[gurps] [VEHICLE] of the week 731 ? Planetary Defense Battery

[Onno Meyer]

Anthony replied to me:

> > Call it up to -20 or -25 for a sub at 500m in the deep ocean or near the
> > bottom anywhere else - as the bottom depth and hence the maximum
> > dive depth goes up, the water becomes murkier, too . A ladar with 500 
> > miles nominal range should do the job if there is no stealth.
> 
> Not exactly. That -20 is an obscurement modifier; it stacks with range 
> modifiers. A 500 mile range sensor (scan 27) would have a minimum 
> penalty of -34 (-14 for 500 yards range, -20 for obscurement) for a net 
> modifier of -7, and that's if you already pretty much know the exact 
> position of the sub.

Initial detection comes from a radscanner, as mentioned in the first mail.
The ladar is required because a radscanner is not targeting-capable. 

Say my sub has a submerged weight of 2,500 tons, which gives a volume
of 80,000 cf and a size modifier of +8. With TL9 radical stealth and instant
chameleon, the signature is -5. 

Put the sensor into an aircraft at 4,000 yard altitude looking directly down,
and the distance/obscurement modifier is -40. (For more altitue, increase 
the sensor size accordingly.)

Size, range and prior detection add up to -41. A 5,000-mile sensor has a 
scan rating of 33, for a net -8. Sounds bad, but one step above the VE170
cutoff of -9, and that means highly skilled TL9 neural nets can try the 
roll. (A 500-mile sensor but no stealth would be -1, good enough for a 
mere human operator.)

Of course diving a few hundred yards more would make the required 
sensor completely prohibitive, as would a spot of deep, murky water. 

On the other hand, TL9 beam weapons could not penetrate that much 
water, either, so the sub would be limited to large missiles (by VE112,
they would need 1,000 miles direct fire range from 500 yards). 

Space defense subs would dance a deadly ballet, their general location
known, drifting up to fire weapons, thereby exposing themselves to 
pinpoint attack, then dodging down again to a depth where only other
submarines can reach them.

Going to TL10 and up totally changes the picuture. At TL10+, jammers
can affect ladar, and in Traveller meson guns become available. 

Last but not least, Traveller frowns upon robotics, so even at TL9 the 
sensor might have to be bigger to compensate.