CT Sensors: Detection and identification

[Rupert]

The roll could be kept opposed, and each side adds the appropriate DMs, but perhaps just one roll (by the players) is more simple. Then, the DMs could be potentially translated into something like:

If ship has military-grade sensors, +2​

If any crewmember has navigation skill, +1​

If any crewmember has electronics skill, +1​

If any crewmember has naval experience (navy or scouts), +1​

If any target is active (pinging, maneuvering), +1​

If targets are X or more ships, +1​

If targets are X or more small craft, +1​

If target has "gone cold", -2​

If target has stealth hull, -1 (per level?)​

​

The value for success (detection) on the roll would be a fixed value, or one that also depends on distance to the target(s).

So, why would anyone go active in terms of sensors? What advantage does it give?

 

[mike wightman]

A longer range target lock.

 

[Spinward Flow]

So, why would anyone go active in terms of sensors? What advantage does it give?

Under "most circumstances" ... the use of active, rather than passive, sensors is to obtain More Detailed Information™ than can be obtained by passive scanning alone. The downside to active sensor scans is that they basically "give away your position" because the active sensor scan is a source of energy (sound, radiation, etc.), creating a situation of Signature: Automatic.

If your position is "not a secret" then active sensor scans make sense, because you're not trying to hide your location and/or movements.

Passive sensors are often times "good enough" for detections (there's something out there!).
Active sensors may be required to get "more information" than just a (Y/N?) on a detection contact. Active sensors are also often times (but not always!) required for detailed targeting information of high enough quality to allow for engagement with weapons (missiles, directed energy, etc.).

 

[Rupert]

A longer range target lock.

So, you would only go active when you know there's something to be locked up - i.e. after a check for surprise. This does not give a reason to ever run active sensors when not already fighting or about to fight. So it's not a real decision, but a newbie trap.

Under "most circumstances" ... the use of active, rather than passive, sensors is to obtain More Detailed Information™ than can be obtained by passive scanning alone. The downside to active sensor scans is that they basically "give away your position" because the active sensor scan is a source of energy (sound, radiation, etc.), creating a situation of Signature: Automatic.

If your position is "not a secret" then active sensor scans make sense, because you're not trying to hide your location and/or movements.

Passive sensors are often times "good enough" for detections (there's something out there!).
Active sensors may be required to get "more information" than just a (Y/N?) on a detection contact. Active sensors are also often times (but not always!) required for detailed targeting information of high enough quality to allow for engagement with weapons (missiles, directed energy, etc.).

Great... after you've established there's something to get that more detailed information on. But this is a 'surprise check', so you don't know there's anyone out there (though you may suspect it), and going active is just making it easier for them to surprise you.

Now, if you rule that you can't reliably lock up someone without going active, you have a situation where those that stay passive probably get surprise, but can really only use it to run. Though with it only being a +1, and the same +1 as for manoeuvring, being active might be worth it to be able to shoot immediately, and is something you may as well do if you're manoeuvring (which most ships are if they're jump ships going to and from the 100D limit).

If you can 'go active' when you get surprise and use that to get a lock and shoot before the other side can react, then nobody will go active (which might be what you want, of course - but then get saying 'if you're active, you never get surprise' works as well, because there's no actual upside to being active outside of combat).

 

[Spinward Flow]

Great... after you've established there's something to get that more detailed information on. But this is a 'surprise check', so you don't know there's anyone out there (though you may suspect it), and going active is just making it easier for them to surprise you.

I presume that at some point you've watched WWII submarine movies, where one of the most common plot points is the submarine vs destroyer duels, with the destroyer pinging away with active sonar searching for the submarine to improve the accuracy/precision of depth charge settings. Needless to say, the submarine will try all sorts of tricks to camouflage their signature on active sensor scanning (including the "ground clutter" option of settling on the ocean bottom) in an attempt to mask their presence among the active sensor return ping information that needs to be interpreted by the sensor operator.

As far as "surprise" goes ... not all "threats" are intelligent adversaries. Some can be environmental, particularly in space.
Consider the humble impactor/debris on an inertial orbit ... minding its own business, not bothering anyone ... and then SUDDENLY(!) there's this manned craft hull that gets in the way.

The manned craft can be "surprised" by the impact, caused by an intersection of orbital trajectories, if the manned craft wasn't tracking the impactor/debris before the collision. Depending on the size and signature of the impactor/debris, it's entirely possible that passive sensors wouldn't be "enough" to detect the impending collision in time for the manned craft crew to take any evasive action ... hence ... SURPRISE!

Conversely, a periodic repeating active sensor potentially could have illuminated the impactor/debris early enough to provide adequate warning to prevent a "surprise" collision (because, enough early warning to evade).

If it helps, ask yourself why lighthouses placed around rocks and reefs near shorelines were such a necessity in the Age of Sail ... and how without an "active" sensor illuminating the surroundings, environmental hazards could be extremely deadly to craft and crews operating on passive sensors (Mk I Eyeball, Mk I Ears, at night) only. We don't often think in terms of rocks/reefs/shoals vs wooden hulls in Traveller, but the analogy still applies when dealing with zero-g rendezvous and maneuvering around potential hazards ... such as Belter prospecting/mining operations ... and even interplanetary transits under maneuver drive power.

Space may be BIG ... Really BIG ... but it's not Utterly Empty.



The problem you're going to run into with your line of thinking is that you're looking for a cut 'n' dried binary answer to a question ... while hand waving away all of the important context that goes into the asking of that question.

There are going to be contexts in which "silent running" offers advantages against an intelligent adversary ... but would be fatally flawed if deployed against an environmental hazard ... and the converse is also true. Blasting your environment with active sensors makes a lot of sense in a context of environmental hazard avoidance (including steering clear of minefields!), but could be a disadvantage when dealing with an intelligent adversary who is stalking you.

Different tools have different uses.
The trick is being intelligent enough to know which tool to use when.



Case in point ... in the aerospace realm ...

 

[kilemall]

For MTU, I have a particular emphasis on stealth and signaling via active sensors.

Passive on passive/stealth may see the sneaky smuggling small craft slip by. Banging away on radar/lidar has a signal of potential aggression which might escalate into some thing it may not have otherwise.

I also require a lock on to get those intel bits, the idea being that one needs the precise distance to calibrate all sensor feeds and get hull form, extrapolate tonnage/EMF output/IR/M drive generation and thus minimum power plant, etc. An impatient/time critical assessment may require active now rather than passive build up of data later.

 

[Janitor_Prime]

There are other ways to use "Active" sensors and be passive. Multiple ships. Alternating active and passive between friendly ships. One ship lights up the target with active sensors and others in passive have more accurate returns to their passive sensors. The ship that was active, after a brief time returns to passive and another ship then goes active. Probes, fighter craft, and shuttles using active sensors to illuminate targets or to narrow a search area. Probes especially, the cover a wider area and are expendale, like sonar buoys in anti submarine warfare.

 

[Rupert]

I think for the purposes of the suprise roll idea I'd go with something a little different for active sensors (being 'active' in terms of manoeuvre, using a broadcast radio, etc. can stay the same).

If using active sensors, a ship is giving up a chance of surprising anyone in exchange for a considerably lower chance of being surprised themselves. So when Active, a ship is automatically detected by anyone with functional passive sensors (so can't surprise anyone). However, the surprise check is still rolled (it'd be an opposed roll), but the active ship takes no penalties or bonuses for being 'noisy' or being 'cold' and gets a +2 bonus (maybe more) for being active. If the active ship wins, neither is surprised, if it loses it is surprised and the other ship is not. If both ships are active, no surprise.

 

[Vido]

Some possible additions:

Possible DM of -2 for running a specific computer program, Scramble, which confuses/jams sensors. It might require previous detection (by the "scrambler" vessel) to adjust returns and such.

Whenever detection occurs because of the roll, there could be a second table to determine range of encounter. Easiest way to do it for my game (using range bands, 1 band/hex is 10000 km) would be for the "winner" of the detection throw to to roll some dice:
- To determine encounter distance, roll 4d6 (averages ~15, which is about 0.5 light-seconds) for the number of bands (hexes) in distance to the target. Multiply by four if ship has military grade sensors. Divide by four (or just roll 1d6) if target is "running cold", or by eight if target is in orbit around a world.

 

[Janitor_Prime]

So, you would only go active when you know there's something to be locked up - i.e. after a check for surprise. This does not give a reason to ever run active sensors when not already fighting or about to fight. So it's not a real decision, but a newbie trap.

You have to ping someone with your active sensors to get the return ping for IFF (Identification, Friend or Foe).
When you have more ship per ton than the other guy. (i.e. 800 ton Broadsword vs 200 ton Corsair)
Intimidation, you want the other guy to shut down and surrender.
You are Customs and Law Enforcement.
You need a detailed information to gather intelligence on a combatant vessel.
When you have to positively identify the target before firing. The enemy vessel may not be a combatant vessel, such as a hospital ship.
In a very active system, you don't want to kill the merchant just coming out of Jump Space and into a active anti piracy action.

 

[Wol]

You could consider B. Macintosh’s Definitive Sensor Rules or some such variation.

 

[kilemall]

You could consider B. Macintosh’s Definitive Sensor Rules or some such variation.

Link?

 

[Wol]

A copy is here.

Definitive Sensor Rules

A related discussion is here:

W

Post in thread 'Definitive Sensor Rules for T5'

Sep 3, 2017

Definitive Sensor Rules by Bruce Allan Macintosh. Last drafted for T4.1; adaptable for most Traveller versions if you choose.

A copy is here:
http://www.mu.org/~joe/traveller/house/sensor.rules.html

However you will find a few adapted version on the web.

regards

• Wol

I am pretty sure I have some additional correspondence from him if I can find it. Bruce really knew his stuff.

regards

 

[Wol]

FWIW in CT comparative ranges from Mayday are hexes of 300,000 km and notes for use with HG that “Two ships which have matched courses are considered to be at boarding range, Otherwise, all ships within five hexes of each other are at short range. Ships seperated by more than five hexes are at long range. Ships beyond fifteen hexes are out of range, and cannot fired upon”.

So 1,500,000 km and 4,500,000 km.

Classic Traveller has 1m = 100, 000km and detection rules:

“Ordinary or commercial starships can detect other ships out to a range of about
one-half light-second; about 1,500 millimeters. Military and scout starships have
detection ranges out to two light-seconds; 6,000 mm or 6 meters.
Ships which are maintaining complete silence cannot be detected at distances of
greater than half detection range; ships in orbit around a world and also maintaining
complete silence cannot be detected at distances greater than one-eighth detection
range. Planetary masses and stars will completely conceal a ship from detection.

Tracking: Once a vessel has been detected, it can be tracked by anyone up to
three light-seconds (about 9,000 mm, or 9 meters).”

Starter Traveller uses 10,000 km range bands but is otherwise the same as Book 2.

regards

 

[Wol]

Finally, Grand Survey has rules for sensor use, ranges, including in ship combat. They don’t appear terribly consistent with other material but I have not looked closely.

regards