Re: Detection vs Identification

aebrain@dynamite.com.au wrote:
> 
> >One point which was pretty much conceeded (and
> >backed up by calculations) was that, using current technology, you
could
> >detect the Space Shuttle's manuvering thrusters in the asteroid belt,
> >and its main engines out beyond Pluto. Thus, if you're using thrust,
you
> >can't hide.
> 
> That is, assuming you're using a reaction drive based on chemical
rockets. A
> reasonable assumption in some cases (Vector movement, relatively low
ranges),
> not in others (any Cinematic).

	Well, pretty much assuming you're using a reaction drive at all
(ANY
reaction drive is going to be detectable, at least if it's causing any
discernible acceleration...and what's the point in having it on if it's
not moving you anywhere?)
	As for reactionless drives, that one I can't swallow. I am
willing to
grant that there may be a way to make an FTL drive without violating any
natural laws (especially if it involves leaving the universe for
awhile). However, I don't believe that you CAN make a reactionless drive
that doesn't violate conservation of energy, momentum, angular momentum,
etc.

> There are 2 different problems regarding what we usually call
"detection". 
> There's 'Detection' and 'Identification'. Thus using a reasonable
radar, we 
> may be able to 'Detect' pretty much everything of reasonable size
within the 
> volume of interest. But 'Identification' - sorting out which objects
are 
> harmless chunks of rock, and which are planetbusters, is something
else 
> entirely.

	Agreed, but I can't see that as being much of a problem at
TACTICAL
ranges, only at strategic ranges (for the record, i consider anything
within 1e6 km to be 'tactical ranges' (even though I do NOT believe that
there are any reasonable weapons with engagement ranges anywhere NEAR
that), and 'strategic ranges' is considerably farther away. From Earth,
say, 'strategic ranges' is sort-of 'nearest planet' (unless the target
is manuvering, in which case it's on the order of 2-3e9 km).

> Useful Identification clues:
> 
> Any EM emissions higher than background, including weapons, active
sensors,
> communications, waste heat, exhaust. In the case of weapons, active
sensors
> and exhaust, these are likely to be very useful in Detecting the
object in the
> first place.

	Definitely. You thrust, you're spotted (if you keep it up for
any
length of time, which you have to in order to change your course by any
significant amount).

> Any Gravitational anomalies, ie densities lower or higher than they
have any
> right to be. This can be judged by either some form of mass detector,
or more
> likely the behaviour of the object with respect to the solar wind, or
> radiation pressure.

	I don't see these as being all that useful. I think the useful
range on
mass detectors is likely to be fairly short (but I haven't seen any
calculations either way, so it's just a thought). As for solar
wind/radiation pressure, it's only really noticible on things DESIGNED
to catch it, and given how quickly it drops off with distance from the
sun, I can't see it as being useful (if you have the resolution to
detect that, you can read the numbers off the hull anyway).

> Any anomalous reflectivity of EM from the background, such as a silver
ship,
> a facetted ship with extreme lobes etc, different reflectivity to
differnt
> wavelengths, or most particularly the absorbtion spectrum: what
material is
> the surface made from?

	Reflectivity is a good measure. So is black body temperature (ie
if
it's different from the measured temperature, or peaks in a different
region of the infrared). Another thing is for those ships with
'directional radiators.' Because a radiator's efficiency as a radiator
drops off fairly rapidly as you make it directional, a radiator that
only radiates through (say) a 60-degree cone is likely to be as big as
(or bigger than) the rest of the ship. Of course, this is also VERY
close to the breakeven point (the point at which your radiator absorbs
as much heat as it radiates, thus becoming useless).

> But the real kicker here is its Kinetic motion. In general, harmless
objects
> do not change their course from a ballistic trajectory, and those that
do (as
> the result of elastic collisions or outgassing) leave unmistakeable
traces,
> and do not alter their motion much. (OK, in collisions they can, but
in a
> predictable way, unlike outgassing)

	And, in general, massive objects don't collide very much (if
they were
going to, they probably already have). ANY non-ballistic object is going
to draw attention to itself, and keeping your fleet ballistic VASTLY
reduces what you can DO with it (especially if there aren't any
interesting targets in your immediate trajectory after your last jump).

> Some things can be easily Identified: ships that fire, ships whose
comms you
> intercept (though even there, it's possible that an el-cheapo robot
drone
> could mimic a real ship). Others are more difficult - is that "shiny"
object a
> piece of debris from aprevious battle, or a frigate? Or even a large
piece of
> tinfoil dropped to get your attention while the real ship is
elsewhere? A
> quick pulse from a laser might help find out - if the object recoils,
it's low
> mass (or a real ship using a reactionless drive that's attempting to
make you
> think that), if its return spectrum shows a composition of silica with
a bit
> of nickel and iron, it's an asteroid (or a ship with a cammo net). But
if it
> emits a Terrawatt beam, or suddenly pulls a 6g acceleration, you know
it's not
> natural. In the former case, it's a ship, in the latter a ship or
decoy.

	Well, if it accelerates at all, you can likely determine thrust
(from
exhaust, see above for 'reactionless drives'), and acceleration, which
gives you a pretty good idea of mass (yes, you can defeat that by making
your decoys as heavy as your ships, but in that case why not just build
more ships). As for the 'shiny object' if it's moving on a trajectory
towards something important, it may be dangerous so burn it. If it
isn't, don't do anything until it accelerates. After all, unless it's
heading right at you (in which case it's a danger WHATEVER it is), an
object per say isn't all that dangerous to you.

> As regards waste heat - a coolant laser should do the job of taking
the
> radiated temperature down to reasonable levels. Remember that if
anything is
> "of interest" it's probably relatively close to an unshielded fusion
reactor,
> ie a Star, so will heat up accordingly.

	First, what IS a "coolant laser?" I've never encountered that
term, and
I have NO idea what it could be. Second, yes, blackbody temperature has
to be taken into account, but an inhabited ship CAN'T be a blackbody
(not even close, because of the crew), and THAT can be detected.

> What this means for FT is that depending on your exact PSB, we could
go from
> "everything detectable and identifiable at several LY" to "everything
> detectable and identifiable within the Solar System" to "you only
detect and
> or identify when you're up close and personal".

	Agreed, as long as 'up close and personal' is 'a million km or
so.'
Now, all you have to do is imagine weapons that can DO something at that
range....

-Brian Quirt