Extended Sensor rules for T20 (long)

[tjoneslo]

T20 sensor/spot rules.

These rules are an attempt to get the D20 spot rules to scale from creature to starship ranges. They are scaled for human eyeball on a planet. They may be a touch too math intensive and fiddley for the average D20 player.

Sensor rules are based upon the Spot rules in the D20 core rules book. Each +10 to the spot/sensor check give a x10 range to spot objects or spotting objects 10 times smaller.

Spot Checks are for characters using their eyes (enhanced or not). Sensor checks are for computer enhanced electronic sensors. The Base roll is:
1d20 + (Spot/Wis or T/Sensor/Int) + Sensor Strength + situation + time = Range DC + Size

Using the computer to perform sensor sweeps uses the computer's T/Sensor skill.
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">DC Range Example
0 -2 10 m
5 -1 100 m
15 0 1000m, 1km, Close range
25 1 10 km, Short range
35 2 100 km, Medium Range
45 3 1000 km, Long Range
55 4 10 kkm, Very long Range, Close Spaceship Range
65 5 100 kkm Extreme Range, Short spaceship range
67 Medium Space ship Range
69 Long Spaceship range
70 1 Light Second
72 Very Long Spaceship range
75 6 1 Mkm, Extreme Spaceship range
82 Far Spaceship range
85 7 10 Mkm, System Wide Spaceship Range
95 8 100 Mkm, 1 AU
105 9 1,000 Mkm 10 AU, Interplanetary range
115 10 100 AU, Outer System
125 11 1,000 AU, Oort Cloud
135 12 10,000 AU
145 13 1 light Year
149 1 Parsec
153 2 Parsecs
155 14 10 Light Years, 3 Parsecs (Pc)
165 15 30 Pc, Sector Range
175 16 300 Pc</pre>[/QUOTE]DC formula = 15 + (log(range in km) * 10)
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">Size Modifiers: See Size table P?? (Currently p90)

Medium -0
Large -1
Huge -2
Gargantuan -4
Colossal -8
Large Starship -9
Huge Starship -11
Gargantuan Starship -13
Colossal Starship -17
Planets -(70+Size Digit)
Gas Giants -90
Stars
M Class -100
K Class -105
G Class -110
F Class -115
A Class -120
B Class -125</pre>[/QUOTE]Situation Modifiers (from PHB P133). The page also has some description of cover modifiers like mist, fog, darkness, etc.
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">Hide Concealed Cover
1/4 -2 -4
1/2 -4 -8
3/4 -6 -12
9/10 -8 -16
Full -10 -20</pre>[/QUOTE]Distracted -5 (in combat, "Just Looking around")
Wide angle sensor sweeps -10
Already spotted +5 (Spotting something being pointed out by another)

Time modifiers. Taking longer to perform observations gets better results. All are full round actions.
Personal Round (6 Seconds) +0
Max Spot Check Bonus (18 sec) +3
Vehicle Round (60 Seconds) +5
Starship Round (60 Minutes) +10
Astronomy Scan (10 Hours) +15

Starship Sensors: Vehicle Sensors:
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">Model Scan Weight Cost Scan
Model 1 +26 1 1500 +2
Model 2 +30 1.5 2250 +5
Model 3 +34 3 4500 +7
Model 4 +38 6 9000 +10
Model 5 +42 12 18000 +12
Model 6 +46 25 37500 +15
Model 7 +50 50 75000 +17
Model 8 +54 100 150000 +20
Model 9 +58 200 300000 +22
Model 10 +62 400 600000 +26</pre>[/QUOTE]Examples:
Spotting a 1/2 hidden huge grav tank at 1 km range in the rain
DC = 15 (range) - 2(Huge) + 4(Concealed) + 2 (Rain Cover) = 19

Spotting Mars from Earth by eye:
DC = 95 (Range) - 73 (size) - 3 (Long look) = 19

Using a Model/8 Sensor suite to scan a system 1 Pc away:
DC = 149 (range) - 90 (size) - 15 (Astronomical survey) - 54 (computer scan) = -10 (auto spot gas giants)
DC = 149 (range) - 70 (size) - 15 (Astronomical Survey) - 54 (computer scan) = 10 (spot planets)

IR and LI sensors negate some of the cover or concealment penalties, but will not actually add to the sensor rating. Most Binoculars are in the +1 to +3 range.

Some common sense must be applied. While powerful sensor can scan through cover, literally interpreted, the rules allow for spotting the local star through a planet.

Starship Combat
To make the Starship combat less involved with larger numbers, we can subtract a constant from all the numbers involved and make the system much more useful. In the case of Starship Combat subtracting 44 (10 (time) + 8 (size) + 26 (base computer sensor)) from the range modifiers, use the Starship Size modifier table, the whole process becomes less math intensive.
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">DC Range Computer Scan
16 Close Range Model/1 +0
22 Short Range Model/2 +4
23 Medium Range Model/3 +8
25 Long Range Model/4 +12
28 Very Long Range Model/5 +16
31 Extreme Range Model/6 +20
Model/7 +24
Model/8 +28
Model/9 +32</pre>[/QUOTE]So the roll becomes:
1d20 + (sensor/int) + Scan = Range DC + size

Examples:
Corsair looking for the Free trader at medium Range
DC = 23 (Medium Range) - 0 (Medium ship) - 4 (Computer scan) = 19

Free Trader Scaning for Corsiars
DC = 23 (Medium Range) - 0 (Medium Ship) - 0 (Computer scan) -5 (scanning) = 25

This underlines the importance of good sensor operators. And while a little unrealistic, encourages the analogy of starship combat as sub hunting combat.

Advanced rules

Active vs. Passive sensors: In reality there are two kinds of sensors, passive and active.

Passive sensors include eyes, cameras, LI, IR, UV, radio telescopes and other similar sensors. Passive sensors rely on either reflected light or emissions from the target to be able to spot it. This makes the passive sensors very sensitive to the condition of the target and interference in between. The concealment/cover and conditions tables have been set for the passive sensors so no adjustments.

Active sensors include Radar, Ladar, and other sensors using a beam of energy (like radio waves, microwaves, laser light and so on) to illuminate the target. Active sensors are more able to penetrate the interference of the target: Ignore the concealment and other conditions penalties, halve the penalties for cover. The penalty is you are lit up like a spotlight making it easier for other to spot you. Add your active sensor rating as a bonus to others trying to spot you.

For example: Eniri is using the +5 sensor on his large scout g-carrier to try and spot the Huge vargr APC hidden in the trees some distance away.
Eniri DC = 25 (10 km range) - 5 (Sensor) - 2 (huge) + 6 (3/4 concealed) - 5 (vehicle round) = 19
APC DC = 25 (10 km range) - 5 (Sensor) - 1 (large) + 2 (1/4 concealed) - 5 (vehicle round) + 5 (scanning) = 21

Eniri rolls a 4, plus a sensor skill of 5, and misses the APC. The APC driver misses Eniri. Sure the APC is around, Eniri turns on the active sensors to get a better look. This negates the concealed modifier on the APC, but gives a bonus to the APC to see Eniri:
Eniri DC = 25 (10 km range) - 5 (sensor) - 2 (Huge) - 5 (vehicle Round) = 13
APC DC = 25 (10 km range) - 5 (sensor) - 1 (large) + 2 (1/4 concealed) - 5 (vehicle round) + 5 (scanning) - 5 (active sensor) = 16

Eniri spots the APC but the alert sensor operator in the APC pinpoints Eniri. And the chase begins.

Weapons fire:
Most high energy weapons have a very bright signature, making it immediately apparent they have been fired and making it very easy to spot both the source of the fire and the unfortunate target.

For starship weapons, Add the USP battery factor of the firing weapon to the spot roll for sensing the firing ship and (if the shot hits) the target ship. Fusion and Plasma weapons are +1, Meson weapons are +2 for spotting the target.

Missiles are a special case, they are +0 on firing, + USP on detonation to the target ship. You can (in theory) spot missiles to intercept them, on the starship scale they are Fine (-8) size. Nuclear missiles are +20 on detonation.

Detail table for personal/Vechicle combat ranges:
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">DC Range (m)
1 36 35
2 45 45
3 57 60
4 71 70
5 90 90
6 113 115
7 142 145
8 178 180
9 224 225
10 282 280
11 355 350
12 447 450
13 563 600
14 708 700
15 892 900
16 1123 1150
17 1413 1450
18 1779 1800
19 2239 2250
20 2819 2800</pre>[/QUOTE]The DC is the DC to spot/sense at the given ranges. The First range colum is an exact measure, the second is a rounded set of values. You can see the progression between DC 6 and 15, and extend the table to other ranges as needed. At 35m or less the range DC is always 0, so keep under cover.

Listen Checks:
The same scaling chart applies for Listen checks but with a -10 modifier. This is the sound of normal conversation. Louder sounds are easier, softer sounds harder: Shouting or yelling: +3, Combat: +5, Jet engines, sonic booms, large explosions: +13.
Quiet things: Trying to move quietly in armor: -5, trying to move quietly not in armor: -10, Move Silently: -15, Cat Stalking: -19.

Atmosphere density also applies a modifier: Dense: +2, Standard +0, Thin: -2, Very Thin: -4. Note: for aliens evolved for different atmosphere types, scale the chart up or down. For Example, the Virushi eveolved in a Dense atmosphere: for them the chart reads: Dense: +0, Standard -2, Thin: -4, Very Thin: -6.
Obviously, you can't make hearing checks in a trace atmosphere or vacuum.

Sounds underwater are +10 modifer.

Example: Garraag, Vargr scout has lost his hunting party in the deep woods. They are 500 meters away, having a grand time shooting at baby Tree Kraken. Garraag takes a few seconds to listen for the sounds of the shots and the shouting:
DC = 13 (range) + 10 (Hearing check) - 3 (Time) - 2 (vargr's ears) - 5 (combat) + 6 (3/4 cover) = 19

Garraag arrives just in time to help the hunting party fight off the momma tree kraken.

Commuicators:
Communicators are a special case of sensors but can use similar rules. Each Comm system is rated in power (+0 to +whatever). Comm system use check:
1d20 + t/comm/int + (Transmitter power + Reciever sensitivity)/2 = Range DC + Situation Modifiers

There are no time or size modifiers.

A close range Comm would have a power/Sensitivity of +5. For normal operations with untrained persons, this gives the Comm about a 1 km range. DC = 15 (Range) - 5 (Transmitter) = 10, Take10 on the roll. A skilled comm person can get up to 10 km under good conditions. Person doing the transmission must make the roll. Missing the roll means bits of the conversation were lost. Roll once per transmission, rolling again only of conditions change (longer range, jammed, etc).

Like active sensors, using comm systems also gives away the position of the transmitter. Add the Transmitter power as a bonus to any sensor trying to detect the transmitter.

Jamming and interference:

An Active sensor may be used as jammer, confusing the active or passive sensors of another vehicle. The craft doing the jamming adds their sensor rating, the T/Sensor skill and +4 for the Electron Weasel feat, minus the range DC to the target of the jamming and applies this as a negative modifier to the all sensor scans done by the target. Any unjammed sensors get a bonus to detect the jamming sensor equal to the jammer sensor scan rating.

Jamming communications works the same way. Subtract the Jammer strength minus the range DC to the reciever from the communications roll.

Natural Sources of intereference can also be used to jam sensors. Take the power of the source object, subtract the range DC and apply the difference (if greater than 0) to the scan DC. For example, flying out of the sun (+110) at 1 AU (-95) gives a +15. So unless you are really big, or their sensors are really sharp, they can't see you until too late.

 

[Savar]

Vary Cool, will be vary helpful

 

[Qstor2]

Thanks. These look great! Something like this should be in the players Guide.

Mike

 

[far-trader]

Originally posted by Qstor2:
Thanks. These look great! Something like this should be in the players Guide.

Mike

Gah! I can only hope by "something like" you mean much more condensed/simplified. Don't take that wrong, I appreciate you showing your work and the examples.

Sorry tjoneslo but I looked at it and my brain started shutting down. I can't fairly comment on it beyond that. It may be brilliant work, and you have put a lot of work into it apparently, but it looks waaaaaay too complex to be useful in the kind of game I want at first glance. Maybe it's just the lack of sleep last night. Maybe I'll give it another look when I feel more able to comprehend the complexity.

 

[BetterThanLife]

Whoa, that is way too much work. I am with Far Trader on this. It is too complex for gaming it.

 

[robject]

Sigg has CT sensor rules along these lines, though perhaps somewhat condensed; you may be able to find them by searching COTI.

Similarly, Bruce Macintosh et al wrote the "Definitive Sensor Rules" for T4, which were at about this level of detail. Like Far-Trader and BTL, its detail did not appeal to me.

Ah, here's Sigg's old sensor rules. I don't know what his latest edition is -- these are at least two or three years old.

I'd probably only use sensors with miniatures and a hexmat, and set the active sensor range = the computer model 'R' in hexes. Passives would be a quarter that, perhaps?

Target number for detection ("signature") would be ship size code or less on 2D, modified by various running modes (planetoid = -1, cold = -2, quiet = -1, full accel = +1...). Size codes are per Traveller (7 = 10-99 tons, 8 = 100-999 tons, 9 = 1000-9999 tons...).

Assume military sensors are TL15, model 9, while civilian sensors are TL8, model 1. Add the two numbers together.

8+1=9 which = range of 0.5 light seconds

15+9=24 which = range of 2.0 light seconds

Therefore add 0.1 light seconds range per TL above 8 or per model above 1.

Sensor model is equal to computer model.

The ranges above are for active scans. Passive scans have a quarter of the above range.

Ships have a passive (radiated) signature equal to half of the power plant number (round down) or the maneuver rating used during that turn.

Planetoid hulls reduce the radiated signature due to the power plant by 1; buffered planetoids reduce it by 2. This reduction is not applied to the signature due to maneuvering.

The ship's passive signature is multiplied by 0.25 light seconds and subtracted from its range to decide if it is within the sensor range of a scanning vessel.
e.g. a ship with a passive signature of +3 is detected if it moves to within 1.25 light seconds of a ship with military sensors (TL15, model 9).

Ships have a reflected signature based on hull size (and configuration USP):
less than 100t, -1
100t-999t, +0
1000t+, +1
5000t+, +2

USP
1-3, +0
4-6, +1
7-9, +2

The ship's reflected signature is multiplied by 0.25 light seconds and subtracted from its range to decide if it is within the active sensor range of a scanning vessel,

e.g. a ship with a reflected signature of +1 is detected if it moves to within 2.25 light seconds of a ship with military sensors (TL15, model 9).

Once a ship has been detected it can be tracked out to 3 light seconds, but once it moves beyond the sensor's auto spot range (modified by target signature) then a roll of 8 or more on 2d is required to maintain the target lock.

DMs:
+ signature for the sensor type
+ gunnery skill (or navigation -1)
- 1 per 0.25 light seconds outside auto spot range.

Notes:
these rules are based on the Traveller 2300 game Star Cruiser.
If you want to play cat and mouse then I would recommend changing the scale of LBB2 combat to 30cm = 1 light second, it fits better on a table top
1 G maneuver changes vector by 1cm.
laser to hit range modifiers become:
25cm+, -2
50cm+, -5
75cm+, -8

Active sensor jamming
A ship inside the active sensor range of an opponent may try to fool his active scans by running the ECM program. This actually consists of broadcasting false returns etc. using their own active sensor.

The attacking ship has to roll 12+ to obtain a sensor lock.
DMs:
+ 1 per level of gunnery skill (or navigation -1)
+ targets reflected signature
+/- 1 per relative TL
+/- 1 per relative computer model

If the attacking ship runs its own ECM program in ECCM mode then it gains a bonus of +4 to the roll to obtain a sensor lock.

Sensor Drones
A sensor drone is a specially modified missile with its warhead removed (or downgraded) and an active/passive sensor system installed. It maneuvers the same as a normal missile.
The drone’s sensors have half the range of the equivalent ship mounted sensors, and the drone can only go active a limited number of times depending on TL. The TL also determines the maximum model of sensor that can be installed. If the drone does not use its maneuver drive it may deploy a folding array to increase its sensor range to the same as that of an equivalent ship mounted system.

Number of active scans equals TL/3 round down.
Maximum sensor model equals TL/5 round down.

Sensor Decoy Drones
These are missiles that are modified to exactly mimic the passive and reflective signatures of the launching ship.
Their warhead is removed and replaced with extendable radiator panels and vanes that are designed to radiate the same heat signature and provide the same target profile as the reflected signature of the launching ship.

Once launched the drone(s) and the ship should be replaced with identical counters. Each then maneuvers separately and provides a problem for the attacking ship.

To identify a bogey as a drone or the ship roll 10+ on 2d.

DMs:
+/- 1 per relative TL
+ 1 per level of gunnery skill (or navigation -1)

Alternatively, just shoot them all [Wink] the decoy can only take one hit.

Area Jammer Drone
this is a missile modified to transmit as much white noise as possible to confuse active sensors. If the line of sight to a target passes within 0.1 light seconds of the drone then the active ship must roll to penetrate ECM as for active jamming, above.

If the target ship is also using ECM jamming then the active ship must make two roles to obtain a target lock.

 

[tjoneslo]

Originally posted by far-trader:
Sorry tjoneslo but I looked at it and my brain started shutting down. I can't fairly comment on it beyond that. It may be brilliant work, and you have put a lot of work into it apparently, but it looks waaaaaay too complex to be useful in the kind of game I want at first glance. Maybe it's just the lack of sleep last night. Maybe I'll give it another look when I feel more able to comprehend the complexity.

It is just a complete brain dump of an idea and needs cleanup work. Were I to write this in a set of rules, it would be shorter and divided into at least four parts (one for personal spot/listen rules, one for handheld sensors and combat, one for vehicle sensors, and the last for the starship sensors).