Advanced Force Fields

If you've ever tried to build the force screens in Ultra-Tech with Vehicles, you'll discover that they don't work. In fact, they don't even come close to working -- the personal force screen should be 8.5 lb and $10k, the backpack screen should be 25 lb and $25k, the heavy screen should be a staggering 5700 lb and $7 million. Now, given that Ultra-Tech predates Vehicles, and was given stats based on the 'looks good to me' principle, we can hardly expect it to conform entirely to Vehicles -- but this suggests that the two aren't even working from the same basic principles.

So...can we come up with a formula which comes closer? As a matter of fact, we can. A weight of DR²/20,000 works out to 2.5, 17.5, and 70 lb, which is close enough to the original 2/25/75 that we can believe we're working from the same principles. It also has a certain appeal based on how weapons construction works -- x4 weapon weight gives x2 damage, so why not have x4 shield weight give x2 DR. Still, it hardly seems appropriate that weight be completely unrelated to the size of the thing being protected; in addition, with Space 3e, truly large weapons stop scaling that way.

So, how can we create a fix for this? If we want to maintain maximum compatibility with Vehicles and Space, the following formula works:

The minimum area of any screen is equal to
The price of a screen is weight*125 (per 'cheap' screens in Space 3e)
For 2x cost, a screen may be 'compact' and half weight. For 4x cost, it may be 'very compact' and 1/4 weight. In addition, assume that 'standard' screens when overloaded merely require cool-down time of about ten minutes, 'compact' screens require repair, 'very compact' screens are destroyed.

This means that a standard personal screen (8 lb, $1,000) becomes DR 200 * 20 sf (8 lb, 40 kW), 'very compact', includes a C cell, total 2.5 lb, $4,100, lasts 9 minutes; a backpack screen becomes DR 500 * 50 sf (50 lb, 250 kW), 'very compact', includes a D cell, total 17.5 lb, $25,500, lasts 42 minutes. A heavy screen remains impractical. Higher tech screens actually have less endurance, rather than more. Still, this would be tolerable, if it weren't possible to come up with something better...

However, it is. Consider this scheme:

First, give your screen a 'strength' and a 'size', where 'size' is the largest object (measured in yards) the screen can protect, and 'rating' relates to DR. 'Size' cannot be less than 'strength' -- the screen can protect a smaller area, but gets no bonus for doing so. In addition, at TL 12 'size' cannot be less than 10; at TL 11 it cannot be less than 50. For a deflector screen, strength and size must be equal.
Now, from these, we compute a 'rating'. The screen rating is equal to strength * size, unless size > 100, in which case it is equal to 0.01 * strength * size * size. For a deflector, rating is equal to size² or 0.01*size³.
The base weight of the screen is equal to 2 * rating, in pounds. Halve weight for deflectors.
The base cost of the screen is equal to $100 * rating.
The base power consumption of the screen is equal to 5 * rating kW.
The base DR of a force screen is 25*strength at TL 11, (TL-11)*50*strength at higher tech levels. The base DR of a deflector screen is 0.25.
Apply modifiers from the table below to get final cost, weight, and power consumption
Finally, volume is equal to weight/50.

Basic Screen Options
TL	Weight	Cost	Power	DRmod	System
11+	*2	*2	*2	*2	+1 Deflector PD (max 3+TL/2)
11+	*0.5	*2	*1	*1	Compact Screen.
	When overloaded, screen takes damage equal to HT.
13+	*0.25	*4	*1	*1	Ultra-compact screen
	When overloaded, screen is completely destroyed. Not available for deflectors

Force Screen Variants

While these basic rules are suitable for a wide variety of science fiction force fields, and probably cover the most common form, there is actually quite a lot of variation in force field behavior, depending on your source. Some of the variants I am aware of are listed below. Most of them are either given cost/weight multipliers, or DR modifiers. DR modifiers are listed as a percentage; just add all modifiers.

Overload Variants

The standard GURPS overload formula actually probably isn't the most common form of screen burnout; that honor probably goes to the 100/100 overload screen (it is extremely rare to shoot through screens without burning them out first). A variety of the more common overload variants are below.

Explosive Overload A screen with explosive overload will explode violently when overloaded, doing (rating)d6 concussion damage, which will be internal to the affected module.
Safe Overload: When overloaded, the screen drops until it can shed an energy level, but is otherwise unaffected.
No Overload: The screen has no energy levels, and never overloads.
Fragile: Any hit penetrating the shield automatically overloads it.
20/100 Overload: The screen has 100 energy levels, and takes one energy level per 5% of its base. It loses 1 energy level per second.
100/100 Overload: The screen has 100 energy levels, and takes one energy level per 1% of its base DR. It loses 1 energy level per second. Any damage past what is needed to overload the screen is not stopped.
Slow Discharge: The screen does not discharge as fast as normal; it loses only one energy level per minute (or 1%/5 seconds).
Separate Faces: The screen has separate faces, which are overloaded and discharge separately. Multiply weight, cost, and power consumption by the square root of the number of faces (typically 4). For double cost, you can shift energy levels from one face to another at a rate of 1 energy level per turn.

TL	Weight	Cost	Power	DRmod	System
11+	*.5	*.5	*1	*1	Explosive Overload
12+	*2	*2	*1	*1	Safe Overload
11+	*1	*1	*1	*0.5	No Overload
11+	*.5	*.5	*1	*1	Fragile
11+	*1	*1	*1	*2	20/100 Overload
11+	*1	*1	*1	*5	100/100 Overload
11+	*.5	*.5	*.25	*1	Slow Discharge

Stoppage Variants

There is quite a lot of variation in what a force screen will stop; again, it is rare that more than one or two types of stoppage behavior is appropriate to a given setting.

Barrier: The force screen basically acts just like a wall. Common for 'doors' and the like. Usually also a dual screen. Ground and water drivetrains cannot be used through a barrier screen (use a flexible or impermeable screen).
Cutting Screen: Variant on a barrier screen. Any object intersecting the screen when it is turned on will be cut through if possible -- figure 1d(5) cutting per 20 DR, every turn until the obstruction is removed. Assume this damage also acts as an attack on the screen itself, to a maximum of whatever damage is required to cut through the object.
Flexible: The force screen acts like a somewhat squishy wall; it can be deformed but not penetrated by damage (figure about 1" per 10 ST or damage). A form-fitting flexible screen is treated as nonrigid armor (i.e. every '6' on damage gets a point through).
Impermeable: An impermeable screen does not permit air to pass through it; this may require life support for those inside. Generally speaking, any rigid screen is also impermeable.
Filter: A filter screen keeps out dust and the like, and will stop wind, but gas can still pass slowly through the screen.
Walk-through: The screen can be penetrated by low-velocity (1 yard/second) objects. Melee weapon use through the shield is possible as long as the blow is quite slow -- you may use thrusting weapons at half ST, and +2 to active defense rolls.
Velocity-limited: Low-velocity projectiles are not stopped by the field. See the full description in UT 2.
Energy Screen: Like velocity-limited, but more so. Full effect against lasers, disrupters, paralysis beams, neural weapons, X-ray lasers, grazers, and disintegrators, and any other weapons which use electromagnetic energy. Half effect vs blasters and pulsars, but ignores the armor divisor for a pulsar. No effect vs other weapons. +100% DR.
Kinetic Screen: Reverse of an energy screen. Full effect vs explosions, guns, fire, flamers, stunners, screamers, gravetic weapons, and fusion weapons. No effect vs lasers or particle beams. +50% DR.
Energy-absorbing Screen: Like a standard screen, except that it actually absorbs the power of attacks that hit it. It has 1/10 the normal power requirement, and when discharging it actually generates 0.001 * DR² kilowatts of power. May also be explosive. In some settings it may draw heat from the atmosphere, in which case it will tend to overload if used in atmosphere.
Disintegrator Screen: a disintegrator screen, rather than creating a field that stops attacks, creates a field that protects against projectiles by destroying them as they pass through the field. A disintegrator screen damages objects which touch it, as per a cutting screen (though it is not limited to objects intersecting the screen when it is turned on). It also protects against projectiles by destroying them -- use normal DR against projectiles (attacks which do enough damage to penetrate are large enough or fast enough to get through without being destroyed). Against large projectiles (anything the screen cannot destroy in a turn) it does not provide any protection. Armor divisors are effective against a kinetic screen -- as a rule, armor piercing ammunition is denser, harder, and tougher than normal ammunition. Disintegrator screens are ineffective against energy weapons, and are only overloaded by large objects.
Proportional: The screen will not stop more than a certain percentage of the force of an attack.

TL	Weight	Cost	Power	DRmod	System
11+	*1	*1	*1	*1	Barrier Screen
11+	*1	*1	*2	*1	Cutting Screen
12+	*1	*1	*1	*1	Flexible Screen
11+	*1	*1	*1	*1	Impermeable Screen
11+	*1	*2	*1	*1	Filter Screen
11+	*1	*1	*1	*1	Walk-through Screen
11+	*1	*1	*1	*1.5	Velocity-Limited
11+	*1	*1	*1	*2	Energy Screen
11+	*1	*1	*1	*1.5	Kinetic Screen
12+	*2	*2	*.1	*1	Energy-Absorbing Screen
11+	*1	*1	*2	*1	Disintegrator
11+	*1	*1	*1	*1.1	Proportional: 98%
11+	*1	*1	*1	*1.25	Proportional: 95%
11+	*1	*1	*1	*1.5	Proportional: 90%
11+	*1	*1	*1	*2	Proportional: 80%
11+	*.25	*.25	*.25	*2	Proportional: 50%

*Any system not listed does not affect the stats of the screen.

Shooting out from inside a shield

The standard GURPS force screen allow you to fire out from inside the screen without penalty. Force screens in literature are quite variable on this issue, however; many force screens somewhat restrict firing out through the screen. Many screens are 'dual' screens, actings as barriers from both inside and outside. Dual screens will also affect reaction engines; how they interact with reactionless engines depends on your preferred technobabble.

Slow: A slow dual screen requires at least a turn to form, allowing people to notice that it is going on, and shoot, get through it, whatever.
Flicker: A flicker screen can't be shot through, but can be activated and deactivated instantly. You can block with Force Screen (a PE combat skill)/2, which allows raising the screen in time to block an attack; once activated, it is on until the next turn. A flicker screen which is discharging draws full power, but can be otherwise 'off'.
Fast Flicker: Similar to a flicker screen, but can be flickered many times a second. Will shut off long enough to fire weapons, and then reactivate. You can only shoot through the screen by waiting for someone to shoot out, in which case assume that the screen will block anyway on a roll of (TL) or less on 3d6.
Portal: A portal screen can be fired through by creating small holes in the screen. The holes can be fired through at -10 to hit. Bonus depends on how fast the holes close -- halve the above bonuses.
Tuned: A tuned screen can be set to permit specific frequencies of energy through; typically this only applies to lasers, though it might also apply to gravmops. You can automatically detect the frequency a screen is tuned to if the vehicle fires; otherwise this requires an AESA roll at -5 or a Radscanner roll at -10; the active sensor attempt will be noticeable. A tuneable energy weapon is double cost, except for rainbow lasers. Bonus depends on whether the screen has a preset frequency, can be changed slowly (as an engineering task), or can be changed quickly (as an Electronics/Screens task). A tuned weapon should also take one of the above options (usually 'slow')

TL	Weight	Cost	Power	DRmod	System
11+	*1	*1	*1	*2	Slow Dual
12+	*1	*1	*1	*1.5	Flicker
12+	*1	*1	*1	*1.2	Fast Flicker
12+	*2	*2	*.1	*1	Portal
11+	*1	*1	*2	*.9	Preset Tuned
12+	*1	*1	*1	*.8	Slow Reconfiguration
12+	*1	*1	*1	*.7	Fast Reconfiguration

Shape Oddities

The standard force screen is assumed to be a sphere or oblong shape. Still, there's a lot more possible shapes out there.

Plane Shield: Instead of being a sphere, a plane shield is a flat plane, with the same size limitations as a normal screen. A plane shield at least half the size of the user may be used as a shield -- it has PD 4 if built as a force screen (and may be overloaded), half normal PD if built as a deflector (max 4).
External Node: The force field forms as a flat plane stretched between several (three or more) nodes (divide weight/cost between the nodes). The nodes themselves lie outside of the protected area, and may be destroyed without destroying the screen.
Internal Node: As above, but the nodes are inside the screen.
Form-following: The force field conforms to the shape of an object. The total surface area of the protected object cannot exceed 10 * Size².
Grid Shield: The force field conforms to the shape of a grid along the surface of a vehicle (can be cloth or other materials). The grid is 0.1 lb and $10/sf. Otherwise identical to a form-following screen.
Projective Field: The force screen can be projected about other objects, rather than being around the vehicle itself. Maximum projection range is a multiple of the size of the screen. The projected screen has half DR (and half ST, for manipulator fields).
Simple Shape: The field can be formed into simple shapes; useful for fitting around odd-shaped structures, or for forming a streamlined field (any field at least half again larger than the contained vehicle can act as 'superior' streamlining).
Complex Shape The field can be shaped into more or less any desired shape, though complex shapes need to be programmed in, and may take a while to form.
Manipulator Field: A barrier force screen can be designed so it can actually be used to apply force to objects. It normally has a ST of (Base DR)/5, and does not discharge while being used in this way. ST can increase to equal DR at a cost of gaining 1 energy level (or 10%) per turn the extra strength is used. You must also take simple or complex shape; if you take complex shape the screen may do cutting or impaling damage.
Force Objects: The field can be used to create 3-dimensional force 'objects'. In order to do this, simply take 'projective field' and 'manipulator field'. Note that a DR 10 screen will seem about as strong as a normal human being under normal circumstances.
Force Holoventure Zones: Allows creating a solid version of a holoventure zone. Objects created within the area use their size (in yards) as their SR for determining DR, ST, etc; the screen must have enough Size to cover the entire holoventure zone (a normal holoventure zone has a maximum length of 5*sqrt(number of units) yards).

TL	Weight	Cost	Power	DRmod	System
11+	*0.5	*0.5	*0.5	*1	Plane Shield
12+	*0.5	*0.5	*0.5	*1	External Node
12+	*1	*1	*1	*1	Internal Node
13+	*1	*2	*1	*1	Form-Following
12+	*1	*1	*1	*1	Grid Screen
12+	*2	*2	*1	*1	Projective Screen -- range = size
12+	*2	*2	*1	*1	*10 range for projective screen. Max x1000
12+	*2	*4	*1	*1	Simple Shape
13+	*4	*8	*1	*1	Complex Shape
13+	*2	*4	*2	*1	Manipulator Field
13+	*20	*100	*10	*1	Force Holoventure

Sensor Oddities

Force screens might have a variety of odd effects on sensors. The standard GURPS force screen prevents use of active sensors to probe inside the field, and prevents use of passive (but not active) sensors from within the field. Note that this makes almost no sense.

Standard Screens

Starship Screen: a 1-space screen is Size 100 (covers a Size +10 vehicle), Strength 100 (cDR=50 * TL-11, or 25 at TL 11), Power consumption 50 MW, 10 tons, price $1,000,000. *8 units gives *2 strength and size.
Star Trek Screens: starship-grade screens with 20/100 energy levels, 4 faces, and slow discharge; this gives them *1 weight/volume/cost, *2 DR, *.5 power consumption. Arguably they also have proportional: 95% or 98%, since they seem to occasionally get battered through the screens.
Lensman Shields Lensman shields have no special properties other than 'velocity-limited'.
Traveller Black Gloves A traveller black globe is a TL 12+ force screen with barrier, energy absorbing, explosive overload, and fast flicker (dual). If equipped with TL 12 capacitors, a 1-space screen is DR 6,000, 10T, $1,000k, and draws 5 MW or outputs 36 MW. It is opaque, and invisible to sensors.
Deflector Shield (TL 11) PD 8 deflector, Size 1 (rating-1), Rigid, Plane Shield, Compact. 1 lb, $800, 10 kW, lasts 15 minutes on a C cell.
Deflector Belt (TL 12) PD 6 deflector, Size 2 (rating-4), impermeable, form-fitting, compact. 2 lb, $1,600, 20 kW, lasts 9 minutes on a C cell.
Ward (TL 12) PD 8 deflector, Size 4 (rating 16), plane field. 32 lb, $3,200, 160 kW, lasts 112 minutes on an E cell.
Personal Force Field (TL 13) Size 2, Strength 2 (rating 4), ultra-compact, form-fitting. 20 kW, 2 lb, $3,200, lasts 10.5 minutes on a C cell.
Backpack Force Field (TL 13) Size 5, Strength 5, ultra-compact, form-fitting. 125 kW, 12.5 lb, $20,000, lasts 17 minutes on a D cell.
Heavy Force Field (TL 13) Size 10, Strength 10, ultra-compact. 500 kW, 50 lb, $80,000, lasts 42 minutes on an E cell.

c. Anthony Jackson, Jul 11, 1999