I agree with Leonard. A world with any kind of significant population and sufficient technology is going to regulate ships in nearby space very, very tightly.

I would imagine it looks a lot like civil aviation in the US today. A private plane can fly pretty much where it wants to when far from any major airport, but the closer you get to one, the more rules there are about allowed behavior. At some point you have to contact traffic control and do what they tell you to do. So by analogy, a Free Trader way out in the Oort cloud, or even in unused parts of the inner system, can do whatever it wants to. But get within a few light-minutes of the mainworld and all sorts of rules kick in.

One rule that probably does apply throughout the system is that your velocity vector may never be aimed such that, if you lost power at that moment, you'd impact something important reasonably soon. In the outer system, violating this rule will probably just result in nasty messages from traffic control. Nearer the mainworld, you probably get one warning, followed shortly by missiles.

For docking, I'd actually expect the process to be automated; you hand over remote control of your ship to the station's computers, and they guide you in. This being Traveller, you'd have sophonts closely monitoring both sides of this process. Or for even more age-of-sail flavor, require that a sophont "harbor pilot" physically board the inbound ship and take over for the final stages of piloting it into port.

On Tue, Jan 23, 2018 at 10:35 PM, Caleuche <xxxxxx@sudnadja.com> wrote:

Then the computer can just run that forward to determine the
positions when the players visit.

Given that interplanetary travel is pretty much "point and shoot"
with multi gee constant acceleration drives, all you need to do is
figure out the positions to get the distance, which won't change
significantly during the trip.

We do this thing from time to time (actually, our Traveller games don't resemble what you guys play at all, ours tend to be setups of situations where we attempt to nail a ship-to-ship railgun shot - which isn't easy and interplanetary flight is a typical thing too)

Here's our good ship Hamiltonian, in orbit of Home which conveniently has no moon, is earthlike in mass, and has a system with a single gas giant in it (named Hot chi). Hamiltonian can accelerate at 9.81 m s^-2. The following plot is to scale and advances at 1 day every 8 seconds, presuming your browser's motion gif player respects playback at 24 fps:

https://i.imgur.com/vKzsx5I.gifv

After 10 days in orbit (only the last day in stable orbit is plotted), Hamiltonian breaks orbit at 1g, line of sight for Hot chi. Home is in a fairly similar to earth orbit at about 1.05 AU semimajor axis, and this is hot chi:
Eccentricity 0.0029896
Semimajor Axis 1651939205556 meters
(AU) 11.0425 astronomical units
Inclination 0. degrees
Longitude of the Ascending Node 354.386 degrees
Argument of Periapsis 3.22045 degrees
True Anomaly 357.251 degrees

Distance between Home and Hot chi at the start of the flight is 9.98456 AU. Time until turnover is 390208 seconds, and total flight time should be twice that (and characteristic energy at that point is a terrifying 7.3 * 10^12 J/kg - hyperbolic excess velocity 3.82 * 10^6 m/s - about 1% c).

Pretty fast, however, we cannot ignore Hot chi's own velocity. In the 9 days, 46 minutes it takes to reach the point that Hot chi was at the start of flight, it has moved 0.0469 AU, or 550 Earth Diameters. As you mention, you can compute where Hot chi will be in 9 days (if you are in a predictable system), and that gets close enough (or your players just come to rest relative to their destination and then fly a second leg to their destination, but that doesn't seem as elegant).

It doesn't work for railgun shots when your target is in orbit of a planet, though, and it's a relative of the same problem. You have distance to your target, compute flight time of the railgun shot, then compute where the target will be after the railgun shot flight time, which is a different distance and therefore a different flight time for the rail gun shot and so on. The problem is not hard if your target is not in orbit and your shot is not influenced by gravity, but I'm not really sure how to approach the problem in a closed form way for the situation that the target is in orbit.
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