Re: Sensors

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On Wed, 30 May 2001, Ryan Gill wrote:

> >At 7:17 AM +0200 5/30/01, Derk Groeneveld wrote:
> >[snip]
> >But as for actives being a little pen light, well, I'm not sure I
agree.
> >Active _tracking_ is a little pen light, but active search sensors
are
> >more like a whopping wide beam.
> 
> Thing is, unless you are talking about the SPY Phased array systems, 
> most are distinct systems. The general search not being very good at 
> figuring accurate range and height (in the Anti-air role).

Accurate _height_ I'll grant you. But with modern multi-beam radar
(which
is a bit of a misnomer, since they still use one big transmit fan, only
creating the multibeam in receiving), they get a useful height
measurement. As for figuring accurate range, search radar can give you
a range measurement of approx. 100m resolution. Good enough until you
have
to direct gunfire. And then you need a tracker to have a sufficiently
high
update rate, anyway.

Oh, by the way. SPY sure isn't the only phased array system anymore. And
I
think there's interesting challenges for SPY out there, as far as
capabilities go, as well ;)

And yes, on most configurations search and tracking radar are seperate
systems. All I'm saying is that actives don't have to be 'little pen
lights'; that only applies to actual trackers.

Also, I don't see a reason why a phased array couldn;t make a wider
search-beam; just a matter of different phase shift parameters to your
array on transmission.

> >Mmmm. I guess you can use mm radar in space at a lot longer ranges
than on
> >earth; on earth atmospheric dampening greatly limits mm waves.
> 
> Lots less water vapor to absorb your signals.

Yup. I'm just trying to remember whether there are other factors that
would reduce mm radar performance, other than absorbtion.

> >I'm not familiar with Cepheid variables? As for
> >triangulation, with the ranges involved with space combat, I doubt
you
> >could do it with the sensors on one ship alone. I'm not familiar with
> >inferometric ranging, so I have no clue how that'd work for you ;)
> 
> Cepheid variables are stars that pulse regularly and are used to 
> determine how far objects are. They are a medium sized yard stick. 
> Distances being from inside our galaxy to the Amdromeda Galaxy or so.

Ah, ok :)
 
> Inferometry is where you use two widely spaced telescopes to give you 
> a much wider 'virtual' lens. The use of the Very Large Array in the 
> South Western American desert is an infero-metric array. Larger 
> arrays have been coordinated by tying the inputs for two (or more) 
> telescopes on opposite sides of the country or even the world at the 
> same time at the same targets. In radio telescopes and in opticals it 
> gives you a bigger "lens" to look through.

Okay; sound spretty much like what we do with phased arrays over here;
even if that's a whole lot of small transmit/receive antenna's spaced
not-all-that-far-apart.
 
> This larger lens allows a better clarity of the object. Figure two 
> ships operating at a great distance 10-20 MU's communicating over 
> tight whisker beam to coordinate their efforts. They'd get a very 
> good idea of what's there.

Does it allow for better 'clarity', or for more resolution at
cross-angles? Mmm.If this works anything like phased array, though,
you'd
need position info on your friendly ships, in the order of magnitude of
your sensor wavelength, or is this not as sensitive to phase shifts?
 
> > Given a good set of lenses you can determine ranges based on angles 
> between two prisms space a few meters apart over thousands of meters. 
> The distance of the Earths orbit (2 AU) has been used to determine 
> distances of stars in our side of our galaxy over tens of thousands 
> of AU.
> 
> Two Telescopes of about 40 inches across on either side of a 
> Vandenberg should be good for a few tens of thousands of kilometers 
> at least. When I want to shoot him, I zap him with a ranging laser 
> for final accurate distance and let fly with my big beams and torps.

But tens of thousands of kilometres isn't very far, in space? 

> In game terms this would be dealt with by two ships adding their 
> passive die rolls to see what the target is. If you really want to 
> figure it out, but it uses several ships to figure it out. I wonder 
> if range should play a part.

Mmm. I'd allow it for actives, as well.. More complicated, but not
impossible :) 
 
> (there are system now that can track a star and keep tracking a star, 
> why not a tight comm laser that can track to an object and back, 
> after all NASA bounces lasers off mirrors on the moon regularly).

Not a problem.
 
> >Also, the drives might have unique resonance frequencies etc? Sir,
we've
> >seen this ship before, it's .... Then again, there might be a wartime
> >tuning of this frequency to a different one than peacetime?
>  
> Yep, witness the way in which magnetic fields of US vessels is 
> manipulated upon leaving port.

Isn't this degaussing against magnetic mines? If not, I've learnt
something new again :)

Cheers,

   Derk
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