Focus Focus Focus

Lasers.

Light is bound by inflexible rules.

Luckily, GURPS:Traveller is kind of miracle tech.

The standard TL10 turreted laser is 250MJ and X-Ray in frequency.  The 1/2 range is listed as 17,000 miles with a max range of 51,000 miles.

Taking the mean of the frequencies (0.010 to 10 nm) a 1.5m lens gets us a 0.22m spot at 17,000 miles and a 0.67m spot at 51,000 miles.

We chose a 1.5m lens because most of the art-work shows a turret that's about 1.5m tall, so that's the largest lens we could honestly mount.

The discharge rate is one second, so our 250mJ is 250,000kW.

Our one second pulse puts 6,415.78 MW per square meter on the target at the 1/2 damage range.

That's a lot.  Enough to get through 4" of steel (DR 280).

Taking it out to max range...

We only have enough energy delivered to punch DR 33.  This is because we're putting the same energy over a larger area.

Oops, that's the TL10 turreted laser listed in GURPS: Traveller Starships.  The TL10 laser from GURPS: Traveller (main book) is 360 megajoule.  Its 1/2D range is 20,454 miles giving it a spot of 0.27m diameter.  It plunks 6,381.94 MW per square meter and can punch four inches of steel in a one second pulse.

As an aside, changing the diameter of the lens to 1m changes a lot.  For the 360 MJ unit that increases the spot size to 0.4m drops the beam intensity at the target to 2,836.42 MW per square meter and drops penetration to a mere 1.86" (130 DR) at maximum range the diameter of the beam is 1.21m and delivers enough power to penetrate 0.2" of DR 70 per inch steel (or DR 14).  The 250MJ laser spot increases to 0.33m in diameter and drops to 2,851.6 MW per square meter and a bare 1.87" of penetration (131 DR) and less than 1/4" (14 DR) at the listed maximum range because the spot has spread to 1m diameter.  Those numbers tend to line up better with the listed DR for ships and their dice (6dx50(2) for the 360MJ and 5dx50(2) for the 250MJ), the real difference is the the 360 gets 3,454 more miles.