1/5.

Homogenous: Things that lack vulnerable internal parts or mechanisms – such as uniformly solid or hollow objects (e.g., melee weapons, shields, and furniture), unpowered vehicles, trees, and walls – are even less vulnerable! This includes animated statues, blobs, and anything else with Injury Tolerance (Homogenous). Impaling and huge piercing have a wounding modifier of x1/2; large piercing, x1/3; piercing, x1/5; and small piercing, x1/10.

Diffuse: A target with Injury Tolerance (Diffuse) is even harder to damage! This includes swarms, air elementals, nets, etc. Impaling and piercing attacks (of any size) never do more than 1 HP of injury, regardless of penetrating damage! Other attacks can never do more than 2 HP of injury. Exception: Area-effect, cone, and explosion attacks cause normal injury.

Extraterrestrial Environments

Atmospheric Pressure

Regardless of its composition, an atmosphere may be difficult or impossible to breathe if its pressure is wrong. We measure air pressure in “atmospheres” (atm.); 1 atm. is air pressure at sea level on Earth.

Body Mercury Venus Earth Luna Mars Asteroids Europa Io Ganymede Callisto Titan Triton Pluto (KBOs)
Atmosphere (atm) Vac 90 1 Vac 0.4 Vac Vac Vac Vac Vac 1.5 Vac Vac

Trace (up to 0.01 atm.): Treat an atmosphere this thin as vacuum (see Vacuum, B437).

Very Thin (up to 0.5 atm.): The air is too thin to breathe. Earth’s atmosphere becomes “very thin” above 20,000’. If you lack protection (e.g., the Doesn’t Breathe advantage, or a respirator and oxygen tanks), you suffocate – see Suffocation (B436). Vision rolls are at -2 without eye protection.

Thin (0.51-0.8 atm.): Earth’s atmosphere is “thin” between 6,000’ and 20,000’. Thin air is breathable if oxygen is present in Earthlike percentages, but it is hard on unprotected individuals. Increase all fatigue costs for exertion by 1 FP. Vision rolls are at -1 without eye protection. Finally, anyone who breathes thin air for an hour or more must check for “altitude sickness.” Make a daily HT roll at +4. Critical success means acclimatization – do not roll again. Success means no effect today. Failure means headaches, nausea, etc., giving -2 to DX and IQ. Critical failure means the victim falls into a coma after 1d hours; see Mortal Conditions (B429). Roll against Physician skill once per day to revive the victim before he dies.

Dense (1.21-1.5 atm.): The air is breathable, with some discomfort: -1 to all HT rolls, unless you have a pressure suit. If the air contains more than 50% oxygen, you must wear a “reducing respirator” that lowers oxygen partial pressure, or suffer -2 to DX due to coughing and lung damage.

Very Dense (1.51+ atm.): As “dense,” but a reducing respirator is required if the air is more than 10% oxygen. Usually quite hot from greenhouse effects. You risk “the bends” (B435) if you experience over 2 x native pressure and then return to normal pressure. With Pressure Support 1, the bends are only a risk when returning from over 10 x native pressure. With Pressure Support 2 or 3, you are immune to the bends.

Superdense (10+ atm.): As “very dense,” but the atmospheric pressure is so great that it can actually crush someone who is not native to it, unless he has Pressure Support or an armored suit that provides this advantage. On initial exposure and every minute thereafter, roll vs. HT at a basic +3, but -1 per 10 x native pressure. If you fail, you suffer HP of injury equal to your margin of failure. If your Size Modifier is +2 or more, multiply injury by SM. With Pressure Support 2, read this as “Over 100 x native pressure” and “-1 per 100 x native pressure.” With Pressure Support 3, you are immune to pressure. Visitors to Venus, or deep inside Jupiter, experience hundreds of atmospheres of pressure! Such atmospheres are often poisonous, which presents a separate problem.

These rules assume you are native to 1 atm. and can function normally at 0.81-1.2 atm. If your native pressure differs from 1 atm., multiply all the pressure ranges above by your native pressure in atm. For example, if you’re native to 0.5 atm., a “dense” atmosphere for you would be 0.61-0.75 atm. and a “thin” one would be 0.26-0.4 atm.

Low Pressure and CO2 Poisoning: Mars

The Martian atmosphere is lethal to normal humans, with both low levels of oxygen and lethal quantities of CO2 (which produces rapid convulsions, unconsciousness, and death). As a result, ordinary humans must live in habitats or vehicles with life support. A person with the advantage Doesn’t Breathe, a respirator or vacc suit, or special genemods or biomods (see Andraste biomod, CT64, or Yousheng, CT49) can venture out without ill effect. Otherwise, a person breathing Martian air loses 1 ST (as fatigue) each second. If he passes out, he takes 1 point of damage every (HT seconds) and will eventually die. A person can hold his breath before losing fatigue; see p. B91. Note: these effects are faster than the CO2 rules in GURPS Space, which apply to much lower CO2 concentrations.

Extreme Pressure: Venus and Gas Giants

The atmospheric pressure on Venus is roughly equal to being 3,000 feet underwater on Earth. Vehicles, cybershells, and suits must be specially designed to operate in the pressure, which usually means DR 100+ and/or the advantage Pressure Support (B77). If a vehicle or suit is not properly designed for Venus, make a HT roll every minute at +2 to avoid a leak. (If HT is not known, e.g., for a suit, assume a value of 12.) For characters, the Pressure Support advantage at the 10-point level or better protects them completely. For characters with 5 points of Pressure Support, or none, roll a Quick Contest of ST each second, with the air pressure having a ST of 100. Pressure Support at the 5-point level gives +10 to this roll. Failure does thrust/crushing damage for ST equal to the amount he lost by. This is reduced by DR effective against all crushing attacks.

Gas giant pressure varies from near-vacuum to many times that of Venus. Rules for operations in gas giant atmospheres will be covered in Transhuman Space: Deep Beyond, though characters or cybershells capable of surviving Venus can survive in the mid to upper levels of such atmospheres.

Cryogenic Atmosphere: Titan

Titan’s dense pressure (1.5 atmospheres) means visitors can wear unpressurized heat suits, air masks, and oxygen tanks – there is no need for pressure suits on Titan. Its air is unbreathable, but the -300°F nitrogen-methane atmosphere will kill anyone directly exposed to it before they can suffocate. If someone is in a sealed suit, they will still suffer normal freezing effects unless the suit has a life support system.

A human exposed to Titan’s atmosphere takes 1d-3 damage per second. A HT-6 roll (HT -8 if breathing it) must be made any time damage is taken to avoid shock. On a failure, the victim cannot take action until he is warmed up and receives First Aid. (On a critical failure, his heart stops, and he dies in 3d minutes unless resuscitated by CPR or defibrillation.) Someone in shock still takes damage from the cold and must continue to make HT rolls to see if his heart stops. If a patient recovers from shock, he is conscious but incapacitated for (24 – HT + 1d) hours. If his heart stopped but he was resuscitated, add 3d hours, 6d if defibrillation was required.

Different Gravity

A world’s gravity is measured in “Gs,” with 1G being Earth-normal conditions. In comparison, Mars has 0.38G and the Moon has 0.17G.

Microgravity is extremely low gravity (e.g., that of an asteroid or small moon) – for game purposes, anything below 0.1G.

Zero gravity is weightlessness, or “free fall,” as found in space and aboard any spacecraft not spinning, accelerating, or otherwise generating artificial gravity.

In higher or lower gravity, mass stays the same, but weight changes.

Body Mercury Venus Earth Luna Mars Asteroids Europa Io Ganymede Callisto Titan Triton Pluto (KBOs)
Gravity (G) 0.37 0.91 1 0.17 0.38 Micro 0.13 0.18 0.15 0.13 0.14 Micro Micro

Encumbrance and Move in Different Gravity

If local gravity is more than 1G, multiply the sum of your body weight and the weight of everything you’re carrying by (local gravity in Gs)-1. This is the extra weight you’re carrying due to high gravity. Add this to your encumbrance when determining Move.

Example: You weigh 150 lbs. and are carrying 30 lbs. of gear. On a 1.2-G world, that amounts to an extra weight of (150 + 30) x (1.2 – 1) = 36 lbs. Since you’re already carrying 30 lbs., your total encumbrance is 66 lbs.

If local gravity is less than 1G, multiply the weight of the gear you’re carrying by the local gravity, and use the modified weight to determine your encumbrance. There is a similar reduction in your body weight; this does not affect encumbrance, but it lets you jump further (see below). In very low gravity, you may be able to move faster than your Basic Move by making a series of running broad jumps instead of walking!

In zero gravity, you float in space (unless using magnetic boots, thrusters, etc.). If you can’t fly, you must push off from a solid surface to move. Your Move when doing so is equal to ST/2, rounded down. You will keep going at that speed until you grab or collide with something!

Actions in Different Gravity

In gravities other than 1G, the jumping rules (B352) need modification. Multiply your normal jumping distances by the ratio of 1G to local gravity. For instance, under 1.25G, you jump 1/1.25 = 0.8 times as far, while under 0.2G, you jump 1/0.2 = 5 times as far. (Exception: Do not multiply the bonus high-jump distance you get from a running start!) If this lets you jump at least twice as far as normal, use the rules under Super Jump (p. 89) to determine how fast you can move by bounding along.

When throwing (B355), multiply distance by the ratio of 1G to local gravity, just as you would for jumping. Damage from thrown objects does not change, as this is based on mass.

The minimum ST required to use a firearm of Recoil 2 or more without penalty increases by 1 per loss of 0.2 G. Projectile max ranges are divided by local gravity. Half-damage range is unaffected.

Gravity also affects falls. Multiply terminal velocity by local gravity. See Falling (B431) for what this implies.

In zero gravity, your skills and DX rolls are affected as well; see Free Fall (B197). This does not apply when firing beam weapons (unless they have Recoil 2 or more) or operating vehicles or tools specifically designed for zero gravity (e.g., a spacecraft).

Spin Gravity

Space travelers often find themselves in spacecraft or habitats that simulate gravity by spinning. Due to the Coriolis force, spin gravity does not behave quite like real gravity. If a person moves in the direction of the spin, he feels an increase in “gravity”; move in the reverse direction, and gravity drops. Individuals unused to spin gravity are at -2 DX. Double this penalty when jumping, throwing, or using low-speed missile weapons like bows; halve it in an extremely large spin-gravity habitat (spin radius of 3,000 feet or more per G).

Each week in a spin-gravity environment, a character should make an HT roll to adapt to this environment and eliminate the penalties. Those with the G-Experience advantage halve all penalties; those with the Motion Sickness disadvantage double all penalties and get no HT roll to adapt.

G-Increments and Attribute Penalties

If local gravity differs from your home gravity (see Home Gravity, B17), you might become disoriented and suffer physiological effects. The change in gravity you can tolerate without penalties is your “G-Increment.” This is 0.2G unless you have the Improved G-Tolerance advantage (B60).

In higher or lower gravity than usual, count the number of G-Increments from your home gravity, rounding down. This determines the penalties you suffer. For instance, an Earth native used to 1G treats 0.81G to 1.19G as zero G-Increments, but 0.8G or 1.2G counts as one G-Increment.

DX: You are at -1 DX per G-Increment of difference (-1 per two full G-Increments, if you have the G-Experience advantage, B57). This applies to activities that require agility or judging ballistic trajectories; it affects Broadsword, Driving, and Guns, but not Beam Weapons or Lockpicking.

IQ: You are at -1 IQ per two full G-Increments of higher gravity, due to reduced blood flow to the brain and general fatigue. Lower gravity has no effect.

HT: You are at -1 HT per two full G-Increments of higher gravity, because the heart has to work harder. Lower your FP score by the same amount. There is no effect in lower gravity – although microgravity or zero gravity might cause space sickness (see Space Adaptation Syndrome, below), or even have lasting ill effects in the long term.

See Temporary Attribute Penalties (B421) to learn how attribute penalties affect secondary characteristics and skills.

Space Adaptation Syndrome (“Space Sickness”)

Those who are not native to micro- or zero gravity (“free fall”) may become nauseated and disoriented by the constant falling sensation. Roll against the higher of HT or Free Fall when you first enter free fall. The Space Sickness disadvantage (B156) gives -4.

On a success, you are unaffected. On a failure, you are nauseated (see Afflictions, B428), which may trigger vomiting. If you begin to retch while wearing a vacc suit, you may choke; treat this as drowning (see Swimming, B354). Roll against the better of HT or Free Fall every 8 hours to recover. If you suffer from Space Sickness, you cannot adapt!

High Acceleration

Make a HT roll whenever you experience a sudden acceleration (“G-force”) of at least 2.5 times your home gravity. Treat a home gravity under 0.1G as 0.1G for this purpose.

Modifiers: -2 per doubling of acceleration (-2 at 5x home gravity, -4 at 10x, and so on); +2 if seated or lying prone, or -2 if upside down.

On a failure, you lose FP equal to your margin of failure. On a critical failure, you also black out for 10 seconds times your margin of failure.

A sudden acceleration may throw you against a solid object. If this happens, treat it as a collision with that object at a velocity equal to 10 x G-force of the acceleration.


Space travelers and colonists may be exposed to radiation due to solar flares, cosmic background radiation, nuclear or antimatter accident, radioactive waste, or attacks by nuclear, radiological, or particle beam weapons. Radiation is especially common in space, away from Earth’s magnetic field and thick atmosphere. This is one reason why Titan and Mars, with reasonably dense atmospheres, are more attractive places to settle than other bodies.

Radiation exposure is measured in rads. The more rads you take, the more likely you are to suffer ill effects. The GM should keep track of each character’s radiation injuries, noting each dose and the date on which it was received. Each one heals separately from all others received; after a month, it starts healing at a rate of 10 rads per day. However, 10% of the original radiation injury will never heal (except via cell repair using nanotechnology). For example, suppose someone spends a day in a “hot” environment and accumulates a 200-rad dose. After 30 days, that particular injury starts to heal. After another 18 days, at the 20-rad level, that injury stops healing.

Radiation Hazards

Cosmic Rays: These are generated by interstellar supernovas and contain nuclei of helium, carbon, iron, and heavier elements. They can smash through matter, leaving a train of ionized atoms that can kill a living cell. Unshielded individuals venturing beyond the atmospheres of Earth, Mars, Titan, and Venus may notice these impacts as bright flashes in their eyes every so often, even in total darkness. Cosmic rays inflict 1 rad/week. Only massive shielding protects people. See Radiation Protection, B436.

Earth’s Van Allen Belt: 4 rads/day.*

Fission plant accident: 1,000 rads/hour or more (in close proximity).

Nuclear blast: One-megaton fission air burst or space burst at 2,000 yards: 6,600 rads. Jupiter’s Radiation Belt: 18,000 rads/hour within 125,000 miles of Jupiter (out to the orbit of Thebe), 3,600 rads/hour out to Io, 600 rads/hour out to Europa, 10 rads/hour out to Ganymede, 0.01 rads/hour out to Callisto.*

Solar Flares: See The Sun, THS30.

*Beta radiation levels produced by these belts are orders of magnitude higher, but won’t penetrate even thin shielding like a vacc suit or spacecraft hull.

Effects of Radiation on Living Things

Every time a living character accumuluates at least 1 rad of radiation (but no more than once per day for continued exposure to the same source), he should roll vs. HT on the Radiation Effects Table (B436), using his current total accumulated dose.


Extreme Cold: Vacuum and Trace Atmospheres

Without a significant atmosphere to trap heat, areas in the inner solar system not exposed to sunlight (such as Luna or Mercury at night, or any area in shadow), or just about anywhere in the outer system, are freezing cold. See Cold, B430. Insulation is good enough to allow vehicles and colonies to withstand any degree of cold, even on Pluto, as long as there is a power plant to provide heat. A power loss or malfunction doesn’t doom the inhabitants immediately; the temperature drops gradually (depending on the size of the area), giving time to make repairs or call for help.

Extreme Heat: Venus and Mercury

The extreme temperatures on Mercury’s day side and Venus will quickly kill any unprotected individual. See Heat, B434. Vehicles, cybershells, or suits require DR 100 and life support or a cooling system; cybershells require DR 100 or Invulnerability (Heat). For each 10 points of DR (or fraction thereof) the individual lacks, it takes 1d damage per minute; if the vehicle or cybershell has a Size Modifier of +2 or more, multiply by its Size Modifier. If a vehicle’s DR is 100 or more, but it lacks adequate life support or a cooling system, damage is 1d per minute, multiplied by its Size Modifier as above. If a device has both inadequate DR and an insufficient cooling system, these effects are cumulative.


Vacuum and Trace Atmospheres

Vacuum is the absence of air – but these rules also apply in trace atmospheres, where there is almost no air. If you are exposed to vacuum without protection (e.g., a vacc suit or the Vacuum Support advantage), the following rules apply.

Breathing Vacuum: You can’t hold your breath in vacuum – and you may rupture your lungs if you try (1d of injury). If you exhale and leave your mouth open, you can operate on the oxygen in your blood for half the time listed under Holding Your Breath (B351). After that, you begin to suffocate (see Suffocation, p. 436).

Rapid Decompression: If a habitat loses a lot of air due to combat damage or to a meteor puncture, or if a respirator suddenly goes bad, a space traveler may find himself trying to adapt to rapidly falling pressure. Popping ears are a sure sign of a pressure change (IQ +4 to notice for anyone with space experience, IQ for anyone who has received even a basic passenger briefing). If your ears keep popping, pressure is still going down. If the situation is not stabilized quickly, the spacer must get to a pressure suit, escape pod, etc., or be in vacuum. Pressure loss is a terrifying thing. The GM may require all aboard to make a Fright Check (see B360); experienced spacers should roll at +4.

Explosive Decompression: When an area suddenly goes from normal pressure to little or none (a “blowout”), body fluids boil, blood vessels rupture, and eardrums pop. Take 1d of injury immediately, and roll vs. HT to avoid the bends (see The Bends, B435). Also roll vs. HT+2 for each eye; failure means One Eye or Blindness, as appropriate. Finally, roll vs. HT-1 to avoid Hard of Hearing. Use the Duration of Crippling Injuries rules (B422) to determine how long these disadvantages last.

Extreme Temperatures: Vacuum itself is neither “cold” nor “hot,” but in the absence of air, surfaces in shadow will eventually grow very cold, while those in sunlight will become extremely hot. For example, on the moon – with its month-long “day” – the temperature can range from -243°F (at night) to 225°F (at noon).


Light Sources & Vision Modifiers

Ambient Natural Light

Light Source Modifier
Bright Day +0
Overcast Day -1
Twilight -3
Clear Night – Full Moon -4
Clear Night – Partial Moonlight -5
Overcast Night – Full Moon -6
Overcast Night – Partial Moonlight -7
Clear Night – No Moon (Starlight) -8
Overcast Night – No Moon (Starlight) -9

Artificial Light

Light Source Modifier @ Max. Range Additional Penalty/Range Summary
Bright Indoor Light (Office) / Continual Light 3 Spell 0 @ 5 yds. -1 / 5 yds. -1 @ 5-10, -2 @ 10-15, -3 @ 15-20, etc.
Dim Indoor Light (Warehouse, Emergency) / Bonfire / Overhead Street Lights -1 @ 4 yds -1 / 4 yds. -2 @ 4-8, -3 @ 8-12, -4 @ 12-16, etc.
Large Campfire / Fireplace / Continual Light 2 Spell -2 @ 3 yds. -1 / 3 yds. -3 @ 3-6, -4 @ 6-9, -5 @ 9-12, etc.
Torchlight / Continual Light 1 Spell -3 @ 2 yds. -1 / 2 yds. -4 @ 2-4, -5 @ 4-6, -6 @ 6-8, etc.
Candlelight / Light Spell -5 @ 1 yd. -1 / 1 yd. -6 @ 2, -7 @ 3, -8 @ 4, etc.


Type Modifier
Light (Can see silhouette through concealment.) -2
Medium (Know approximate location within 1 yd – must select approximate area to attack.) -4
Heavy (Can not see at all – must blindly select area to attack.) -6

Commonly Referenced Rules

Transhuman Space Garrion