To extend the above answer, combat should be treated similarly to ship construction with several levels of complexity based on the nature of the conflict.
At it's simplest, an RPG level movement/combat system should be able to handle questions like "if the pirate takes off an hour after I do and has 3G thrust to my 2G, how many shots will he get at me before I make the Jump horizon?" Complex? Yes, but VERY much an RPG-scale situation, and one that shouldn't bring a game to the 45-minute halt it often does.
You should also be able to determine a large space battle quickly (by something other than fiat, if necessary), but be able to tell the hapless PCs how much of the battleship around them is left when the power to their brig cell fails...
At the same time, whole-day naval affairs should be possible, possibly as single battles or as week-long system-wide invasions. Gamers are a varied bunch, after all.
Of course, part of that variation arises as "what is Traveller?", and that is the toughest part of the design process. Tuning ship design, movement, and combat to a particular ideal is fairly easy. Making it work for everyone is tough.
