Re: A couple of quick replies

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On Sun, 25 Mar 2001, Richard and Emily Bell wrote:

> > > 2) Advanced Sensors - My take is opposite - advanced sensors are
passive.
> > > The better the quality, the less need for active sensors, hence
the less
> > > detectable.
> >
> > Basic sensors are by definition passive, unless you include 'Hello??
> > Anyone there?". Anything above basic will probably be to some degree
> > active. But yeah, I can think of some very advanced passive ones as
well.
> > So maybe it would be: Basic - passive. Enhanced - active  & passive.
> > Advanced: Mainly passive, some active etc.
 
> Actually quite the opposite.	Truly basic sensors (more basic than the
basic level
> sensors described in MT), such as those mounted on freighters are
entirely active
> because they only have to avoid objects, not shoot at them, and power
is cheap
> while sensitivity is expensive.  FT warships (including the Komarov
and Von
> Teghettof) are actually too small and maneuverable for the double
transmission
> delays of active over passive sensors to provide an adequite fire
control
> solution.

I may have used the wrong term, buty I was referring to the d4 you get
for
Mk1 eyeball...

And we were discussing stargrunt rather than FT ;)

> Warships will not use active sensors in the same fashion as the
civilian
> vessels.  Warships will use their active sensors to take a snapshot of
a
> bogie first detected by passive sensors.  The snapshots are taken with
> microwave "flashcubes"  derived from explosively pumped, high powered
> microwave weaponry, which are destroyed by the energies that they
focus
> on the target (vessels carry a large number of these small and
> expendable devices).	The vessel's passive sensors (and those of other
> vessels in the formation) use the reflection of the single pulse to
> determine range, size and shape of the target.  Because these images
are
> used to aid in the passive tracking, they need not be taken very
often. 
> As the pulse is very short and the target does not know when the pulse
> is arriving, there is very little that the target can do besides being
> unreflective.  A method under investigation to defeat stealth coatings
> are broad-spectrum flash cubes powered by small nuclear devices. 

On the other hand, such extremely high powered pulses are just about
impossible not to detect. Also, there's a lot you cannot measure this
way,
which you could measure with a longer, low powered signal, like target
speed (doppler shift). Problem with super-broad band flashes is that you
need super-broadband receivers, which means receiving a HECK of a lot fo
noise. And since you're doing only very short pulses, you have no means
of
discerning between noise and a coherent signal, no processing that can
help to any extent, except inbetween successive PULSES. Which is orders
of
magnitude less effective than what you can get from a coherent signal
processing.

Instead of going for very 'loud', short pulses, you could use long,
modulated, much lower power signals. harder to detect, and give you a
big
performance boost against noise.

I'm curious where this idea came from, and what makes you state it as if
it were chapter and verse? Is it FT canon?

> The PDS's employ a more conventional active sensor system as the range
> is much smaller and a fire control solution is needed sooner than
would
> be available from target motion analysis. 

Makes sense.

Cheers,

  Derk
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