Does the 100D rule add anything?

[Lapthorn]

Well... does it? What does the 100D jump limit add against a simple rule that said you need to be 800,000 km from a significant gravitational mass (let's say, more massive than your ship) to jump safely?

I pick 800,000 because the average world, by the dice, is size 5 i.e. 8,000k in diameter.

Downsides of the 100D rule: 1) the main one is if you take account of stellar jump limits, a lot of worlds should be jump-masked. The more I think about this, and playing around with various system-generation rules, jump masking could have profound effects. e.g. jump masked worlds requiring days more travel to reach from the jump point would presumably see much less traffic than a more easily accessible world.

2) Adds book keeping

3) I've never known what to do about jumping to asteroid belts. Even the biggest asteroid in the solar system's main belt, Ceres, is less than 1000km in diameter. You should be able to jump out almost right on top of it. Maybe that isn't much of a problem, but it has always irked me.

 

[rancke]

Downsides of the 100D rule: 1) the main one is if you take account of stellar jump limits, a lot of worlds should be jump-masked. The more I think about this, and playing around with various system-generation rules, jump masking could have profound effects. e.g. jump masked worlds requiring days more travel to reach from the jump point would presumably see much less traffic than a more easily accessible world.

2) Adds book keeping.

(Terminology: Jump masking is having a jump limit between you and your destination; being inside a jump limit is being jump shadowed.)

Jump shadowing and jump masking could add considerable interest to a campaign if the rules and the worldbuilders actually paid attention to their existence.

3) I've never known what to do about jumping to asteroid belts. Even the biggest asteroid in the solar system's main belt, Ceres, is less than 1000km in diameter. You should be able to jump out almost right on top of it. Maybe that isn't much of a problem, but it has always irked me.

I don't see the problem.


Hans

 

[Carlobrand]

Well... does it? What does the 100D jump limit add against a simple rule that said you need to be 800,000 km from a significant gravitational mass (let's say, more massive than your ship) to jump safely? ...

Are you playing CT? Consider the case of the free trader running out to some low tech E port. This world is size 2: 3200 km diameter with a jump shadow extending 320,000 km. There is a pirate in orbit, silent: he cannot be detected until you're within 18,750 km. Would your players prefer a rule that restricts their jump within a range of 320,000 km, or one which restricts their jump within a range of 800,000 km?

Yes, stellar jump shadows can create a headache, but mostly with canon conflicts. And, it doesn't have to. Aramis once pointed out an article showing that the jump shadow correlated closely with tidal stress: the fact that gravity pulls harder on the part of your ship closest and a wee bit less hard on the part farthest, resulting in a stretching stress.

Under that model, a body's jump shadow varies by density. Comes out to the cube root of the density. So, an Earthlike world with a molten metal core has a density we will arbitrarily declare to be 1 and a jump shadow of a hundred Earth diameters. The Sun, with a density a wee bit over 1/4 of Earth's, would have a jump shadow of about 63 Solar diameters, which puts it somewhere between Mercury and Venus. The big mother giant stars are even less dense, so diffuse that their upper atmospheres are thinner than air, sometimes not far from being vacuum: their jump shadow may be no more than one or two diameters.

(The only problem spot is a white dwarf, with densities from a couple thousand to ten million times greater than a planet's, could conceivably have a jump shadow of a thousand to thirty thousand diameters. Fortunately a white dwarf, the corpse of a star that's gone nova, is around the size of a planet, so while the white dwarf itself is difficult to approach, whatever remnant of the system survives is still easily accessed by jump.)

 

[Aramais]

Jump shadowing has some interesting facets for your system. The MOST interesting facet is this: it means that piracy is possible. If reviewed, and thought about, it tends to militate against gas giant refueling, because the jump can't be safely accomplished close to the giant. Combat is thus prolonged, and more dangerous.

It's not just about book-keeping, it's about opportunities for adventure.

 

[robject]

It's not just about book-keeping, it's about opportunities for adventure.

Or at least, that's what it's there for. Anyone can make anything into a homework assignment.

 

[aramis]

assuming just the 100D and every celestial body generates it, including ships...

It enables piracy, as Carlo notes.
It discourages GG refuelling ops, as Greg notes. Keep in mind also, a typical GG under the Traveller system model① is typically between 0.5 and 3 G-weeks transit away.②
Jupiter at closest is about 0.84G-weeks transit time; at furthest about 1.02 G-weeks transit.③ If you don't have 2 G's, it's faster to jump to the GG if you need to get there... Jupiter takes about 2.5 G-days transit to the jump point.

It puts worlds in systems with large primaries (Class Ia, Ib, II, III) having their habitable zones deeply within the exclusion. This adds texture; it also means those worlds shouldn't generate nearly as much trade, due to much increased shipping costs.

It also sets a must-fight area - if caught within, unless you have higher acceleration, you're caught.

noting that T5 makes any intervening body's exclusion zone a jump to that intervening body, it also makes stars several AU of blockage.

If it's an approximation for tidal force
much the same, except that gas giants no longer block a a 20th of an AU or more... instead, due to much decreased density, they drop off about 1/3 as far. Further, Only Types Ia and Ib and dim II's block their hab zones.

If you reduce it to 1 diameter
You can jump from high orbits, or jump into reasonable orbits. Pirates not longer have room to catch someone; it becomes entirely a groundside activity.

Gas giants no longer really need the same caliber of high guard operation; it's shallow enough that a running battle using Traveller space combat rules can be survived long enough to jump.


Footnotes
① The system model is badly broken versus real world; it was developed in the 1980's, and we all had only the Sol system to model after, plus some wild guesses from science. Oh, how wrong it's turned out to be.

② note that a G-week as distance is an exponential measure of distance; divide by the drive thrust to get time taken, assuming midpoint flip.
Using the TNE established 10m/s/s G and 150 Mkm AU, 1 G-Week is 6.09 AU; using real world 9.8m/s/s and 149,597,871 km AU, it's 5.99 AU. To convert AU to G-Weeks: Gwk=√(Dau/X) where X=6.09 or X=5.99, by your game preference of units. For simplicty, one could also use X=6.

③using Traveller units, rather than real world.

 

[Lapthorn]

Thanks all for the interesting observations.

I am not advocating getting rid of some kind of jump exclusion zone around worlds. I was just making a probably quite footling point about why bother with 100D given the complications that arise from jump "masking" of hab zones; a fixed 800,000k zone around any world would seem to do the same job and get away from jump masking by stars.

I follow the point about adjusting the jump shadow by stellar density, which we can gauge from the luminosity. However, I'd have thought the vast majority of worlds we're interested in visiting would be orbiting FGKs on the main sequence, i.e. luminosity IV-VII - if only because the vast majority of stars are in that category (>98%).

Now the point here is the 100D limit is linear (100 times D), but the hab zone drops off as a quadratic (square of star's radiation output). That means hab zones around smaller stars (not huge ones) will be shadowed to a greater extent.

The point about T5 creating jump route blockages is likely to be irrelevant I'd have thought given the vast difference in orders of magnitude between interstellar distances and stellar jump shadows. It must be billions to one that there would be an object in your direct line of jump. That would be even more the case if you took account of space being 3D not 2D.

 

[Hemdian]

Any discussion of the 100D rule wouldn't be complete without pointing out this article. It looks at gravity and tidal force and some game implications thereof. (It might be a little dated now as it was one of the first things I ever posted on the internet.)

 

[CosmicGamer]

The point about T5 creating jump route blockages is likely to be irrelevant I'd have thought given the vast difference in orders of magnitude between interstellar distances and stellar jump shadows. It must be billions to one that there would be an object in your direct line of jump. That would be even more the case if you took account of space being 3D not 2D.

Not sure why that is just a T5 thing. If going from system A to system B, the destination planet for system B could currently be orbiting on the "far side" of it's star. It's also possible that the star of system A is between the departure planet and it's destination. A gas giant could extended traveling when it eclipses a destination.

I assumed there were travel seasons with higher and lower volume due to planetary orbits creating temporary hindrances to jump travel. I don't have the collections of add on publications others have which probably discuss such?

 

[rancke]

Not sure why that is just a T5 thing.

It could be a T5 thing by virtue of actually paying attention to the ramifications. GT had rules for when a PC ship encountered jump masking (though I think it lumped jump masking together with jump shadowing), but the trade rules were based on the assumption that transit time always was to a non-shadowed/masked destination. Nor did any setting material refer to the problem.

Perhaps the T5 trade rules include spending extra time jumping to a shadowed/masked destination and how to increase the costs to account for that?

(My suggestion: For every extra day the trip will take, increase fares by 10 percentage points.)

If going from system A to system B, the destination planet for system B could currently be orbiting on the "far side" of it's star. It's also possible that the star of system A is between the departure planet and it's destination. A gas giant could extended traveling when it eclipses a destination.

I assumed there were travel seasons with higher and lower volume due to planetary orbits creating temporary hindrances to jump travel. I don't have the collections of add on publications others have which probably discuss such?

I've tinkered with all of these concepts. Travel seasons is an especially interesting world-building concept.


Hans

 

[atpollard]

Perhaps the T5 trade rules include spending extra time jumping to a shadowed/masked destination and how to increase the costs to account for that?
(My suggestion: For every extra day the trip will take, increase fares by 10 percentage points.)
Hans

... or move the highport ... well, higher.

 

[rancke]

... or move the highport ... well, higher.

Then the trip won't take any extra time. For the ship, that is; the passenger will have some additional in-system travel to do. But the ship won't have to charge extra.


Hans

 

[aramis]

IIRC: Masking - being within the 100D limit of another body
IIRC: shadowing - being on the far side of an intervening body's 100D limit

The first appearance of stars blocking access to planets was in JTAS.

CT core never mentions the stars, only the planets & moons.

CT didn't generate the stellar data until late - Book 6 was about 1983. The ramifications didn't actually become part of canon until later.

Also, few worlds are ever going to actually be blocked by stellar shadowing unless they're also already masked, or by the stars in the departure or arrival systems. The most likely causes of shadowing are intervening worlds in one system or the other, bigger ships, and the local star.

 

[rancke]

IIRC: Masking - being within the 100D limit of another body
IIRC: shadowing - being on the far side of an intervening body's 100D limit

I have been claiming that it's the other way around every time the question has come up for as long as I can remember, and no one, including you, has ever corrected me. You are shadowed when you are inside a world or sun's shadow and you are masked when an object masks your destination from you.


Hans

 

[Carlobrand]

I have been claiming that it's the other way around every time the question has come up for as long as I can remember, and no one, including you, has ever corrected me. You are shadowed when you are inside a world or sun's shadow and you are masked when an object masks your destination from you.


Hans

Yup, I see an entry from 2007 where Hans said that.

I also see an illustration in Gurps Far Trader, page 59, which appears to support his definition.

 

[aramis]

In any case, the realistic odds of being blocked by a star are very slim for main sequence stars, and were it not for the 2D mapping, it would be pretty fair to say that it's almost impossible to not get there due to a star outside the system you're in or the system you're going to. Space is 3D... systems do not all share the same ecliptic (That the Kepler project has found so many that have occulting orbits is mildly surprising, mathematically).

 

[rancke]

In any case, the realistic odds of being blocked by a star are very slim for main sequence stars, and were it not for the 2D mapping, it would be pretty fair to say that it's almost impossible to not get there due to a star outside the system you're in or the system you're going to.

But the stars of those two systems have a very decent chance of masking a jump even if neither shadow their worlds. Personally I'd simply ignore the possibility of being masked by any other star except by referee fiat (and said fiat to be used very sparingly).


Hans

 

[Lapthorn]

Travel seasons is an especially interesting world-building concept.

I do like the concept - sounds like the Trade Winds, paying attention to the monsoon etc.

However... wouldn't it be more likely system authorities would just build travel facilities in un-masked (or un-shadowed... whichever it is) locations, say well outsystem? This could probably be done in most systems close to sources of fuel like gas giants, ice worlds or Kuiper belt objects.

Passengers and freight would still need to get out there. I can imagine a class of fast (at least 3G) transports arising for the purpose. A 5G shuttle would get you out to 6AU in a bit less than 3 days. Which is still faster than waiting 2 or 3 months for Jenghe to be unmasked (or unshadowed) for traffic incoming from Regina (for example).

Low-priority freight (and low passengers?) could get slung out on a solar sail, or on a reaction-drive barge taking the long way round, slingshotting the gravity wells.

 

[GypsyComet]

I do like the concept - sounds like the Trade Winds, paying attention to the monsoon etc.

Vinge's Snow Queen uses a form of seasonal access to great social effect, but this is enabled by a more limited FTL scheme and smaller body of stars to travel from.

In Traveller terms this would be similar to having an isolated system within J6 of only one other system, while also orbiting a supergiant (perhaps as a far-flung binary). When the world is on the close side of the companion giant, you have only its own star's effects to consider, but for some part of its Great Year, travel to that world takes weeks each way. Unless the supergiant has fuel stops of its own you have to build ships that can specifically handle the long cruising times or double jump, and you already had to do that just to get that first jump.

 

[Carlobrand]

...However... wouldn't it be more likely system authorities would just build travel facilities in un-masked (or un-shadowed... whichever it is) locations, say well outsystem? ...

Requires some minor adjustments to canon, places where the adventure says you arrive at X Starport but are now arriving at X Deep Space Port with a trip of a few hours or more ahead of you to reach the adventure site.

Also requires a deep space port with its own maneuver drives since it has to exceed what would ordinarily be its orbital speed at that position in order to maintain an ideal position with respect to the planet it's serving.