Thoughts on a TU w/o captal starships

[Reynard]

"so you don't know just where the starport is going to be."

As I said in the other post, those ship computers are very powerful to store and calculate known systems' orbital bodies and that includes a system's starport. Normal traffic plot a course to drop themselves as close to their target as possible usually the system starport. Since there are no hard rules for determining jump shadow, normal game situations assume plotted courses regularly avoid such shadow events. As everyone keeps saying space in a system is a big place. What isn't that big is where space traffic control wants you to be.

 

[Jeraa]

"so you don't know just where the starport is going to be."

As I said in the other post, those ship computers are very powerful to store and calculate known systems' orbital bodies and that includes a system's starport. Normal traffic plot a course to drop themselves as close to their target as possible usually the system starport. Since there are no hard rules for determining jump shadow, normal game situations assume plotted courses regularly avoid such shadow events. As everyone keeps saying space in a system is a big place. What isn't that big is where space traffic control wants you to be.

And you conveniently ignored the rest of that paragraph. You do not know how long you will be in jump space, so you don't have a clear idea when you will emerge, so you don't have a clear idea where the starport will be. The jump will take 148+6D hours. The roll of 6D will tend toward 21 hours, you can arrive as much as 15 hours before or after that time. You can arrive at the exact coordinates you wanted to, but because the time is variable and can't be accounted for before hand, the starport is on the opposite side of the world when you emerge.

Unless you are trying to say the the length of the jump is known beforehand, but that would be wrong. If the length of the jump were known before jumping, we wouldn't need the rules for synchronized jumps in High Guard. All ships involved could broadcast their jump length time to other ships and just jump at appropriate times so as to arrive together.

 

[h1ro]

Planets move on their orbits and move quickly. Given that time in jump can vary, the actual distance from the planet when you emerge can't be plotted. It's also why a ship should have to match the velocity of its target planet, not the one it's leaving. Best practice would perhaps be to plot exiting J space at the median position that the planet will be in at the jump exit window. With the ship at a velocity that matches the target planet, at least the distance you need to cover isn't going to be increasing.

ETA, Jeraa said pretty much the same thing I did and beat me to posting.

 

[Jeraa]

Also, arriving on the opposite side of the planet from the starport isn't a bad thing. You are already having to fly (usually) hundreds of thousands of kilometers to get to the planet from the 100D limit, so it isn't like a few more thousand kilometers is going to add any appreciable time.

Average world size is 5 (2d-2, average roll is 7 to 7-2=5). Mars is given as an example of a size 5 world. The 100Dlimit of a size 5 world is 800,000 kilometers. Mars has a circumference of a bit over 21000 km. You only need to travel half that at most (but would be doing so in orbit, so it would be more than half that). Still, 21000km is only a bit over 2% of the distance of the 100D limit. You add no appreciable time traveling in orbit around the planet compared to the time spent crossing the 100D distance.

In other words, arrive as close to the starport as possible is not needed and would give no real benefit.

Lets look at the worst possible situation. A size 10 world has a 100D distance of 1.6 million kilometers. The circumference of such a world is around 50000 kilometers. Again, you travel at least half that (as you are going only 1/2 way around) but even going all the way around adds no appreciable time compared to the time spent traveling 1.6 million kilometers to get there.

 

[h1ro]

To put some numbers to my post and using Earth as an example:

Earth moves on it's orbit at 29.6km/s

In one hour it moves 106,560 km

The jump window is 6d6 hours long. Minimum time 6 hours, maximum 36 hours. The minimum the Earth will move in the jump window is 639,600km, the most is 3,836,160 km. The average is 2,237,760km.

Earth is 12,750km in diameter, the 100D point is 1,275,000 km.

You can plot to exit J space on a stellar orbit parallel to the target planet at the median point and if you're lucky you will have just 1.275 M km to travel but chances are the distance will be greater.

In most games I've played the numbers are ignored and we just say the ship exits at the 100D point. I don't know of any rule in any version that talks about matching velocity of the target system, I am not fluent in the older versions so don't break your keyboard if I'm wrong, my context is almost always MgT and MgT doesn't talk about this stuff. Talking numbers in MgT is a big no no. It surrounds you and yet no one talks about it. It's ok, I get it, its a game we don't want to talk about numbers.

If you want to start introducing this stuff cos you think the space is crowded and there's a significant chance of hitting another ship as one or both exit J space, be my guest but really, there is more than enough space and most starports, even those outside the 3I, are operated by the 3I and this stuff will have been calculated to facilitate safe transit between systems. I really don't think we need to concern ourselves with it in a small ship or large ship universe.

 

[Reynard]

The jump time effect is commonly understood especially after many thousands of years. A ship's astrogator is attempting to plot the most optimal exit knowing about the jump time differentiation. With the amount of differentiation as a known fact of error of 149 to 154 hours, your computer virtually maps out all known object locations within that frame. You are not jumping blind. You will not be putting yourself in the path of the starport, let alone the planet itself, but you will be somewhere along the track of at or near the 100D mark. How often do you hear an exiting starship is not at the 100D if that's what they were aiming for? That's an accurate jump. A referee can mess with the party with an 'inaccurate' jump which is not a misjump.

"When the ship exits jump space after an accurate jump, it tends to arrive close to the target world, but outside or on the verge of the hundred-diameter limit. Inaccurate jumps dump the ship somewhere in the inner system, requiring a long space flight."

A misjump is far worst for both time and distances even at it's kindest results while even a inaccurate jump is merely inconvenient such as being on the opposite side of the target planet or near the orbit of Venus instead of Earth. Either case you aren't in the normal traffic region or in immediate danger. Unless your crew is doing some really stupid things, they have a very good idea where they will end up when the engineer fires up the drive.

 

[baithammer]

How can the astrogator know whats happening in the target system when there is no way to communicate or use sensors on the target?

 

[Sigtrygg]

Historical data, either gathered by long range sensors (hence years old) or more likely provided by a jump ship from the system in question (a week old).,.

you then use your ship computer and the generate program to build a model of the destination system and then calculate your jump solution. You then feed that into your jump program and press the big red button - alternatively slip in a jump cassette which has a pre-programmed jump solution.

Kepler (orbits), Newton (laws of movement, law of universal gavity), Einstein (General Relativity), Miller (a final solution for quantum gravity and hyperdimentional transit)

 

[Reynard]

Essentially, the scout service does extensive surveys of systems plotting as much information as possible and necessary for normal safe travel. As a system develops local traffic and sensor capabilities, the information is constantly updated but most system objects will have constant, predictable patterns. This will become part of a ship's astrogation data base and the computers update the vector calculations constantly. You don't need to be in the system directly to know where stars, planets, significant bodies and things like starports and other artificial objects that follow regular patterns will be when you plot travel. An update carried by the x boat system, will be available anywhere when your ship is portside when new, critical information for a system such as construction of a new orbiting facility.

 

[phavoc]

"When the ship exits jump space after an accurate jump, it tends to arrive close to the target world, but outside or on the verge of the hundred-diameter limit. Inaccurate jumps dump the ship somewhere in the inner system, requiring a long space flight."

I've always considered this line to be poorly worded. An inaccurate jump would dump you potentially anywhere in the target system, or even at the system's edge, at the Oort cloud, or even further out. Depending on the failure you would, generally, appear somewhere on the line between your target and your origin. At least that's how the jump drives work - in a straight line. The way the rules are constructed you should sometimes have travel more than the standard 100D limit because you straight line destination is in the jump shadow of a sun, a gas giant or another planet. While jump masking would be rare, it wouldn't be unheard of. By having this as a navigational concept it gives the ref more opportunities for them to appear in different areas, thus making it more likely to encounter something off the beaten path.

Historical data, either gathered by long range sensors (hence years old) or more likely provided by a jump ship from the system in question (a week old).,.

you then use your ship computer and the generate program to build a model of the destination system and then calculate your jump solution. You then feed that into your jump program and press the big red button - alternatively slip in a jump cassette which has a pre-programmed jump solution.

Kepler (orbits), Newton (laws of movement, law of universal gavity), Einstein (General Relativity), Miller (a final solution for quantum gravity and hyperdimentional transit)

Data will (almost always) be older than a week, but for the most part all major planetary objects will have their paths plotted, logged and your ships computer can easily calculate their new position when necessary. Orbital mechanics and uber computers make this a very simple task.

 

[Reynard]

"Many roleplaying games have a ‘rule zero’ which marks out a referee’s fiat, the notion that the referee is free to ignore or change any rule to fit in with his campaign."

This is how referees use the inaccurate jump to spice up an event or encounter without actually rolling for it. Since there are no jump shadow mechanics, this could represent the event of a jump shadow disturbance at the ref's discretion.

The concept of being far off within the system is already covered by a misjump sending you days off course possibly into the out system. Going into the Ort cloud would be the kind side of rolling on the -3 or worst effect misjump.

 

[heron61]

It makes sense to me that the variable length of a jump means that you won't know where in the 100 diameter sphere around the planet you'll arrive, but without some form of misjump, given that jumps are limited by gravity wells, I think it's reasonable to assume that if you want to arrive 100 diameters from a given planet, you will, since my thought is that the jump targets that particular gravity well, so that the planet moving around is star won't affect that. The rules support this and it makes sense given what we know about jump drive.

OTOH, a misjump means you may not have gotten that right, and may end up multiples of hundreds of diameters away, which could easily be several million km.

 

[steve98052]

Has anyone calculated the amount of trade available between systems in the Spinward Marches?

Gurps Far Trader has the rules for it. You might find some examples on CotI?

The TravellerRPG wiki includes World Trade Numbers for every system, and from those it's easy to calculate Bilateral Trade Numbers. At least one (and maybe all three) of the co-authors of GURPS Far Trader was an economist as his day job, so the economic model is pretty well grounded -- but because the full model is more complicated than most people want to bother with, there are levels of simplification.

. . ., but 100,000 Dton freighters are a bit large and break the idea of LOTS of ships traveling to and from other planets.
. . .

One conclusion from Far Trader that is easy to explain without plagiarizing the book is the idea that huge scheduled freighters carry almost all of the freight volume between systems large enough for them. (Similarly, but not stated in the book, lesser routes would have most cargo carried by medium sized scheduled freighters.) The freight remaining for free traders is everything on routes too quiet for corporate freighters to bother with, and the round-off error between big freighters on busy routes.

The end result is that for low-volume routes, free traders get as much as they want of the small traffic volume (proportional to the product of the two worlds' economy sizes, though the book simplifies with tables). Above a certain amount of total traffic, the amount available to free traders maxes out. Of course, it's always variable, based on die rolls that simulate fluctuations in traffic from what the corporate freight lines predict.

- - -

Avoiding collisions

For a small world, 1000 miles (1600 km), the 100 diameter limit is a surface with area of 4πr^2 = 4×3.14×1600×1600 = 32 million square km. If we divide that area by the 127 hexes a ship could be coming from (which includes in-system jumps), and also divide it by departure time to the nearest second within a two day cycle (longer than the usual 36 hour maximum variation in jump duration), each target point is about 1.5 square km on that surface, which is a bit small, but still much larger than any ship. And it can be expanded as much as necessary by aiming for volumes just outside the 100 diameter limit, rather than just the precise surface of the 100 diameter sphere -- or by increasing the length of the time slices. Even with fairly large relative velocities for incoming ships, the chance of collision could be reduced to zero with math that I could do if I thought it worth the bother. As previously noted, space is big.

 

[AnotherDilbert]

The TravellerRPG wiki includes World Trade Numbers for every system, and from those it's easy to calculate Bilateral Trade Numbers. At least one (and maybe all three) of the co-authors of GURPS Far Trader was an economist as his day job, so the economic model is pretty well grounded -- but because the full model is more complicated than most people want to bother with, there are levels of simplification.

It's pretty simple to calculate WTNs and BTNs. Just get the sector data from TravellerMap and spreadsheet it.

The system contains a few obvious bugs, but once you have fixed them it generated some interesting data.

Here is the total trade for Regina (to Spinward Marches and a few neighbour sectors):

There is quite a lot of passengers, the numbers for Regina are elevated by 10 times for being Rich and Capital. There's even a steady trickle of passengers for distant Solomani Rim sector.


The busiest port in the sector is Mora:

A more representative port is Cogri (2419 CA6A643-9)

The majority of the trade generally goes to a (or a few) near HiPop system(s).