Inaccurate Jumps in Traveller

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HalC
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Inaccurate Jumps in Traveller

Postby HalC » Thu Jan 11, 2018 2:52 pm

Hello Folks,
Old "ex-COTI" member here...

Question that I'd like to ask pertains to inaccurate jumps in MgT. To wit:

In the early part of the example of play on page 3 of the Core Rule Book (CRB) 1st edition, it says:

"Referee: Anyway, you’ve just jumped to the Cogri system. You’re
about two million kilometres out –
Chris (Morn): ‘Accurate’ as usual, Kathya! Only twice as far away as
we should be."

That's when I wondered at the time I purchased the pdf - "Where are the rules for inaccurate jumps as far as determining how distant from your targeted break out point into normal space one should be"?

I was sort of surprised to see that the Astrogator's skill has no bearing on how accurate or inaccurate a jump would be, and even more surprised to find that I couldn't locate anything on how to determine distances off the plotted exit point, one can end up. I got to thinking "is this just the GM taking license to choose what he'd like to portray thing - ie, fiat" because I couldn't find anything.

Then I looked closer at the task rules, and spotted something that had me wondering...

page 50 talks about levels of success or failures, and a failure by 1 is only a marginal failure - one in which the GM can allow the player to scrape a success, but at cost.

Page 141 talks about what is required for a successful jump, and lists that any modified roll of 0 or less is a misjump, any modified roll of 8+ is a successful jump, and any other roll is an inaccurate jump that is a minor set back.

I know that CRB 2nd edition has come out, but I currently don't have the book nor the funds at the moment to pick it up. My question is "has this been fixed at all" in the sense that there are now specific rules to determining the distance one finds oneself with an inaccurate jump?

I've taken a look at other Traveller Systems trying to find rules pertaining to inaccurate jumps, and I'm not overly fond of the T5 methodology for that. Megatraveller has "Jump mishaps" that when superficial, makes time in jump space last 1d6+4 days instead of the usual 6,7,7,7,7,8 days it could (rolling 1d6). If the mishap is minor, the distance further away from the intended break out point, is 1d6 x8 hours further away (which begs the question, is this going to be true whether the ship has 1g maneuver drives or 6g maneuver drives). If I were mean, I suppose I could simply figure out how long it takes for a 6G ship to travel 48 hours and say that is the max distance of an inaccurate jump, and then divide that max range by 6 to get a 1d6 distance, or by 12 and get a 2d6 distance table or what have you.

So I guess in my own long winded way, I'm asking if CRB 2nd edition fixed this, or do I have to create my own table and work it from there?

the line "+ the Effect of the divert power Engineer check" has me wondering...

Let's say you have an engineer with Engineer(Jump) at +1. I roll 2d6, and get a 9. Plus 1 makes it a 10. Needing an 8, I make my success by 2 levels. This becomes an effect bonus of +1 per page 51. Does that mean that when I make the final roll for entering jump, that I roll 2d6+1 for the engineer's jump effect? That means that I have to roll a 7+ on 2d6 to have a normal jump, and any other roll means an inaccurate jump?

What if the number of levels of failure determine just how far away the ship ends up missing its original intended exit point? So, in the case above, rolling a 2 when I needed a 7+ would be -5 levels of effect for the mis-aimed jump?

Let's see how this works from the Astrogator's side of things. See, from where I sit, here's the logic behind jumps and everything that goes into it.

Astrogator's numbers have to be spot on. If they're off, then the BEST accuracy that the Pilot and Engineer can hope for is by how much the astrogator was off by.

Pilot's maneuver has to be spot on. He's got to approach the jump point with the right velocity and the right angle to match what it was the astrogator wanted. If he flies too fast, he enters the jump point at the wrong time. If he's not on the approach angle properly, then he enters the jump space jump point at the wrong vector.

Engineering has to apply the energy properly at the proper levels at the proper time, in a uniform fashion (which was one reason that unrefined fuel supposedly caused problems with jumps - the power might spike or drop unexpectedly).

If EVERYTHING goes right, then the aim is true, the follow-up by the pilot hits the mark, and the engineer insures the jump space entry itself (its formation etc) is perfect. The ship goes PRECISELY where it is supposed to go.

The only real wildcard then, is how long one remains in Jump space itself! More on this in my next post.
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Re: Inaccurate Jumps in Traveller

Postby AnotherDilbert » Thu Jan 11, 2018 3:08 pm

HalC wrote:
Thu Jan 11, 2018 2:52 pm
So I guess in my own long winded way, I'm asking if CRB 2nd edition fixed this, or do I have to create my own table and work it from there?
Prepare to make your own table...
HalC
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Re: Inaccurate Jumps in Traveller

Postby HalC » Thu Jan 11, 2018 3:37 pm

At one point in time, I asked others "Has anyone ever seen material suggesting that time in side the ship does not pass at an equal rate to time external to the ship while in jump space?" The reason I asked is this...

If the time in jump space is variable - and the time experienced within the ship matches the time in the universe, then the issue of firing a bullet (ie, aiming a ship to exit jump space into normal space at a specific point in time) becomes much harder. The time spent in jump space that is longer than 168 hours exactly, or shorter than 168 hours exactly, means that the star system itself moved how ever many miles per second it does, and the planets within the given star system also moves at how ever many miles per second it too is moving, for a combined net effect of missing the target point in a big way.

On the other hand, if time within the ship passes differently than time in normal space, then from the eyes of an observer in normal space, the ship spent EXACTLY 168 hours in jump and came out exactly where it was supposed to. The difference being, the people experienced more or less than the 168 hours that the universe had observed.

That is why I am VERY interested in Inaccurate Jumps in the Traveller Universe. For my traveller universe? Hitting a 100 diameter limit (of stars or planets) results in the ship being precipitated out of the INTENDED exit point, and coming out at the 100 diameter limit instead. This causes a "turbulence" effect, that results in Jump Sickness. As was posted elsewhere in some thread here at Mongoose Forums...

The disconnect between the jump universe and the normal universe isn't smooth.

This is why navigators in my traveller universe try to avoid hitting the 100 planetary diameter or stellar diameters where possible. But when you add in the effects of an inaccurate jump - it may come to pass that a close shave on a 100 diameter limit becomes a full fledged crash against that boundary.

For me? Jump Shadows was never what CT or MT was about. So, if you're within a diameter limit of 100 while attempting to ENTER jump space, there is a problem (always has been part of the rules from CT). Once you enter Jump Space, nothing matters. Once you TRY To exit into normal space - if you're within 100 diameters, the normal universe rebels against that jump exit event, forcing the ship out AT the 100 diameter limit (hence, the jump turbulence/sickness issue).

In the end, I would like to be able to create a unified system for jumping:

Jump spatial Accuracy that is based on Astrogator's skill and the Pilot's skill. This is the initial aim point of the ship when it breaks out of Jump space into Normal space.

Jump temporal Accuracy (which affects accuracy via time) is based on the navigator's skill. This is what determines the +/- 10% in hours for duration of the Jump itself.

Having the rolls get broken up into separate components like that, helps to determine the final exit point in a way that does away with the need to have a Jump Shadow or precipitation into normal space with intervening objects like asteroids, comets, wandering dwarf stars or wandering planets etc.

For me, CT "Jump space" was distinctly different than was Star Wars hyperdrive. The way it is now, Traveller Jumps are essentially Hyperdrives in effect.
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Re: Inaccurate Jumps in Traveller

Postby HalC » Thu Jan 11, 2018 3:47 pm

AnotherDilbert wrote:
Thu Jan 11, 2018 3:08 pm
HalC wrote:
Thu Jan 11, 2018 2:52 pm
So I guess in my own long winded way, I'm asking if CRB 2nd edition fixed this, or do I have to create my own table and work it from there?
Prepare to make your own table...
For some reason, I heard that as "get used to disappointment".

Now all I need is for someone here to send a Smiley so I can ask "why are you smiling?" ;)

As for making my own table, I probably will. I am going to have to at least include the options of 2 million km - just so that it can be used as if explaining the stuff on page 3 of the CRB.
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Re: Inaccurate Jumps in Traveller

Postby AnotherDilbert » Thu Jan 11, 2018 4:54 pm

By canon you should not miss:
JTAS24, p34 wrote:One of the benefits of the jump drive is its controllability: jump is predictable. When known levels of energy are expended, and when certain other parameters are known with precision, jump drive is accurate to less than one part per ten billion. Over a jump distance of one parsec, the arrival point of a ship can be predicted to within perhaps 3,000 kilometers...

I run with much higher inaccuracy.
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Re: Inaccurate Jumps in Traveller

Postby ShawnDriscoll » Thu Jan 11, 2018 6:01 pm

I'll ask my players how they want to handle jump travel, if it's going to come up in a game session. Then ask them how they want to handle misjumps. That way, if they come up, we're not halting the game while looking things up in the book.
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Re: Inaccurate Jumps in Traveller

Postby Reynard » Thu Jan 11, 2018 9:32 pm

I've participated in games in which our group experienced inaccurate jumps (IT WASN'T MY FAULT!) and we discovered we would have to spend a few more days catching up to the gas giant or mainworld we had planned to exit next to. Actually a good time for the ref to roll encounter chances.
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Re: Inaccurate Jumps in Traveller

Postby Condottiere » Fri Jan 12, 2018 12:59 am

If the narrative is linear, misjumps tend to be plot driven.
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Re: Inaccurate Jumps in Traveller

Postby HalC » Fri Jan 12, 2018 2:02 am

Condottiere wrote:
Fri Jan 12, 2018 12:59 am
If the narrative is linear, misjumps tend to be plot driven.
I tend to run sandbox style and go with the dice. The player(s) tend to drive the story with the gm (that's me!) Giving them multiple plot threads they can pursue as desired. It avoids railroading them to a larger degree and gives them more latitude in choices (from my perspective).

The main reason for exploring accuracy of jumps is that the more time spent in normal space, in my opinion, the more possible the need for armed turrets.

I tend to use GURPS TRAVELLER for my games, but I also try to picture life in the 3rd Imperium. Suppose you have a class C starport with say, a single 400 dton cruiser on station at the main world, and another cruiser at the nearest gas giant. The third cruiser is on R&R status. The on duty cruiser is grounded at the ground port ready to head into space at a moment's notice. By moment's notice, I mean within 20 to 60 minutes. Further suppose, ground control for the starport is always a turn behind the cueball as far as intentions go - that is, they have to query the starships about intentions, warn them that they are on dangerously close orbits or convergent flight plans, and to veer off. That's one turn to become aware of the situation, warn off the transgressors, and alert the naval forces that a situation is unfolding.

Then the readiness state of the ship comes into play. Does the commander wait until he has a full crew aboard, or does he lift ship short-handed? Are the crew disciplined enough to be ready fast enough? Then, the question arises...

Can the prey avoid the pirate that is lifting off the surface after them, reach jump status outside the 100 diameter radius, or will the prey have to face the pirate? Then? If the pirate can catch up and board the prey, can it off load the freight/cargo before the authorities can intervene? Once the authorities reach the scene, can the pirate reach the nearby jump limit of 100 diameter before naval engagement damages it's ship?

Factors involved are: when does the pirate match vectors with its prey? Does the naval element race like a bat out of hell to get to the scene, only to get one or two shots off, and then take time to turn around - or does it try to match vectors and lengthen its engagement envelope?

Vectors movement (normal space) is the only time an enemy action can affect merchant ships. Marc Miller envisioned a universe where pirates exist. The pirate's job therefore, is to work within the game rules (be the pirate a pc or npc) and either find a way to make it work, or prove it can't be done.

Jump accuracy is one way to lengthen normal space maneuver time. Normal tempo of human reaction time is a way to explore why reaction forces don't hit the panic button until they know for certain they are needed, and maybe, the crew availability is such that they are missing a turret gunner or two, or they have the navigator trainee instead of the seniormost navigator on hand etc. Maybe the navigator doesn't plot the most time efficient course to reach the engagement envelope with optimal fire options for his commander.

Someday - using strictly MgT rules, or BY rules, run the piracy scenario outlined above using Fantasy Grounds, and release actual game life of the runs as an html file, for people to enjoy, analyze, etc, and take it from there..

For my sandbox universe, however, I'd like to figure a way to increase normal space maneuvering time with our having to use the newer jump shadow rules or precipitating out of jump space via planetary masses intruding into jump space. I'd like to make the navigator's skill actually MEAN something in game play. Coupling jump accuracy at a spatial level with time spent in jump space at a temporal level seems to be a possible way to go.

Maybe, each level of success in the temporal goal determined how well the navigator can make it. Maybe, each 2% time shaved off from normal time in jump space is a -1 penalty to the navigator's roll? Time will tell whether or not this idea is worth pursuing or not. ;)
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Re: Inaccurate Jumps in Traveller

Postby Condottiere » Sat Jan 13, 2018 1:27 am

Image

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Linwood
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Re: Inaccurate Jumps in Traveller

Postby Linwood » Sun Jan 14, 2018 3:02 am

AnotherDilbert wrote:
Thu Jan 11, 2018 4:54 pm
By canon you should not miss:
JTAS24, p34 wrote:One of the benefits of the jump drive is its controllability: jump is predictable. When known levels of energy are expended, and when certain other parameters are known with precision, jump drive is accurate to less than one part per ten billion. Over a jump distance of one parsec, the arrival point of a ship can be predicted to within perhaps 3,000 kilometers...

I run with much higher inaccuracy.
This may be part of the solution for you, HalC. If the jump is spot-on the exit will be within 3000 km (times distance in parsecs perhaps). Maybe double this per point of negative Effect - or multiply by 1D per point of negative Effect if you want more variability (or to reflect damage, unreliability, or local spacetime oddities).
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Re: Inaccurate Jumps in Traveller

Postby HalC » Sun Jan 14, 2018 8:41 am

Linwood wrote:
Sun Jan 14, 2018 3:02 am
AnotherDilbert wrote:
Thu Jan 11, 2018 4:54 pm
By canon you should not miss:
JTAS24, p34 wrote:One of the benefits of the jump drive is its controllability: jump is predictable. When known levels of energy are expended, and when certain other parameters are known with precision, jump drive is accurate to less than one part per ten billion. Over a jump distance of one parsec, the arrival point of a ship can be predicted to within perhaps 3,000 kilometers...

I run with much higher inaccuracy.
This may be part of the solution for you, HalC. If the jump is spot-on the exit will be within 3000 km (times distance in parsecs perhaps). Maybe double this per point of negative Effect - or multiply by 1D per point of negative Effect if you want more variability (or to reflect damage, unreliability, or local spacetime oddities).
I recall that JTAS 24 article fondly... ;)

It goes on to say...

"Error in arrival location is also affected by the quality of the drive tuning, and by the accuracy of the computer controlling the jump; these factors can increase jump error by a factor of 10."

By that section of the article, it would seem that the largest error can only be off by about 30,000 km per parsec - and that only if the drive tuning (skill roll against the Ship's engineer presumably) is off AND somehow, the computer not being up to snuff.

Now if one went with that concept, then we shouldn't see anything worse than 30,000 km per parsec traveled. High Guard does have a jump accuracy issue in that when a ship fails to engage (mishap) its jump drive properly (much as is done in MgT), the distance that inaccuracy can significant.

"Minor: A jump relativity error occurs, but when the ship emerges in the destination system, it is 1D times 8 hours from the destination world"

If we substitute "destination world" as being the aimed for exit point, the question that is begged is "1d times 8 hours" absolute (meaning 1d6x8 hours for a jump 1, 2, 3, 4, 5, or 6 drive) or 1d6 times 8 hours for a 1 g drive (since those were relatively more common in the earlier versions of Traveller back in those days)?

Now, in the vignette from the Core Rules Book page 3, we have:

"Referee: Anyway, you’ve just jumped to the Cogri system. You’re
about two million kilometres out –
Chris (Morn): ‘Accurate’ as usual, Kathya! Only twice as far away as
we should be."

Ok, that's not a rule, since the jump accuracy issues in MgT are categorized in any way shape or form that I can see - it is the only thing I have to work off of. 2,000,000 km is decidedly larger than 3,000 km. Note too, that the character (Morn) is complaining that it is only twice as far as the last time. So we have two examples of how inaccurate the jump can be in that particular referee's campaign. One could infer (and it would be an inference, as there doesn't really seem to be an implication!) that the GM (author) who wrote that passage intended perhaps 1d6 x 1,000,000 km. Alternatively, it could just as easily have been 1d6 x 500,000 km (where the last jump got a roll of a 2, and this jump got a 4 perhaps?).

There is always the problem with material written after the golden age of Traveller (Classic Traveller) in the sense that what is written for the game universe is not always in lockstep with the original. JTAS 24 was written well before Jump Masking and other associated rules were introduced. Earlier material did allude to the fact that being within 100 diameters of a star or world would cause problems, but at that time, the diameters for stars were not part and parcel of the game materials.

To the best of my knowledge, there has been no specific clarification on whether or not time is asynchronous or synchronous in the sense that time experienced within a ship is the same time that passes in jump space. We are already experimenting with how time flows with the use of atomic clocks (and have experimented with that decades earlier than when I am writing this now). It wouldn't have taken a big stretch of imagination for experimenters to question whether time passes in synchronization with the normal space in Jump space.

That being said, there have been instances where real world physics has been alluded to with respect to "visible astronomical data for a world light years away would be out of date by the time the viewer is seeing it (as regards to jumping accuracy no less!). So, if I am carefully to hit a moving target that is far away - I have to "Lead the target" such that when the bullet arrives - it intersects the target by the time the bullet is in the space occupied by the target (which wasn't there when I fired the bullet initially). So if it requires that the bullet travel precisely 3 seconds to hit its target, and the target is moving 6 feet per second - if you're one second too early, you miss. If you fire the bullet one second too late, you miss. The "+/-" 10% time duration of the Jump drive effect seems to line up perfectly with the issues of being too soon or too late - and the bullet (the ship) missing its planned for exit point into normal space suffering those issues.

If a planet is moving at a rate of 22 miles (35.4 km) per second in a given direction - a miss by 16.8 hours means that the planet will have moved 16.8 x 3600 x 35.4 km or 2.141 million kilometers. That is with PERFECTLY dead on accuracy for the originally aimed for destination point. Now, in the grand scheme of things, assuming the jump aim was accurate within 3,000 km - we should have no further a miss of that aimed for point than say, 2.144 million km.

Doing the math for MT, an inaccurate jump that misses by 1d6 x 8 hours, means a miss (if I did my math correctly!)

08 hrs: 4,064,256 km
16 hrs: 16,257,024 km
24 hrs: 36,578,304 km
32 hrs: 65,028,096 km
40 hrs: 101,606,400 km
48 hrs: 146,313,216 km (almost one AU in distance!)

Note that these values are a straight acceleration using 1/2 Acceleration (9.8 meters per second) * Time in seconds squared. The distances would be shorter if using the accelerate 1/2 way there, and decelerate the remaining half to reach a zero relative velocity at the end of the journey.

So, that's one outtake on misjumps from Megatraveller. T5's accuracy for jumps is even worse such that a ship aiming for earth, could end up beyond the orbit of pluto (if I'm reading THOSE rules correctly).

Next post will discuss GT misjumps and jump mishaps.
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Re: Inaccurate Jumps in Traveller

Postby HalC » Sun Jan 14, 2018 9:14 am

GURPS TRAVELLER requires three rolls for a ship to enter Jump Space. They are: Piloting (Starship), Astrogation (Jump Space), and Mechanic (Jump-Drive). Mishaps (ie failed rolls) are as follows:

Piloting mishap: No Jump

Astrogation mishap: Different results based on 1d6 that can be the ship exited near a solitary object in deep space, near a world or gas giant other than the destination or a random point on the 100 diameter sphere of the star.

Engineering mishap: Traditional "Misjump" but with a twist. It can either be enters into jump space, goes no where for 2 weeks and ends at the same point, no jump (per piloting mishap), or the traditional roll 1d6 for the number of dice to roll for actual misjump distance from jump space entry point.

The problem with requiring three rolls against 3d6 values to enter into jump space, is that if you need 12's for all three skill rolls (for example) the odds of entering jump space (Statistically speaking) are:
.741 (the odds of success by rolling a 12 or less on 3d6) x .741 x .741 or roughly 40%. Why? Because ALL three rolls have to be successful, if even one fails, the entire process results in a failed jump. Contrast this with the original Traveller rules where entering Jump Space was automatic (CT) or in subsequent rules such as MgT where you have to roll an 8+ on 2d6, any roll that was zero or less resulting in a misjump (otherwise, an inaccurate jump).

Frankly? I like (repeat LIKE) what Mongoose did with that.

Next post will contain suggested concepts for refining the rules regarding Jumps in Mongoose Traveller 1st edition (I don't know what the second edition rules look like as yet).
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Re: Inaccurate Jumps in Traveller

Postby HalC » Sun Jan 14, 2018 10:30 am

Page 50 of Core Rule Book states for "Effects" in the table upper left corner:

-1 Marginal Failure: the character has almost succeeded, and the Referee may permit him to scrape a success if he takes a significant consequence.

Using that concept?

Modify the wording on page 141 under Astrogation:

From
"If the check is failed, then the astrogator must plot the Jump again."

To
"If the check is failed with a Task chain modifier of -2 or worse, then the astrogator must plot the jump again. If it is failed with a Task Chain modifier of -1, a Navigation Mishap has occurred." Use the Navigator's Task Chain modifier for any rolls on the "Jump inaccuracy table" if needed.

Leave the rest of that paragraph untouched.

Next, introduce a role for the pilot. How tightly he adheres to the Navigator's flight profile/plan, determines whether or not the plan is executed as it should be. If the Pilot gains a Task Chain modifier of -2 or worse, a Pilot Jump Mishap has occurred.

Follow the rules in JUMP! as written, but add the following:

In the event of a Navigator Mishap or a Pilot Jump Mishap, the JUMP! result can never be better than an inaccurate jump. For each Mishap that has occurred, apply a -3 penalty to the Inaccurate jump table roll.

Note: the reason for the -3 penalty to the table roll, is to insure that "normal" jump inaccuracies that occur because of a pilot issue or a navigator issue or both, fall below the possible die rolls for a simply ordinary "inaccurate jump" result due to engineering power issues. Since the Engineer's roll directly determines a misjump or not, I figured it best to leave his role in this strictly for entering jump, and let the pilot and navigator affect the jump inaccuracy table.

As a consequence of the modifiers, the results of a single 1d6 roll will span between -5 to 10 (+2 effect for navigator and +2 effect for pilot good for a +4 overall bonus for a total of 17 results). If one were to use 2d6 for the table, the resulting range would be -4 to 16 (or 21 possible results).

The idea for the table then, would be to populate the "least" major scatter at the high end of the table, and the worst of the scatter at the lowest value possible for the table. So for example, if you wanted to tack on an hour at most, for the inaccurate jump result - you would need to calculate the distance travelled at 1G for 1 hour and set that as the best possible result for an inaccurate jump. If you don't want to have anything worse than say, a 1 day additional delay due to a badly rolled "inaccurate" table result (which requires that both the Navigator and the Pilot both have mishaps while performing their appointed tasks) - then calculate how far a ship can travel in 24 hours (86,400 seconds) and apply that. Maybe you want the worst possible inaccurate jump result to be 2 day's additional delay - then change your table that way.

Now all that remains, is creating such a 1d6 or 2d6 table...
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Re: Inaccurate Jumps in Traveller

Postby Linwood » Sun Jan 14, 2018 4:11 pm

Now that you’ve got me thinking about this - maybe the die progression for the error should follow a power-law assumption. For example, a marginal result leads to 1D error, a -1 Effect is a 2D (2^1) error, -2 Effect = 4D error (2^2), -3 Effect = 8D error, etc. (This works better if it’s in a table rather than handing the players a formula...).

A possibly more player-friendly approach would be to keep the same die roll but increase the multiplier for the result. For example, a -1 Effect might mean 1D*3000 km (for distance error), a -2 Effect 1D*30000 km, a -3 Effect 1D*300000 km, and so forth.

A thought on the Pilot error - if the crew deliberately goes to a known safe state (zero relative motion with respect to the system primary?) before initiating the jump, maybe that would provide an auto success (or a Boon) on the Pilot check. That would likely add a normal-space time penalty before entering the jump. (I think this may also revive the discussion on whether you carry your normal-space velocity with you when you exit, which is the subject of another thread somewhere in the forums...)
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Re: Inaccurate Jumps in Traveller

Postby steve98052 » Thu Jan 18, 2018 8:23 pm

As I remember the GURPS Traveller rules for jump, an ordinary failure resulted only in a minor problem. For a piloting error, the ship might emerge from jump on an inconvenient vector; for an astrogation error, the ship might emerge from jump in the vicinity of an outer planet, rather than the main world; and for an engineering error the ship might have used excess fuel, or the jump drive or power plant might be thrown out of tune and need some extra maintenance.

It's only on a critical failure that something seriously bad happens.

In a non-stress situation -- not in an abnormal hurry, not in combat, not under-staffed, not stressed and exhausted from something bad that happened right before boarding, not operating a damaged or under-maintained ship, etc. -- a qualified crew can do a "take 10" and skip the roll, if their skills are high enough that a roll of ten is a success after applying modifiers.

If Mongoose doesn't already include similar rules, I'd house-rule them into effect, because rolling dice in non-dramatic circumstances isn't fun.
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Re: Inaccurate Jumps in Traveller

Postby BigDogsRunning » Fri Jan 19, 2018 12:35 am

steve98052 wrote:
Thu Jan 18, 2018 8:23 pm
If Mongoose doesn't already include similar rules, I'd house-rule them into effect, because rolling dice in non-dramatic circumstances isn't fun.
Yes! That! I'm totally on board with this. Some Ref's like that. I don't do it, and I don't care for it as a player.

The reality is that if the way that things are currently balanced with skills, stats, and difficulty rolls is indicative of how the universe works, then you've got ships disappearing all the time due to misjumps. Banks wouldn't loan money for ships if there is a 1/36 chance of mis-jump even assuming solid crew and well maintained ships. They would simply find other ways to do things.

Require a roll if there are extenuating circumstances, absolutely. But, unless there is a plot reason, or special circumstances, can we assume that the bugs have been pretty much worked out such that professionals can do their job with some degree of predictability? I'm not saying spot on, there is already a completely uncontrollable time variable, which can be used to determine base accuracy.
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Re: Inaccurate Jumps in Traveller

Postby HalC » Fri Jan 19, 2018 1:09 pm

GURPS Traveller misjump rules aren't quite the same as Mongoose Traveller (HAH!), but for what it is worth:

"A critical failure (or a simple failure, if the crew is rushed or fatigued) on any roll means that a potential mishap exists; roll again, with any success indicating that the mishap has been avoided, but the failure still counts. A second critical failure results in disaster. Mishaps can take several forms:"

It then goes on to specify what the various types of misjumps are, including the traditional roll 1d6 dice to determine distance from jump space entry for its exit point. Other possibilities are largely what Mongoose Traveller describes as "inaccurate jumps" - target system is still reached, but not exactly where you intended to exit into normal space at.

The "take ten" rule seems more like a house rule, and if it isn't, I'd be happy to be pointed towards where it is listed. :)

Much of what was written about piloting error giving an odd vector, astrogation error giving an "inaccurate jump" result, etc - all seem to be "house rules", but interesting none the less. I'd be interested in how the GM applied those results!

As I mentioned upstream of this thread, that the whole purpose of standardizing the inaccurate jump concept, was to try and get away from the "new concepts" for Traveller that I don't much like as compared against Classic Traveller (CT). To wit:

Entry into Jump space was possible even as close as 10 diameters to a planet or star. Early CT didn't give diameters for stars, but later on, did. Jump Shadows and gravity affecting jump space was not part of the cannon material for CT. Exit into Normal space could not occur within 100 diameters, and resulted in the craft being shunted to the 100 diameter limit.

The next issue involved is the fact that piracy was considered to be mainstream enough that the original CT ship building rules included turrets and pirate encounters etc. NO real thought was given to what the rules themselves implied, nor did the rules do much more than make for a nice story telling vehicle without paying attention to implied issues. Take for instance, the issue of unrefined fuel. In the early days of CT, Scout ships could use unrefined fuel without chance of misjump. Military ships had a better chance than did commercial ships. No reasons were given, just that that them were the facts so to speak.

Per CT:

"Misjump: Each time the ship engages in a jump, throw 13+ for a misjump: Apply the following DMs: +I if using unrefined fuel (and not equipped to do so), +5 if within 100 planetary diameters of a world, +15 if within 10 planetary diameters of a world. If the result is 16+, then the ship is destroyed."

Elsewhere it adds:

"If naval ship - 1, If scout ship -2"

So, in theory...

A ship that was jumping with unrefined fuel, with all engineers present, maintenance up to date, etc could jump from 100+ diameters using unrefined fuel and only have a 1 in 36 chance of a misjump due to fuel (if commercial), no chance of misjump if military or scout.

If a ship were within 100 diameters to just over 10 diameters distant, it had the following chances of misjump:

Commercial: +1 for unrefined fuel, +5 for within 100 diameters for a total of +6, with a 13+ being a misjump (ie, a roll of a 7+), 10+ for total destruction.
Naval: +1 for unrefined fuel, +5 for within 100 diameters, -1 for naval ship or a roll of 8+, 11+ for total destruction
Scouts: +1 unrefined fuel, +5 within 100 diameters, -2 for naval ship on a roll of 9+, 12+ for total destruction

Once HIGH GUARD introduced purification plants, it did away with the issues of unrefined fuel entirely. GURPS TRAVELLER has a few other oddities involved where there are no "power plant fuel expenditures" on the basis that fusion plants use sufficient quantities of water to fuse into energy - that would last 200 years from a small amount. Fuel purification plants in GURPS TRAVELLER is a trivial thing on the whole. As a consequence of this, the whole "unrefined fuel issue is largely moot.

In any event - using the GURPS suggested rule that worlds with a water hydrogaphic value of 4 or less, likely would pass laws making wilderness refueling from water sources illegal, and that such worlds would likely use gas giants to produce refined fuel or at least unrefined fuel. Problem is? I was curious what was involved with respect to creating a "refueling corporation" using strictly GURPS rules presented in either of GURPS TRAVELLER STARSHIPS, GURPS STARPORTS, or GURPS FAR TRADER. I took the time to determine whether or not a corporation could serve the needs of Ianic in Lunion, and if so, how much would the corporation need to float as an initial stock offering value, and then finance their necessary vehicles, equipment, payrolls, underground storage tanks, etc.

Net result?

1x Base station with Jump 1 capacity, low manuever drive, large amounts of tankage for storage (useful not only for multiple jump-1 transits, but also for storing fuel harvest from a gas giant during operations

2x specialized skimmers designed to skim fuel from a gas giant using the Fuel skimming rules present in GURPS TRAVELLER STARSHIPS

5x 800 dton "Oilers" with Manuver 3 drives and the bulk of their cargo capacity used for unrefined fuel tanks. Transit times when full, would take up to 3 days to go from gas giant to main world (when worlds were furthest apart from each other, and less time when worlds were closer). The time required to transit normal space with these ships would be used to refine the fuel during the voyage.

Ultimately? The company could ONLY make a profit if it sold refined fuel only, as the cost of transferring unrefined fuel was not cost efficient.

I wonder what that "exercise" would look like using MONGOOSE TRAVELLER rules? I used the GURPS rules because it had ground tankers costs, along with how long it takes to pump a given amount of fuel, along with everything else necessary (including stock offering rules on the stock market).

In any event, I digress. For my Traveller Universe, I need a way to make it that ships have a longer time in normal space - something that accurate jumps cause issues with. I need to have some "justification" for pirate attacks - without being too heavy handed and requiring the newer "jump shadow" rules, or Gravity precipitating ships out of Jump space. Heck, even T5 seems to make it possible for a larger Dreadnaught ship to be able to precipitate a normal 200 dton freighter out of Jump space if at ANY Time, the ship transverses the "jump line" of the jumping ship while it is in jump space. Uuugh.

So:

IMTU (In my traveller universe):

Being shunted from planned exit point due to a planetary mass or stellar mass to its 100 diameter limit causes minor damage and jump sickness "buffeting".
Time is linked within Jump/Normal space to the extent that 1 hour in jump space is 1 hour in normal space.
Planets move, stars move, etc - requiring that navigators plan on where their target will be when they exit from jump space into normal space.

As a consequence of the three things above - Navigation does require some precision. If an astrogator doesn't know what the movement vector of target star is, trying to hit the star system during jump can be a bit of a problem. Trying to hit a main world or gas giant within that same star system, can be a problem if you don't know where they are at any given time.

An excerpt from Stellar Kinematics - wikipedia:

"Hypervelocity stars (designated as HVS or HV in stellar catalogues) are stars with velocities that are substantially different from that expected for a star belonging to the normal distribution of stars in a galaxy. Such stars may have velocities so great that they exceed the escape velocity of the galaxy.[11] Ordinary stars in the Milky Way have velocities on the order of 100 km/s, whereas hypervelocity stars (especially those near the center of the Milky Way, which is where most are thought to be produced), have velocities on the order of 1000 km/s."

How far can a star system move if the time in jump space takes 1 hour longer or 1 hour shorter than planned?

60 seconds x 60 minutes = 3,600 seconds per hour. 100 km/second x 3600 seconds = 360,000 km. That's if your target point is missed because the ship is 1 hour early/late. At 16.8 hours early/late, the distance one is off by when aiming to hit a given point becomes... 16.8 x 360,000 km or 6,048,000 km (or about .04 AU's distant). Our own star moves at about 230 km per second for reference point.

That doesn't take into account if the original aim point is off for any reason.

In all? I rather like the approach that MONGOOSE took with its enter Jump! rules. Any negative value is a classic Misjump up to 36 parsecs in distance, or outright destruction. Anything up to a given point is an accurate jump, any other roll is an inaccurate jump. Simple and Elegant to my eyes.

Thinking aloud here so to speak:

If maximum penalty for accuracy is based on time spent in jump space being off by +/- 10% of 168 hours, and that ends up being about 6 Million km off - for a 100 km speed difference between two stars, what might it be like with one star going 230 km one direction, and about 250 km per second in roughly the same direction (ie closer to the galaxy core)? That's only really a difference of about 30 km per second, not 100. That's like trying to shoot at a truck travelling 18 miles per hour faster than yours. Not impossible to be sure. If stars that are clustered together are more or less travelling the same direction at more or less the same speed, they probably shouldn't be travelling to much faster than each other (sort of like Earth's time to complete one full revolution around the sun versus say, Mar's revolution). As a consequence, perhaps 6 million km should be the worst a ship can be off for an inaccurate jump. At 1G acceleration, this is about 13 hours travel per MegaTraveller page 21 Referee's Sourcebook.

-3 steps: off by 3 Million plus 1d6-1 x .5 Million km?
-2 steps: off by 1.5 Million plus 1d6-1 x .3 million km?
-1 step: off by 750,000 km plus 1d6-1 x .15 Million km?
0 step: off by 3,000 km plus 1d6-1 x .025 Million km?

Putting this in perspective?

.01 AU's is safe 100 diameter jump distance from an A size world
.07 AU's is safe 100 diameter jump distance from a gas giant.

6 Million km is .04 AU's, 3 Million km is .02 AU's. 1.5 Million is .01 AU's. The chart above will give distances that are no greater than .04 AU's, and as little as 3,000 KM if the success roll is 0 steps (ie made it exactly. Any Positive steps of success make it to be 3,000 km exactly (per parsec travelled!).

Does this seem to be a bit more reasonable? If one is off by 6 million km, that adds about 13 hours to the journey through normal space. If off by 3 million, it adds about 9.6 hours journey to the travel time. At only .1 AU distance extra, travel time at 1G will be about 6.7 hours. In terms of 20 minute High Guard turns (CT that is), we're looking at an additional 30 turns at .04 AU's, about 28 or 29 extra turns, or about 18 extra turns journey times.

Seems workable to me for my campaign.
Condottiere
Chief Mongoose
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Re: Inaccurate Jumps in Traveller

Postby Condottiere » Fri Jan 19, 2018 7:02 pm

If your jump is off by either time or distance, it's not necessarily a misjump, rather within the margin of error.
NOLATrav
Mongoose
Posts: 145
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Re: Inaccurate Jumps in Traveller

Postby NOLATrav » Fri Jan 19, 2018 8:02 pm

I have for quite a while been using this, based on the final Jump! roll:

Effect +1 or greater: arrive at 100D limit, -10% jump duration
Effect 0: arrive at 100D limit, normal jump duration
Effect -1: arrive 100 + 10-60 Diameters, +10% jump duration
Effect -2: arrive 100 + 20-120 Diameters, +20% jump duration
Effect -3: arrive 100 + 100-600 Diameters, +30% jump duration
Effect -4: arrive in neighbouring system life zone or 2D x 10M km away from target, +1D days jump duration
Effect -5: arrive in Oort Cloud or 1D x 100M km away from target, +1D days jump duration
Effect -6: arrive in neighbouring parsec, +1D+1 days jump duration
Effect -7 or less: exit jump 1D x 1D parsecs away, +1D+2 days jump duration

I never do the 'ship destroyed' thing as that's just cruel to the players.

Also, jump is more difficult IMTU (J1 is Routine, J2 is Average, J3 is Difficult, etc), the pilot has a check to make and the Engineer has to make a Divert Power roll in addition to the Jump roll. Ships under 50K dtons can't carry fuel purifiers and unrefined fuel has -DMs, as well as the missed maintenance DMs. Ships can jump from inside 100 diameters but at serious penalties. On the flip side, Computer Processing / 5 (or Core Proc / 20) provides a +DM and if the Astrogator has jumped the route before the plotting task is one level easier.

I only use this for the first few jumps of a campaign so the players understand the possible vagaries of jump and after that only if it brings something to the table. So far the worst that's happened is after hurrying out of a system the players were in jump for almost 10 days and exited around 400 diameters. They were freaking out those last three days and yes there were a few pirates lingering in the system they jumped to...

I had forgotten about jump sickness... going to have to think about that! :twisted:

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