T4 Only: So how to use the sensors?

[warwizard]

What is meant by sensitivity?
Let's start by defining terms using the mk. 1 eyeball as our sensor.

The object to be sensed is defined as a 100 dt sphere starship with Jump 1 1g and thruster plates and antigravity and G-comp installed.

So we have a 13.9 approx. diameter black ball.

We need to have Sensitivity + signature - range >0 to have any chance to see it and a 2.5 to automatically see it.

visible signature assumes it is being illuminated by the local star.

so range 1 is 1 meter, range 2 is 10 meters, range 3 is 100 meters and so on.

We can determine that the ship is automatically spotted to range 3 range 4 is easy range 5 is hard and you are not going to spot it at range 6 (100km), so that puts the sensitivity of the mk. 1 eyeball at 6.0 or less.

That was in full daylight, let's put the thing in shadow, it's now night and the moon's not up, can we see it 1 meter away? well it occludes stars across 60 degrees of our vision so yes we can see it by what it obscures. 10 meters away, still yes, 50 meters? and we have a chance of not seeing it.
so signature -2.5 - range 2.5 = -5 + sensitivity 6 means a standard task of difficult.

What about fog? if we have a modifier to vision of -1 due to haze/light mist then 1km in daylight becomes our limit.

So there is the example of seeing something. Signature may be modified by not being illuminated, or there may be other items obscuring the signal (clouds, dust, planetary atmosphere), the signal may also be blended in with the background. (truck with a bank of lights mounted on it and shining becomes invisible when it is in the line of sight to the sun, by providing light that would have been blocked by the truck)

The FF&S design sequences show PEMS starting at 12.5 sensitivity, but what does that mean?

How far away can I detect the standard ship mentioned above? and Tgt lock?


Sensitivity range
1 1m
2 10m
3 100m
4 1km
5 10km
6 100km
7 1000km
8 10,000km
9 100,000km (3 1/3 hexes)
9.5 500,999km (16.65 hexes) Auto
10 1 million m (33 1/3) easy
11 10 million m (333 hexes) difficult
12 100 million meters (3,333 hexes) Impossible
12.5 500 million m (16665 hexes) No chance

So now instead of being illuminated by the sun it's hiding behind an asteroid and has been powered off for weeks:
(Vis sig -2.5) (IR sig -2) (Active sig no change)
Our auto points are in the same hex at 7.5 for visible, and 8 for IR, so our no chance point moves to 165 hexes and the impossible level task is at 33 hexes.

 

[warwizard]

Target lock is a modifier of -2 so we need to get within 10,000m of that hiding ship to target lock it, and that is why you need the active sensors.

 

[warwizard]

Now for the active sensors:

The illumination: Sensitivity - range factor is a mod to active signature. This represents the energy reflecting off of the hull.

So an active 13.0 illuminating a target at range 11 adds 2 to the signature when trying to detect the object
this gives us 13 +2 -11 = +4 an auto detection and an easy target lock at 333 hexes. The object of the scan and any other sensor platforms in a 60 degree cone of that search radar all get a +mod on their passive detection and target lock attempts equal to the power of the active sensor - range (min 0) you can assume that nearly everybody in range will detect and some will be able to target lock the emitter.

That brings us to a tracker like a LADAR, it cannot make detection attempts, but it can be handed off a target lock from a scanning type sensor, and illuminates the target with it's laser and has a +2 to maintain the target lock.

Next up is stealth and countermeasures

Stealth is built into the hull or retrofitted and include but are not limited to:
Hull shaped to reflect the active sensor energy away instead of back towards the sensor, coatings that absorb the energy, vastly more radiator area for the engineering plant to frequency shift the IR emitted to longer wavelengths.

These measures are taken into account when generating the ship's signatures. Some affect only one portion of the signature like the military ultra black coating only affects the visible light signature, while stealth features like hull shape affect the active signature, and the radiators affect the emitted signature.

I've posted a 1 m3 missile in the T4 section that without any stealth effects has a -1 emitted, -2 visible and -.5 active signature, and not using any, a -2.5 for gravetics.
It has enough surface area to allow it to place 1000X the radiator area to change it's emitted signature by another -1.5 to a -2.5. The military ultra black could be applied for the visible signature reduced to a -3 and a couple of levels of shaping the hull to reduce the active signature by another -1, however this costs the missile fuel endurance and extra mass dropping it's performance to perhaps 17 g's for 2 hours.
So we then have a missile with a -2.5E, -3V, -1.5A -2.5G that may have done it's maneuvering well out of passive sensor range and is now coasting closer... it just might be able to reach range 8.1 (15000km) without the target with it's 12.5 P sensor ever detecting it 12.5-8.5 -2.5 =1.0, a difficult detection task, and no chance at target lock.

 

[warwizard]

Counter measures:
Chaff: designed to have large surface area and reflect back a larger signal than the ship deploying the chaff. Effective against active sensors and LADAR (-.5 to maintain detection or target lock per batch of chaff in line of sight)
Anti laser aerosols: a charge of this generates a laser reflecting cloud similar to that of a sand caster and attenuates the signal of LADAR beams and the reflection off the hull. (-1 sig per cloud between the ship and the sensor)
Electronic counter measures receives and retransmits active sensor pulses to cause the active sensor to read incorrect velocity data. Over powers the active sensor's real return pulses, ineffective against higher tech level sensors. Adds to chances of maintaining target lock, provides - DM to hit the target with meson fire and missiles, no effect on speed of light beam weapons other than meson guns. May be combined with chaff to divert fire onto chaff.
Jammers: countermeasure is that of flooding the spectrum with noise, thereby causing the sensors to attenuate the received signals so as to not burn out the detector elements and thereby fail to detect the return signals.
This is generally best done from a drone or a missile accompanying a salvo of real ones as the only way to target lock the real missiles is to destroy the ones broadcasting the jamming.
The last resort jammer is that of detonating a nuclear device in the line of sight to the sensing ship, breaks target locks and detections.

 

[warwizard]

Now we come to the question of field of view.
T4 allocates surface area to the antennas, Brilliant lances gives us locations and bearing arcs for turrets, combine the two and you have field of view issues no matter where you place your antenna.

If you are accelerating to change vector your nose mounted antenna will not be able to scan behind you, and when jumping into a system you NEED to be able to collect sensor inputs from all directions at the same time. so there is a need to have multiple antennas to enable 360 by 360 degree sensor coverage.

Ok if you have a cube or sphere shape you could get by with just two antennas mounted on opposite corners or sides but that needs a greater than 180 degree field of view. Field of view is missing from sensor design sequences. So what is reasonable?

Ok let's look at the F-15's old AN-APG-63 radar system from the 1970's
It was a steerable beam phased array on a gimbaled flat disk that had about 135 degrees of movement plus the beam could be steered for additional coverage. So while it could indeed look nearly backwards it could only see some 45 degrees at any one instant, that is what I'll call the IFOV.
We also have some full sky instruments looking for GRB's that have an IFOV of the entire horizon (about 180 degrees).

What is the tradeoff for more field of view? The answer is you have less sensitivity. This is why a LADAR tracker can have a +1 sensitivity while using only .015m2 area compared to the PEMS's .1m2. The LADAR only has a few degrees of IFOV compared to whatever the PEMS array has.

Proposed house rule:
The scanners as listed in the design sequences have a 45% IFOV at the listed area and sensitivity. You may double or halve the IFOV by applying a .5 mod to the scanner's sensitivity, and 1/4x or 4x the IFOV for a +1 mod to sensitivity so a standard PEMS 12.5 has IFOV of 45 degrees, you could get a 13.5 for the same area if you cut your IFOV to 11.25 degrees, or get a 180 degree IFOV at 11.5 sensitivity. This is something the sensor operator may do on the fly so to speak. a 1/4 IFOV will take 16X as long to scan the same sky as the standard configuration, so that's a second trade: off time to scan a given area is X4 or X16 if you reduce your IFOV.

So how does all this play out?
Merchant jumps into the system with his PEMS scanner set to 180 degrees and he rotates his ship to sweep the scanner across the full sky in the first 30 seconds. Referee conducts sensor task with sensitivity at 11.5, and reports the presence of the high port and some ships that are maneuvering away, but nothing is close.
Merchant then reconfigures the array for a 90 degree IFOV and sweeps the sky for two more minutes at 12.0 sensitivity, getting a few more detections.
Then they set it to the standard 45 degrees and begin an 8 minute sweep at 12.5 sensitivity, picking up an inbound powered down small craft. A further reconfiguration to the 11.25 degree configuration to attempt to target lock the small craft with an effective sensitivity of 13.5.

 

[mike wightman]

Thanks for taking the time to do all of this. That last post is particularly useful for coming up with stuff to use as standard procedure on a starship.