Everything I know about Jump I learned from MWM

[Rover]

Captain Jack, you are correct in that Gravity is a function of mass. I only mentioned density as a comparison. I guess I was unclear. Basically in bodies of equal size a less dense body will have lower gravity and given the inverse square relationship a body will reach that jump limit much closer to the body in question.

So that would mean if you need 91.3D to reach Earth's Jump Limit as stated in the linked to article, you would need less than 91.3 D on a less dense body like the sun.

I see I am going to have have to break out the paper and pencil and do some calculating.

 

[captainjack]

Captain Jack, you are correct in that Gravity is a function of mass. I only mentioned density as a comparison. I guess I was unclear. Basically in bodies of equal size a less dense body will have lower gravity and given the inverse square relationship a body will reach that jump limit much closer to the body in question.

So that would mean if you need 91.3D to reach Earth's Jump Limit as stated in the linked to article, you would need less than 91.3 D on a less dense body like the sun.

I see I am going to have have to break out the paper and pencil and do some calculating.

Ah I think I see now. You're just discussing it in D units. So, it makes sense. if it has 91 D units for earths jump limit, based on earth, then a less dense body will have a smaller jump limit in D units.



For the sun the value of D is 1.4 million Km, for the earth, the D value is
14 thousand km. And just for fun an AU is 150 million km.

Still, the actual gravity is the issue, as it is determining the distance to a gravitational cut-off, right ? What I see is that the 1/2 earths density detail about the sun has to be an average, a widely dispersed one; it is much denser at the core, which is much bigger than earth. Mass has to be the issue; the surface (?) G of the sun is 28gs. I haven't run the numbers, but I do suspect that a pure gravity based jump limit will be larger than the simple 100x diameter limit for a star.

 

[Rraurgrimm]

*peeks out of the foxhole and looks around if the first wave has already passed*

Just because that question came up during our last session: will the crew aboard a ship know after having entered jumpspace for how long they will remain in there? Is there some canon source or is it simply personal preference if that time can be calculated then, 'welcome aboard the Far Trader XYZ, we successfully entered jumpspace heading towards Jewell and the estimated time of arrival will be ..:.. ship time.' - so it is not a rough estimate anymore?
Why did the question come up: due to events aboard, the players started to suspect something to happen upon exiting jumpspace (a mutiny aboard ship, a 600t-passenger liner that had just been overhauled and they had reasons to suspect mutineers amongst the workcrews). Now they wanted to know if they would have to stand guard (with shifts) during the earliest recorded time of exiting jumpspace and the latest - or if the more or less exact time could be calculated once one was in jump.

And another question that came up coincidentally: afaik, a jump bubble surrounds the ship in jump space. The lanthanum grid in the hull enables the ship to do such somehow. There is no real canon source on how big this bubble is (at least none that I know) - but I faintly recall having read a desperate spacesuit-crawl on the surface of a ship in jump from one airlock to another.
Question - if there is such a jump bubble: would it be permeable - or could f. e. the atmosphere of a ship in jumpspace fill the jump bubble? Thus, could a damaged ship leaking air already - which is still jump capable - enter jumpspace and have the jump bubble slowly fill with what may be left of said air until the ship is being sealed? Of course, the air would simply get lost when exiting jumpspace - either in jumpspace or in normal space. But during jump?
And yes, questions about other vigors of being inside that jump bubble (radiation comes to mind, strange patterns causing insanity or seizures, etc.) put aside.

 

[Andrew Boulton]

SOM says the jump bubble extends about 1m from the hull, and implies that the duration is known.

 

[far-trader]

*peeks out of the foxhole and looks around if the first wave has already passed*

...SECOND WAVE INCOMING!



I thought these were answered somewhere above. Might have been somewhere else. Didn't see the answers here on a quick look so on to my quick responses...

...will the crew aboard a ship know after having entered jumpspace for how long they will remain in there?

Yes, and precisely so. Even before entering imo, once the jump is plotted.

The first is canon, exact quote and source escapes me at the moment, words to the effect 'time is known once jump is...' (debatable intent, after engaged or after plotted). If I'm recalling correctly.

In my opinion it simply cannot work (despite Marc stating so) as an actual random duration. It only works as a metagame random. Otherwise there is no way to know where you will arrive at which makes a whole host of other game presumptions wrong.

...a jump bubble surrounds the ship in jump space. ...would it be permeable - or could f. e. the atmosphere of a ship in jumpspace fill the jump bubble?

...jump bubbles, jump grids :nonono: (canon be damned on this imo).

My recollection is about 1m clearance as Andrew notes, and any contact is instant obliteration. Even close proximity is exceedingly unhealthy (death, injury if you're lucky and the exposure is brief). That hull-crawl in jumpspace is a desperate near suicidal gamble iirc.

So specific to the air leak question, no, the bubble won't fill with the atmo and result in retaining breathable (albeit thinner) atmo through jump. It will leak out and be destroyed* upon contact with jump space

* catastrophically imo, I treat jumpspace/matter interactions as total antimatter/matter annihilation, even a small amount of matter contacting jumpspace is going to cause a huge explosion, the air leakage scenario damage would depend on how much/fast the air hits jump space, in MTU it would contact immediately where the leak is and create a very hot spot, probably nothing the hull couldn't handle though it may exacerbate the problem, causing the leak to grow quickly unless patched from the inside or otherwise stopped, immediately seal off the section and pump the air out of it would be my action plan, followed up with vacc-suited crew patching it from the inside in the now vacuum

 

[rancke]

In my opinion it simply cannot work (despite Marc stating so) as an actual random duration. It only works as a metagame random. Otherwise there is no way to know where you will arrive at...

There's no need to know precisely where you will arrive. All you need is a maneuver drive that will allow you to move from where you arrive to where you want to end.

...which makes a whole host of other game presumptions wrong.

What presumptions? I can't think of any myself. Some game conventions that are wrong in the sense that they simplify a complex situation for game purposes, sure, but that's not the same thing at all.


Hans

 

[far-trader]

There's no need to know precisely where you will arrive...

What presumptions? I can't think of any myself.

Not just where but when, and quite precisely, and before the jump drive is engaged (at the time of the plot, for the conditions of the plot).

The earliest clear one being the CT HG tactic of entering a system with your Black Globe engaged to (word to the effect, can't hunt up the exact quote right now) "sneak unseen past an enemy blockade to surprise attack at a world by dropping the BG at the appropriate time".

There is a whole set of dominoes that fall if the reality is a random time and location: Vector retention. Jump masking. Purposeful 100D precipitation limits. etc...

So the choices are:

Stick with random time and location as real, and ditch a lot of tactical and colour notes.

Treat random time and location as metagame (contradict Marc on ONE issue) and keep all the other (actually useful and interesting) canon Marc et. al. have also stated as game reality.

 

[E.D.Quibell]

Not just where but when, and quite precisely, and before the jump drive is engaged (at the time of the plot, for the conditions of the plot).

The earliest clear one being the CT HG tactic of entering a system with your Black Globe engaged to (word to the effect, can't hunt up the exact quote right now) "sneak unseen past an enemy blockade to surprise attack at a world by dropping the BG at the appropriate time".

There is a whole set of dominoes that fall if the reality is a random time and location: Vector retention. Jump masking. Purposeful 100D precipitation limits. etc...

So the choices are:

Stick with random time and location as real, and ditch a lot of tactical and colour notes.

Treat random time and location as metagame (contradict Marc on ONE issue) and keep all the other (actually useful and interesting) canon Marc et. al. have also stated as game reality.

IMTU you know how long you are going to be in jumpspace only when you have entered jump.

So if you misjump but you have a good jump drive/grid/coil then you know that you are going to be in jump for a month (or however long it's going to be). If you don't have a good jump drive/grid/coil due to anything (battle dammage) you can't be sure your jump clock is acurate.

Otherwise as Dan says there are a bunch of assumptions that you can't use.

I also use jump flash, so the black globe activation has to be split second perfect to catch the flash, and to do that you need to know when you are comming out.

IMTU and as always YMMV.

Best regards,

Ewan

 

[rancke]

Not just where but when, and quite precisely, and before the jump drive is engaged (at the time of the plot, for the conditions of the plot).

The earliest clear one being the CT HG tactic of entering a system with your Black Globe engaged to (word to the effect, can't hunt up the exact quote right now) "sneak unseen past an enemy blockade to surprise attack at a world by dropping the BG at the appropriate time".

That one I'll grant you. You can't do that if jump duration is uncertain. So either one or the other has to be wrong. But why do you take it for granted that it's the throwaway tactics that is applicable only in those extremely rare situstions where you happen to have a fleet composed only of ships that are equipped with black globe generators that is true and not the rule that applies to every ship in Charted Space?

There is a whole set of dominoes that fall if the reality is a random time and location: Vector retention. Jump masking. Purposeful 100D precipitation limits. etc...

Wrong, wrong, and wrong. Vector retention isn't affected, jump masking isn't affected, and purposefully hitting a jump limit in order to be precipitated out near a moving world is the key to getting the basic rules for jump to work.

So the choices are:

Stick with random time and location as real, and ditch a lot of tactical and colour notes.

Ditch one note that quite possibly has never applied at any time in the OTU and definitely won't apply to most campaigns.

Treat random time and location as metagame (contradict Marc on ONE issue) and keep all the other (actually useful and interesting) canon Marc et. al. have also stated as game reality.

One very fundamental issue (and potentially extremely useful for plot purposes -- being able to have one ship take off in pursuit of another and arrive half a day earlier than the quarry has all sorts of plot possibilities).

You're right about the described BG tactics being impossible. What else have you got?


Hans

 

[McPerth]

I cannot give you a canon source here, and I'm not sure if I've readed it or it was my interpretation about something I readed, but I've always assumed that you don't know exactly how long will you stay in jump, and surely not before initiating it (if so, the whole problem of jump coordination to arrive more or less at once with your companion ships would be out of order, just jump when you know you all will).

My thinking about that (and what I use in MTU) is jump time is uncertain even when on jump. Even so, before exiting jumpspace and returning to normal space, the ship's sensord detect the jump buble debilitating, and a jump exit alarm sounds, so warning the crew (and maybe pasengers) know they're just going to return to normal space, so any preparation they might have to do may be done (going to general quarters if they expect truble, fully mann sensors/drives, etc.).

As I said, this may be only my interpretation of my (uncomplete, I agree) knowledge of traveller universe and rules. The most close to cannon I can quote is on the narrative given in Emperess Marava supplement (MT), where it says the captain of the ship was reviewing manuals when the bell anunciating the return to normal space warned him, so hinting (IMO) than he didn't know the exact time of jumpspace exit. But that's only narrative, and not always coherent with canon...

 

[Rraurgrimm]

Thanks for the replies, they roughly go along the same lines as the discussion within our group (and we could not remember the canon sources).

 

[Antony]

Don't know if it first appeared in earlier editions but in TNE jump duration is rolled for and can be 6-8 days in length so 7 days on average.

 

[aramis]

Don't know if it first appeared in earlier editions but in TNE jump duration is rolled for and can be 6-8 days in length so 7 days on average.

Same is true in MT, T4, and T20.

 

[Rraurgrimm]

Oh, I knew about that - 168 hours, +/- 10% - but the question was: "Do the travellers aboard a starship know about the more or less exact time this particular jump will take - and when do they know about it?" IMTU, one can calculate the actual duration of the jump once the ship has entered jumpspace. So the crew knows exactly when to be on alert to prepare for exiting jump. Any bets on how long exactly this jump will take are made just before the ship enters jumpspace.

*edit*
And yes, that random factor would make astrogation a game of chance, not to mention fleets jumping as a collective unit. Things like planetary orbits and other stellar bodies' movement during that random amount of time - not to mention the target system itself moving which may have a different speed and vector in comparison to the system the ship departed from - could not be calculated properly. IMTU, a fleet *can* jump in loose formation if they use the astrogation calculations of a single ship, adapted by a slight margin for the other ships in the fleet. Upon exiting jumpspace, they may find themselves distributed with a small random factor (+/- 3.000km) among a small region of space - but the jump duration will be about the same (+/- a few minutes) for each ship of the fleet.
Everything else like the vectors of the target and the original system - are part of the astrogation calculations more or less so the only thing one has to worry about is the movement of stellar bodies in the target system. So one usually prefers to have up-to-date astrogation charts of every system and the gravitational sources inside those systems - and jumps slightly above or below the ecliptic to avoid the known planets and their movement during the random time if one intends to jump close to the target world.
But that is just our TU.

 

[HiverLord]

FWIW, IMTU I use 149hrs + 6D6 hours (155-185). Not "quite" canon, but close, and boiled down to a quick die roll.

Just my Cr 0.02 worth of input.

 

[rancke]

FWIW, IMTU I use 149hrs + 6D6 hours (155-185). Not "quite" canon, but close, and boiled down to a quick die roll.

149+6D6 average 170, wich is off by 2.

T20 uses 147+6D6 hours (p. 352), which is slightly under +/- 10%. I use 140+8D6 because I'd already been using that for a long time when T20 came out, and also because it's slightly easier to add 140 to a die roll in your head than to add 147. It's slightly over +/- 10%. The "truth" is probably in between, but a more accurate throw would be awkward (143½+7D6 ).


Hans

 

[HiverLord]

149+6D6 average 170, wich is off by 2.

T20 uses 147+6D6 hours (p. 352), which is slightly under +/- 10%. I use 140+8D6 because I'd already been using that for a long time when T20 came out. It's slightly over +/- 10%, and also because it's slightly easier to add 140 to a die roll in your head than to add 147. The "truth" is probably in between, but a more accurate throw would be awkward (143½+7D6 ).

Hmmm... guess I was probably tired when I started using those numbers (no surprise there. )

Your numbers look better (again, no surprise), so I'll start using them instead.
Thanks!