Jump Occlusion

[Magnus von Thornwood]

Me too.

This is how I explain Jump IMTU,

Imagine a rubber band being stretched from the ship location to the destination, that is what the astrogator is doing calculating where to stretch the rubber band. The Jump drive is spun up the rubber band is stretched and when the ship pops into jump space the end of the rubber band on the ships side is let go. The ship rides the wave to the destination and is popped out of jump space with the same momentum it had when it entered.

It only takes a week for the "rubber band to contract". Now the bigger the jump drive the farther you are able to stretch the "rubber band" which stores more energy causing the ship to still only take a week to "ride the wave" to the destination. It simply goes faster in jump space.

Jump space is a parallel universe with varying laws of physics than our own universe. Our universe makes its presence felt in jump space through the force of gravity. Hold a rubber band stretched out, have someone pinch the center of it and let one end go. That would represent a gravity well interrupting a jump.

Granted I never really got into Physics, didn't even have to take it in college, but to have the actual ship go from particle to wave and stretch out over a parsec distant, I’m not going for it. Creating a wave that physically affects a parallel universe, punching into that universe and riding the wave to the destination, I personally like that better.

It's my story and I'm sticken with it.

I totally dig this description. Very cool.

 

[Dagrill]

P. 372, RC, makes it clear the exit is at 100 diameters of the 1st object which interfered with the jump course. The only way this makes sense is with the explicit wave collapse model, mentioned on...

Checking only at exit means you can be forced out willfully- for some, this is a benefit, but it means piracy will not be the smash-n-jump versions; any survivor, and the local monitor or cruiser pulls you back out. It also means that planets in your way at entry won't be there at exit, but others could.

Checking at both start and end time is the worst of both - plus it's logically inconsistent, to boot. Plus renders hop and skip much less useful.

Checking whole duration of course makes the most logical sense, but is still suboptimal. It makes pulling ships out easier, but it also means frequent jump courses require positive traffic control. Otherwise, an arriving capital ship pulls up to a week's traffic back out, fuel used, and having gone nowhere.

Hi,

I agree this doesn't make a whole lot of sense, as no system can control the arrival of ships and the arrival of a squadron of the emperor's finest could seriously mess up local trade.

Also looking at page 335 on Jump fields it wouldn't necessarily be 100 diameters, in the examples March Harrier has a 107 diameter minimum and Neon only 78.

I'm going to us this as potential cause of mis-jump though atlthough I haven't decided exactly hoe,

Regards

David

 

[atpollard]

Checking only at exit means you can be forced out willfully- for some, this is a benefit, but it means piracy will not be the smash-n-jump versions; any survivor, and the local monitor or cruiser pulls you back out. It also means that planets in your way at entry won't be there at exit, but others could.

Checking whole duration of course makes the most logical sense, but is still suboptimal. It makes pulling ships out easier, but it also means frequent jump courses require positive traffic control. Otherwise, an arriving capital ship pulls up to a week's traffic back out, fuel used, and having gone nowhere.

Now there is a whole different breed of piracy ...
... a pirate capital ship arrives at a small system and pulls back up to a week worth of merchant traffic into it's waiting claws ... no more loitering at the 100 diameter jump limit waiting for someone to arrive.

 

[rancke]

Now there is a whole different breed of piracy ...
... a pirate capital ship arrives at a small system and pulls back up to a week worth of merchant traffic into it's waiting claws ... no more loitering at the 100 diameter jump limit waiting for someone to arrive.

You still have to loiter for the days it take for the jump fields to collapse.

A pirate ship strong enough to defeat the local system defenses could do something pretty much like that under the old rules too: just arrive, beat up the defenders, and wait for incoming traffic for the next 14 days.


Hans

 

[HG_B]

Now there is a whole different breed of piracy ...
... a pirate capital ship arrives at a small system and pulls back up to a week worth of merchant traffic into it's waiting claws ... no more loitering at the 100 diameter jump limit waiting for someone to arrive.

Take your pirate ship and jump a lightyear along the track to do it. No pesky system defenses to interfere.

 

[arentol]

Doesn't Page 374. Blockage. First sentence resolve this entire discussion:

"The existence of a gravity source (larger than the ship in jump) on the ship's course (at any point along the course AT THE MOMENT THE JUMP BEGINS) forces exit from the jump at 100 Diameters in front of the object."

This is the definitive section on blockage and occlusion, and as it makes clear you can NOT bring an object in after the fact to block a transit at the point of departure. Regardless of Cat's in boxes and collapsing waves and all that, the rules say a post-launch block simply does not work, so it doesn't work.

This also solves all concerns about traffic control because once the ships Astrogator determines the local area is clear the only way the ship could be blocked at its launch location is if another ship arrives via jump super-close to the ship in the last few seconds before the jump drive kicks ins, and even at the busiest system in the galaxy the odds of everything necessary for that to happen from a timing, size, and location standpoint are worse than winning the Powerball Jackpot, twice, in a single week, with only one ticket per drawing.

As to the occlusion rule itself.... For pre-scouted jumplines it should never happen. For direct jumps that aren't scouted the odds should be lower than the book indicates. IMTU I would use 6D-6, giving about a 1% chance on a 6 parsec jump, and even that is high in my opinion because....

Space is HUGE folks. Just absolutely massive. I mean ridiculously so. Even though everything that exists is in it, all that exists relative to the size of space itself, is almost nothing at all. Even considering just the galaxy itself, which relative to all space is stuffed full of stuff, you would still have better odds of going into the cleanest clean-room on the face of the earth and throwing a grain of sand and hitting a piece of dust floating in the air, than of accidentally running across a blockage larger than 100 tons on a random 6 parsec jump in our galaxy.

 

[sporegnosis]

Only reaction drives would work should you choose to build them. Personally, I think it was a totally screwed idea from the beginning. I'm liking CT more and more, though I will "cherry pick" other versions.

The real problem, as I see it, is that nobody is playing the same game anymore and the necessity for house rules drives us all further apart.

Traveller appears to be splintering from what was a tree with a strong trunk into a tree with weak branches.

With all these house rules, I'm definitely gonna need a bigger house soon.

I would propose that only moon sized stellar bodies affect jump lines and ships in j-space.

 

[esampson]

With all these house rules, I'm definitely gonna need a bigger house soon.

I would propose that only moon sized stellar bodies affect jump lines and ships in j-space.

I'll do you one better. I would propose (and I proposed this earlier) that 100D be considered to be nothing but a convenient reference point to help us avoid harder math. The true thing that causes occlusion is (IMO, and I know the rules as written don't really support this) is gravity. 100D is where the gravity will, on average, be low enough not to interfere.

In the case of 'small' interstellar objects (small in this case may still encompass things displacing hundreds of thousands of tons) you would have to get extremely close for them to occlude jump (and that's assuming they have enough mass to do it at all).

Am I saying that I'm going to whip up a chart of corresponding gravitational fields and when my players want to jump I'll go through and calculate out the mass of the planet, their distance, then translate that into a roll? No. I'll just use the 100D rule for the most part. I'll just remember that its more of what you might call 'a guideline' (arrrr).

 

[Murdoc]

I'll do you one better. I would propose (and I proposed this earlier) that 100D be considered to be nothing but a convenient reference point to help us avoid harder math. The true thing that causes occlusion is (IMO, and I know the rules as written don't really support this) is gravity. 100D is where the gravity will, on average, be low enough not to interfere.

In the case of 'small' interstellar objects (small in this case may still encompass things displacing hundreds of thousands of tons) you would have to get extremely close for them to occlude jump (and that's assuming they have enough mass to do it at all).

Pretty much my view as well.

Am I saying that I'm going to whip up a chart of corresponding gravitational fields and when my players want to jump I'll go through and calculate out the mass of the planet, their distance, then translate that into a roll?

I would, but then I'm very much a simulationist. Heck, I'd bother to figure out the gravity of a capital ship to see how close it'd have to be to stop an ACS from jumping, if it suited the plot.

Doesn't Page 374. Blockage. First sentence resolve this entire discussion:

"The existence of a gravity source (larger than the ship in jump) on the ship's course (at any point along the course AT THE MOMENT THE JUMP BEGINS) forces exit from the jump at 100 Diameters in front of the object."

Ok, so what if that object moves, does this ship come out at the spot where 100 diameters used to be when the ship entered jump, or something else? And since TIJ is not changed, that seems to lend some credence to the wave-collapse model.

 

[esampson]

...I would, but then I'm very much a simulationist. Heck, I'd bother to figure out the gravity of a capital ship to see how close it'd have to be to stop an ACS from jumping, if it suited the plot. ...

Just to give some idea of the numbers involved, if we assume the 100D 'limit' translates to 0.000025 Gs (the amount of gravitational influence one would experience 100Ds away from the surface of the Earth) then a capital ship massing 100,000 metric tons (this is mass, not displacement which makes things a bit harder to calculate but works in the cap ship's favor because it probably weighs more than its displacement) would exert a gravitational field strong enough to stop another ship out to a distance of a bit over 5 meters. :rofl:

It should probably be noted that that 5m distance is from the center of mass of the cap ship and not the outer edge, so it's going to need to be made out of something pretty dense.

In short, using that kind of model ships basically cannot affect each other's ability to jump. Not without some kind of gravitic device designed to mess up jumps. I think this does contradict some of the things written in T5, but for me it is still the best solution.

As for the issues of things being on the jumpline at the moment of jump, in all honesty I would ignore that as well. Since there clearly is some sort of correspondence between j-space and r-space (otherwise why would those masses on the jumpline matter?) I would hold that the ship really does 'travel' along the jumpline. It still remains in j-space with everything that has always entailed but as an example if an occluding mass were to cross the jumpline at the midpoint three and a half days into the jump then three and a half days into the jump the ship is violently precipitated out at the occlusion. If an occluding mass were to cross the jumpline 10% into the jump then it would need to cross the line about 16 hours into the jump to cause the ship to precipitate out.

Of course this leads to the problem of people voluntarily occluding for short range fast hops. I want to reach a planet quickly so what I do is maneuver to a position where I can target a system past it and then precipitate out at 100D. If the rules caused engine damage (especially if it were heavier the earlier into the jump you were) it would alleviate that problem, but now we are adding yet another house rule to the mix.

 

[HG_B]

Of course this leads to the problem of people voluntarily occluding for short range fast hops. I want to reach a planet quickly so what I do is maneuver to a position where I can target a system past it and then precipitate out at 100D. If the rules caused engine damage (especially if it were heavier the earlier into the jump you were) it would alleviate that problem, but now we are adding yet another house rule to the mix.

Just rule that the jump is always ~168 hours. "Early" precipitation just causes it to stop in J-space until the jump drive finishes running its programed flight.

The crew knows nothing until they return to N-space.

 

[esampson]

The only problem with that is that because everything in space is in some form of motion you can pretty much guarantee that ships would precipitate out with the occlusion long gone.

(Hmmm.....unless you were to rule that somehow the occlusion 'drags' along the ship in J-Space. That could possibly work)

 

[HG_B]

The only problem with that is that because everything in space is in some form of motion you can pretty much guarantee that ships would precipitate out with the occlusion long gone.

I don't see the problem with that. For instance, a Mars sized object (traveling at 24 km/sec [Mars's orbital speed]) occludes halfway through the jump.

When the ships precipitates out, the object would be ~7,257,600 km away. At 1G that is 15 hours away.

What problem do you see?

 

[esampson]

I don't see the problem with that. For instance, a Mars sized object (traveling at 24 km/sec [Mars's orbital speed]) occludes halfway through the jump.

When the ships precipitates out, the object would be ~7,257,600 km away. At 1G that is 15 hours away.

What problem do you see?

The fact that everything in space is in motion. Mars is travelling at 24 km/sec, but the sun itself is travelling around the Milky Way at 250 km/sec, so now you are 72,500,000 km away. Also, as an orbiting planet Mars has a pretty stately orbital velocity and its location is pretty well known. The things that are more likely to precipitate out a ship are things like unknown comets, wandering planetoids, and rogue planets and they will probably have velocities relative to the target system that are substantially different.

 

[HG_B]

The fact that everything in space is in motion. Mars is travelling at 24 km/sec, but the sun itself is travelling around the Milky Way at 250 km/sec, so now you are 72,500,000 km away.

NO. Who said that you killed your velocity relative to the Milky Way? Please cite new rule on this.

 

[esampson]

Sorry. Just an example. Since you would be coming from a star relatively close you're right, your radial velocities would be similar. My point was that the stellar velocities wouldn't be identical. The stars themselves are in motion, and not merely around the galactic axis. And of course the real problem remains that your most likely occlusions are going to be objects that have managed to achieve escape velocities from their home solar systems so that they can be wandering through deep space.

 

[HG_B]

Sorry. Just an example. Since you would be coming from a star relatively close you're right, your radial velocities would be similar. My point was that the stellar velocities wouldn't be identical. The stars themselves are in motion, and not merely around the galactic axis. And of course the real problem remains that your most likely occlusions are going to be objects that have managed to achieve escape velocities from their home solar systems so that they can be wandering through deep space.

Doesn't matter. The velocities aren't going to be THAT different within your local group. The object, over that time period, will be easily reachable with M-Drives. You still haven't expressed what the rule problem would be. So, the object travels after it occludes. That has always been the assumption with planetary objects in Trav that could mask/occlude.

 

[esampson]

Actually, the object would be (almost) completely unreachable with your M-Drive since you would probably be over 1000D away from any mass (either by actual diameter measurement or gravitational equivalency). However that is a completely different can of worms and after crunching through some numbers I realize that you're correct. That occlusion really will probably not have moved as far away as I originally thought. Even if the relative velocity of the object was an order of magnitude higher it would only extend the chase to a couple of days and starships usually carry several weeks worth of maneuvering fuel.

 

[Murdoc]

Just to give some idea of the numbers involved, if we assume the 100D 'limit' translates to 0.000025 Gs (the amount of gravitational influence one would experience 100Ds away from the surface of the Earth) then a capital ship massing 100,000 metric tons (this is mass, not displacement which makes things a bit harder to calculate but works in the cap ship's favor because it probably weighs more than its displacement) would exert a gravitational field strong enough to stop another ship out to a distance of a bit over 5 meters. :rofl:

Not so funny. If that's what it is, that's the way I'd play it, simple as that.

It should probably be noted that that 5m distance is from the center of mass of the cap ship and not the outer edge, so it's going to need to be made out of something pretty dense.

That could possibly explain why the hanger bay of an Imperial Star Destroyer is so close to the middle, so that captured rebel ships can't 'jump' away while inside.

The only problem with that is that because everything in space is in some form of motion you can pretty much guarantee that ships would precipitate out with the occlusion long gone.

(Hmmm.....unless you were to rule that somehow the occlusion 'drags' along the ship in J-Space. That could possibly work)

Hmm, that could solve the whole "conservation of momentum" (p373, Vectors are Preserved) problem, where your destination and origin planets are travelling at two very different velocities, relative to each other, making your ship come out at some hugely different velocity it has to correct for that has always been ignored in Traveller so far. Maybe we should use this!

 

[esampson]

Not so funny. If that's what it is, that's the way I'd play it, simple as that.

I was finding humor in the fact that to us 100kg humans a 100,000 metric tons seems like an enormous mass. To the universe it isn't even enough to generate an infinitesimally weak gravitational field (see below).

That could possibly explain why the hanger bay of an Imperial Star Destroyer is so close to the middle, so that captured rebel ships can't 'jump' away while inside.

Maybe because of the gravitic plating or something, but not because of the ship's mass. You can only consider the center of mass for gravitational equations when none of that mass extends past you. Mass extending past you actually exerts an influence away from the center of mass, lessening the gravitational field at that point. If you are in the center of the starship then the gravitational forces from all the bits of the ship cancel each other out, so the example 100,000 ton mass would have to have a diameter of less than 10 meters to ever exert enough gravity to precipitate out a ship (using my house rule).

Hmm, that could solve the whole "conservation of momentum" (p373, Vectors are Preserved) problem, where your destination and origin planets are travelling at two very different velocities, relative to each other, making your ship come out at some hugely different velocity it has to correct for that has always been ignored in Traveller so far. Maybe we should use this!

Feel free to use it. Heck, I may even decide to make it part of my campaign. However, as was pointed out the actual relative speeds are unlikely to be that different and the ships have an entire week in j-space to alter their vectors (according to the book as written). With a week's worth of acceleration even a 1G ship could overcome a vector differential of nearly 6000 km/s. If you were to jump clear to the other side of the Milky Way galaxy, which would pretty much maximize the relative velocity differences short of jumping into a system near the core as it whips around a supermassive black hole, the velocity different would only be about 500 km/s, less than 1/10th of what a 1G ship could overcome.