This article originally appeared in Pyramid #22

GURPS Vehicles Designer's Notes

by David L. Pulver

The second edition of Vehicles is a complete redesign of the original version. It's based on (and compatible with) the design system in GURPS Robots and is the combat and design system for the new GURPS Autoduel worldbook (scheduled for October release) and GURPS Mecha (January 1997).

If you have the old edition, what's good about the new one? First off, it covers many subjects the original overlooked, including trains, starships and space combat, and even time machines. Also, the new rules are more detailed in some areas, simpler in others overall complexity is about the same, but the system is much better organized, so designing vehicles is a lot easier. A major feature is a complete weapon design system which can handle everything from catapults to nuclear missiles; it can even be used to create small arms, like rifles and pistols.

Inevitably, the book ended up a little long (well, very long!) and a few things had to be trimmed. Here, then, are some of the "outtakes" from GURPS Vehicles, Second Edition.

Asteroid Ships

A vessel constructed in space may use an asteroid as its body. This requires finding one of the correct size and composition (nickel-iron is ideal) to hollow out.

Certain restrictions apply to the design. Motive and flight subassemblies are not allowed, nor can it have hydrodynamic lines, streamlining, or any of the following components: rowing positions, sails, drivetrains, paddle wheels, magnetic levitation.

Structure: The frame strength must be either heavy or extra-heavy. Treat the structure as TL5 and very cheap. However, the vehicle is not wood, it's stone or iron; and isn't flammable.

DR: The body must be given DR 100 or more of TL5-metal armor, representing its rock and nickel-iron hull. This armor adds weight but not cost. It's free! This free DR may not exceed DR 1 x body area, or DR 100, whichever is more.

Camouflage: This is the real reason for using an asteroid. As long as its outer layer of armor is rock (see above) and the only subassemblies it has are pop turrets, it can disguise itself as an asteroid. If it has landed (e.g., on an airless world) it could be a boulder or hill. As long as it is not maneuvering, accelerating, decelerating or doing anything else to attract attention (firing, using radar, etc.) it will simply appear to be a rock to most sensor scans; the exceptions to this are sensors that can detect power emissions or life forms.

Modular Vehicles

At TL6 or higher, vehicles can be designed to break down into modules for easy transport. The weight and volume of each individual module is the vehicle's empty weight and volume divided by the number of modules it breaks down into. Disassembly or assembly time is 0.01 man-hours per cf of vehicle body size times the number of modules. If total volume is less than 100 cf, a mechanic's toolkit is required to assemble the vehicle. Otherwise an actual machine shop is needed. A Mechanic skill roll at +2 is required to assemble or disassemble the vehicle properly. Failure means the time was wasted, but another attempt may be made; critical failure means a vital part is damaged. This option weighs 0.1 times the structural weight and costs four times the structural cost.

Collapsible Tanks

At TL6 or higher, a vehicle can carry flexible fuel bladders that can be erected on deck or within cargo space of any vehicle. Doing so takes about an hour and a Mechanic roll, and allows transference of fuel to the vehicle's regular fuel tank. If a vehicle with collapsible tanks attached performs a maneuver over 1.5 g or an acceleration or deceleration over 30 mph/s the tank ruptures, spilling the fuel (and check for fire). A collapsible tank is identical to an ordinary fuel tank with the ultralight option, except it is 1/10 cost, has only DR 2, and when collapsed takes up only 1/10 volume (i.e., .015 cf per gallon).

Electrolasers

Rules for electrolasers can be found in GURPS Space and GURPS Ultra-Tech. To build them, use the rules for designing charged particle beam weapons except that TL is 9, damage is Spcl. and at the end of the design process, divide damage and range by 2.5, double the power requirement, and halve the cost.

Habitat Modules

Some large vehicles, such as colony ships and space stations, contain large urban or green areas inside them. Each module described below is about the size of a city block and includes lighting, temperature control and air recycling. Volume of all modules is 2,000,000 cf; other statistics vary.

Housing: This module contains one or more apartment buildings or a few dozen houses, plus grounds, walkways, etc., providing long term accommodation for up to 100 people (half that many in luxury; twice that many in cramped conditions). The module weighs 300,000 lbs. at TL7, 250,000 lbs. at TL8, 200,000 lbs. at TL9+. Cost is $500,000, power 2,000 kW.

Farm: An acre or so of open space with a few buildings devoted to agriculture and food processing. Up to 10 people or robots can work it efficiently, each such worker can grow sufficient food to feed 10 people. Using crop rotation, the farm can continuously feed about 100 people. Weighs 200,000 lbs. at TL7, 150,000 lbs. at TL8, 100,000 lbs. at TL9+. Costs $500,000, power 4,000 kW.

Factory: A large industrial park, capable of operating efficiently with a dozen workers or robots. Contains warehouses, minifacs, etc. Weight is 600,000 lbs. at TL7, 500,000 lbs. at TL8, 400,000 lbs. at TL9+. Costs $10,000,000, power is 20,000 kW.

Park: A landscaped green space, possibly with entertainment or exercise facilities (pools, stream, swings, etc.). In a pinch, it can provide camp grounds for about 100 people. Statistics as farm, but halve cost.

Plaza: A mall or concourse area, with a dozen or so medium size establishments, plus open space for a thousand or so people to congregate. It has the same statistics as Housing.

Improved Access Space for Passengers

A vehicle with short-term passenger accommodations can be given "improved access," enabling passengers and crew members to move the length of the passenger compartment without displacing other passengers from their seats, or "superior access," with aisles big enough to allow serving carts and the like to move freely. The former requires cf of empty space at least equal to half the volume of all passenger seats; the latter requires cf of empty space at least equal to the volume of all the passenger seats. Vehicles with long term accommodations are assumed to have superior access to all bunks or cabins at no increase in volume.

Multi-Stage Rockets

A vehicle can be built with several bodies containing rockets and fuel stacked one atop the other. As each runs out of fuel it is jettisoned, reducing weight and improving performance. Number the stages from 1 to however many are installed, and assume they are stacked one atop the other. Build each stage as its own vehicle, generally with a body and no subassemblies (although sometimes wings or pods, or hardpoints with booster rockets, are added.) All stages must have the same streamlining. Stages that are intended to be jettisoned normally contain no components other then engines and fuel.

Do not work out statistics (other than cost and volume) or the vehicle's performance until all stages have been designed and stacked together. A stage can be jettisoned by the vehicle operator. If so, all stages "below" it are also jettisoned.

Combined Statistics and Performance: Calculate the statistics (weight, volume, etc.) using the combined weights and volumes of all the stages together. Recalculate a new surface area for the vehicle for use when calculating aerodynamic drag only; rather than adding the surface areas of each stage's body together, the volume of all bodies is added together, and a surface area based on this combination, plus the combined surface areas of all subassemblies, is used. After these combined statistics are calculated, determine the performance generally only air and space performance using just the propulsion systems, fuel and energy in the first stage (including any systems attached to hardpoints, subassemblies, etc.). Note, however, that wings or contragrav on any stage may provide lift.

2nd Stage Statistics and Performance: This is used after the first stage is jettisoned. Same as above, but recalculate statistics as if the first stage vehicle did not exist, and use only the propulsion systems, fuel, etc. in the second stage to determine performance. Use a similar procedure for latter stages.

New Space Drives

Cold Gas Thrusters (late TL5) are little more than a valve and a nozzle on a tank of compressed gas, but are cheap and safe to use. They are common on "thruster packs" or "scooters" for spacers operating in zero-gravity. They use liquid argon as a reaction mass; it is cheap and non-flammable. Argon is 11.7 lbs. and $0.15 per gallon.

Electric Rockets (late TL7) include arc jets, resistojets and plasmadynamic thrusters. They use electric power to heat hydrogen before ejecting it as reaction mass, rather than igniting it with an oxidizer like a chemical rocket. They are fairly inexpensive and can use cheap, light fuel. They are used for applications where fuel economy is more important than high thrust.

Underwater Rockets: Any solid, chemical, fission, antimatter thermal or non-optimized fusion rocket can be modified to function underwater. Build the engine normally, but thrust is halved in air and underwater due to nozzle design. For +5% to weight, volume and cost, underwater fission, fusion or antimatter systems can use the surrounding water as reaction mass, eliminating the need for fuel; thrust is still half normal.

Type and TL Weight Fuel Usage Power
TL5+ Cold Gas Thrusters 0.010 x thrust 4.4A 0
TL7 Electric Rocket (60 x thrust) + 20 4H 80
TL8+ Electric Rocket (20 x thrust) + 10 2H 80

Location, Weight, Volume, Power, Fuel: See p. V36.

Cost: Multiply the weight by $25 if electric rocket or $15 for cold gas thrusters.

Nuclear-Pumped Lasers

A nuclear weapon can used to energize an X-ray laser or Gamma-ray laser beam in fact, this is the only way that such weapons can be built in the foreseeable future. A nuke-pumped laser is built like a regular X-ray laser or graser except it appears one TL earlier, costs twice as much, and must be designed with minimum output of 1,000,000 kJ and cyclic rate of 1+.

The weight, volume and cost includes the lasing array x-ray or graser lasing rods and a specialized nuclear device designed to pump it. A nuke-pumped xaser or graser explodes as it fires, as a (kJ output/10,000,000) kiloton nuclear explosion, with all normal radiation and electromagnetic pulse effects. (Damage of nuclear explosions is 12d x 2,000,000 per kiloton.) For example, a bomb-pumped 4,000,000 kJ x-ray laser would be a 0.4 kiloton nuclear blast. A nuke-pumped weapon is destroyed after firing for one second.

For obvious reasons, bomb-pumped X-ray or graser weapons of this sort are generally installed in disposable satellites or robotic missiles. Deployment and use of these weapons may be severely restricted by law or international agreements!

Outboard Motors

These should be built as a screw propeller plus a power plant in a pod attached to the rear of the body. The effect will be correct: less volume required in the body (as no access space is required for power or propulsion systems in pods) at some slight increase in body weight (due to the area of the pod).

Plasma Blasters

In many SF backgrounds, plasma guns don't really exhibit the fire hose behavior of GURPS flamers instead they fire individual plasma bolts similar to the TL12 fusion guns of Ultra-Tech fame, but not as powerful. Such "plasma blasters" are TL9 weapons that are built exactly like neutral particle beams, but cost 1.5 times as much. In game terms, they function exactly like neutral particle beams (not like flamers!) with two exceptions: a hit inflicts burn rather than impaling damage (no multiple after subtracting armor), but also spatters white-hot plasma over the immediate area. Anyone within two yards takes 1/4 the blaster's damage, and anything flammable (wood, paper, etc.) catches fire.

Satellite-Guided Munitions (SGS)

Cheap global positioning system (GPS) receivers are available at TL7 and can be added to missiles and artillery shells, using satellite guidance to give the same performance as more sophisticated systems for a fraction of the cost. The firing vehicle needs a GPS system or datalink with someone with one, and there must be a friendly GPS system to link with. Note: if using a non-military GPS receiver, the data is less precise: halve the bonus to hit.

SGS Guided Missiles are exactly like TL7+ inertial guidance, but with half the weight and cost, a +4 bonus to hit; no effect underwater or out of line of sight of a GPS satellite.

SGS Guided Shells have the same weight and half the cost of laser guided shells, but give a +4 bonus to hit in indirect fire if proper map coordinates of the target are available and the target and the firing vehicle are in contact with each other.

Spin Gravity

In space, if superscience cannot provide artificial gravity generators, some degree of gravity can be simulated by spinning the vehicle on its axis.

A more-or-less cylindrical or toroidal craft capable of space travel can use maneuvering thrusters to spin itself; a space station can be spun by tugs when it is constructed. In general, a vehicle can be built to be spun if it does not have flight subassemblies (wings, rotors, etc.), a lifting body, or non-retractable ground motive systems. More complex forms of spin gravity (e.g., mechanically spinning only a portion of the ship) are also possible, but are beyond the scope of this article!

The maximum practical gravity that can be generated through spin depends on the ship's dimensions: a smaller vessel cannot be spun fast enough to simulate Earthlike gravity without nauseating its occupants through coriolis force. As a playable abstraction, assume the maximum simulated gravity (g) possible is the square root of (body volume/5,000). The core 10% or so of the vehicle's body will be in zero gee; usually crew and passenger accommodations will not occupy these areas.

Individuals unused to spin gravity will be at -2 DX (-1 DX if they have G-Experience). This penalty doubles when jumping, throwing, or using low velocity missile weapons like bows; it goes away if the user successfully adapts (HT roll every week).




Article publication date: November 1, 1996


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