Jump Shadowing/Masking

[fusor]

Considering other past editions also reference gravity as the limiter then all editions are wrong. Wow. Could you point out official sources that say somehow 'size' of a planetary body is the basis for fields of 100D around it that causes jumps to fail.

It's a 100 diameter limit. Gravity at 100 diameters is different for every object with different masses. Therefore gravity cannot be the limiter. Maybe they do explain it as "gravity" in some cases (I notice in TNE (p218) says "As gravitational fields interfere with the alignment of the jump drive (and may cause a jump mishap - see page 227), ships do not usually jump until at least 100 diameters away from the nearest world." , but that simply can't be true - if it was gravity then the limit would not always be at 100 diameters around an object, it'd be where gravity was at a specific value instead.

I'm not going to look for every quote in every book, but for example Mega Traveller's Referee Companion says on page 20:

"Jump Points: Jump points are locations at which it is possible to enter jump safely. By definition, a jump point is any point at least 100 diameters out from every star, planet, and satellite in the system. In order to enter jump safely, a ship must leave a world and travel out at least 100 diameters. If the planet is within 100 stellar diameters of a star, the ship must also travel at least 100 stellar diameters out from the star. If the world is within 100 diameters of a gas giant, the ship must travel at least 100 diameters from the gas giant. For example, in the Sol system, Venus is within 100 stellar diameters of Sol; a ship leaving Venus for a jump point must travel not only 100 diameters out from Venus, but also 100 solar diameters out from Sol."

So no mention of gravity there at all. Either way, the explanation isn't what's important - the practical fact is that 100 diameters has always been defined as the limit. If books have explained the limit as being due to gravity then they're wrong because it's physically impossible for the gravity at 100D to be the same for every object.

And yes, I wholeheartedly agree that it doesn't really make any physical sense for size to be the limit instead of gravity (which is why the alternate "gravity as limiter" idea has been proposed so many times in Traveller's history), but that's Traveller for you. And quite frankly, if the rules and explanations aren't consistent or clear between editions, then that's also Traveller for you. It's usually armwaved as some weird thing to do with jump physics.

But honestly, whether it's size or gravity (and which one is better) is a whole different argument for another thread.

Which I referred to and you somehow passed over then I expanded saying it doesn't really get used in the game. Read EVERYTHING I wrote.

I wasn't quoting that just for your benefit. And it changes nothing said here anyway. The OP is asking if anyone does use it, and the answer is "well, they should, because it's in the game".

 

[ShawnDriscoll]

Sounds like someone is trying to use Traveller as a simulator again.

 

[Sigtrygg]

Dig out JTAS 24 and read the definitive guide to jump by a certain MWM.

Gravity having an effect on jump entry and exit is explicit - if you want I can quote.

The 100D is just a simplification to make a role playing game fun and fast.

 

[fusor]

Gravity having an effect on jump entry and exit is explicit - if you want I can quote.

Quote all you like, it still doesn't work. Which part of "the gravity is not the same at 100D for all bodies" is not making sense?

I'll show it again:

g at the 100D limit for the sun (139 million km) is is 0.0068 m/s²
g at the 100D limit for the earth (1.275 million km) is 0.0002 m/s²

If you take gravity at the sun's 100D as the limit, then the jump limit for Earth should be a lot closer to it than 1.275 million km - it should be where g is 0.0068 m/s² around Earth (more like 240,000 km).
If you take gravity at the earth's 100D ass the limit, then the jump limit for the Sun should be a lot further than 139 million km from it, because the local g has to be 0.0002 m/s² (more like 740 milliion km, or 4.9 AU).

So how are people not seeing that gravity can't be what determines the limit if they also say it should be at 100D?
What effect do you think gravity has here, that it lets ships jump out further from stars than it does planets at some precise multiple of the object's diameter?

Good grief, I'm trying to just point out that the 100D limit has been there operation for jump drives since Day 1 for Traveller, and people here are claiming that it's not. It's in CT, it's in MT, it's in TNE, it's in everything. That ignorant authors got the handwavy explanation for it wrong is not what's relevant here - The point is that the limit is 100D.

The 100D is just a simplification to make a role playing game fun and fast.

Uh-huh, that's why they show the 100D limits for every body. Oh wait, they don't. You still have to calculate it either way. It makes no difference to how fun or fast the game is if it's calculated, or looked up in a table.

 

[fusor]

And fine, JTAS 24 says:
"Entering jump is possible anywhere, but the perturbing effects of gravity make it impractical to begin a jump within a gravity field of more than certain specific limits based on size, density, and distance. The
general rule of thumb is a distance of at least 100 diameters out from a world or star (including a safety margin). [...] The perturbing effects of gravity preclude a ship from exiting jump space within the same distance. When ships are directed to exit jump space within a gravity field, they are precipitated out of jump space at the edge of the field instead."

Also, later on:
"Gravity has extraordinary effects on the function of the jump drive. Jump drive transitions to the alternate universes of jump space are severely scrambled within the stresses of a gravity well; the transition cannot usually
take place within the stresses of a gravity well. When it does, the turbulence created by the gravity well makes the result unpredictable. In some situations, the ship is destroyed; in others, it merely misjumps."

Well great, so gravity messes up the jump drive, and yet a ship can jump out without issues from a gravity field of 0.0067 m/s² around Sol (just beyond its 100D limit) but somehow can't jump out where gravity is 0.0067 m/s² around the earth? Do you see how that explanation can't make sense?

And even though that uses a nonsensical BS armwavy explanation involving gravity, the practical effect is that it's still at 100D from the object (first claimed to be a "rule of thumb" but then later in the same article somehow turns into a hard limit). So that 100D limit is what matters for masking and shadowing in a Traveller game that uses the jump drive. How it's explained is completely irrelevant to this discussion - fact is, it's 100D.

So can we get back to talking about shadowing and masking effects please?

 

[Reynard]

So far, we all are.

 

[rust2]

It's a 100 diameter limit. Gravity at 100 diameters is different for every object with different masses. Therefore gravity cannot be the limiter. Maybe they do explain it as "gravity" in some cases (I notice in TNE (p218) says "As gravitational fields interfere with the alignment of the jump drive (and may cause a jump mishap - see page 227), ships do not usually jump until at least 100 diameters away from the nearest world." , but that simply can't be true - if it was gravity then the limit would not always be at 100 diameters around an object, it'd be where gravity was at a specific value instead.

Well, I would hesitate to judge whether the fictional physical properties of the fictional jumpspace of a fictional alternate universe can be true or not. :lol:

As for Mega Traveller, gravity and jumps, just take a look at page 39 of the Players' Manual: "Entering jump is possible anywhere, but perturbations due to gravity make it safest to begin a jump at least 100 diameters out from a world or star. Ships are naturally precipitated out of jumpspace before they get too deep into a gravity field."

So, gravity, again. Since Traveller's universe is Mars Miller's universe, I would not argue with this, even as I agree that the combination of gravity field and 100D limit makes not much sense in our universe - there is more than enough proof that Traveller's universe is not our universe.

 

[fusor]

So, gravity, again. Since Traveller's universe is Mars Miller's universe, I would not argue with this, even as I agree that the combination of gravity field and 100D limit makes not much sense in our universe - there is more than enough proof that Traveller's universe is not our universe.

If you're really suggesting that gravity works differently in Traveller's universe than it does our own, then please do explain the effect that has on everything else - because apparently you believe that the gravity at 100D of every star, planet, and asteroid is the same, even if they're different mass? How would an asteroid's gravity at 100D be larger than at its surface? Or maybe everything in the Traveller universe has the same mass? That must have fascinating physical implications for... everything.

The amount of mental gymnastics that Traveller fans go through to justify the incorrect material that authors write boggles my mind. Even more so since the simplest solution here is to say "OK, it's just down to physical size instead". But no, apparently we have to believe that the basic physics of the universe, on scales that we would understand and interact with, must be radically different to our own, just because the author waved around some nonsensical technobabble that isn't even consistent in his own article.

But either way, the limit is still 100D. What causes it to be like that doesn't matter.

 

[Condottiere]

Gravity being the trans-dimesnional force, should be actually the primary variable.

 

[fusor]

Gravity being the trans-dimesnional force, should be actually the primary variable.

It should. And it should be a lot easier for everyone if gravity did actually define where the jump limit distance was, so that it wasn't always at 100D. But sadly it's not, and we have to make do with it being at 100D.

 

[Reynard]

Gravity in our universe loses strength over distance as do other universal forces such as light. It's most powerful relatively close to the body and drops off quickly. When Marc and the gang were developing Traveller and the iconic jump drive, they chose gravity as an interesting limiter on the drive's function probably so players don't jump exit two meters from a planet's surface. Since gravity goes a long, long way they made it Traveller simple with '100 diameters' which is reasonable. No in depth science explanation just game jump physics and ease of play. Someone can verify but I think worrying about all bodies having 100D was from MegaTraveller which micromanaged every detail.

Back to the topic (Was just wondering who else likes the concept of jump shadows and masking? Does anybody use it in their games?). I think many gamers have shadow/mask transparent to their games and most works tend to ignore it when you read description of jump use. How often do you read about adventure ships traveling far more than the 100D of their chosen destination because the extra distance needed by the sun's and/or a host gas giant's shadow extending beyond the target's. It's a complication often more a story plot device. Do they really want to calculate every body's shadow in every system? At minimum. it could mean a ref would need to dig out the Scout supplement and calculate the shadow of every system's primary and note what possible destinations could be in the shadow. I bit of work just to tell players they need to burn extra fuel. Nice touch but a damned headache for referees who have enough to create.

 

[Sigtrygg]

I think someone once calculated that the tidal effect of a body gives a result a lot closer to the 100D rule of thumb.

Remember the key handwave in MWMs version of how jump works is 'gravity field of more than certain specific limits based on size, density, and distance' - which fits nicely to the tidal model.

Here is the link - scroll down to the second half to find it.

http://sol.trisen.com/default.asp?topic=10&page=29

 

[fusor]

Gravity in our universe loses strength over distance as do other universal forces such as light. It's most powerful relatively close to the body and drops off quickly. When Marc and the gang were developing Traveller and the iconic jump drive, they chose gravity as an interesting limiter on the drive's function probably so players don't jump exit two meters from a planet's surface. Since gravity goes a long, long way they made it Traveller simple with '100 diameters' which is reasonable. No in depth science explanation just game jump physics and ease of play. Someone can verify but I think worrying about all bodies having 100D was from MegaTraveller which micromanaged every detail.

100D was definitely in CT (it's mentioned there in book 2).

Back to the topic (Was just wondering who else likes the concept of jump shadows and masking? Does anybody use it in their games?). I think many gamers have shadow/mask transparent to their games and most works tend to ignore it when you read description of jump use. How often do you read about adventure ships traveling far more than the 100D of their chosen destination because the extra distance needed by the sun's and/or a host gas giant's shadow extending beyond the target's. It's a complication often more a story plot device. Do they really want to calculate every body's shadow in every system? At minimum. it could mean a ref would need to dig out the Scout supplement and calculate the shadow of every system's primary and note what possible destinations could be in the shadow. I bit of work just to tell players they need to burn extra fuel. Nice touch but a damned headache for referees who have enough to create.

Well, from a game design perspective it seems rather odd for a designer to say "this is a limit" and then totally ignore its consequences on the setting - because yes, otherwise it does imply that the locations of the star's 100D limits should be accounted for and so on, which isn't very practical. And Marc himself does say that ships are pulled out of jump at the 100D limit in his article. How he expects anyone to keep track of this is anyone's guess. But again, that's Traveller for you - full of inconsistencies and things that don't make sense, even from the author himself.

Maybe if there was a way to abstract it out as a probability that would work (e.g. on a 4- on 2d6 the world is jump masked or jump shadowed) but it's not a random thing - it depends on what direction you're travelling into or out of the system, if the target system is behind the sun or whatever.

And so we're left with either having to figure out jump masks and jump shadows, or have a weird, inconsistent system where a ship is only affected by the 100D limit of the planet they're leaving from and the planet they're arriving at, and just ignore everything else in between. Yay Traveller.

 

[rust2]

... because apparently you believe ...

What I believe is that the Traveller universe is a roleplaying game universe, and that any attempt to apply real world physics to such a universe is bound to lead nowhere.

 

[Reynard]

I believe that gravitational limits were probably created to prevent... oh, I'm sorry, warn players not to chart exits or attempt jump very close to a planet. Some editions also have a 10D marker which says something even badder is going to happen if you try. Not having psionics, I can only conjecture the development teams wanted a way to have a region of space for characters to have random encounters rather than fast traveling all the time. There may have also be a spark of logic as not having ships, especially LOTS of ships appearing very close to a world or actually in the atmosphere. Can you imagine submarines hitting the surface within a river of crowded ship ports unannounced?

 

[Condottiere]

Or transitioning while underwater, which means you'd never have to travel through space again, and the pirate you'd meet would be the nautical kind.

 

[fusor]

What I believe is that the Traveller universe is a roleplaying game universe, and that any attempt to apply real world physics to such a universe is bound to lead nowhere.

It's one thing to say "oh, there are psionics or FTL in that universe", and another thing to say "gravity works completely differently in that universe". Everything in that universe would be affected by such a fundamental change, probably to the point where you can't even have planets and stars forming in the first place. Saying "ah, it's an RPG universe, whatever" is a cop-out answer.

The simplest option - which requires no mental gymnastics or nonsensical universes - is clearly to say that while gravity has some effect on drives, the thing that actually limits them is simply the size of the planet or star, *armwave* "because jump physics" *armwave*. That's how it's always actually worked in the game. No further thought is required, and it doesn't require changing fundamental laws of nature because of someone's poorly-thought out technobabble.

 

[mancerbear]

Could we please move the discussion of whether the 100d limit is based on gravity or size to another thread and go back to jump shadow/masking and it's use or not in the game? I'm not really concerned with whether it's gravity or size. The rules say 100d, the fluff says gravity. Hand wave in process. This has gone way off topic and isn't really achieving anything regarding the original topic.

 

[Condottiere]

It's the mechanics for determining it, and how much time you went to invest for determining how that affects each system your players visit.

You're basically supposed to draw a straight line between entry and exit, though I would think a skilled astronavigator understands enough of the forces in hyperspace where he can bend the transition a bit.

 

[fusor]

It's the mechanics for determining it, and how much time you went to invest for determining how that affects each system your players visit.

You're basically supposed to draw a straight line between entry and exit, though I would think a skilled astronavigator understands enough of the forces in hyperspace where he can bend the transition a bit.

Again, it doesn't work like that. The way it's been defined in the setting is that the ship leaves a system and travels in a straight line to its destination. No amount of skill can change that - "bending" or "jinking" the path is not possible.

Once again it comes down to having a consequence of the setting that integrated into the way jump travel works that is troublesome to calculate (and then no way is provided to actually deal with it) - or that's ignored and it's not actually an issue at all (which then means that Marc Miller is wrong about what he himself wrote to supposedly clarify the issue).

What's the solution? I guess the practical answer is to change the setting so that jump drives can't be obstructed by anything except the specific 100D limit of their target. Does it make sense? Not really, but it fixes the problem I suppose (at the cost of some interesting consequences of the technology).