Force Field Rules

In this post I am going to get into an area that I usually avoid, which is specific game rules. The purpose of New Diasporia is to describe a game background. For many aspects of the game any rule system will do, and because many RPG rulesets dedicated to science fiction already include rules for force fields feel free to completely disregard this post if you prefer the rules you are familiar with or are already integrated into the ruleset of your choice.
I should start by stating that these rules are based upon the force field rules for GURPS, which in both the 3rd edition, which I use and the 4th edition which I do not (but sometimes steal shamelessly from) were both developed by David Pulver. These rules are not identical to the generic GURPS 3ed or GURPS 4ed rules, but are heavily modified for New Diasporia.
Force field technology as proposed by the two editions of GURPS are vastly divergent. The 3rd edition rules seem very much based upon black globe force fields from the Traveller background. The 4th edition rule seem much more in line with how force fields are handled in Star Trek or Stargate. 3rd edition Force fields are very massive (at anything approaching reasonable tech levels,) very expensive and as dangerous to the user as the enemy. 4th edition force fields are much more interesting, but, like all of GURPS 4th edition lack the gearhead crunchiness of the 3rd edition rules, like how to design force fields for vehicle or spacecraft use.
They are also substantially lighter and cheaper.
Specs are standard GURPS with the noted exceptions. Power is in Megawatts (MW), Volume is in cubic feet (cuft). Mass is in pounds (lbs). Cost is in Parliaments (1P~$1000). Radius of the coverage area for spherical or hemispherical fields are in feet (ft). Tech Level is in New Diasporia TL. Damage Resistance (DR) is the standard GURPS characteristic that describes the protection offered by armor or any object when it is hit. PF is the Protection Factor, the amount of protection given against gamma radiation.

Force Screens	Power	Volume	Mass (lbs)	Cost (P)	Diameter (ft)	TL	DR
Heavy Force Screen	*	12	1500	1500	45	B	4000
Medium Force Screen	*	6	250	250	30	B	1000
Light Force Screen	*	2	25	25	15	B	200
	* External
Personal Force Field	C/.25	0.00028	2.5	8	Conformal	A	60
Tactical Force Field	D/1	1.2	10	20	Conformal	A	150

Force Screens can be scaled to cover larger areas by simple multiplication. A medium force screen which covers an area enclosed by a 60 foot sphere would cost P500, mass 500 lbs and be about to same size as a heavy force screen covering an area enclosing a 45 ft sphere.

Small vehicle force fields are typically conformal, that is they conform to the shape of the vehicle. Therefore the relevant parameters for a vehicle force screen are the DR and the Surface Area in ksf. The power consumption of a force screen is equal to its Surface Area in ksf times its DR divided by 100 or:

Power (MW) = Surface Area (ksf) * DR / 100

To calculate the mass of the projectors and the associated hardware multiply the Power by 11.8.

Mass (lbs) = Power (MW) * 11.8

The cost is equal to the power divided by ten in Parliaments.

Cost(P) = Mass * 2.5

Military vehicles and spacecraft larger than 400,000 cuft are typically spherical and use spherical force fields. Battle Riders and Mobile Fighting Vehicles (MFV) even though they can be as small as 2000 cuft also usually spherical and use spherical force fields.  Cost and the Mass of the field equipment tend to favor spherical fields.

In ablative mode the screen loses one point of DR for every 10 points of damage it takes. It will regenerate 1 DR per second for every 10 DR the field started with.
If the force screen is to be used in absorbent mode it must have an energy sink. This generally takes the form of a bank of rechargeable power cells.
As long as there is capacity in the energy bank the screen will absorb all of the hits it takes. DR is converted to MW based upon the amount of energy that is deposited on the screen by the weapon. For this purpose 100 DR is equivalent to 1 MW. A standard E power Cell can hold up to 2880 MWs. A ships energy bank can hold over a million MWS of energy.
Once the energy bank is full the screen will degrade in seven levels. It will bump a level each time it absorbs one half of its rated DR. It can also bleed off this energy at one level per 10 seconds. All of the energy must be bled off the screen before it can be turned off or its mode shifted, or it will catastrophically fail.
A screen can be switched from one mode to the other while it is in operation. All of its other properties can also be manipulated without turning it off.
To calculate power factor divide the DR by 100. For every cDR increase the PF increased by a factor of 10. So a DR 100 field provides a PF of 10. A DR 200 field provides a RF of 100, etc.