GT: Far Trader: Jump Masking

[RainOfSteel]

Ye ol' Dunce Cap™ is now officially in place.

I'm hoping someone can answer a pair of questions I have about Jump Masking as detailed in GT: Far Trader.

• P. 59: Jump Masking Diagram: The world's 100D limit is shown, the star's 100D limit is shown, and in this diagram, neither overlap. A light-grey cone is drawn from the world's 100D limit out past the star's 100D limit. Text in this cone says "Masked Jumps". I don't follow. The area encompassed by the light grey cone is outside of both the world's and the star's 100D limit, so how are jumps "masked" in an area that is not encompassed by a 100D limit? Or is that not what it means?
• P. 60: Jump-Point Masking Table: Free: Under the definition of "Free", it says, Free is the chance that any point on the main world 100D limit will be unmasked by the jump limit of hte stellar primary . . . , ok I'm losing it right there. How does a star's 100D limit "unmask" a planet's 100D limit? If it can do it at all, why only in limited cases?</font>

More questions may follow . . .

 

[Malenfant]

1 - Because ships coming to the planet from the direction of that cone will not be able to get to it, as they will intersect the star's 100D limit first. They'll drop out of jump when they hit THAT, instead of going straight to the planet.

2 - See above. I'm guessing it's a fudge so you don't have to calculate which side of the star the planet is on relative to the system the ship left from.

Technically I guess you'd need to have "almanacs" that tell you when a planet is unmasked by its star's 100D limit....

 

[far-trader]

My own questions on the GT material this involves if I may.

Is it considered by the rules that the two (any two) sytems may not have the same orbital plane relative to each other and so there is no masking shadow to worry about as (in an extreme and ideal case) you are jumping in and/or out perpendicular to the orbital plane?

Or is GT firmly applying a very flat very 2D galaxy model where every star system has an orbital plane matching that of the galaxy?

Or did they just not consider that particular detail while adding the others?

 

[RainOfSteel]

Malenfant,

So, allow me to see if I understand correctly before I say anything else.

GT:Far Trader is saying that Jump Masking is based on travel vector, and not on point of exit from Jump Space.

And that the position of objects in both origin and destination solar systems are relevant to the course of that travel vector in Jump Space?

 

[Malenfant]

Originally posted by RainOfSteel:
GT:Far Trader is saying that Jump Masking is based on travel vector, and not on point of exit from Jump Space.

And that the position of objects in both origin and destination solar systems are relevant to the course of that travel vector in Jump Space?

That's always been my interpretation of it, if you want to be completely 'realistic' about it. I always envisaged the jump path as a line drawn between the origin and destination points, and if that line intersects a 100D limit on the way then it drops the ship out of jumpspace. That's only really likely for stars though, since it's really unlikely that any other planet's 100D limit would happen to be in the way of any given path. I think that's what MWM implies in his JTAS jumpspace article too.

I guess the 'ecliptic orientation' of the system is too complex a factor to worry about (otherwise you'd have to figure out not only the positions of every planet in both systems at the time of jump, plus account for 1 week travel time, but you'd also need to figure out relative angles of orientation). There are clearly abstractions involved, in order to keep everyone sane

.

 

[RainOfSteel]

Sorry, the most sane thing to do would never have been to invent this feature/restriction of Jump Space travel.

Every solar system's ecliptic is set at its own tilt in relation to the galactic ecliptic, a largish fraction of solar system ecliptics will not be edge-on to each other, not to mention that planetary revolution will leave the world open a lot of the rest of the time. Given these factors, it's only more a mystery why Jump Space was retconned as a new restriction that wouldn't apply most of the time, anyway; followed on with an abstraction for determining when worlds are vector-blocked by their stars that is far too frequent. While simultaneously not noting the orbit the mainworld occupies so it's impossible to see if it is swamped by the star's 100D field, the only concern that should matter (and, as I understand it, there are plenty of worlds for which this is a sufficient problem).

I suppose I'll have to house-rule to avoid this problem.

IMTU: Only the exit-point of the jump matters. It may not exit into a gravity field that is too strong, planetary or stellar. Period. There is nothing else (and no need for it).

 

[Malenfant]

Originally posted by RainOfSteel:
[QB]Given these factors, it's only more a mystery why Jump Space was retconned a new restriction that wouldn't apply most of the time, anyway; followed on with an abstraction for determining when worlds are vector-blocked by their stars that is far too frequent. While simultaneously not noting the orbit the mainworld occupies so it's impossible to see if it is swamped by the star's 100D field, the only concern that should matter (and, as I understand it, there are plenty of worlds for which this is a sufficient problem).

I don't think it was ever 'retconned'. Like most things in CT, I think it was always implied that this was the case, but it was never properly explained or fully considered.

Since CT is the disorganised mess that it is, I can't find any references to how jump drives work at all in the corebooks or the supplements. It's probably mentioned in there somewhere but I can't be bothered to wade through it all to check.

I'm sure some other rules afficionado will find a reference though...

 

[RainOfSteel]

In CT, I think it was that the 100D limit was never applied to stars.

The idea that the star's position in Real-space could block a course in Jump-space, that is something completely new (EDIT ADD: since the introduction of Traveller in 1977).

I've seen several references to an article written by MWM, and AFAIK, that is supposed to be where it became canon.


(Yes, yes. Someone will come along and show me otherwise . . . <sigh />, if T5 will do nothing else it will (or it should, anyway) centralize all the techonology factoids and assumptions in one place for each relevant topic.)


However, never having read MWM's article, and GT: Far Trader not explaining it as such (AFAICT, anyway), I'd always assumed that it solely and exclusively referred to a star's 100D limit swamping the mainworld itself.

GT: Far Trader has only been mine for a year. The way Jump travel works has been pretty much fixed IMTU since 1981.


EDIT--04/18/2005--2349
Added a correction about what "new" means in relation to the timing of the appearance of Jump Masking.

 

[Jamus]

im pretty sure the 100 diameter limit is due to the affects a stars gravity well would have in j-space.

 

[RainOfSteel]

Originally posted by Jamus:
im pretty sure the 100 diameter limit is due to the affects a stars gravity well would have in j-space.

I'm going to have to disagree with any approach that allows anything in Real-space to affect Jump-space in any way that isn't a Jump Drive entering it, riding in it, or exiting it; that is a mechanism that is less than TL-20+; or that isn't a GM-initiated "Jump Mystery".

With gravity fields affecting entry and exit only.

 

[Malenfant]

Originally posted by Jamus:
im pretty sure the 100 diameter limit is due to the affects a stars gravity well would have in j-space.

That's probably the handwave used to explain it. Problem is, it doesn't actually make any sense. Look at the table here. Look at where the g-field of an M0 V star gets down to 0.01 m/s2 - at 0.42 AU. M0 Vs are about 0.305 solar radii, or about 0.0014 AU in radius.

By comparison, the g-field of a B9 V star, which is 3 solar masses (10 times more massive than the M0 V) reaches 0.01 m/s2 at a distance of 1.33 AU from the star. These stars are about twice as big as Sol, or 0.0093 AU in radius.

OK. So we have a 0.3 solar mass star with a g-field of 0.01 m/s2 at 0.42 AU, and a 3 solar mass star with a g-field of 0.01 m/s2 at 1.33 AU.

Now, if you used the usual 100D here, the 100D limit for the M0 V star would be at 0.28 AU, and the limit for the B9 V star would be at 1.86 AU. So is the g-field the same at both these distances? No.

For the 0.3 solar mass star, the g-field at 0.28 AU is 0.021 m/s2. For the 3 solar mass star, the g-field at 1.86 AU is 0.0049 m/s2. These are not the same

.


So there you go. Proof that at the gravitational field strength of two stars with different mass at the 100D distance are different. So 100D can't be based on gravity.

 

[RainOfSteel]

Oh, I know! The 100D Jump Limit is based on freakin' magic! There, problem solved . . .

. . . all except for the pesky fact that this is an SF game.

 

[far-trader]

Originally posted by RainOfSteel:
Oh, I know! The 100D Jump Limit is based on freakin' magic! There, problem solved . . .

Works for me

I'm kidding again

I was actually concerned that my idea of polluted vacuum for the reason was going to be a no go but figured I'd see what a knowledgeable take on it would be. Thanks Malefant. It did sound a little too "ethereal" in the literal sense.

OH, I guess that reference is in the other thread about jump masking over in the playtest forum. Never mind

 

[Malenfant]

Wasn't my decision to make; see this long debate for the history and context of Mr. Miller's decision.

It is worth repeating this. In bold.
It would seem that this is exactly how MWM was intending Jump to work - you DO get precipitated out when you intersect a 100D limit.

 

[mike wightman]

Originally posted by Malenfant:

It would seem that this is exactly how MWM was intending Jump to work - you DO get precipitated out when you intersect a 100D limit.

He also states that jumps can not take place inside the 100D limit - that changes things

Oh, and the jump limit is based on D, not mass

 

[Jamus]

I had thought the density of the body is what the 100d limit is based on not the actual diminsion of the object iirc. the 100d is a measure of the gravity well and its affect on r-space and j-space more than the physical object.

imtu the j-drive works by manipulating gravitic fields and using those fields to bend space/enter j-space via an artificial gravity well, sorta like a controlled mini black hole. Think the big ships in Babylon 5.
Any body of mass in the area when those grav fields are activated could interfere with the process and throw the whole thing off resulting in mis-jumps or worse.

Oh, I know! The 100D Jump Limit is based on freakin' magic! There, problem solved . . .

. . . all except for the pesky fact that this is an SF game.-RainOfSteel

No, magic is cheap and easy artificial gravity that is so common it is not even factored into ship construction costs. its as cheap to install and produce artificial gravity as not. thats magic.

But then thats my little rant with traveller. imtu I allow that Art-grav costs 2% of the ships hull to install and can be damaged/rendered inoperable in combat or malfunction. still cheap enough that it doesnt really affect any current designs. my main problem is that arti-grav is something for nothing in otu.

 

[Malenfant]

Originally posted by Jamus:
[QB] I had thought the density of the body is what the 100d limit is based on not the actual diminsion of the object iirc. the 100d is a measure of the gravity well and its affect on r-space and j-space more than the physical object.

nope, density and mass have nothing to do with the OTU 100D limit - it's purely down to radius.

 

[Anthony]

Officially, density and mass are irrelevant. A fairly popular unofficial hack is to base it on the tidal effect, which at least comes close to the 100D rule for most planets (assuming 100D is correct for the earth, you wind up with 100D * (Density/5.5)^1/3)

 

[RainOfSteel]

------------------------------
Chris Thrash

Thank you for the general enlightenment and revelations.

I also went over and read parts of the thread you posted a link to, and learned much more.

------------------------------


Well now, isn't this a classic predicament?

On one hand, 100D Jump Limits are based solely on the size of the object.

But then, they're not just governed by that, because gravity can 'œscramble'� things.

And, to top it off, in true Traveller fashion, the information is all over the place, but mostly not in actual rulebooks (save for GT).


Okee, Dokee.


There are two main thrusts here.


The 'canon'� 100D Jump Limit & Masking system.
The Gravity Jump Limit & Shadowing system.

'Masking'� refers to objects in Real-space being able to block & influence courses in Jump-space.

'�Shadowing'� refers to gravity fields blocking or influencing entrance to and exit from Jump-space, and nothing else.


100D Jump Limit & Masking

• -------
  PROS
• Quick to calculate Jump Limit thresholds
  -------
  CONS
• 100D Jump Limit: It's based on 'Diameters'� of an object. By itself, the 'Diameter'� of an object cannot tell us anything. Specifying that all objects have a density of 1 (Earth), is not an answer.
• 100D Jump Limit: Huge snap of the ol' suspenders of disbelief.
• Masking: No apparent reason for existing.
• Masking: No need to exist. Jump Drives and Jump Space are a necessary handwave to make our interstellar adventures work. The basic handwave must be accepted. Strenuous effort should be expended in the avoidance of additional unnecessary handwaves. 'If it ain't broke, don't fix it.'� (And yes, I now know Masking has been discussed since way back in 1985.) We must ask ourselves, would everything continue on, working normally, if this weren't here. The answer is: yes! We must then ask ourselves, does this break game mechanics and even the flavor and feel of the game (except GT, which was set-up for it in advance)? The answer is: yes!
• Masking: Solar ecliptics are tilted at their own individual angles, substantially reducing the possible interaction of Object-Blocking, but Solar ecliptic angles aren't generated or stored, and there is no way to successfully take this into account. By not having Masking, we needn't worry about leaving out an important bit of Astronomical Cosmology from our considerations (when we aren't forced too). By having masking, we are unnecessarily forced to ignore a bit of Astronomical reality, reducing the overall strength of the base handwave (Jump Drives). Or, if you pull too hard on the suspenders of disbelief, they do have a tendency to snap, hard, in your face.
• Masking: There are a laundry list of potential problems (courses in Jump-space become known, communication with ships in Jump-space becomes known, etc.). Questions about these potential problems only arise when Masking is put forward. They vanish, never to have existed, if Masking is withdrawn.

Gravity Jump Limit & Shadowing

• -------
  PROS
• Produces Jump Limit thresholds based on physical phenomenon known to science (gravity).
• Rings 'True'� and makes 'Sense'�.
• Isn't plagued by the problems of the 100D Jump Limit & Masking system.
  -------
  CONS
• Isn't Canon: T5 is coming up, and this can be fixed lickety-split.
• Appears, on the face of it, to be slightly more complicated than 100D Jump Limit & Masking. But when you take into account all the issues and problems with 100D Jump Limit & Masking, Gravity Jump Limit & Shadowing suddenly takes on a whole new light.

I will continue to strongly and mightily recommend the abandonment of the 100D Jump Limit/Masking based handwave.

The past is the past. It's decisions need not mandate the future. Isn't that what we're doing? Forging ahead?


------------------------------


On the thread Chris Thrash posted, I back-tracked until I got to TheDS's statement on page 2. The part where he claims it was a disaster.

I cannot agree with the whole post more wholeheartedly.

------------------------------

I shall allow myself to enter one more problem with 100D Jump Limit & Masking to the list of suspender-snappers: Black Holes, having 0 Diameter, have no affect on Jump Drives whatsoever. Not on entrance or exit, and not while on "course" in Jump Space, either. That is, if we can finally decide whether gravity does or doesn't have an affect on things.

------------------------------


If 100D Jump Limit & Masking was introduced in 1985, and required GT to explain it further, and GT:Far Trader for yet more illumination, and an article over on the JTAS site in 2000 . . . isn't it obvious that the whole idea was just too much for no gain?

We gain by dropping it and we lose by keeping it by every measure I can think of.

 

[Jamus]

nope, density and mass have nothing to do with the OTU 100D limit - it's purely down to radius.

gonna have to ask why the size of a planet or star should matter if not for the gravity well said body would imprint on the fabric of space?

to me it is all about the affect of gravity on space. everything else is secondary to j-drive operation. and to be honest OTU really doesnt explain j-space or j-drive nearly enough.