Onno Meyer wrote: > Hello Hal, > > I'm not supposed to do any programming on my vacation, but a > little design can't hurt :-) > > * Will your program be two-dimensional or three-dimensional? > The error of pressing everything into the ecliptic rivals > what you get from circularizing orbits, so if you do one, > why not the other? >
Orbital inclination is not addressed in GURPS Space; so Hal would have to wing it. Possibly adapt the guidelines for determining a planet's axial tilt for this? I'm assuming that precession of the orbit is going to be ignored, as you have to be _really_ close to the Sun before it is at all noticable. > * There might be four of five kinds of object on your map. > > - The sun, at the center of it all, as reference point. > - Planets moving around the sun. > - Possibly moons moving around the planets. > - Constant-acceleration spacecraft, with an accel stat. > - Variable-acceleration craft, where accel changes over > time and delta-V is limited. It might be possible to > to ignore time spent accelerating, and to assume an > instant vector change followed by coasting. > > I'm ignoring solar sailers, interstellar rocks, etc. > Heh. Do note, though, that because thrust from magnetic sails falls off much more slowly than gravity does (4/3 power vs. 2nd power, IIRC), even their meager thrusts end up swamping the Sun's gravity by the time you get to the outer system. But yeah; figuring trajectories of craft whose thrust depends on distance from and orientation relative to the Sun is not something to be thrown in lightly. > * There should be a "tabletop display" with a zoom function > and a clock which can be slowed, stopped, accelerated and > reset. > > * The position of the planets could be calculated like that > of a coasting spacecraft, subject to the gravity of the > sun, and moons could be coasting around their planets. > > As mentioned, that is probably overkill. Have the planets > move on a circle around the sun, and the moons move on a > circle around the planets. They move with the clock. > Well, ellipse; not circle. But yeah. > > * For spacecraft, the first stage of the project covers > movement from one planet to another. Enter start time, > accel or delta-V, and the destination, and the system > calculates a flight plan. This is shown on the tabletop > display the same way planetary orbits are show, with > hash marks representing time. Probably ships get a > smaller time scale, and different hash marks. > > * Really useful, and really difficult, would be various > "intercept calculator" options -- ship A moves from Mars > to Ceres, can ship B from Earth make an intercept or > even rendezvous? If so, where and when does it happen? > > I'm using intercept to describe "same place, same time, > different vector" and rendezvous for "same place, same > time, same vector". > It gets messier when the ship being targeted sees the incoming craft and decides to evade. Hello, strategic space combat simulator... > That sounds like something like the running example/exercise > for a semester-long course Object-Oriented Programming 101. > Indeed. Considerably less ambitious, but still valuable, would be something that merely tells you where all of the planets and their satellites will be at any given time. I'd revise things later to include transfer orbits (launch and arrival windows), then perhaps steady-thrust trajectories and eventually space sails. (I am not a fan of the plasma sails that Transhuman Space posits: the whole point of sails is that you don't have to worry about fuel, and the need to keep a plasma sail's plasma replenished as it inevitably leaks out pretty much kills that point.) -- Jonathan "Dataweaver" Lang _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
