Redirected Jump exit point

[Hal]

Hi Guys,
The following thread is directed towards those who like to fiddle with their traveller universe more than towards those who like the OTU orthodoxy (no slight intended to EITHER groups by the by)

As GM, you are being put on the spot to make a GM ruling. You've taken the time to create the data on star system Omnicron for which the players intend to jump into. They intend to target Omnicron IV as their destination. So now you watch as they plan on using the rule that any attempt to exit jumpspace within 100 diameters of a world shall result in the exit point being shunted to 100 diameters. So you inform them of this fact - that they will be shunted. But that pesky player playing the Navigator asks you the following "Ok, WERE do we get shunted to?" Because as GM, you noted "OK, your vector is towards 183 degrees, with a built up velocity of 5 turns worth of 2g's (or 10 G's worth of velocity). The player plugs in the data for his ship's velocity, uses the formula for length of time it will take to slow his ship's velocity to zero, then begin the long task of chasing the planet. Surprised, the players discover that it takes a fairly longer time to chase a planet than expected! So the players complain after the session that the GM's decision on where their ship ended up after being shunted as patently UNFAIR!

As there doesn't seem to be any real rules created in any of the Traveller incarnations regarding shunted exits, I have the following proposals to make. Some of you may find this fun to inflict on your players, andn some of you may find it a real pain in the buttocks

First, you need to have a policy regarding how shunts work for your game universe. Second, you need to have a way of figuring out how Jump Drives work within your universe and consider the ramifications involved. As this is all "In your Traveller Universe", this is clearly an issue that depends on what you want.

Jump Drive shunted exits: Most people consider that jumps are an in/out affair without paying too much attention to what is going on in jump space. It might even be fair to state that few even bother considering a unified methodology for their universe saying "You arrive - it will take you 3 hours to land on the planet" and move their campaign story onwards from there. But others might want to explore the possibilities inherent in Jump space navigation and its effects on game play. In addition? GM's now have a BUILT IN reason for why jumps take a variable amount of time between entry into jump space and exit from jump space without even having to tweak the rules all that much. Simply put - any ship that tries to exit into the forbidden 100 planetary diameter range, have to "wait" until that planet is no longer projecting that "shadow" onto normal space. If a ship is just on the edge of the FRONT of the planet's zone, it has to wait until the planet has moved enough to uncover that exit point. So the GM checks the data and discovers the following:

Planetary velocity is 21 miles per second
Planetary Diameter is 5,000 miles

So you tell your players:

"Ok, the planet you're trying to reach has a diameter of 5,000 miles. 100 planetary diameters makes that a range of 500,000 miles. But since you came out in front of it, you also have to wait until its BACK half of 100 diameters is no longer covering your jump exit point. Hmmm. 500,000 miles x 1.6 (since the planet moves on a curved path and you estimate that it shouldn't be the full 2x100 diameters) is going to be 800,000 miles divided by 21 miles per second. That means you have to wait some 38095.2381 seconds or nearly 10.58 hours! The planet is receding away from you - and your vector is pointing your ship AWAY from the planet as it recedes. Ok Navigator, time to earn your keep."

The larger the planet, and the slower it moves through space - the longer those "interrupted exit" times will be for your Traveller Universe. Since it is strictly a math issue - the players can't really state "hey, that was arbitrary and unfair!". Just smile, point out that jumps are only accurate to within 3,000 km per parsec jumped, and inform them that the shaved their exit point TOO close to the planet's jump masked point. Of course, you don't plan on springing this "surprise" on them without warning right? So tell them HOW jump space navigation works in your world, and let them do the figuring out. Let THEM do the math scut work and then smile as you apply the results to the game.

Next post will contain another idea that can be used within a Traveller Campaign...

 

[Hal]

Ok - so you've decided that entry into a jump space results in falling down a lonnnnng tunnel through Jump space, with the exit point at the planned navigational location the ship desires to go. That's what the navigators are paid to do - figure out how to set the settings on the jump drive to where it will take them to their designated exit point. But then you wonder "Hmm, if it is a straight tube, what happens when you BEND it at the end?" Jump space TURBULENCE cry you! Delighted, you hop up and down and decide upon the following game mechanics for your universe:

Ships that enter into jump space and exit where planned, have minimal jump space sickness incidents. Ships that enter into jump space but discover the hard way, that their exit point was inside of the planet's 100 planetary diameters, will discover that their shunt point has moved their "tunnel" enough that it bent. The closer you are to the center of the planet's mass, the worse the turbulence. If you're right on the edge of the planet's 100 diameter location, the turbulence is far less and hardly an issue. So you devise the following chart:

Within 10 diameters: Roll versus piloting skill. Success minimizes jump sickness rolls to a normal saving roll versus a stat (or however you make saving rolls within the game system of choice). Within each 10 diameters closer to the planet's center - the roll is modified by a penalty of X (what ever you decide is appropriate of course). Ships within 50 planetary diameters will suffer a damage check against the Jump Drive. Ships within 40 diameters suffer a damage check of two against the jump drive, and one against the power plant.

The idea here is to make the navigators AVOID having their exit point shunted aside - as that will make transition into normal space easier.

Now, players have a reason to check into the data you as the GM, painstakingly compiled on various star systems within your Traveller Universe. NOW it matters how accurate navigation is at plotting the exit points from Jump space into normal space.

 

[Malenfant]

I can't help but feel you're overthinking this somewhat. For starters, players shouldn't be having to do navigational maths, that's what Astrogation rolls are for. Second, is it really actually all that important when and where most ships jump out?

Most of the time in the game itself you're not going to worry too much about this - the only time you're likely to do so is if there's something plot-related to throw at them. Otherwise you can just brush it off with "you jumped out 10 hours late and/or a few thousand km off the mark, so you arrive at the starport a bit later than scheduled" and then carry on from there. Given that this is pretty much the norm in the OTU (people arriving later or earlier than planned) I doubt that anyone at the starport will be too critical of it - anyone saying "we wanted this yesterday!" doesn't appreciate the in-game reality of the random jump time.

 

[Hal]

This is yet another idea that can be useful for Campaigns where GM's are involved with starship movement within his universe. Ultimately, it depends upon how much time and effort you want to put into maintaining your universe...

The following information pertains ONLY to game masters who desire this level of detail for their campaign. It is a very simplified rule that can be used without TOO much effort for their campaigns and if you're reading this, it means you already have the tools to do the work... a computer

Assuming perfectly circular orbits - the time it takes for a planet to complete one full cycle becomes an important piece of data. Convert the time it takes to complete one orbit around the sun into days. Divide this value by 360 (the number of degrees in a circle). This is the value you enter into the field "movement per day in degrees". Next, create a field titled "Start location". This is where the planet was relative to the sun, on day 1 of year zero. If you have percentil dice, rolling percentiles and multiplying it by 360 is a good way to figure out what "percentage of a cycle" it had completed

Now for the fun part. Determining where a planet is NOW or even IN THE FUTURE.

Lets say for the sake of example, that you have a world whose year is 492 days. Its motion would be equal to 360 degrees divided by year length or 0.731707317 degrees per day. You also rolled an 87 on percentile dice and determined that on day one of year zero, it had completed 87% of its circuit - or 313.2 degrees of movement. In your campaign, it is now day 213 of year 1107.

1107 x 365 + 213 = 404267 since day 1 of year 0.

404267 x .7331707317 = 295805.122 degrees of travel

Dividing by 360, you have a remainder of 245.122 degrees. The planet is CURRENTLy at the position on its orbit of 245.122 degrees.

Now, how does this help the GM? If one uses the direction of "EAST" to represent the direction of zero degrees (or 360 degrees), and use counter-clockwise movement to represent an increasing direction, or clockwise to represent a decreasing direction in degrees, he can determine on graph paper precisely where a planet is relative to any other planet within the star system. He can also state to his players "Ok, on this graph paper, plot where you want to come out of jump space."

Why bother with all of this? Well - for one thing, you have a way of predicting where a planet will be on any given day. Want to plot an intercept course from where a ship is to where a planet will be? Remember that equation in the little black books where T = 2 x (D/A)^.5 and where D = A x T^2/4 were written? Shortest course intercept between a ship's current location and where a planet will be based on the "Time" element can now be calculated within your game. I a player wants to manuever out to a Gas Giant that orbits 3.2 AU's from a star, and is starting at a world that is 1 AU from a star - you might want to be able to determine WHERE both planet and gas giant are relative to each other - then determine where the Gas Giant will be after 2.1 days journey. The "navigator" can be given the task "Ok, since your character is the navigator, here's the calculator, here's the formula, and here are the numbers - you figure it out"

It can be done easily enough. It can also be turned into a "Mini-game" for your players as they work out the numbers. Of course, sly dog that you are as the GM, you already have a spread sheet created that does all the scut work and need only use at most, 2 minutes to pull up Excel (or its Mac counterpart), 30 seconds to type in a few numbers, plus any other time you need to spend tweaking the results until you like them. Not a LOT of time to add a little more detail.

 

[Hal]

Originally posted by Malenfant:
I can't help but feel you're overthinking this somewhat. For starters, players shouldn't be having to do navigational maths, that's what Astrogation rolls are for. Second, is it really actually all that important when and where most ships jump out?

Most of the time in the game itself you're not going to worry too much about this - the only time you're likely to do so is if there's something plot-related to throw at them. Otherwise you can just brush it off with "you jumped out 10 hours late and/or a few thousand km off the mark, so you arrive at the starport a bit later than scheduled" and then carry on from there. Given that this is pretty much the norm in the OTU (people arriving later or earlier than planned) I doubt that anyone at the starport will be too critical of it - anyone saying "we wanted this yesterday!" doesn't appreciate the in-game reality of the random jump time.

Agreed - this level of detail isn't going to be for everyone. More importantly however, it gives the GM a reason to throw a plot related item at the players. If he does throw it at them, he's got the detail to back it up and say "Ok, so you arrived X hours late". If a player says "But hey, doing the math, I figure only 6 hours late - how come you're making us be 10 hours late?" - what do you do then? Of course, as GM you can say "Shaddup and play" or you can say "Hmmm. You're right. Ok - 6 hours late". Thing is? If 10 hours late makes the difference between bringing a cargo in on time or bringing it in late (and suffereing a penalty in payment) you can almost bet that the playerrs are going to howl at the delay <g>

 

[whartung]

I agree that the detail is available for those who want to use it. But I disagree on using the planets shadow as an explanation for the jump variability.

I mean, it's a fine idea, and jump shunts have to be dealt with somehow, but shadows are the reason fo the 10% time shift.

If they were the reason, then the variability could be simply mitigated by simply using better placement of the target position.

If the difference between arriving on time and being stuck in jump space for 10 more hours is a 1/2 hr extra travel timee, then my navigator had damned well better "aim" farterh in front of the planet to ensure that doesn't happen.

if jump times aren't that accurate, then you simply make sure your landing "zone" is big enough based on that variability to not encounter a jump shadow from a moving planet. This should be Navigator 101 IMHO.

This also implies that all Jump Out points will trail the planet, and all Jump In points will lead the planet (something I've never really thought about).

The reason for this is that if you start maneuvering to a trailing jump point, you're going to get there that much faster as the plenet is moving away in the opposite direction. So, while you need to be at the 100D limit for the planet, it doesn't mean you need to actually travel that far, as the plenet is leaving you behind as well.

In the same manner, jumping in to the path of the planet means you'll be arriving that much quicker as you get a free speed boost from the planet approaching you.

Now, the 1 and 2G drives are actually QUITE fast, so it's not clear how much the planetary orbit speed actually affects the calculation. I don't know if it will save seconds, minuts, or hours from you time to jump out or your time to maneuver in after jump.

Have to run the numbers sometime I guess.

 

[Malenfant]

Originally posted by Hal:
Agreed - this level of detail isn't going to be for everyone. More importantly however, it gives the GM a reason to throw a plot related item at the players. If he does throw it at them, he's got the detail to back it up and say "Ok, so you arrived X hours late". If a player says "But hey, doing the math, I figure only 6 hours late - how come you're making us be 10 hours late?" - what do you do then? Of course, as GM you can say "Shaddup and play" or you can say "Hmmm. You're right. Ok - 6 hours late". Thing is? If 10 hours late makes the difference between bringing a cargo in on time or bringing it in late (and suffereing a penalty in payment) you can almost bet that the playerrs are going to howl at the delay <g> [/QB]

Well, no... if the GM wants to throw a plot hook at them that only works because they arrive early or late, then he just goes right on ahead and throws the plot hook at them

. If anything this whole discussion is teaching us that Jump is wacky and variable, so people can calculate all they like but the random element is always there. If they say "but we should have been no more than 6 hours late" then the GM has every right to shrug and say "well, that's Jump for you".

Anyone penalising a trader for bringing in something late is probably not someone who should be in the interstellar trade business - if it's a known fact that jump arrival times are to some extent unpredictable then that will always be factored into any arrangements (ie you always give an extra week for transit time, for example). The only time a client will have reason to be pissy at a trader is if they're late because of their own actions.

Jump isn't for people who have to be at a place at an exact time (again unless they say "ok, I'm going to actually plan to get there a week earlier than I need to be" to cover insystem travel time, jump variability etc). But anyone who expects to be at their destination in exactly 168 hours is going to be disappointed.

 

[MR TEK]

calculating planitary motion and using that to cotroll transit time adds all sorts of addition bits of flavor.

Having a defined jump in zone, and jump out zone, leads directly to traffic patterns, which make sense, but had nothing driving them before.

A variation is does your jump vector follow your dirction of motion in realspace, or is it independant?

In other words, does the diirection you are travelling at jump, restrict your target. If it does, there would likly be jump initiation zone for each potential destination, and you could infer a ships destination from which zone it jumps from.

by the same token, ships travelling tword an incoming zone could be safly assumed to be trying to intercept inbound traffic, and ships comming bak from exit zones would also appear suspicious.

There would even be fines for traviling towards port in an outbound traffic lane, or away from port in an inbound traffic lane as tthese would be navigation hazards.

Yes space is vast, but with limited sensors on a commercial ship, the unsertanties of ships moving opposit to the traffic pattern, (by definition their relitive velosities would be very high,) would be very rough.

Yes the possabilities of collision are very small, but they have now moved from lottery type odds to odds that insurance carriers charge substantial extras for.

 

[GypsyComet]

Of course, even with 1G applied perpendicular to (and away from)the orbital path, that 10+ hour wait will be shortened considerably.

Of course, if you have a planet in the right orbit for that orbital velocity, the star's jump horizon may be a far more dominant concern than the planet's...

 

[far-trader]

The problem to be aware of, and I don't think I see many thinking about, is vectors won't always be 100% helpful even if they can be set up to go exactly where you want. It seems to me the old CT method of zeroing the vector before jumping makes a lot of sense.

Take the (extreme and simplified) example of two Type A Free-Traders going from Yres/REGINA to Pixie/REGINA. I hope I don't mess up the math, I'm just using the old travel times tables and typing as I go.

Case 1: "Safety First" or "The Tortise". Our first Captain believes slow and steady wins the race so he plots a course for 100D and full burns half-way, does his flip and full burns again to zero his vector. This takes about 17.6 hours by the old tables since Yres is a Size A world. He jumps and a week later arrives at 100D from Pixie with zero velocity. The trip to the port will take about 2.2 hours since Pixie is a Size 1 world. Total real space trip time is about 19.8 hours.

Case 2: "Faster is Better" or "The Hare". Our second Captain is all about speed, no time to waste on zeroing vectors and such nonsense. He burns for that 100D with no thought about flipping until he comes out of jump at the other end. His trip out from Yres takes only 8.8 hours and his passengers are cheering as they leave the first ship behind. A week later they come out of jump 100D from Pixie and flip over to slow down. By the time they do slow down they have passed Pixie some 6.6 hours ago. It'll now take about 13.2 hours (not too sure about this actually, it should be less) to get back to the port at Pixie. Total real space trip time is about 30.8 hours. The passengers are not too happy to arrive at Pixie and find the other ship has been there for about 11 hours already.

Naturally the smart Captain will plot his burns so he can make the best time at both ends (and improve on The Tortise a bit) but I've yet to see someone figure that out without first playing The Hare or being told. And of course the difference isn't so bad in less extreme cases or applicable in the reverse scenario, going from a small world to large world.

So what difference does 11 hours make? Well that depends on the game

 

[Malenfant]

Originally posted by GypsyComet:
Of course, if you have a planet in the right orbit for that orbital velocity, the star's jump horizon may be a far more dominant concern than the planet's...

Digging up the old chestnut of jump shadowing/masking, one thing we noticed when working on the Antares system was that its 100D limit was HUGE - 1,000 AU in radius! Our mainworld was orbiting a Brown Dwarf at 2,000 AU from the star, and we figured that the 100D limit could block off significant traffic from certain parts of the sky. Assuming that ships precipitated out of jump the moment their path intersected the supergiant's 100D limit, they could arrive up to 3000 AU from the planet if they were unlucky! That's a heck of a burn to do to get to your destination, so the implication would be that as the BD orbits Antares (completing an orbit in about 23,000 years), new jump routes to nearby systems open up depending on the orientation of the bodies involved.

As it is, ships would only be able to jump to the mainworld from an anti-Antares direction - any ships coming from behind Antares (from the perspective of the mainworld) would be caught by the jump shadow.

 

[Hal]

That is why when I use jump in my traveller universe - Jump shadow doesn't exist. The only times that mass of anything matters is at the moment of jump, and at the moment of exit. Otherwise, anything in between - even something as statistically insignificant as a wandering snowball laughingly called a lost comet (ie an iceball wanding through space without a star system to belong to) can interrupt a ship's journey between where it entered jump space and where it is forced to exit. This isn't TRAVELLER as I knew it in the late 70's onwards - it is STAR WARS with its hyperspace drive. But that's for those who write the Traveller rules to live with one way or another. Me? I play with the rules that makes best sense to me and for the benefit of my friends. Any rules tinkering I suggest is generally meant for others to enjoy (or not!) as they see fit.

 

[Malenfant]

To be fair, comets etc in interstellar space won't affect ships at all. The chance that a ship's path intersects that of a comet out there are infinitesimally small... ditto for asteroids within system too.

I don't believe in letting dice dictate what happens to a ship in transit - a misjump or jump precipitation should only happen if the GM has a plot that requires it to happen, and a ship certainly shouldn't be destroyed just because of a bad dice roll. That way players don't get pissed off, and a GM isn't left standing there looking like a lemon saying "sorry guys, the dice said your ship blew up on re-entry".

 

[marvo]

I agree with Far-Trader on this one. Zero your vector before jumping. The way I look at it is that the curvature of space is different to the curvature (or not) of the jumpspace/wormhole. As Far-Trader pointed out, accelerating towards your target in real space may leave you with a large vector going the wrong way when you exit jumpspace. In real space it looks like a straight line, but the wormhole may be a large loop ending at 90 degrees or more from your original direction. Myt house rule is that any shunt or failed astrogation role gives you a random direction vector. I determine this with a D12 (keeping it 2d for playability.)

Also jumping blind into a system at 10,000kph could be very dangerous. Sure it's almost all empty space, but the 'almost' will kill you at high speed. I can see where this would be a usefull military tactic, but not for the average trader.