Originally Posted by Whyte
It depends on the hows:
1. How big is your setting?
2. How quickly do you want the PCs to be able to get from planet X to planet Y?
3. How much time does the jump (or recharge afterwards) take?
4. How often do you want them to travel?
5. How important is travelling to the campaign: is it an adventure on its own, or will it be simply skipped?
Since you wish to tie it to the star mass, it implies to me that you do want the travelled distance to matter. Stellar masses are roughly from 0.1 Msol to 100 Msol, with the massive stars very very very very very rare. In practice, most of the stars that the PCs would ever visit would be in the 0.1 - 1 Msol bracket (earth-like planet's host star would probably be even closer to something like 0.7 - 1.3 Msol, so you get very very small range if you focus on 'typical' space opera planets), with stars more massive than 3 Msol or so being so rare as to not really matter for campaign planning (save perhaps as a military base, see below). Since the more massive stars are very unlikely to host habitable planets and they are so rare, any benefit you might gain from a longer jump is negated by the need to travel there, first.
One way to make the big stars matter would be to make it jump-time always a fixed length, regardless of the distance jumped, and make the distance x*(Msol)**2 (factor times mass squared). This means a star of 10 Msol would have a jump distance 100 times more than a normal sun-like star, which would definitely make them more desirable, almost like wormholes in other scifi (Honor Harrington comes to mind). The squared mass also means that the smallest red dwarfs might stay uninhabited or even unexplored, since they might be too far from another star to get back to it with a jumpdrive: say 0.1 squared is 0.01, and if the distance to the nearest other star is about 1 parsec, you need x = 100, or that star becomes a dead end for FTL.
So, lets say that the jump takes a day, your setting is 1000 parsecs across, and you want your PCs able to travel that in a month. In other words, you want 30 jumps to cover that 1000 parsec distance, which means each jump should be about 33.3 parsecs. Since you probably have suitable 1 Msol stars within that 33.3 radius that are more or less along a straight line, that would imply to me that something like x = 50 parsecs would be fine, allowing for a slight fudge factor. Note that if you use the squared mass, this means if you have a 5 Msol star somewhere in your setting, they can reach any point of your setting in one jump: 50*5**2 = 50*25 = 1250 parsecs. Makes for a very nice place to have a fleet presence at, so that you can reinforce any part of your empire in a day (from when you hear that something is wrong, which might take longer). Such higher mass stars would become nexi for high-speed interstellar travel, funneling trade through them. Which has a nice 'geographical' result for trade patterns, meaning you have more 'neglected' systems farther away from the high mass stars, where tramp freighters might ply their trade.
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