Detecting Ships [Holy War]

[robject]

Warning - this is a holy war subject.

By The Traveller Book, civilian ship sensors can detect ships at 1.5 LS, and military (including IISS) sensors can detect ships at 3.0 LS (if I recall correctly). Both can track out to 9.0 LS.

This implies that one-on-one starship combat is generally tactical, not strategic, and that "sub hunts" are not unreasonable. It implies that ship technology as a whole "keeps up" with sensor technology, in that power plants are not generally broadcasting their presence beyond a couple light-seconds.

In other words, everything that our various sensors detect -- heat, light, neutrinos, EM, everything -- is well-shielded by basic Traveller technology.

According to The Traveller Book, higher technology improves detection range, but it doesn't lay bare the presence of ships in a system: detection still must be local and rigorous.

 

[BytePro]

Sure, RL may be different, but Traveller is fiction - the above matches my basic idea of the rules.

Once detected - bearing, displacement over time and/or frequency shift are usually available and 'hiding' or 'evading' would generally only be a potential option with low enough velocity and large enough objects to 'hide' behind or in or suitable decoys. Ships don't disappear just because they 'speed away', though quality and accuracy of track will change over time (but generally a lot of time to get to velocities and distances where this is relevant).

Sans highly unusual situations creating the equivalent of a thermocline (solar flares, 'ion-storms', gamma-ray bursters, nova, etc), and without active counter detection methods - going 'quiet' and most 'sub-hunter' tactics probably aren't directly applicable.

Also, detection ranges are for combat purposes and real-time scans - jumping in and scanning a system for hours, say, should exceed these ranges (light minutes, hours and possibly days).

Shielding etc., does nothing by nature to prevent 'sticking out' in the ambient noise of whatever detection tech is being used - depends on the nature of the 'noise'. Use of a black globe, for instance, would generally be readily detectable against a background like a planet or star.

 

[far-trader]

Actually 0.5 ls civilian detection, 2.0 ls military and scout detection, and 3.0ls tracking. Looks like you were recalling the mm ratings (1500mm, 6000mm, and 9000mm)

I wonder if one couldn't argue that the rules apply exactly as they are described and still have room for additional details. What I mean is:

One-on-one ships are very limited by their single source sensors (base listed detection and tracking ranges).

Civilian ships have very simple small sensor installations, a single receiver point, a very short base-line. This limits them to 0.5 ls for detection.

Military ships have more complex extensible sensor installations for long-base lines, multiple receiver points, and active sweeps. This increases the detection range to 2.0 ls.

Multiple ships increase the chance of detection* and the range of detection by linking their sensors for an even greater base-line.

* possibly adding a roll for detection, made each turn, possibly including difficulty DMs for beyond base range (and TL, see below)
​

I like the shielding vs detector comparison but then there should be a TL modifier. A TL13 ship's detection/tracking of a TL9 ship should be easier and/or longer, and a TL9 ship's detection/tracking of a TL13 ship should be harder and/or shorter.

I would even like to see Skill have some effect to add to the Role Play side as opposed to simply making the game even more Roll Play.

 

[aramis]

3LS is ~900,000km not even 1" of arc accuracy (more like 1.1").

I don't think jump flash was taken into account in CT core - TTB made numerous changes, but not for realism - only playability changes, it seems. In fact, the first descriptions of what a ship looks like going into or emerging from Jump that I recall are in MT.

Which also gives difficulties. For the typical System+ PEMS ranges for military craft, detection is a task, Simple (3+ on 2d) DM+(Sensor Skill or Computer Model) DM-Range.
It's unclear what this range DM is - range in squares or range in ship range bands. I always use range bands, otherwise it's less than CT sensors.
And, using range bands past "Visual", Interplanetary range sensors give a passive scan roll of
Visual 3+ (VDist or less)50km
Near 4+ (Reg - Plan)5kkm
Far 5+ (FarOrbit) 500kkm
Extreme 6+ (Extreme Orbit) 5Mkm
Interplanetary 7+ 1AU
System 8+ 1kAU
Substellar 9+ 100kAU
Stellar 10+ 1Pc
Interstellar 11+ 2Pc

Table is for moderate emmission average size ships. Large or high sig targets are 2 points easier, small AND low are 2 harder. This puts almost all ships in the numbers shown, and all warships 2 points easier. Given the average computer is 5+ on a warship, and minimum 4, a warship autodetects ships out to at least extreme orbit - 5 Million kilometers.

Far Orbit to Extreme Orbit PEMS would be 4 points harder unless neutrino sensors are mounted; FO PEMS with 10kW Neutrino are the same detection chances as an Interplanetary PEMS without one.

It's possible to extrapolate the table out further...
Interstellar range PEMS sensors with 10kW Neutrino, stellar PEMS with 1kW Neutrino, or Substellar PEMS with 0.1kW neutrino should be 4 points easier

 

[shadowcat20]

There was a point made in the lost fleet series that I found interesting and never seems to be mentioned.

When a ship jumps in system, it takes real /Light time to see something insystem. If a ship is an light hour away it will take an light hour for the system to see the new ship that just appeared. Also the ship will see things as they were as of the sending time ago. IG. they see the system as of a light hour ago. As you get closer you will get a more accurate read on what is happening based on closing distance/time to target. Makes sense unless there is some magic sensor that reads and sends FTL.

So for a sub hunt you are getting a read on a ship based on the time/distance it was from the searching ship. The farther away the harder it would be to accuratly predict where the target will be. Vectoring speeds will help a bit as you can not turn on a dime and power applied to change course would be easy to read. Makes decoys something worth thinking about for Traveller.

These random mumblings have been brought to you by,
Shadowcat20

 

[Hyphen]

There was a point made in the lost fleet series that I found interesting and never seems to be mentioned.

When a ship jumps in system, it takes real /Light time to see something insystem.
(snip etc)

This was mentioned in TNE; I *think* it was in Brilliant Lances. The attacker gets to see where the defender was, hours before the "light cone" of the attacker reaches the defender.

 

[far-trader]

...The attacker gets to see where the defender was, hours before the "light cone" of the attacker reaches the defender.

Only if the attacker pops in well beyond the inner system.

Mars 11.48 Light Minutes to 13.83 Light Minutes

Jupiter 41.17 Light Minutes to 45.34 Light Minutes

Saturn 1.22 Light Hours to 1.37 Light Hours

Uranus 2.49 Light Hours to 2.73 Light Hours

Neptune 4.05 Light Hours to 4.12 Light Hours

Pluto 4.02 Light Hours to 6.70 Light Hours

In the inner system it's less than 1 CT combat turn. Even Jupiter is only 2 or 3 CT Combat turns.

And of course if you pop in beyond the inner system and that is your target, it's going to take you days to get there. So much for your element of surprise

 

[BytePro]

...And of course if you pop in beyond the inner system and that is your target, it's going to take you days to get there. So much for your element of surprise

Catch a Comet's Tail!

 

[aramis]

Only if the attacker pops in well beyond the inner system.

Mars 11.48 Light Minutes to 13.83 Light Minutes

Jupiter 41.17 Light Minutes to 45.34 Light Minutes

Saturn 1.22 Light Hours to 1.37 Light Hours

Uranus 2.49 Light Hours to 2.73 Light Hours

Neptune 4.05 Light Hours to 4.12 Light Hours

Pluto 4.02 Light Hours to 6.70 Light Hours

In the inner system it's less than 1 CT combat turn. Even Jupiter is only 2 or 3 CT Combat turns.

And of course if you pop in beyond the inner system and that is your target, it's going to take you days to get there. So much for your element of surprise

Your math is off.

Earth's orbit is 8.3 LM
Jupiter's is 43.2LM
This gives a 34.9 to 51.6 range to Earth.

 

[far-trader]

Your math is off.

Nope

Not because it isn't wrong, it may well be, but because I simply lazily snagged the first numbers I found without much reading

So it's not my math (though it is my poor use of materials, guilty)

Thanks for the correction

 

[aramis]

Then your PROCESS is off, Dan.

The range of distances is ALWAYS larger-smaller orbit to larger+smaller

Closest approach is always the distance from sun of the larger orbit less the distance from sun of the smaller orbit.
Furthest is opposition - where they simply add, as the sun's in the middle. So, it's always at least a 16.6 LM variation from earth... but noting that Uranus and neptune are sufficiently large orbits that their eccentricity is notable.

 

[Carlobrand]

First, what is "holy war"? Sorry to be so ignorant.

Second, I'm very confused about the nomenclature around sensors. The better ones are described as "substellar," "stellar," and "interstellar," but that seems to be a wild exaggeration compared to their game rules behavior - at least in MegaTrav. Putting aside the game rules, I can see the value of sensors revealing activity throughout the local stellar system, but 1 or 2 parsecs off? Wouldn't that information be a year or two out of date? Are they really supposed to be sensing activity a parsec over, or is that just manufacturer advertising hype?

 

[Gray Pennell]

So the relative short range for sensors works to keep the light distance question mute. While radio transmissions will be heard, and you could spot the enemy out to the 3AU or so the details needed for combat should not occur till the target is much closer. At closer rangers you get specifics such FFI, armaments, physical condition, solid doppler shift data etc allowing weapons lock.

 

[steventirey1985]

First, what is "holy war"? Sorry to be so ignorant.

Best guess - hotly debated topic, with multiple diffirent (and correct) answers depending on your rules system of choice.

Putting aside the game rules, I can see the value of sensors revealing activity throughout the local stellar system, but 1 or 2 parsecs off? Wouldn't that information be a year or two out of date? Are they really supposed to be sensing activity a parsec over, or is that just manufacturer advertising hype?

3-6 years out of date. At those distances, your not actively looking for anything. Its more passive, and detecting large objects, like planets and gas giants. Not little ships. (At least thats what T20 says. I assume other versions of the rules have similar limits at those ranges).

 

[far-trader]

First, what is "holy war"? Sorry to be so ignorant.

No need to apologize. I'm guessing in this case it's the usual internet flame-war material with a canon (holy writ to some) twist There are a few Traveller tropes that fall into this category.

 

[far-trader]

So the relative short range for sensors works to keep the light distance question mute...

Pretty much At least I see it that way too.

 

[aramis]

First, what is "holy war"? Sorry to be so ignorant.

Second, I'm very confused about the nomenclature around sensors. The better ones are described as "substellar," "stellar," and "interstellar," but that seems to be a wild exaggeration compared to their game rules behavior - at least in MegaTrav. Putting aside the game rules, I can see the value of sensors revealing activity throughout the local stellar system, but 1 or 2 parsecs off? Wouldn't that information be a year or two out of date? Are they really supposed to be sensing activity a parsec over, or is that just manufacturer advertising hype?

Holy War (Internet Slang): A topic that often results in arguments, and about which the input assumptions determine a singular reasonable outcome per set of input assumptions, but for which the input assumptions often can't be agreed upon.

The MT sensors rules themselves are a holy war topic; there is the -1 per movement unit reading of the wording, the -1 per ship combat range band reading, a -1 per personal combat range band and another using the range factors on MT:RM page 88 are used as the Defense DM, presuming that the sensor use tasks were supposed to use that as a factor. Plus, there's an alternate set of tasks in World Builder's Handbook.
Note that, for that page 88, it's contiguous with -1 per range band of ship combat ranges out to Far (Far Orbit), then widens. Each of them produces different results.

Using the ship range bands comes close to maximum detection range of a 100Td ship.

I suspect that someone decided to alter the sensor mechanics late in the development; using an easy task and the sensor range mod on RM p. 88 opposed by the actual range looked up on that same table works REALLY well, provided you remember the task DM limit of ±8. That table use is evident enough that it has independently evolved at least 4 times (Myself, and 3 other GMs).

And, yes, all sensors are a window into the past; in the case of your eyes, that door 3m away is 0.01 nanoseconds in the past (300,000,000m/s, 1/100,000,000; the other end of the street you see 1 ns into the past. The moon you see is the moon of 1.5 seconds ago; the sun is 8.3 minutes ago.

You never, ever see the present. (And that's all before accounting for the 10 ms delay of your brain.)