“Ship encounters may be made an easily included part of adventures by abbreviating the movement requirements. In essence, when an encounter occurs, shots (if they occur) are traded without regard to range initially. When one vessel elects to flee, the referee then states that a certain number of shots may be made before the ship is out of range.” – Traveller, Book 2
From the beginning, Traveller offered a range of options for space combat. Although most of the combat rules were geared towards models on a tabletop – unusual considering that personal combat is largely abstracted – you could play on graph paper or using the abbreviated movement rules above.
I tried all of them at various times, and spent a lot of time calculating intercept courses and times for typical engagements which in hindsight would have been better spent on my college coursework; but the abbreviated movement rules work fine for the average roleplaying session, so why use anything more complex? Unless you have a 170 foot table or a seven foot piece of millimetre graph paper, you won’t fit most of the ranges in anyway – short laser range goes up to 150″, which is 12′ 6″ on the table or 6″ on the graph paper, so most of the time the only DMs that come into play are those for computer programmes and obscuring sand.
So, in my opinion the abbreviated movement rules are the way to go. (Periodically I think “I should use Savage Worlds because the abstract chase rules work better than this tabletop stuff.” Then I remind myself, “Oh yeah, Traveller already did that.”)
That begs the question, how many turns are combatants in range before the fight ends? My view was that most engagements would involve a craft with 1G acceleration (Types A, M, R, Y) somewhere near the main world of a system, as ship encounters occur when you’re leaving a world or arriving there. Consequently, the limiting factor is when that ship reaches either the surface or the 100 diameter limit, which won’t take more than 45 turns at 1G (time for a zero-zero intercept of something a million miles away, which is the jump limit for a size 10 world).
Anyway, 6D turns seems a reasonable approximation, and to be honest most space combats don’t last that long; a single laser hit has about a 10% chance of crippling your ship, a single missile hit has about an 80% chance, so the odds of surviving 20 turns of shooting from an attacker are not good, even in a Type C, which is the toughest ship in the game.
The weak spots are the power plant and manoeuvre drive, and only the Type C has high enough drive letters that it can take more than one hit there without being immobilised. So unless you’re driving a cruiser, if you’re unarmed you seriously consider surrendering or dumping your cargo and hoping the pirate goes for that instead; and if you’re armed a warning shot should realistically make most pirates think twice about pressing an attack against you.
Usually, PCs are operating a ship with drive letter A, and once that has been hit you’re facing a multi-million Credit bill to replace it, assuming you don’t crash into something or drift off into the Big Dark and asphyxiate.
How much is your cargo worth again?