Spaceships battle - Autonomous Kill Vehicle raid on a tanker

Just ran a GURPS 4E spaceship test combat. I didn't rig the dice: but the outcome to such combat tend to be decisive, brief, and scary.  This combat ends with a critical hit: not a great sample combat. Sometimes, dice just don't cooperate.

Setting

An ageing Lewis-class Heavy Space Transport Vehicle registered as HSTV Mook is approaching a belt station with a hold full of solid-phase water.  It has decelerated and is near its 10% margin of error delta-V store (10 mps left ). It is moving at mere 1.5 mps relative to a small asteroid from which a rogue butterfly Autonomous Kill Vehicle (AKV) is waiting in ambush. The intended path places the asteroid in within 1.5K miles of the path of the HSTV.

Step one: Find out the detection range when the AKV becomes aware of the target. Roll 8 on sensor check: it spots the target at a range of 5LS (~1M miles).

The AKV is fully aware of the approaching giant robotic tanker at about 1 million miles. It knows from its database that the target's defensive lasers systems will be weak in short range. 

Step two: Let's determine the range of detection for the HSTV. The Mook has Sensor/7 and is scanning for danger in the asteroid. It rolls 12 and gets Long range (10K miles). The initial state of the engagement will be:

Time: 0 min; Range: Long; Aspect: Front; Scale: Close; Turn: 10-minutes; Velocity differential: 1.5mps;

I picked this scale and turn length because the acceleration bonus is set to 0.01G/0.03mps. This allows the AKV 18 meaningful thrusts increments while the HSTV has a large number of single thrust per turn to fight it out. At detection range, there is simply not enough thrust to avoid the combat even in the standard scale. However, the 1.5mps differential indicate that this will be a fast pass.

The HSTV detects the AKV and has to make a hard choice: accelerate and hope to survive the AKV's brief fire, or maneuver. Either way, the HSTV is going to have to dig into its emergency margin of reaction mass. The captain of the HSTV decides to try its luck in order to stay on schedule and enter the defensive perimeter of a nearby port.

Time: 83 min; Range: Long; Aspect: Neutral, Front; Scale: Close; Turn: 10-minutes; Velocity differential: 1.5mps;

The HSTV decides to perform an evasive action. It turns to face away and applies 0.03mps (9.97mps left), thus giving it a +1 dodge bonus and presenting a rear aspect. The Gunner opens fire with very rapid fire 3MJ laser. 

Gunnery(beam)-12, SM+6, range -12, 3000 pulses +11; 6 vs Gunnery(Beam)-17. Critical success (no dodge). 

Effective 300KJ at half effect due to range: 4 dD of damage.

Hit Location (AKV front, 28 dDR): No damage.  

The AKV knows that the HSTV will be passing through the engagement area very fast. It decides to use a nominal amount of delta-V to match the HSTV vector and cancel the fast pass status (0.05mps removed, 0.5mps left).  

Gunnery(rail)-12, SM+10, range -12, 30 shots @ 3mps +5, sAcc -7; 3 vs Gunnery(rail)-8 critical hit (no dodge).

Shot 1: 1890 dD, fatal fuel tank shot (more than -10XdHP).

Shot 2: 2310 dD, fatal fuel tank shot. 

While the HSTV fire pulses of laser, weakened by distance and ineffective against the AKV's diamondoid armor, 30 electromagnetic 14cm projectiles are fired from the AKV. Two of them hit the HSTV rear shred through the ship completely.  The debris from the HSTV continue on toward the port at nearly 1.5 miles per second. The AKV determines that it cannot intercept to salvage and enters the "relocate for new raid" routine as it is down by some reaction mass and most of its electromagnetic gun ammunition. 

Insights

Laser were next to useless, so the AKV took a gamble and shot the heavy stuff. The critical success was enough to get two shots in despite the recoil. A single 14cm railgun projectile, hitting at 3mps, clearly will do terrible things to a realistic spaceship. I think that the captain of the HSTV should have maneuver out of the combat area using the delta-V reserve during the 83 minutes after detection but before the engagement began. Since the AKV only has 0.55mps in reaction mass, a chase was not an option.