Re: Sensors

Some thoughts on sensors, mainly stolen from the way sonars
and radars work in naval warfare today.

These principles should hold true, regardless of whether the
radiation is standard Electromagnetic ( such as Radio,
Light, Gamma Rays...), Gravitational (via vibrating singularities
and Forward Mass Detectors), or via Herr Professor Doktor
Von Kuckucksheim's Aether Perturbation and Modulation
Gornokifier (Patent Pending)

Sensors can be grouped into 2 types - Active and Passive.

Passive Sensors

Passive sensors rely on the radiation of the target being detected.
As different targets tend to have different radiation "signatures",
Passive sensors are very good for Identification.

"Those Engine Theta-Curves look like one of our old Heath-Robinson
Mk IVa's, Ma'am. Our database confirms they match those of the
Kinshasa, a Victoria-class Battlecruiser we sold to the PAU..."

Passive sensors can be either quite long ranged, or quite short,
depending on whether the target is trying to hide or not. If the
target is doing a lot of energetic stuff, like firing beam or similar
weapons, or using Active sensors, or even using a lot of thrust,
then they can be detected from Yonks away, depending on your
PSB background. If you're using Fusion Torches for drives, a
Yonk could be several light years.
Even if not acting energetically, targets are bound to give out
some signature: it's difficult hiding mass, it's difficult hiding
thermal emissions, and it's difficult not occulting backgrounds.
Generally, the larger the vessel, the greater the signature
when running silent, but even an escort operating active sensors
will stand out a mile by comparison.

"All Hands Here This! Rig for Silent Running! Engage Cloaking
field!"

Passive sensors on the other hand are not so good for localising
the target. Tracking via passive means is a statistical process,
the more measurements you have over time, the tighter your
estimate of the target's position, course and speed becomes.

"We first detected an active transmission on the Kappa band
at azimuth 40, elevation -10, range unknown at 0100. Classification
as Military-grade ESU Active Search Sensor. We lost the
contact shortly thereafter, regaining at 0170. Initial Target
Motion Analysis suggested a range between 100 and 200 MU,
which was refined at 0340 to 130 MU. +/- 5, well outside
counter-detection range.."

Passive sensors - including data relayed from other friendly
vessels - are not in general accurate in localisation enough
to be used as fire control solutions. YMMV on this one,
area.volume effect weapons may be OK, and seeking
weapons such as MT or SM missiles may just have their
homing radius reduced on the very best of solutions.

Active sensors 

Active sensors don't rely on the target being co-operative
enough to emit: they operate by shining a beam of radiation
in the target area, and measuring the return. As you know
the exact characteristics of the outgoing radiation, and can
make it as tight a beam as desired, you can get a pretty accurate
fix on the target's position instantly, quite adequate for aiming
weapons.

"At 2120.2, target's range was estimated as 35 MU, +/- 0.4.
We engaged active fire control, and locked on immediately
at a range of 34.87365. Fire was opened at 2120.4, and several
hits were registered at 2122. Return fire commenced at 2124,
 with no effect..."

Active sensors are good at localisation, but not so good at
identification. The physical size of the returned energy may
give you an estimate of the target's reflective area, and hence
it's physical dimensions, but you'd get most of your identification
through analysing the kinetic motions.

"Initially, target 456 was thought to be an NAC Cruiser of the
Furious class. Upon illumination by our fire control radars,
it immediately executed a 90 degree turn characteristic of
Kravak evasive manouvres..."

For navigational safety (avoiding errant asteroids...) any civilian
ship needs a minimal active sensor. Military ones would be
longer ranged and more powerful, but usually have a civil-grade
active sensor as well as a backup, and when they're pretending
to be civilian vessels.
Fire Control sensors can be operated in a scanning mode, and 
indeed some systems may be "track while scan", dual Fire Control
and Search.
The signature of any military grade active sensor would be
unmistakeable. It says to all nearby "Hello, I'm definitely a warship,
and you can make a pretty good guess who I belong to, and maybe
even what class I am."

Both active and passive sensors can be jammed. A good analogy
is trying to see something on a dark night. An active sensor would
be a combination of your eyes and a torch. Passive sensors would
be just your ears. An active jammer would be a blindingly bright flare
near the target. A passive jammer might be a boom box in the
area with volume set to Maximum, playing heavy metal.

Note that jammers can be detected at very long range indeed, even
more so than the beam of an active sensor.

OK, that's enough about the generalised theory. My next post
will be about games design, and how to model complex processes
using simple mechanics. In it, I'll be unashamedly copying some
of the good ideas that others have had and put on the list, and
trying to justify a set of sensor rules for FT, embodying most if
not all of the principles above.