JTAS sensor rules

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Tupper
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JTAS sensor rules

Postby Tupper » Sat Oct 17, 2020 1:33 am

I was reading the sensor rules (from JTAS volume 4) this morning, and struggling to make sense of Emissions Control. Maybe I've misunderstood what the rules are supposed to simulate, or maybe I'm misunderstanding the rules themselves. Hopefully someone can help!

My read of how sensors work is that a ship has active and passive sensors. Using active sensors makes you really easy to detect, but in exchange improves your ability to detect other ships. Hence turning off your active sensors is prudent from a stealth perspective. EMCON allows a "halfway house" where you operate your active sensors in a less effective fashion, but that makes you less likely to be detected.

Ignoring EMCON, the sensor rules seem to simulate this. If you turn on your active sensors, you get automatically detected by anyone "nearby" (where "nearby" is defined as one range band closer than their sensors' range). If you don't turn on your active sensors, you don't have this problem, but have to make do with a -2 on any detection rolls you make.

Turning on EMCON, however, gives your ship a -1 penalty to be detected, and a -2 penalty to detect other ships. Presumably, since it's active, it still gets detected automatically by "nearby" ships. Extreme EMCON turns these penalties to -2 and -3 respectively.

So now my choice as a ship with EMCON is:

Only passive sensors: -2 to detect others. No advantage to hiding at any ranges.
Extreme EMCON: -3 to detect others. Automatically detected by nearby ships. Advantage to hiding at longer ranges (-2).
EMCON: -2 to detect others. Automatically detected by nearby ships. Advantage to hiding at longer ranges (-1).
Full active: +0 to detect others. Automatically detected by nearby ships. No advantage to hiding at longer ranges.

This set of choices seems to make EMCON attractive because it makes me harder to detect at long ranges (than if I just went passive), and has no advantage in terms of detecting other ships over and above being passive (indeed extreme EMCON is *worse* than passive).

My read of how sensors worked would be that if I wanted to avoid being detected (regardless of range) I should prefer being passive. [Not the case because having EMCON active sensors makes me harder to detect at longer ranges]. If I wanted to detect other ships, I should prefer being using EMCON to being passive only [Not the case because I get the same -2 penalty to detect using EMCON or a worse penalty if I use extreme EMCON].

Can anybody figure out what I'm doing wrong?
Linwood
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Re: JTAS sensor rules

Postby Linwood » Sat Oct 17, 2020 2:57 pm

Other people on this forum are far better than I at working out the intricacies here. The one thing I'd add is that I'm not certain it's appropriate to penalize a ship in some situations using passive sensors only in the case of a target that's EM active - active sensors, radio communication, maneuver drive running, etc. Active sensors certainly can aid in identification and targeting, but I doubt they're needed to simply find a ship that's actively broadcasting.
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Re: JTAS sensor rules

Postby Annatar Giftbringer » Sat Oct 17, 2020 7:00 pm

I struggled with these very questions myself a lot, until the penne finally dropped (or I at least found a solution that works for me!)

How can you get worse modifiers by using sensors a little compared to not using them at all? Sounded very weird and wrong to me, but there is an important distinction between passive and active radar, one that’s not stated outright in the article. Active sensors lets you find anything that’s within your reach, while passive can only show those that themselves are transmitting.

So in a way passive and active are two very different things, hence extreme EMCON with severe negative modifiers can still discover ships that a ship running with passive sensors only can never find, regardless of modifiers. This does place some additional burden upping the GM (you can’t just look at the tables, you have to forge your own narrative a bit) but it makes for fun and exciting gaming!

Imagine a dark room filled with people, rather than a number of ships in space. Each person has an electric torch. Using active sensors is akin to turning the torch on, it means one can easily sweep the room and see anyone not hidden, but is also very easy for everyone else to see the lit torch.

One person using passive sensors (their eyes) can see everyone with lit torches, but not others with their torch off.

EMCON might represent quick on/off cycles, and/or low-powered lights. A weak light flashing briefly is harder for others to see, but it also gives its wielder a less-good view of the room. This can be partially mitigated by using night vision goggles, or better sensor packages for ships.

Not a perfect analogy, but I hope my point comes across :)

Also, the detection modifiers table on p.41 of JTAS vol.4 does agree with Linwood. Even with sensors in passive mode it is possible to detect a ship based on its m-drive output and other factors, but at a slight disadvantage compared to if using active sensors.

Finally, the auto-detect issue... I’m honestly not sure how to play it, but personally I’m leaning towards not letting auto-detect apply to a ship using EMCON, otherwise there’d be little reason to use EMCON
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Re: JTAS sensor rules

Postby Ursus Maior » Mon Oct 19, 2020 7:32 pm

I find it best to use these rules together with the transponder rules from the Companion. Imagine that most ships are civilians with their civilian sensor package being turned on and the transponder broadcasting the identity of the ship all the time. Your average sneaky pirate with a Type-A vessel will see his prey coming for (literally) thousands of miles, despite running his sensors passively, simply because a transponder broadcast and active radar cannot be missed, especially if the civvie is burning his drives to reach a safe port before it gets dark.

Said pirate will not see the Type-T class Patrol Cruiser, lurking off his bow in the deep black sea. Not spending any thrust, but running active sensors under EMCON, the crew of the Type-T can generate for themselves a well informed overview of the situation and pounce onto the cheap pirate, as soon as he starts threatening the tramp merchant.
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Re: JTAS sensor rules

Postby Sigtrygg » Mon Oct 19, 2020 9:32 pm

The waste heat from a GigaWatt fusion reactor will produce a lot more of a signal than a few kW radio transmission from a transponder...
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Re: JTAS sensor rules

Postby Linwood » Mon Oct 19, 2020 11:02 pm

I don't think there's an allowance in the rules for heat output and reactor size in the sensor rules. Should there be one? That might offer another option - reducing your ship's reactor output to make one's ship less visible. Although I'd assume Stealth systems handle this in various ways.
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Re: JTAS sensor rules

Postby MongooseMatt » Tue Oct 20, 2020 11:55 am

Linwood wrote:
Mon Oct 19, 2020 11:02 pm
I don't think there's an allowance in the rules for heat output and reactor size in the sensor rules. Should there be one? That might offer another option - reducing your ship's reactor output to make one's ship less visible. Although I'd assume Stealth systems handle this in various ways.
We have considered this, and it might make an appearance if we do High Guard II.

There are certainly some interesting things to play with here, but it has to be weighed against ease of play.

If you want to investigate something like this, I would recommend checking out 2300AD next year...
Matthew Sprange

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Re: JTAS sensor rules

Postby Linwood » Tue Oct 20, 2020 2:49 pm

Thanks Matt!!!!
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Re: JTAS sensor rules

Postby Sigtrygg » Tue Oct 20, 2020 6:31 pm

Linwood wrote:
Mon Oct 19, 2020 11:02 pm
I don't think there's an allowance in the rules for heat output and reactor size in the sensor rules. Should there be one? That might offer another option - reducing your ship's reactor output to make one's ship less visible. Although I'd assume Stealth systems handle this in various ways.
There is no stealth in space without magic tech...
if there is a magic heat sink in Traveller it has been a closely guarded secret for over forty years now.
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Re: JTAS sensor rules

Postby Ursus Maior » Tue Oct 20, 2020 9:35 pm

Linwood wrote:
Mon Oct 19, 2020 11:02 pm
I don't think there's an allowance in the rules for heat output and reactor size in the sensor rules. Should there be one? That might offer another option - reducing your ship's reactor output to make one's ship less visible. Although I'd assume Stealth systems handle this in various ways.
Actually, I was pondering the idea for some time, too. JTAS4 sensor rules modify detection by output of thrust. It would make sense to modify detection by power points used per round. Of course, EMCON in a modern military sense incorporates that concept. So, much like "jump-dimming", EMCON could incorporate reducing power to non-essential systems during combat operations.
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Re: JTAS sensor rules

Postby Ursus Maior » Tue Oct 20, 2020 9:42 pm

MongooseMatt wrote:
Tue Oct 20, 2020 11:55 am
Linwood wrote:
Mon Oct 19, 2020 11:02 pm
I don't think there's an allowance in the rules for heat output and reactor size in the sensor rules. Should there be one? That might offer another option - reducing your ship's reactor output to make one's ship less visible. Although I'd assume Stealth systems handle this in various ways.
We have considered this, and it might make an appearance if we do High Guard II.

There are certainly some interesting things to play with here, but it has to be weighed against ease of play.

If you want to investigate something like this, I would recommend checking out 2300AD next year...
I understand the weighing of detailed rules and playability. I gets out of hand, quite quickly. But if HG II is something you're actually thinking about, may I interest you in rules on how to detect missile launches?

We've seen wonderful additions to missile combat in various supplements now, the Naval Campaign rules, HG of course and others, such as JTAS. But what remains unsolved, is when exactly a missile (or torpedo) launch will appear on sensor screens of ships in sensor range. Missiles will likely use full thrust at launch (but optionally maybe won't), so by JTAS4 that means something like a +8 or +15 bonus on detection. But missiles and torpedos, and even salvos, are comparatively small targets to acquire at 3-48 per dton (including options from the Companion). So it stands to reason that missiles might not show up on screens immediately, if fired from afar. This might be a thing for good remote-ops gunners.

Infact, would this something you'd be interested to flesh out in the upcoming JTAS series? I got some ideas. :mrgreen:
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Re: JTAS sensor rules

Postby Geir » Tue Oct 20, 2020 10:15 pm

Sigtrygg wrote:
Tue Oct 20, 2020 6:31 pm
There is no stealth in space without magic tech...
Yes and no. It is true that you can detect a lit fart out to Uranus(no really!), but only if you know what you're looking for. Great resolution means smaller aperture. Telescopes like Pan-STARRS take more than a day to scan the sky once and have abroad aperture, but they aren't sensitive enough to see that little flash of methane. So if you don't know where something is, you might not find it in a timely manner if it's quiet. Think of the 10-50 meter asteroids we don't detect until AFTER they just missed Earth. Now, once you know where something is, it would be hard to lose lock on it unless the target is deploying active countermeasures...


And as for High Guard II, hey Matthew, if you do that, I'd love a crack at the play testing... too many things seem off... like, I may be slow, but I just realized the smart move is to always make missiles launchers fixed mounts. Cheaper, don't use power, or tonnage, but can hold as much as a triple turret, and technically, if you read the crew rules, they don't need gunners assigned. Only disadvantage I can see is in a dogfight.
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Re: JTAS sensor rules

Postby MongooseMatt » Wed Oct 21, 2020 8:28 am

Geir wrote:
Tue Oct 20, 2020 10:15 pm
And as for High Guard II, hey Matthew, if you do that, I'd love a crack at the play testing...
If/when we do High Guard II (not even sniffing around the schedule yet) we will make it a grand public event - not just playtesting but getting you all involved as to what should be included.
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Re: JTAS sensor rules

Postby NOLATrav » Thu Oct 22, 2020 8:13 am

Since MgT2 has brought Power points/management back to the game, I’ve been providing sensor DMs based on the number of power points being used when ships get in range of one another. Cut the M-Drive, give your potential enemy a -DM. Etc. it works great for us, we’ve had some fun “running silent” scenarios where the PCs cut power to a bunch of systems after setting a course, drifting close until they pounce. They love it.
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Re: JTAS sensor rules

Postby Ursus Maior » Thu Oct 22, 2020 1:23 pm

I was thinking in a similar direction. What is your DM formula? I was thinking something like 25% increments going from +1 to +4. Alternatively +1 per 100 power points?

Also, size should somehow play a part in detection, if not so much in target acquisition.
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Re: JTAS sensor rules

Postby AnotherDilbert » Thu Oct 22, 2020 3:39 pm

Ursus Maior wrote: Alternatively +1 per 100 power points?
You probably want an exponential scale, since large ships like battleships can easily use 100000 Power.

Something like:
<1 Power: -3
<10 Power: -2
<100 Power: -1
<1000 Power: 0
<10000 Power: +1
<100000 Power: +2
<1000000 Power: +3

This would place many small craft and small ships at -1.
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Re: JTAS sensor rules

Postby NOLATrav » Thu Oct 22, 2020 4:51 pm

We’re playing in a small ship ATU right now so my sensor DM scheme stops at 10,000 Power. But AD’s suggested scale above is spot on.
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Re: JTAS sensor rules

Postby Condottiere » Thu Oct 22, 2020 6:04 pm

Distributed power grid with linked mini reactors.
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Re: JTAS sensor rules

Postby Ursus Maior » Fri Oct 23, 2020 8:59 am

The exponential scale totally makes sense. I especially like that it adds negative DMs for minuscule power consumption (and generation). I think I will just copy that for my game.
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Re: JTAS sensor rules

Postby TheMachine » Fri Oct 23, 2020 12:39 pm

AnotherDilbert wrote:
Thu Oct 22, 2020 3:39 pm
Ursus Maior wrote: Alternatively +1 per 100 power points?
You probably want an exponential scale, since large ships like battleships can easily use 100000 Power.

Something like:
<1 Power: -3
<10 Power: -2
<100 Power: -1
<1000 Power: 0
<10000 Power: +1
<100000 Power: +2
<1000000 Power: +3

This would place many small craft and small ships at -1.
I like this a lot. It's what I've been expecting to read since this thread started.

I'm definitely pinching it for our game. In fact, I might add even more granularity at the low end (where players mostly live). Like so:

<1 Power: -4
<10 Power: -3
<32 Power -2
<100 Power: -1
<316 Power 0
<1000 Power: +1
<10000 Power: +2
<100000 Power: +3
<1000000 Power: +4

Or possibly:

<1 Power: -4
<10 Power: -3
<32 Power -2
<100 Power: -1
<1000 Power: 0
<3162 Power +1
<10000 Power: +2
<100000 Power: +3
<1000000 Power: +4


What do people think? Overkill?

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