Safe Jump Distance from Stars

[mike wightman]

The ability to be stopped by an intervening a gravity well IS from CT sources. 2nd year of JTAS...

Hmm, I can't find a reference to ships being pulled out of jump space by gravity wells in any early JTAS article, what am I missing?

I can't find a reference to jump masking or shadows in the first two years of JTAS articles either. Is it hidden in an adventure or world description I wonder? An issue number, article or better yet a direct quote would help pin it down.

In MWM's Jumpspace article in JTAS 24 he says this:

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 the least 100 diameters out from a world or star (including a safety margin), and ships generally move away from worlds and stars before beginning a jump. 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.

On the other hand, there seems to be a built-in safety feature for ships trying to leave jump space within 100 diameters of a world. Ships naturally precipitate out of jump as they near the 100 diameter limit.

So you have to be 100D away from a star or planet to initiate jump, and if you try to leave jump space too close to a planet or star you would instead precipitate at 100D. I have always read the original article as confirming that a ship in jump space can not be affected by anything in the normal universe - so there is no such thing as being pulled out of jump by an interveneing object because you are not in this universe..

I know that Marc has changed his mind on this, first with the GT jump shadowing and jump masking canon, and then the rules in T5 nail it to the mast.

But back in CT days...

 

[McPerth]

Don't really need LBB6 to get the diameter of large stars and project the jump limits will be far past any Goldilocks zone.....

True, you don't, but, again AFAIK, LBB6 was the first to introduce the different star clases. Before it, the star was not defined and you only had the UWP for the mainworld, not caring about the rest of the system.

At least that's how it goes in LBB3 and TTB. maybe some JTAS article of other publication told about star clases before LBB6, but, if so, I'm not aware of it (or have missed the article).

 

[aramis]

@Mike:

From the same article:

On the other hand, there seems to be a built-in safety feature for ships trying to leave jump space within 100 diameters of a world. Ships naturally precipitate out of jump as they near the 100 diameter limit.​

It's quite vague; until seeing the draft of T5, I'd have agreed with you about it. But Marc has been quite firm; I am noting that nothing in JTAS 24 says "when you approach the intended object's 100D limit"...

Marc has implied strongly several times over the last several years that intervening bodies blocking jumps has always been his intent, at least since that article was in draft.

Which leads back to the above, coupled with Marc's abject insistence upon any intervening bodies causing dropout... With jumps of under 8, it's pretty unlikely. I've even run the math, as instructed by Marc, for truly 2-D interaction rates. Even such, Size IV-V-VI stars don't present much of a cumulative block (assuming random positions in-hex) until we get to hop drives (10+ Pc) and Size III-II-Ib-Ia stars (which can fill large chunks of a hex).

 

[flykiller]

any intervening bodies causing dropout... With jumps of under 8, it's pretty unlikely.

it would be very depressing to be forced out of jump at some long-gone distance from any world with only three weeks of fuel in the tanks. how unlikely is "unlikely"?

 

[aramis]

it would be very depressing to be forced out of jump at some long-gone distance from any world with only three weeks of fuel in the tanks. how unlikely is "unlikely"?

Givens:
Type G1 V to G5 V are about 1 solar diameter
1 parsec is 44334448 solar diameters
the 100D radius is a 200D blockout diameter
1 star randomly in 1 Pc hex

2D calc: P=blocked radius / width P=200/44334448 P=0.000004511164771917313

3d calc P= πRs²/π(0.5pc)² P = 100²/22162224² P = 2.0359791200835365e-11

For bigger stars, in 2D, multiply P above by R in solar diameters
In 3D, by R² (R still in solar diameters); some Size I stars hit 800+ diameters.
800 solar diameters is P=0.000013030266368534633.

To find the cumulative chances of safe transit: Multiply (1-P) for each hex of distance.

 

[mike wightman]

@Mike:

From the same article:

On the other hand, there seems to be a built-in safety feature for ships trying to leave jump space within 100 diameters of a world. Ships naturally precipitate out of jump as they near the 100 diameter limit.​

Thanks Aramis, that is the article I thought you meant.

It's quite vague; until seeing the draft of T5, I'd have agreed with you about it. But Marc has been quite firm; I am noting that nothing in JTAS 24 says "when you approach the intended object's 100D limit"...

Yup , I know Marc changed his mind on this for T5, and earlier GT. Thing is I think the GT authors misinterpreted Marc's article.

In the passage you quoted if you take the underlined section without the context of the bold section you can reach the conclusion that ships in jump space can be unintentionally pulled from jump.

With the bold section it is clear that the ship itself must be 'trying to leave jump space'.

Marc has implied strongly several times over the last several years that intervening bodies blocking jumps has always been his intent, at least since that article was in draft.

Fair enough, but we can only go by the rules and articles as written.

 

[aramis]

Thanks Aramis, that is the article I thought you meant.

Yup , I know Marc changed his mind on this for T5, and earlier GT. Thing is I think the GT authors misinterpreted Marc's article.

In the passage you quoted if you take the underlined section without the context of the bold section you can reach the conclusion that ships in jump space can be unintentionally pulled from jump.

With the bold section it is clear that the ship itself must be 'trying to leave jump space'.

No, it's not. Separate sentence. The latter sentence being separate, and the former being non-absolute, and Marc having insisted T5 is NOT a change from CT on that, you are mistaken.

That a significant number of people through the years also have interpreted it this way (I wasn't one until the T5 discussions- not all of which were on the board), shows that it was merely pooly worded.

 

[mike wightman]

Separate sentence but in the same paragraph, therefore same subject.

There at two sentences that flat out state a ship has to be trying to leave jump space for the 100D limit to matter, there is only the one sentence about precipitation that can be misinterpreted, which is immediately preceded by one of the sentences saying a ship has to be trying to leave jump space.

That is all we had to go on 'til GT.

 

[creativehum]

Separate sentence but in the same paragraph.
There at two sentences that flat out state a ship has to be trying to leave jump space for the 100D limit to matter, there is only the one sentence about precipitation that can be misinterpreted, which is immediately preceded by one of the sentences saying a ship has to be trying to leave jump space.

Sentences in the same paragraph and all that.

Leaving aside any Talmudic reading of T5 (a game written almost four decades after Classic Traveller came out), I understand the quoted passages exactly as Mike reads them. The ship is "trying to leave jump space" -- which means, quite clearly in context, approaching the desired destination.

My bigger question about all of this is what does it get anyone playing the game? Is the Referee tracking every celestial body in case one of them should intervene? If the odds are so low that it will probably never come up, what is the discussion about?

In the context of Classic Traveller (and this thread is in the CT sub-forum) I am genuinely curious about what is gained from fact.

As far as I can tell, the entire purpose of the 100 diameters jump limit is to provide tension about ambushes, pirates, and hijackings that might take place between starports and safe jump distances (either inbound or outbound).

I'm not saying this stuff can't be vital for game play. I'm just trying to see where it leads.

 

[flg]

You'd think this stuff would have been argued about so much (repeatedly) over the years on this board that people would have figured it out by now.

 

[aramis]

You'd think this stuff would have been argued about so much (repeatedly) over the years on this board that people would have figured it out by now.

Marc said on several occasions that he always intended both shadows (terminal blockage) and masking (intervening object blockage).

Given the low odds of system blockages for jumps ≤ 10 Pc, that it's only hinted at in the article is a failure on Marc's part to communicate that clearly; it was communicated clearly during T5. Jump isn't a parabola. It's a straight line.

Oh, and Marc has said (via email) that all the probabilities for intercept should be figured 2D, not 3D; implication: Jumpspace isn't 3D.

 

[flykiller]

You'd think this stuff would have been argued about so much (repeatedly) over the years on this board that people would have figured it out by now.

well, lots of people just do it their own way. imtu there is no "intervening" anything, you can pop in and pop out whereever you want. of course there may be consequences ....

speaking of blockages, seems to me that the most significant blockage is the local star itself. if the destination is occluded by the local star then you have to maneuver around it. for our g5 star of 499ls that takes up to 36 hours at m2 full vector and up to 48 hours m2 accel/decel.

 

[kilemall]

You'd think this stuff would have been argued about so much (repeatedly) over the years on this board that people would have figured it out by now.

For my part I just came back to the game from a several decade hiatus, with no intent to invest seriously in anything past CT/Striker (although I have, but mostly for idea mining). Therefore I have 'missed out' on all these arguments, and have come to the realization that oh yes it has been argued to death in that intervening time.

Fortunately, either through natural gentlemanly behavior, quiet resigned exasperation or enforced politeness (or likely some combination of all three) a lot of mine and other people's questions/comments are tolerated and often responded to.

 

[whartung]

Fortunately, either through natural gentlemanly behavior, quiet resigned exasperation or enforced politeness (or likely some combination of all three) a lot of mine and other people's questions/comments are tolerated and often responded to.

That, and I think we like to argue.

 

[GypsyComet]

That, and I think we like to argue.

Many of the old geezer population here are TML (Traveller Mailing List) escapees. The TNE wars back in the early 90s taught us what abandoning polite discourse leads to. A few have chosen to forget those lessons, or never learned them despite being there. Some who were not there at all still need those lessons. You'll see names in the archives who made examples of themselves...

For the rest, as long as the heat doesn't get much above a healthy Habanero, we old geezers welcome the discussions. Even the repeats.

That said, the TML did have a list of topics not to bring up, as they tended to bring out the worst in the Chemists, Astrophysicists, and Engineers, not to mention the Historians, Political Ideologues, and the occasional Know Nothing who thought he was one of the above...

You'd think this stuff would have been argued about so much (repeatedly) over the years on this board that people would have figured it out by now.

See that first line in my signature? Hard experience wrote that line. Any two of us could be using the same rulebook and supplement list and still be playing different games. The understanding and acceptance of (admittedly slippery) Canon is just one of the possible differences, and many of us don't realize the scope and scale of the assumptions each of us brings to a game or these boards.