House rules for GURPS Traveller Interstellar Wars

These house rules solve small problems spotted with certain aspects of ISW.

Repulsor house rules

Repulsors are a key to understanding the use of beam weapons in the Traveller universe. As per ISW p.227, one repulsor array gives +15 to dodge a missile. But what about using multiple repulsors, and what about using larger objects than missiles? The following two house rules answer that question.

More than one repulsor array at the same target

In order to use more than one repulsor at the same target, take the square root of the totalnnumber of repulsors and multiply it by 15, and then round off to the nearest whole number. Thus, one repulsor gives a bonus of +15, two repuslors give +21, three repulsors give +25, and four repuslors give +30. Five repulsors would give +33, and thus this would probably the highest number of repulsor arrays used against the same attacker on any warship, since any further repulsor gives only a very tiny bonus compared to the energy spent.

Repulsors against larger objects

If an object that is larger than a standard missile tries to ram a ship protected by repulsor arrays, consult the following table and find the total number of dHp of the attacking object - if an object's dHP all between two categories on the chart, use the next higher valure. The other number given in that line is the total reduction of repulsor dodge bonus for that attacker.

dHP of ramming shipReduction of the repulsor dodge bonus
20
31
42
63
94
135
186
247
368
549
8010
12011
18012
27013
40014
60015
120016
1800 or more17