Re: [FT] Some thinking on sensor and operational level games

From: "Thomas Barclay" <kaladorn@fox.nstn.ca>

> 1) At what range could one likely detect a 
> starship with good passive sensors? By that, I 
> mean optical (visible and not visible spectra) 
> and other similar systems. Something that 
> doesn't rely on "wazoo newtech". 

Reasonable passive sensors:
Types:

EM sensors - ie everything from Gamma-rays to
HF radio, including light. We can do this now.

Forward Mass Detectors (not wazoo as such, we
just haven't seen the need to build them yet).

Particle sensors - Mesons, Neutrinos etc.
We can do this now, but the measuring devices
are huge (for neutrinos anyway).

I've seen posts on sfconsim-l that lead me to
believe that you can detect anything as low
as 24 magnitude by IR Call it a breadbox with a mirror
finish in bright sunlight (not eclipse) near Mars if I've
done my sums right.
 
> 2) How much does the answer to 1 depend on 
> if the ship is thrusting? 

Depends too much on the thrust mechanics. If
a rocket with a plume, we could be talking
detection at a range of Light Years if a matter/
antimatter fusion torch. If an inertialess drive,
who knows? Maybe nothing. Or maybe it
emits tau-neutrinos detectable on the other
side of the Galaxy, after a few hundred millenia.
 
> 3) How much does the answer to 1 depend on 
> if the ship has activated some kind of active 
> sweep sensors or firecontrols?

Regardless of the actual technology, whether it's
using Electromagnetic or gravitational waves, or
particles, an active sensor must both emit and receive
the reflection. This means that the range to counter-
detect will be (relative receptivity) * distance* X *
Y.

X = 2 if inverse-square propagation, else 1
Y = 2 if linear or inverse-square.
Relative receptivity might be > 10 if it's a good ESM
suite, but probably a lot less than 1 if the opponent is
frequency-hopping randomly.

So anything from half the distance to 100 x the
distance, depending. 3x is a good rule of thumb.

> 4) How much does the answer to 1 depend on 
> mass of the vessel?

It depends on the mass (if using gravitons,
gravitational waves, or measuring space curvature,
which the FMD does). It depends on the mass if
what you're detecting is a power plant, assuming
bigger ships require more power. It depends on
the cross-section otherwise - you'll often see the
term RCS or "Radar Cross Section", which is
a combination of the physical cross-section with
the reflectivity.  Anyway, assuming all ships are
homogenous spheres of uniform density, cross-
section is proportional to the 2/3 power of mass.
But differences in reflectivity vs various sensors can
change the cross-section by a factor of 100 or more.
So a stealth aircraft may have a physical cross-section
of 5 square metres, but an effective RCS of 0.01 square
metre.

> 5) How much does the answer to 1 depend on 
> EMCON levels employed? (is silent/black running 
> of any use in space?)

Vs active sensors - marginally. If you're not accelerating,
you might just be a rock. OTOH if you ARE accelerating
at 1 g, you're no asteroid!  Vs passive sensors, it depends..
Usually if you're using more energy to move, or sense,
or fire, you're emitting more. Of course if you're firing
Gamma-ray lasers, and the other guy only has Infra-Red
detectors, you won't be detected. But generally, yes, you
will stand out either more or a helluvalot more, the usual
case being the latter.

> 6) I assume there are three phases to 
> engaging an enemy:
> 
> 1) gross detection - there's something out 
> there, even if it is too far away to tell what or 
> how many

This is the distance that we detect asteroids now.
Basically, if we get a radar return from an object that's
got an RCS of 100 m^2 at 300,000 km, we assume it's
a rock, not Elvis coming home in a non-accelerating UFO.
In a military situation, we can't neccessarily make such
an assumption.

> 2) fine detection - we can tell how many, 
> perhaps what thrust, what mass, are any 
> emitting

It depends too much on the exact mechanics.

> 3) lock-on - we  have a fire control solution
> 
> I assume passive sensors will generally take you 
> through phase 1 and maybe phase 2, but you 
> definitely need to "go active" 
> (sensors/firecontrol) to get 3. 

True. Passive sensors generally are Fuzzy  though
a passive detection may be enough to fire a seeking
or area-effect weapon. And enough passive sensors
for long enough can be good enough for any shot at
short range. Remember your eye is a passive sensor
in daytime. Your eye and a torch is an active obne at night.
At short ranges, you even have coincidence rangefinding, 
if you have 2 working eyes.
 
> 7) Does using active sensors increase your 
> ranges for the first phase of detection?

Usually yes. Consider a torch at night.

> Or are 
> they long enough that your pathetic amount of 
> emitted energy just has no effect?

Usually no. But consider IR goggles and an IR
torch at night vs someone who's relying on eyes
alone, hence the "usually".

> I am sure 
> active sensors would have some impact in the 
> second stage, and obviously firecontrol is the 
> third stage. 

True.

> 8) How feasible are recce fighters or stealthed 
> drones or missiles with sensors and a link back 
> to the ship to extend your active or passive 
> detection radius? Would communications with 
> such a drone or fighter not become 
> problematic beyond <insert arbitrary range>?	
> Or if you had to suddenly manouvre in combat, 
> thus breaking  your hard to detect presumably 
> direct laser link? 

It depends.

> 9) If I have ECM or an area jammer, I assume 
> that I'm making detection level 1 easier and 
> detection levels 2 and 3 harder.

Actually, you're making detection level 2 easier
up to a point. Asteroids and merchants, and
even friendly militaries, don't jam. So we know
you're a confirmed hostile military vessel. What
we don't know is whether you're a single corvette
or a whole Task Force of Dreadnaughts.

Though that's Noise Jamming.

There's also Deception Jamming, where you send
out delayed, advanced or frequency-shifted signals
so that one ship appears like many, or it appears
to be going at a different acceleration or direction,
or even (with sufficiently good electronics) phase-
shifted so that it cancels out an incoming pulse
and you appear not to be there.

We know how to do all the above vs EM signals, but
not vs gravitons etc.

> Turning on the 
> jammer systems would mean people would 
> quickly discover something was emitting out 
> there, but exactly where (more than a general 
> few mu area) might be significantly more 
> difficult to pin down than without the jammer. 

True. I can think of no exceptions off the top
of my head (Noise jamming that is).

> So you'd never use ECM or Jammers until such 
> time as you thought the enemy already knew 
> you were there (otherwise why give up your 
> invisibility). Is this right? Or don't I get how real 
> EW jammers/ECM  work?

I'll give you a typical example of what happened in
an air defence exercise 15 years ago.

We were on a destroyer. The first indication of 
attack was when we detected the I/J band search
radars of the atacking aircraft. As the signal strength
increased, then the bearing became constant, we
flashed up our active sensors as we figured we'd
either been detected or were about to be. Shortly
thereafter we detected a Shadowing aircraft which was
guiding the attacking F-111s in, and had detected us
by passive means, but not located us exactly.
The Shadower then started using Confetti (Chaff) and
active jamming on that sector, which meant that we
had some difficulty seeing the F-111s on radar. We
knew there were at least 2, from 2 different radars,
but there could have been a dozen.

After we'd fired a bit at the F-111s (simulated launch)
and they'd fired at us (ditto) we were suddenly
surprised by a brace of small Macchi trainers that had
sneaked in on an opposite bearing, wave-hopping so
they were out of line-of-sight from us until they were
within 2km. They'd been guided in by the Shadower,
and only popped up to see us (and allow us to detect
them) when there was a real danger that they might
collide with us if they didn't.
The waves were very high, sea state 7, just after a
force 10 gale.

So in summary, you have it right, but the devil's in
the details. Choose your PSB carefully and you can
get pretty much whatever answer you want.

> But any input from people with solid ideas or 
> some sort of domain expertise (or a keen 
> interest) would be worthwhile. 

Well, I've designed a few surface combat systems in
my time that are on board a variety of naval vessels.
And done bits of submarine combat systems too.
( A combat system is the computer network that
takes data from the sensors, tries to figure out what
it all means, displays the result to the crew, controls the
 weaponry, and in advanced cases, makes suggestions
on what to do next).
And I'm currently doing spaceflight avionics for a
research satellite. So I guess that I'm probably 
qualified. Marginally. :-)

One thing to note: it does you no good to detect
something if you can't pick it out from a zillion
other things you're detecting at the same time that
are of no interest to you. As in the traditional needle
in a haystack, or rather, a needle in a stack of pins...
So a needle can be detected (on its own) by eyes
during day on a black background at maybe as much as
20 metres, more if it glints. But put it in a stack of pins,
and you need to be within a few cm to detect it. And
even closer to note the grain of dust in the eye which means
it's the needle you were looking for.