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From fcrary@ucsu.Colorado.EDU (Frank Crary)

In article <C1D842.95p@law7.DaytonOH.NCR.COM> Brian Lane <NETOPRBL@ncsuvm.cc.ncsu.edu> writes:
>Let's say that two sides have somehing the size of a naval destroyer out in
>deep space somewhere. how close would they have to be before radar could
>pick the other ship up, how about passive sensors (what kind of sensors
>would they be?)?

Radar detection would depend on how much power one wished to put into
the signal: Range scales as the fourth root of power. A low power system,
similar to current aircraft systems, might range out to ~200 km. A 
higher power system might extend this to ~1000 km before power consumption
became unreasonable. However, you should also consider ladar: A radar-like
system using laser instead of radio energy. Such a system would extend 
range, but at the cost of a narrower region scanned (or a longer time to
scan over the entire sky...) The issue is also confused by the possible
developments of stealth technology over the 50 years you are thinking of.

As for passive sensors, the real question is one of observation time and
sensors: A modern astronomer, with a good infrared telescope, could
detect such a ship out to an unreasonable range (millions of kilometers),
but the search would take a few weeks to cover the entire sky. What
another warship (which, presumably, wouldn't have delicate, large
telescopes on board...) could do in a reasonable time, is a different 
question. The background is also improtant: If the ship wasn't in
deep space, but had a planet in the background (e.g. is it were
in a lower orbit than the searching ship), passive detection above
the planet's emissions wouldn't be realistic. I think IR would be
the best choice for passive detection, since a ship of the
size you suggest would have to use (and therefore, eventually,
emitt as heat/IR radiation) somewhere between tens of kilowatts and
a few megawatts. Worse, the most effective heat rejection systems
concentrate the heat: Instead of a 1000 m^2 area radiating at 250 deg
K (a cool, dim source), you might have a 10 m^2 radiator panel at
800 deg K ( a hot, bright source.) On the other hand, an unmanned
craft using little power would be very hard to detect passively.

>How close would they have to be to get an adequate fire
>control solution? (I assume the energy weapon they'r using (laser or some
>other energy weapon) would have a longer range than the fire control.)

Well, a pointing accuracy of 1 arcsecond is probably the best that could
be hoped for. For a 100m sized target, that would imply ranges of
about 20,000 km (i.e. well beyond active detection ranges).
Lasers, however, have another limit: Difraction. Beyond a range of
(roughly) the laser optics' diameter squared divided by the wavelenght,
the beam will start to spread and power will decrease as the inverse
square of range. (I.e. a 10 micron IR laser using 5cm diamerer wide
optics will start to spread after (0.05m)^2/(10e-6) = 2.5 km. Higher
frequencies do much better: A 100 nm UV laser from the same sized
optice would travel 250 km before spreading. Also, the laser is still
effective as a weapon after the beam begins to spread, but it's intensity
(and therefore the damage it would do) starts to drop off rapidly with
range.

                                                         Frank Crary
                                                         CU Boulder

From howard@netcom.com (Howard Berkey)

This is an interesting topic for many reasons.  To limit the scope a
little, how about trying to make some assumptions:

1.  There must be something to fight over

As Douglas Adams said, Space is a big place.  Really big.  Therefore,
the chance of an encounter in deep space should be relatively
small.  Most fights would probably take place either in orbit or near
a station or asteroid in orbit.  Another reason for this is that it's
relatively hard for large masses to leave orbit, and thus any defender
would be unlikely to spend large amounts of energy leaving the valuble
object they are defending (planet, station, asteroid) but would rather
let the attacker come to them.  They would also benefit from hiding in
a planet's electromagnetic/gravity/heat fields and thus defeat several
kinds of passive detection.

2.  Orbital velocities are large

And this means that ships would likely be closing on each other very
rapidly.  An obvious consequence of this is that kinetic weapons would
be very effective.  For example, a large number of ball bearings laid
out in your opponent's path would have roughly the same effect on his
ship as a claymore mine on an infantry squad.  It also meand that once
ships were commited to combat, disengagement would be difficult.
Another ramification is that it would be as easy for a frigate to kill
a battleship as another frigate, since all that really matters is
scoring a 'hit'.  Large ships would actually be at a disadvantage,
since the delta-vee required to move them would be larger.  For this
reason, I think ships would tend to be smaller.

3. Most seeker weapons would be nuclear

For obvious reasons, if a seeker weapon was to be used a large
warhead is a must due to the distances involved.  Large direct-fire weapons
would be impractical since they could be defeated by altering
velocities.  High-volume fire would be effective in a manner similar
to the ball-bearing minefield described above, so weapons similar to
Phalanx cannons in an offensive mode would be far more effective than
big guns.  This is another factor which favors small ship design.  And
a small ship could carry externally large numbers of nuclear guided
missiles.  Or submunitions.


Comments?

-Howard



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Howard Berkey						   howard@netcom.com
		"I AM the Lizard Queen" - Lisa Simpson
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