The problem here is that with the exception of Anthony's pre-worked out planetary location table, and that from TRANSHUMAN SPACE, there aren't many options for GM's who want that sort of thing for their campaigns. And while in the scope of game play, travel times that are months at a time using "rules of thumb" that tend to be generic and also tend to require the GM to estimate just how far away the planet is/will be when the player character captain points their ship and says "Onwards navigator", there isn't anything to actually GUIDE the GM. Sure, the max distance from a planet and the minimum distance from a planet to another planet is better than nothing, but it doesn't exist for use of GM's in made up star systems or for planets actual locations to where the GM doesn't have to say "Today, the planet is about 75% of the max distance, but next game session, I might decide that it is 50% of the max distance - without any real notion of where exactly the planet is for real.
I guess that is the ONLY real benefit for the Virtual Table Top concept. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jon Lang Sent: Tuesday, October 11, 2011 10:08 AM To: The GURPSnet mailing list Subject: Re: RE: [gurps] Planetary movement and checking the Math 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 _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
