Re: EW Question

"Thomas.Barclay" wrote:
> Someone (Mr. Beast I believe) suggested that active sensors almost
always
> outrange passive sensors. I have to question this. On Earth, passive
sensors
> tend to have somewhat limited range partly due to the effects of being
> inside a noisy atmospheric envelope. And radars can bang signal out to
a few
> hundred miles without too much problem (just lots of juice).
> 
> However, I question this comment as it pertains to space for several
> reasons: our most sensitive instruments (such as those on Hubble or
other
> similar sats) are probably passive, and can see far farther and far
more
> minor changes than any active system I'm aware of. I'd suspect (no
> gaurantees :) that in 2183, this translates to passive systems that
can
> detect very discreet phenomena at long distances.
> 
> Active systems would be limited by the fact that the density of energy
> (which is a contributor to reflected signal strength) will drop off as
the
> square of distance... so I think it'd be pretty imaginative to say
these
> systems will be able to detect things 100,000 or more km away.... I
would
> think active systems would be limited to a far more restricted
distance.
> They'd offer you faster and more precise data than a passive system,
but
> have a much more limited range.

	Most of this post I can agree with, but I'm not sure about
faster
information. I would think that BY DEFINITION passive sensors HAVE to
give more recent information. Passive sensors obtain information from
the target's emmissions, thus the information that they obtain has
travelled one way (in space, at least, probably at the speed of light).
Active sensors, on the other hand, work by bouncing something off the
target, thus making a round trip (again at the speed of light). I'm
having some difficulty imagining that a round trip at a given speed is
faster than a one-way trip at the same speed. Maybe someone else could
explain this.

-Brian Quirt