Put another way: at Earth's orbit, the Sun's gravitational pull is roughly 0.000006 Gs; and it gets much worse the further you travel from the sun: at 10 AU (roughly the orbit of Saturn), you'd have to toss in two more zeroes ahead of the 6. If your spacecraft are averaging significantly more than that over the course of a trip, then the Sun's gravity is a non-factor on the spacecraft's path; even a lethargic 0.01G would be enough to swamp the Sun's gravitational pull just about anywhere in the Solar System.
It's only when you're dealing with drives with _very_ low accelerations and/or very high fuel consumptions (forcing them to drift for most of the trip) that orbital mechanics become a factor in spacecraft trajectories. That pretty much confines them to modern chemical rockets (high fuel consumption) or solar sails (which lose thrust at the same rate that the Sun loses its gravitational pull). I'd say that in any mature space-faring culture (as opposed to an "early days in space" setting such as contemporary or near-future Earth), you can pretty much ignore orbital mechanics with regard to spacecraft trajectories. Even the Transhuman Space setting has good enough propulsion systems that you can usually ignore the sun's influence when using them. And then there's what I was saying in my original post: unless the spacecraft's travel time is a significant fraction of a planet's orbital period (say, at least 1%), said planet will not have moved appreciably in the course of the trip; and unless the travel time is even longer than that (say, on the order of 10% - a month or so for the Earth, and substantially longer for the outer planets), the curved nature of the planet's orbit won't be an important factor, and you can treat it as if it was moving at a constant speed in a straight line. As such, the orbital motion of the planets is only likely to be a factor for the innermost planet or two of the system - again, assuming decent performance characteristics for your spacecraft. And when you're dealing with the inner planets, bear in mind that the closer they are the Sun, the less distance they move overall; for them, orbital mechanics are probably going to be at least as much about matching their velocities as with matching their positions. -- Jonathan "Dataweaver" Lang _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
