Space Combat - Did I miss something?

[shirgall]

Pardon me for asking, but can some one explain why passive sensors can detect farther that active sensors? ...

Looking at page 160 of the Core Rulebook, active radar/lidar sensors has more detail than passive at the same range band, and go all the way out to Distant when passive has "None" at Long and farther distances. Passive EM has more range than passive radar/lidar but not as much as active radar/lidar.

 

[TankerMG]

First off, thank you for the quick reply!

Yes I understand that concept of 'seeing' as a passive sensor. An active sensor provides more information on the subject, that a passive sensor. It is more than, 'Yeap, it is a speak of light in the sky", the 'clarify and classify' from the old song and basic points of information. Whether it is radar in the air, sonar in the water, or LIDAR in a lunar lander. The sensors provide information to clarify and classify the contact. Your analogy (if I understand correctly) is that my eyeball and brain (from experience and education) interpret the light points in the sky as stars. It takes another sets of sensors to tell me something about those stars.

Cassini space craft use of radio waves and radar allowed for a better understanding of the topographic information of the moons surface of Saturn, which a passive sensor could not do.

 

[TankerMG]

Looking at page 160 of the Core Rulebook, active radar/lidar sensors has more detail than passive at the same range band, and go all the way out to Distant when passive has "None" at Long and farther distances. Passive EM has more range than passive radar/lidar but not as much as active radar/lidar.

First off, thanks for your quick reply. I saw that in Core Rulebook 2022 update, which started me on this wormhole I find myself in.

But thank you for pointing out to me the chart on page 160 of the Core Rulebook and the difference between passive and active makes sense. Thanks!

Now range.
50Km is not far in spatial terms. CT detection for commercial or ordinary ships at 1500mm (.5 light second) and military/scout ships at 6000mm (2 light seconds) in a game scale of 1mm = 100 Km. So that is 150,000 Km detection range for civilian ships and 600,000 Km for Scouts or military ships. I use to equate that to active sensor use.

I see that MgT 2E HG add two more range bands of very distant and far and defined them. It also redefined distant from 50,000 Km out to 300,000 Km (pg 24?).

Is that the answer?
Or
Take the HG range and extrapolate the distances for 'large ships' sensors for range bands of short medium, long, very long and distant?
Or is the answer, b/c of HG, only distant is change plus the two new range bands?

The later would make passive very short compared to active, while the former is more uniform?

I am just trying to figure this out before I use the GM rule in my game. I don't want the players concepts based on the rule book to be faulty. So before I make a statement in game, it needs to make sense.

 

[Condottiere]

In terms of scale and energy output, a star tends to be rather large, and is undergoing a continuous fusion reaction.

Active sensors create a lot of directed noise, that supposedly when it hits something, can bounce back, partial return noise being more than enough, and I would suppose, lessens squared distance, since anything more, would have fried the target.

 

[swordtart]

Pardon me for asking, but can some one explain why passive sensors can detect farther that active sensors? I understand that active sensors will light up light a xenon searchlight in a dark room, but active radar has always had a longer range than passive radar.

Several years of working with individuals in the military (that are way smarter than myself), I understand the basic concepts of EMS, electronic warfare and radars; but the Traveller sensor rules for range seem to be at odds with these concepts.

After figuring out the range, the game concept of detection rules I understand the DMs and difficulty.

If this was already explained why active sensors range is less than passive, I humbly ask that you please post the link So I can read the explanation and understand. Thank you!

Active RADAR/LIDAR can indeed detect further than Passive RIDAR/LIDAR.

Passive detectors require the object to be transmitting in the band you are detecting. Most ships as a function of their normal operation cannot help but transmit in the bands the passive detectors exploit (i.e. Visual, Thermal etc.). RADAR/LIDAR are an exception as they are only turned on when actively scanning (at which point they can be passively detected by others).

It is easier to increase the "power" of the receiver than than power of a transmitter. Consider a crystal radio set, the receiver can pick up signals from 10's of miles away with no power source other than the radio waves themselves. A transmitter capable of producing a signal capable of detection at that range will require a few hundred Watts.

The main reason for going passive rather than active is to reduce your own detectability. To detect actively you are actively transmitting to irradiate the object in question and then passively collecting the return signal. Due to inverse square law as RADAR/LIDAR emissions spread out as the distance from the source increases and less and less of that radiation will hit your target. The energy bouncing back will also spread out as range from target increases.

If you are bouncing your own LIDAR/RADAR off an object the object affects the signal which allows you to obtain finer details depending on the range. If you are detecting LIDAR/RADAR they are transmitting you will only obtain the characteristics of their transmitter since their ship has not interacted with the beam and affected it.

In real-life astute operators can deduce things from the characteristics of an active source e.g. they will know the difference between the signal pattern of an air defence radar vs that of a radar guided seeker on a missile for instance.

 

[TankerMG]

Active RADAR/LIDAR can indeed detect further than Passive RIDAR/LIDAR.

Passive detectors require the object to be transmitting in the band you are detecting. Most ships as a function of their normal operation cannot help but transmit in the bands the passive detectors exploit (i.e. Visual, Thermal etc.). RADAR/LIDAR are an exception as they are only turned on when actively scanning (at which point they can be passively detected by others).

It is easier to increase the "power" of the receiver than than power of a transmitter. Consider a crystal radio set, the receiver can pick up signals from 10's of miles away with no power source other than the radio waves themselves. A transmitter capable of producing a signal capable of detection at that range will require a few hundred Watts.

The main reason for going passive rather than active is to reduce your own detectability. To detect actively you are actively transmitting to irradiate the object in question and then passively collecting the return signal. Due to inverse square law as RADAR/LIDAR emissions spread out as the distance from the source increases and less and less of that radiation will hit your target. The energy bouncing back will also spread out as range from target increases.

If you are bouncing your own LIDAR/RADAR off an object the object affects the signal which allows you to obtain finer details depending on the range. If you are detecting LIDAR/RADAR they are transmitting you will only obtain the characteristics of their transmitter since their ship has not interacted with the beam and affected it.

In real-life astute operators can deduce things from the characteristics of an active source e.g. they will know the difference between the signal pattern of an air defence radar vs that of a radar guided seeker on a missile for instance.

Thank you for the reply, and yes the last part is very true, the sensor, RADAR operator makes a big difference.

When you wrote:
It is easier to increase the "power" of the receiver than than power of a transmitter. Consider a crystal radio set, the receiver can pick up signals from 10's of miles away with no power source other than the radio waves themselves. A transmitter capable of producing a signal capable of detection at that range will require a few hundred Watts.

That depends on the radio receive range band and the radio waves, for far less power and using the right radio waves, the signal can be transmitted much farther. BUT you are correct with the basic radio receiver vice transmitter.

The basics of using passive versus active detection is a tactical question/method. I was asking about the range which Shirgall led me to the sort of answer.

I understand the active versus passive using modern naval wargaming or submarine wargaming, staying silent and reduce your signature until it is unavoidable. That is a tactical employment like you outlined very well.

My question centered to the range in the MgT2E being much less than the original CT. Also it appeared (Until I was corrected) that passive sensors out ranged active sensors.

So am I correct that the core sensor rules are meant for 'Adventure class' starships and commercial ships and the HG sensor rules are for Scouts and Military?

Also how do I rectify the difference between the ranges of the sensors in CT vice MgT2E?

 

[hopsnbaer]

So am I correct that the core sensor rules are meant for 'Adventure class' starships and commercial ships and the HG sensor rules are for Scouts and Military?

Also how do I rectify the difference between the ranges of the sensors in CT vice MgT2E?

I would say one is an upgraded rule. There are often contradictions in the rules over different books. I usually use the later rule.

As to which sensor ruleset to use? I would pick the one that fits your game best. As long as you are consistent it won't matter which one you go with.

 

[rinku]

Keep in mind that passive sensors include observing reflected sunlight. While it's true that passive sensors to require an active transmitter, most situations have a honking great big one a few AU away.

One thing the rules don't currently address is that the further you are away from a star, the less effective it will be at lighting up objects. Ultimately that DOES place limits on sensors, over and above the actual distance between the object and the observer. If you're both 1AU from a star at a given distance from each other, the signal strength from the reflected light will be 1/4 if you are both 2AU, 1/16 if you are 4 AU and so forth.

Out by the gas giants, things get dim.

 

[Sigtrygg]

Passive sensors also detect the energetic emissions from a ship,,,
electronic noise
waste heat
neutrino
gravitic

and any radio, transponder, active sensor, running light, unshuttered window... yes, all that light coming through the clear cockpit window that nearly all ship illustrations show could be detected

 

[Condottiere]

You have to fade into the background, but not too much, to avoid becoming noticeable by creating a black hole.

Which is where black globes come in.

 

[rinku]

In the outer system, those "noise" emissions will show up better, since all the other things are much dimmer.

I'd... not rely on detecting a ship's neutrino output most of the time though. Space is awash with those, coming from all directions. Especially close in to a star, or anywhere near a stellar tech world. Not saying it's impossible with high tech sensors, just that it's on the order of spotting a candle on a sunny day from a long distance. On the other hand, that's where reflected EM radiation works best anyway.

The other stuff, sure. Although if a ship is trying to hide, its best best is to mimic a bit of space junk or rock, ideally radiating it's excess heat from the far side of the hull from where it expects searchers to be located. I expect the gravitics would be switched off in that situation, too.

 

[Condottiere]

It's where all those energy efficiencies for customized systems, pay off.

 

[TankerMG]

Thank you for all of the replies, it is greatly appreciated.