JTAS 4 Sensor operations

[ochd]

The article 'Sensor Operations' in JTAS no. 4 gives some more detailed rules on detecting other ships in space. Thanks to the author and to Mongoose for this, as it is something I have been looking for more information on for a while.

I do, however, have a lot of questions about the new rules, mostly just checking I have understood them correctly. As I'm running Drinax, I have in mind the Travellers using the TL15 advanced sensors of the Harrier.

1. The Harrier's sensor package has a base range of distant. Does this mean that the Travellers can now 'scan for life signs', using NAS, up to the distant range band? And they can also scan for life signs at Very Distant (at DM -1) and Far (at DM -2)?
2. If the answer to at least the first of those questions is yes, then here's what I imagine happening: the Harrier jumps into a system and initially does a passive scan (optical, thermal and NAS). It makes an Electronics (sensors) check with no DM (-2 for passive scan; +2 for advanced sensors). If successful, the Harrier detects that there are signs of life up to distant range away, and possibly beyond. Then, having made contact, the Harrier makes another scan to get more information. This will now be at DM -2 overall, if still just using passive scanners. The Effect of this check would then give further details as to number and types of lifeform. The Harrier can continue to scan, and every 1D rounds make a new Sensors check, with the Effect of each roll cumulating. Have I got that right?
3. If the Harrier uses its densitometer (an active scanner), then any other ship with a densitometer will automatically detect it if it is in range. So, if the other ship has improved sensors and is in long range, or it has advanced sensors and is in very long range, the Harrier will be automatically detected -- even with its Superior Stealth coating. Have I got that right?
4. Assuming I am correct with no.3, are there any circumstances in which the Harrier would use its radar or lidar, given that now it can use its densitometer at the same range, presumably get better information, and with less chance of being detected in return as fewer ships have densitometers?
5. Do sensors improve with TL, even if they still remain the same package? For example, a Gazelle-class Close Escort has military-grade sensors. It therefore has radar, lidar, jammers and EMCOM available but not densitometers or NAS. It is, however, a TL15 ship. Does that mean its sensors operate at the same base range as advanced sensors - ie, distant instead of long?
6. Finally, under this new system, no stat is given with the Sensors checks. Is that intentional -- ie, only the skill level is applied as a DM, not INT?

That will do for now. Apologies for the long post. I think I would like to introduce these new rules into the game, as they seem to be less hand-wavy than what I have been doing at present, but it will have some big implications for game play, I think.

Thanks,

Dan.

 

[phavoc]

I haven't read the JTAS article, but different kinds of sensors (used to at least) have their own specific ranges.

 

[AnotherDilbert]

Disclaimer: I haven't read the article. I only use info in Core and HG, that might have been superseded.

3. If the Harrier uses its densitometer (an active scanner), then any other ship with a densitometer will automatically detect it if it is in range. So, if the other ship has improved sensors and is in long range, or it has advanced sensors and is in very long range, the Harrier will be automatically detected -- even with its Superior Stealth coating. Have I got that right?

Seems about right. Stealth is a form if camouflage, making you more difficult to spot, but if you stand in the open waving a red flag it will not help much.

Think about it like this: You stand in an open field at night. You are wearing dark camo. No-one sees you. Now you turn on a flashlight (active sensor): You see a small area clearly, but everyone will see you...

4. Assuming I am correct with no.3, are there any circumstances in which the Harrier would use its radar or lidar, given that now it can use its densitometer at the same range, presumably get better information, and with less chance of being detected in return as fewer ships have densitometers?

Presumably a densitometer is not a wide area scanner, but a detail scanner. It is not used to discover ships, but scan a small volume for detailed information.

Sensor Types
...
Densitometers (advanced): Determines internal structure and makeup of an object through its natural gravity.

(I fail to see how this would be an active scanner?)

6. Finally, under this new system, no stat is given with the Sensors checks. Is that intentional -- ie, only the skill level is applied as a DM, not INT?

Generally a characteristic DM is always used on a check; if none is specified it is up to the Referee. I guess it's EDU for routine scans and INT for inventive new ways of using the scanner?

 

[ochd]

Yes, this article seems to be a replacement set of rules to those in the core rule books, as they completely change a couple of fundamental things: namely the effect of range and the effect of actively scanning on giving away one's own position.

 

[Anonymous]

Sensor Types
...
Densitometers (advanced): Determines internal structure and makeup of an object through its natural gravity.

(I fail to see how this would be an active scanner?)

I fail to see how it would work, so I'm OK with any claim for it.

You might measure the effect of gravity by the bending of background starlight but how'd you see someone else's internal structure? Or you might wait for the craft to move and detect the gravity ripple but distinguishing the internal structure? That would be like putting multiple objects on a weighting scale at once and getting individual weights.

 

[AnotherDilbert]

You might measure the effect of gravity by the bending of background starlight but how'd you see someone else's internal structure?

Parallax? Use several sensors displaced from each other and measure the local grav field in each, then use a computer to remove the effects of our ship and the local star system. It would assume extraordinarily sensitive grav sensors, but that might be a side-effect of understanding of gravitic manipulation?

 

[Anonymous]

You might measure the effect of gravity by the bending of background starlight but how'd you see someone else's internal structure?

Parallax? Use several sensors displaced from each other and measure the local grav field in each, then use a computer to remove the effects of our ship and the local star system. It would assume extraordinarily sensitive grav sensors, but that might be a side-effect of understanding of gravitic manipulation?

sure u can see a ship like that, but not inside it

you could maybe tell the back had less mass than the front.

 

[AnotherDilbert]

Parallax? Use several sensors displaced from each other and measure the local grav field in each, then use a computer to remove the effects of our ship and the local star system.

sure u can see a ship like that, but not inside it

With this type of arrangement you can build a map of the objects interior:

 

[Anonymous]

I don't understand how that works.

 

[Sigtrygg]

This new interpretation of the densitometer actively emits artificial gravity waves - the stuff we handwave artificial gravity, acceleration compensation fields etc to fall under - these interact with the mass of the object and the return signal can be interpreted.

Note the densitometer in passive mode would be really good at picking up artificial gravity waves... so perhaps a good countermeasure to densitometers would be playing with your artificial gravity generators on your ship - the grav plates, acceleration compensation, grav focussing elements on weapons, the gravitic based drives etc.

 

[Condottiere]

I wouldn't automatically consider using it as an ecks ray machine.

I do think it would be able to distinguish open areas and major components.

Floorboard gravity generation may actually obfuscate matters.

 

[Linwood]

Could you map the target’s artificial gravity fields? That might get you a rough deck plan if there’s sufficient resolution.

 

[phavoc]

The changes, coupled with the gravity sensors in the exploration book, makes sensor range in light years. If, as the exploration book posits, can pick up the gravitational distortion of objects in the Oort cloud and in star systems light years away, then there is essentially no hiding in a star system. The only 'saving' grace to this change is that the sensors are still light-speed limited.

Though something that is missing is countermeasures to the sensors. Every sensor ever devised (for military activity) has had a counter to it.

 

[Linwood]

Either reduce the signature or make it look like something innocuous.

It may be possible to detect the gravity signature from a starship leaving jumpspace in the Oort clouds but probably not much more than that.

A concentrated mass would likely be easier to detect than a widely dispersed set of smaller masses.

 

[Anonymous]

The only 'saving' grace to this change is that the sensors are still light-speed limited.

I still don't intuitively understand "gravitational aberration". You're not wrong though.

 

[phavoc]

Either reduce the signature or make it look like something innocuous.

It may be possible to detect the gravity signature from a starship leaving jumpspace in the Oort clouds but probably not much more than that.

A concentrated mass would likely be easier to detect than a widely dispersed set of smaller masses.

Per the new rules the gravitational sensors can detect jumpspace activity light years away from the sensor. And asteroids and such in the cloud as well. Essentially with sensors based in the inner system you could map entire solar system in real-time - with the provisio that your data is always light-speed limited, so it could be hours, days, weeks or months old, depending on the distance.

 

[AnotherDilbert]

With this type of arrangement you can build a map of the objects interior:

I don't understand how that works.

With a several displaced sensors we can measure the gravity field of the measured object. As I tried to illustrate, the strength and direction of the field varies depending on the angle to the measured object, allowing us to construct a map in the interior. Note how the arrows (field strength) varies around the hole in the object.

Very approximately it's like stereoscopic seeing, but gravity is not blocked by matter so we can "see" into the object. To get any detail we need more datapoints, so we use many sensors, not just two eyes.

Sorry, that is a very vague explanation, but about as much as I have thought about it...

 

[baithammer]

Would be better to say its a negative space sensor, where it maps an object's structure through the negative space from less dense points on the interior.

 

[Linwood]

Per the new rules the gravitational sensors can detect jumpspace activity light years away from the sensor. And asteroids and such in the cloud as well. Essentially with sensors based in the inner system you could map entire solar system in real-time - with the provisio that your data is always light-speed limited, so it could be hours, days, weeks or months old, depending on the distance.

Detecting jumpspace activity sort of makes sense to me - jumpspace entry or exit is inherently disruptive and includes a substantial energy release. If we go with the assumption that maneuver drives have a gravity-related effect (from the discussions on other threads that may not be true) then detection of spacecraft under power seems likely. Stars, planet-sized masses - sure. But there should be a practical lower mass limit below which the sensors can’t reliably resolve the object.

 

[phavoc]

Per the new rules the gravitational sensors can detect jumpspace activity light years away from the sensor. And asteroids and such in the cloud as well. Essentially with sensors based in the inner system you could map entire solar system in real-time - with the provisio that your data is always light-speed limited, so it could be hours, days, weeks or months old, depending on the distance.

Detecting jumpspace activity sort of makes sense to me - jumpspace entry or exit is inherently disruptive and includes a substantial energy release. If we go with the assumption that maneuver drives have a gravity-related effect (from the discussions on other threads that may not be true) then detection of spacecraft under power seems likely. Stars, planet-sized masses - sure. But there should be a practical lower mass limit below which the sensors can’t reliably resolve the object.

Agreed. I have a house rule about jump flashes, which is the emergence of a ship from jump space. It is not omnidirectional in the sense that the amount of energy radiating from the emergence is the same in all directions.

Instead it's strongest in the direction of emergence, essentially drawing a line from your point of origin. It's also stronger the farther you have traveled and the faster you were going when you entered jump. So vessels looking for stealth try to minimize their speed and distance. You can lower your jump flash, but never fully eliminate it. However the energy dissapates quickly and there is a maximum range that it's detectable at. Certainly not the light years postulated by the new sensor rules.