Jump Shadow rule & piracy

F33D

Mongoose
Below is a simple rule/tool to deal with jump shadows and travel times to jump point.

(see this thread for background) http://forum.mongoosepublishing.com/viewtopic.php?f=89&t=52602

Steps:

1)When PC's decide on their destination world, roll a D10. Rolling a 1 means that the world the PC's are leaving from is in its stars jump shadow relative to the destination world. (see diagram below, Earth being the world the PC's are on and Barnard's Star being the destination system.)

shadow.jpg

2) Roll D10 (same as step 1) to determine if the DESTINATION world is in jump shadow of its OWN star.

3) Roll 1D6 on the Shadow Travel time table to determine travel time (continuous accel/decel) to the Shadow jump point. Or, from the arrival point if the destination world is in shadow.

shadow trav times.jpg

If you recall your Astrogation rolls, you will see that a jump may not be accurate. If that is the case when jumping TO a world that is in shadow (Barnard's Star system TO Earth as the above diagram shows) the inaccurate jump may cause the ship to be precipitated out of J-space on the opposite side of the Sun from Earth. That is about 340,000,000 km from Earth. (over a 4 day trip @ 1G)


Piracy: When PC's contract for freight, the company shipping the cargo gets it insured. The info includes all the relevant data about the Star ship that is hauling that cargo. ID, type, armament, departure time, etc. Pirates may have a source inside that Star port insurance office that will tip off the pirates about ships departing to a planet/system that will necessitate the long trip to a jump point clear of the star's jump shadow.

The other side of the coin: (See the 1st diagram above.) Pirates may hang out on the opposite side of Earth's orbit to pick off ships incoming from Barnard's Star system who inaccurately jump into the Sol system...

Have fun with your players...
 
F33D said:
The other side of the coin: (See the 1st diagram above.) Pirates may hang out on the opposite side of Earth's orbit to pick off ships incoming from Barnard's Star system who inaccurately jump into the Sol system...
As well as Naval vessels looking for prowling scallies.
 
Something from me, and I've tried to discuss in that other thread...

To me this is still a 2d discussion of a 3d system. Why can't I just plot to come on above/below the ecliptic high enough to be out of the primaries 100d limit? Why isn't our data libraries and software good enough to have (in thousands of years of Imperiums and jump travel) the orbits of all planets in all at-least common systems etc.. I mean even Stargate SG-1, those pitiful 20th century no-ftl Terrans had a good grip on "stellar drift" and could calculate it to correct the stargate network map they found on Abados.

OF course yes there is a balance of coming in close to save fuel (on the in-system travel) vs. pushing the limit on what is a safe jump, but I have my own theories on that.
 
GamerDude said:
Something from me, and I've tried to discuss in that other thread...

To me this is still a 2d discussion of a 3d system. Why can't I just plot to come on above/below the ecliptic high enough to be out of the primaries 100d limit?

Already answered your Q on other thread. Pls don't clog this thread with repeat Q's.
 
I know this is your program (hence making multiple threads) and you're very proud of it...

but nothing has been answered to my satisfaction - merely waved away and rationalized.

sooo.... maybe you should stop creating multiple threads trying to drive people to your 'cute' web page? *winks*
 
GamerDude said:
Why can't I just plot to come on above/below the ecliptic high enough to be out of the primaries 100d limit?
One can certainly do that, but depending on the position of the
destination system one could have to travel far beyond the star's
100d limit to reach a point where the jump route to the destina-
tion system does not touch the star's 100d limit. When the star-
ship moves above or below the ecliptic and reaches the edge of
the 100d limit in the sketch below, the destinations in the grey
cone are still shadowed by the star:
 

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GamerDude said:
I know this is your program (hence making multiple threads) and you're very proud of it...

No, isn't. I just don't have time to tutor someone through high school right now,
 
Please, everybody, separate and go back to your corners.

The knowledge that stars have jump shadows and that sometimes, it might be impossible for a Starship to directly jump straight to the planet due to it being on the far side of the destination star is something that has not really been covered in Traveller.

Likewise, there are no rules for working out the times required to Jump where the planet of origin is behind the star's Jump shadow relative to the destination system - it all looks like something the Referee will have to rule on, on a case by case basis.

Unless the Jump corridors are curved, enabling the Jump vector to skirt around the star to arrive mathemagically at the destination world's 100 diameter limit, regardless of the worlds' relative positions at the time of departure and arrival - the fine detail behind the Astrogation calculations.
 
Jump shadows are not just put out by starts. Plotting the jump (should, per the rules) require careful planning to avoid jump shadows from planetary-sized objects in the departure and destination system.

Traveling above/below the plane of the ecliptic only helps you avoid jump shadows of the departure system (for the most part anyways). The game mechanics don't really cover these sort of issues. It's pretty much just assumed that when you jump you do your rolls to come out where you planned on coming out.

I'm also not a stellar cartographer, so I don't know how much you have to worry about the star systems being 'above' or 'below' the galactic plane.

Really the calculations only get truly complicated when dealing with multiple jump numbers where you have to pass through additional star systems. Then you may indeed have to boost for a week in standard drive mode just to get the right angle on jumping 6 hexes on the map, and going through 5 star systems. But for systems that are 'next door' at Jump 1 should be relatively easy to do.

And, jump technology and navigation has been around for such a long time its relatively routine for starships. Much like navigation is today with the casual boater - it's pretty much like driving a car. Being a skilled person on matters when the detrius hits the fan. THEN you really need to be on your A game.
 
phavoc said:
Jump shadows are not just put out by starts. Plotting the jump (should, per the rules) require careful planning to avoid jump shadows from planetary-sized objects in the departure and destination system.

Unless you are VERY close to the planet in question, it isn't an issue as literally a few minutes of maneuver would clear the planet from your line of site to the star system in question. In a solar system it is MUCH harder to plot a course to "hit" a planet.

See this link for an idea of the scale of our solar system and how the planets are nothing.

http://www.phrenopolis.com/perspective/solarsystem/
 
phavoc said:
And, jump technology and navigation has been around for such a long time its relatively routine for starships.
The limiting factor would be the quality of the available data about
the positions of stars and planets. Each planetary system (and the
entire galaxy itself) is a mathematical n-body problem which has no
precise solution, only an approximate solution, which would lead to
the need of a safety margin which would increase with the distance
of the jump. I suspect that an astrogator would have to be suicidal-
ly dumb to attempt to leave jump space exactly at the 100d limit of
the destination system's star after a jump of 6 parsec.
 
You move out to 100D, plot your jump and then jump. 168 hours give or take later you get there.

Between you and the far end are light years worth of jump shadows, stars, rogues of all types, gravimetric shifts, anomolies, the odd random wormhole, micro black holes and a whole lot of other things.

So lots of things you need to fly around between A and B.

A decent astrogator, jump space being a very strange place full of windy paths to follow and a jump plot that curves around all the shadows. Problems all solved and the game continues.
 
Captain Jonah said:
Between you and the far end are light years worth of jump shadows, stars, rogues of all types, gravimetric shifts, anomolies, the odd random wormhole, micro black holes and a whole lot of other things.

So lots of things you need to fly around between A and B.

No, there's really nothing to speak of out there, other than space. That's why galaxies can pass through each other without, statistically speaking, any collisions of stars & solar systems.

If you were to shoot a football right through the galactic edge to the other side, odds are you wouldn't hit anything solid.
 
rust said:
the destinations in the grey cone are still shadowed by the star:
That shadow/cone is done from a point at the "equator" (plane of the ecliptic sliced through the star) and shooting directly into the star... *not* from a point above/below the ecliptic.

basically, I'm saying your angle is all wrong with respect to the ecliptic, and depending on where you view things etc changes the shape of how the shadow looks.

I'm not about to get 3d modeling software just to explain it any further.
 
alex_greene said:
Unless the Jump corridors are curved, enabling the Jump vector to skirt around the star to arrive mathemagically at the destination world's 100 diameter limit, regardless of the worlds' relative positions at the time of departure and arrival - the fine detail behind the Astrogation calculations.

That's a nice explanation! I've always assumed that jump travel was necessarily a straight-line, but curved plots provide an alternate way of avoiding the need to maneuver in-system well beyond 100d to avoid jump shadows.

My solution to that problem has always been "There is absolutely no interaction between normal space and jumpspace, therefore there are no jump shadows IMTU.", but curved jump plots allow for jump shadows to be ignored on a routine basis while still keeping them around as a potential plot device if needed. I'll give some serious thought to changing my position on them.
 
nDervish said:
alex_greene said:
Unless the Jump corridors are curved, enabling the Jump vector to skirt around the star to arrive mathemagically at the destination world's 100 diameter limit, regardless of the worlds' relative positions at the time of departure and arrival - the fine detail behind the Astrogation calculations.
That's a nice explanation! I've always assumed that jump travel was necessarily a straight-line ...
It is. In the higher dimensions of Jumpspace, at least. It's Einsteinian spacetime that's curved, which is why Jump is a shortcut ... :D

nDervish said:
... curved jump plots allow for jump shadows to be ignored on a routine basis while still keeping them around as a potential plot device if needed. I'll give some serious thought to changing my position on them.
Always leave room for accidental time travel, the slingshot effect, dimension jumps, mirror universes, and so on and so forth. As plot devices go, they provide decent explanations for Misjumps - "Our multidimensional Jump bubble may have intersected with the Jump shadow of a quantum string filament that happened to pass through normal space at spatial coordinates corresponding to our plotted course, Captain." "In other words, we hit one hell of a bump in the road. And that's why it's Earth in 1926 and we're dressed like Chicago mobsters, trying to drive a car." "Yes, Captain, and badly, too."
 
"Our multidimensional Jump bubble may have intersected with the Jump shadow of a quantum string filament that happened to pass through normal space at spatial coordinates corresponding to our plotted course, Captain." "In other words, we hit one hell of a bump in the road. And that's why it's Earth in 1926 and we're dressed like Chicago mobsters, trying to drive a car." "Yes, Captain, and badly, too."

Random unplanned timetravel. Always good fun.
 
GamerDude said:
rust said:
the destinations in the grey cone are still shadowed by the star:
That shadow/cone is done from a point at the "equator" (plane of the ecliptic sliced through the star) and shooting directly into the star... *not* from a point above/below the ecliptic.
Stars are spheres, so this diagram can be rotated to represent any plane that runs through the centre of the star. Flip it so that it shows a 'vertical' slice rather than a 'horizontal' one - the black dots are now ships boosting out from the planet until they reach the star's 100 diameter limit above/below the plane of the ecliptic. Once they get to the surface of the 100-diameter limit then they can jump to any destination which is 'above the horizon' set by the jump shadow - draw in a tangent to the tan circle which touches a black dot to get an idea of this.

Sol system is intriguing because Terra orbits just beyond the 100 diameter limit for Sol, so for part of the year ships can just boost out to the Terra 100-diameter limit, whilst for other parts of the year they have to boost further to bring their destination into view over the limb of Sol's jump shadow. If you assume that mainworlds tend to be in the habitable zone, then those orbiting cooler stars than Sol (which should be the majority if YTU follows the mass distribution we observe in the real world) will be permanently jump-masked - that is the planet orbits inside the star's jump shadow and ships have to boost out to the closest point on the surface of the stellar jump shadow where they can 'see' their destination before they can jump (a bit like how the 'shelf' and the 'shallows' work for stutterwarp in 2300AD).

If there is a planet in the habitable zone around Alpha Centauri B for instance (ie orbiting at ~100 million km, about where Venus sits in the Sol system) then they are going to be about 20 million km inside the jump shadow cast by their star. For a ship boosting at 1G then even in the best case you can get (when the mainworld is in opposition to a particular destination), you are still quadrupling the transit time to get to the 100-diameter limit compared to an earth sized planet that is orbiting outside the stellar jump shadow. In the worst case, when the mainworld is in conjunction to the destination you are having to boost something like an AU (150 million km) to reach a viable jump point - instead of 4.5 hours you are travelling for nearly 3 days before you can jump.

Regards
Luke
 
It certainly makes for a different feel for pirates - the jumpcusser approach which doesn't work for earth-sized planets becomes much more feasible in a 48-hr plus slog; provided you have the thrust and the sensors, intercepting someone is much more feasible.

Not least because the 'least-time-transit-to-jump' corridor is predictable, as opposed to being a route from the centre of a sphere to any point on the periphery.
 
Somebody said:
But the humans had Carter. The Imperium only has computers :)
Ahh yes dear Samantha... oh the heavenly dreams about her... :D

The rest of you can have Dr. McCay. His sister wasn't half bad (and I think smarter) 8)


Al B.   [B-)
 
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