Recommend clearance between spaceships

[Vormaerin]

Well, the rules vary on that. The JTAS article suggests a successful astrogation check gives a variation of around 3000km per parsec traveled. The rules in the companion generally are generally a variation of around 5 to 20 diameters of the target world, which is rather larger in most cases but not dependent on distance traveled. If you can't control at least the target world you arrive near, then microjumps are no longer a thing.

There's no evidence you can leave jump space inside or otherwise in contact with a real world object that I am aware of. So that's not really the concern. At most, your risk is appearing in the flight path of someone who doesn't have time to react, but that's extremely low likelihood.

However, people don't create jump arrival zones for the primary purpose of preventing collisions. It's for safety and control. The local navy can keep an eye on that area with targeted sensors and possibly nearby ships on station. If ships arrive outside those areas, that can be considered suspicious. Either they misjumped (and probably need help) or they are trying to avoid the normal route for some reason.

Of course, all that assumes you actually have some kind of authority like the Imperium to do that. If you are playing in the Reaches and every planet is a separate nation, there would be rather less of that despite attempts at treaties and whatnot.

 

[Rel Fexive]

"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. Listen..."

 

[DigrizJB]

I would postulate there's a generally accepted rule for approaching a planetary body - inbound traffic below the equator, outbound above the equator, once you're within 100 diameters. Put the designated traffic routes there, where orbital control manages traffic in systems with sufficient technology and traffic. And if you're going the wrong way due to damage or fuel limitations, turn on you hazard blinkers, i.e. repeating broadcast.

 

[Marc]

Orientation would matter.

You'd want to be right side up.

LOL,
In space there is no "right side up", IMO.
I feel it's more of a Batteries Bearing" based orientation

 

[phavoc]

Departure times are predictable.

Arrival times are estimated, assuming an ecks boat precedes it.

Arrival worlds will only ever know scheduled departures - estimates really. Travel time is +/- as always. Basically ships are expected to arrive within a relatively large window. And that window multiplies as more jumps are added to the ships schedule.

 

[phavoc]

I wouldn't think the departure and arrival zones would be the same. While a navigator can "aim" for any point in a system that isn't shrouded, I agree that standardized regions for trade purposes are the norm (especially given how jump tapes work). This just has huge advantages for trade, like being able to put a fighter base on the periphery of these points instead of needing to have a 360 degree coverage of the homeworld at 100D.

The precipitation rules generally suggest you can't come out of jump on top of someone and minimizing any arrival collision risk from coming in close to someone is likely why merchants tend to jump with a 0 vector.

Only the most important worlds are going to have more than a couple ships arriving or departing at once using the trade rules. Only the largest trading ports (like Mora) would expect to have even as many as 10 ships arriving in a given hour.

The volume of space at the 100D level is huge. The arrival "slot" or 3D area is controlled by the departing world - ships will depart in real time there, and each ship's arrival zone is incremented by one (i.e. Ship A gets arrival zone one, Ship B jumping after it will get zone two, etc). The number of zones for each world would be dependent upon normal traffic between the two, with a healthy safety margin. Slots can be updated as traffic grows and the navigational information distributed at any time. Even with jump delays there's still plenty of margin of safety available to logically make it work.

If we hold to the classic CT article that ships will retain their velocity and heading leaving jump space as they do when entering it, civilian ships would be the ones most likely to slow or come to a relative stop before jumping - at least under normal circumstances. If you want to dig further into that concept, then arrival points would always be in front of the planets orbit since you can combine your velocity with the planets to shorten the duration, just as departure would be trailing the planet since you also get to combine the planetary orbital velocity with your own to get to the 100D limit. Though that isn't always practical, depending on your destination and any planetary bodies/asteroids, etc for your straight-line path from origin to destination. If you go too far down that rabbit hole you may have ships accelerating for a day in order to get a clear vector to your destination. There's no way to model that in a game, so it's fine to discuss, but it has no impact on gaming. Which is as it should be really.

As far as the number of ships... that's always been a good question and never has there been a good answer. Should we use real-world modeling for that? If so, the numbers might shock people. The two top maritime ports in the world are Shanghai and Singapore. Shanghai services more than 2,000 container ships per month. And, by tonnage at least, about 20% of the overall tonnage shipped worldwide transits through Singapore. And those are just the two top ports. A busy trade world in Traveller should see more than just a few ships per day - especially since it would include all sizes of ships that the data for major ports doesn't even cover.

 

[phavoc]

I'm not at all convinced that you can predict your arrival location to any level of precision, given the vast distances involved. You're just counting on the incredibly small probability of arriving where another ship is.

That's always been a question - how close CAN you predict your arrival point? Would velocity affect the arrival location error? Would the distance of the jump? The TL of your navigational computer/software package? If you arrive within a few hundred km of your plotted point is that considered a great job?

None of these questions is answered or addressed in the core materials that I can recall. And they would matter if you were doing an escort mission or more than one ship is jumping and expecting to arrive close to one another. I've always assumed accuracy would be a good thing to shoot for, thus a few hundred kilometers from your planned arrival point you are on the mark. For a ship capable of 1G thrust, that's a relatively short distance to cross. Being off by tens of thousands of kilometers seems a bit much to me.

For the idea I came up with, each arrival zone is 50,000km on a side (it's a pretty big cubic area, but still tiny at the 100D limit). And yeah, the odds are small, but accidents happen all the time, hence a society develops safety rules so that you don't have to roll the dice all the time you travel. It seems like a fairly reasonable concept to me for an interstellar society to implement. Humans are infinitely capable of being stupid and careless and I don't see that changing in the 52nd century.

 

[Anstett]

One thing that strikes me in this discussion. For regular freight large scale traders you can expect that they will show up every 14th day with a load of goods.

But the tramp traders will show up randomly both in time and from random systems (within reason). So should there be different arrival zones for the two (and a third for Naval/Scout bases) different types? Then what about random Noble yachts showing up?

What sort of regulations get promulgated and what are the consequences of not following them?

I am in agreement with @phavoc that some systems will have hundreds to thousands of ships entering and leaving (mostly in Core but some other Type A ports too) daily. From a different thread there should be some sensor networks to detect not just stealth but all the traffic swarming around.

 

[Condottiere]

You could auction off approach and departure spacetime lanes, the more convenient, the higher in demand.

Failure to follow assigned lanes would result in fines.

 

[phavoc]

One thing that strikes me in this discussion. For regular freight large scale traders you can expect that they will show up every 14th day with a load of goods.

But the tramp traders will show up randomly both in time and from random systems (within reason). So should there be different arrival zones for the two (and a third for Naval/Scout bases) different types? Then what about random Noble yachts showing up?

What sort of regulations get promulgated and what are the consequences of not following them?

I am in agreement with @phavoc that some systems will have hundreds to thousands of ships entering and leaving (mostly in Core but some other Type A ports too) daily. From a different thread there should be some sensor networks to detect not just stealth but all the traffic swarming around.

I had thought about that and came to the conclusion that this has to be controlled by the system where the ship is departing - the system where the vessel is arriving will have no foreknowledge of unscheduled craft - especially tramp freighters with no regular schedules, private vessels such as noble yachts, even military ships.

So the easy answer is to have pre-determined arrival zones, and have port authority assign it to each departing vessel in a sequential order. Assuming System A has 100 ships/week normally travel to System B. So ship one is assigned arrival zone 1 in System B, ship two is assigned zone 2, etc, etc. Since it takes 168 hours +/- (or a max of 185 hrs, 4.6 days), you can safely assume that the slots could be reused after five days. All of this is based on averages, and ships may see more ships depart on specific days for various reasons. In any event each planet would have a healthy number of slots assigned for usage before they'd reset their counter for safety reasons. System A may have 100 departures/week to System B, though it may have 200 arrival zones assigned to it just to to ensure safety.

Systems that have very little traffic (and may have very little port control for departures or arrivals) would just be assigned a large arrival zone, and ships make transit to the busier system with the expectation that they arrive somewhere within the zone to avoid fines for arriving somewhere they should not be. Navigational data for the entire Imperium could be kept in every ships database, with updates distributed regularly along with normal navigational chart updates. No pilot could claim ignorance since the data is widely available.

Somewhere I wrote this all up (sadly I'm not the best 3D illustrator). In theory it would work for any system, allow for orderly civilian traffic and allots space for military arrivals/departures as well in their own reserved zones.

I did it mostly as a "what if" exercise, trying to figure out how to bring some possible order to chaos. Random arrivals annoy me because it just doesn't seem like how an advanced space-going society would work. Plus it would make more sense if there WAS some sort of system to make piracy more of a believable way for a pirate ship to stooge around the outskirts of a planet and actually have a chance of finding a ship popping into n-space. Otherwise it seems statistically impossible that a pirate would ever be able to bag a ship arriving in another system.

 

[MonsterX]

From the perspective of collision avoidance, it would be better to NOT have a specific arrival zone, because having a specific place where ships are required to jump into will INCREASE the chances of collision (from virtually impossible, to a little bit less virtually impossible, but still.) It would be different if you could space-traffic-control their arrivals, but you can't since they just pop into existence faster than the information about their arrival arrives. Even if you happen to know when and where they intend to arrive, the actual time and location of arrival is only approximate. Spreading out arrivals as much as possible would be the best policy, but impossible to organize given the speed of information, so random is the next best thing.

Having specific zones where arrival is NOT permitted makes more sense - high traffic areas around space stations, areas where the fleet has secret testing etc.

On the question of "keeping" the vector from the departure system when coming out of jump space - this is something which should be resolved in the rules somehow. Stars do not all travel at the same speed or in the same direction (although there is a general trend to circle the galactic core moving spinward) - the differences in their velocity can be in the 10s or more unusually 100s of KPS.

If we assume ship's DON'T retain velocity, then what does that even mean (given that velocity is always relative)? We have to assume they do, so that when they jump they keep up with the galaxy and galactic cluster. The Milky Way is moving about 600 KPS - if we assume they don't keep their vector, a ship would always enter every new star system with a big vector relative to the star system itself and other nearby star systems, which would be weird, and not very fun.

So when they exit jump, they will have whatever vector their departure system had, plus whatever other vector they had from moving about in the lead up to the jump - at minimum they will have the velocity of that star relative to the destination star, and their orbital velocity around the departure star. If the ship has been accelerating at 1g for 1 hour before jumping, that is 36 KPS in some direction or other relative to the departure star. If they've been accelerating all day , it is 864 KPS. While normal Traveller ships can handle these things pretty easily - they have massive delta-v for their M drives - entering jump space with a desired vector in order to have the right vector on arrival would have to be a normal part of astrogration, and implies moving in a certain direction in the departing system before leaving in order to optimize the travel time to the destination world.

From a play perspective, it is probably best just to randomize and abstract all this as part of the astrogation role. Role well and you will arrive quickly, roll poorly and it will take longer.

 

[Condottiere]

1. Moving target.

2. Does require some coordination between neighbouring systems, as there's an agreement that any particular starship jumping in their direction at a particular time, aims to exit at a particular location in relation to the planet, that will, of course, constantly but predictably change.

 

[Jame Rowe]

In atmosphere and orbit, similar clearance as planes.
In space, no one can hear you scream ...  cough at least 1000 km.

 

[Vidgar]

Thank you all, I agreed with many of you.
My Imperial rules are arriving ship jump in the Arrive Zone 100+ dia above the planet ("North" pole ) and departing ships leave in the Depart Zone 100+ dia below the planet ("South" pole). With larger ship jumping in 105+ dia or 110+ dia. This would remove the "accidently" squashing of a 100T Scout by arriving 500,000 Ton Tigress-class DREADNOUGHT.

My original question was on the safe distance between ships when passing (overtaking/head-on) in unpatrolled space between planets. Unless I made an error, Sensors and Weapons only work out to 50,000km so a safe distance is 51,000km.