Detection vs Identification

>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).

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.

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.

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.

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?

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)

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.
 
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.

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".