Retained inertia & jump

[Prime_Evil]

An Albedo Blitz, yes. Nasty, and hard to stop once its had a chance to get moving.

And this is the reason why there must be strong legal and political prohibitions against using this type of bombardment....

With the kind of technology available in a typical Traveller setting, it is trivial to think of numerous ways that you can devastate the surface of an inhabited planet. One of the primary reasons why individual planets choose to affiliate themselves with an interstellar government is that being part of a larger state is an effective deterrent against this sort of thing. Indeed, I would argue that interstellar states derive a large amount of their legitimacy from the fact that they protect member worlds from this sort of assault.

As an aside, I imagine that terrorist organizations might occasionally commit this sort of atrocity, but massive resources will be expended to hunt them down and exterminate them afterwards. Just think about how much money and manpower the US has sunk into the hunt for the leadership of Al Qeada over the past decade....

 

[DFW]

Pick your brain time

...would this work as well or better for the departure and destination gravity wells? I've often felt what should be happening is a balancing of the tidal forces in the jump plot. So 100d departure from a size A world is going to put you at 100d from a size 3 world. With your zeroed vector relative to the world...

...of course then what about deep space jumps, and stellar 100d shadows, and... my head hurts

According to Mach, it would be the preponderance of mass creating inertia. So, that would be the star in a solar system.

As for deep space, (J-drive only takes you 6 parsecs max). That keeps you within what astronomers call; the local standard of rest. That would put you within a speed of ~17 km/sec relative to the surrounding star systems.

BTW, did you read my grav drive post?

 

[far-trader]

Thanks for the info

BTW, did you read my grav drive post?

Sorry, only skimmed it last week, still mean to come back to it for a better read. I expect it all ties together nicely.

 

[Prime_Evil]

Alternately, a Jump drive could "borrow" inertial reference from the Jump Horizon it bounces off of during emergence. This means that you either require a mass for emergence (not supported by Canon, but hey, its your game) or that an emergence mass simply makes this operation *easier*.

A collapsing jump field imparts to its contents the inertial frame of reference of the mass that caused the emergence, or whichever local gravitational field is strongest at the point of emergence. This means that NO, you won't be run over by that world you just popped in front of, because you emerge stationary relative to it. You *might* get run over by a moon that is skating the planet's Jump Horizon, however, or a planet that is skating the star's Jump Horizon.

If you emerge in open system space, the primary star's gravity is likely the strongest jump-relative force around, so you will emerge stationary relative to the star. A planet whipping along nearby is going to overpower the star's local pull long before you are too close to dodge, so a mild navigational error could find you emerging in the Inertial grip of the wrong planet, but for ships with even 1g of thrust, this is pretty trivial unless you were working that last few m3 of fuel when you emerged.

Pardon my scientific ignorance, but I've got a quick question.

Would this approach imply some kind of causal connection between the inertial reference frame that the vessel has when it enters jumpspace and the one that it "borrows"during emergence? After all, observers on the ship experience a transition from one reference frame to another through jumpspace in a causal sequence that appears to be internally self-consistent.

If the trip between the two inertial reference frames must remain causally consistent to observers on the ship, this neatly rules out sneaky tricks such as using FTL drives to perform time travel by navigating through a closed timelike curve (CTC). I know that this isn't covered by the rules, but one of my players once asked why it wouldn't be possible.

Personally, I like the idea that FTL travel is permitted, but causality must be conserved. I'm wondering if you could simply rule that the sequence of events during a voyage must be self-consistent for all observers in all possible inertial reference frames, including those on the ship.

 

[rust]

I'm wondering if you could simply rule that the sequence of events during a voyage must be self-consistent for all observers in all possible inertial reference frames, including those on the ship.

You would only have to declare that in your universe Novikov was right
with his self-consistency principle:

http://en.wikipedia.org/wiki/Novikov_self-consistency_principle

 

[DFW]

Personally, I like the idea that FTL travel is permitted, but causality must be conserved. I'm wondering if you could simply rule that the sequence of events during a voyage must be self-consistent for all observers in all possible inertial reference frames, including those on the ship.

I think that is why trav doesn't really have FLT travel. Lot's of messy things crop up.

 

[Reynard]

Reading various Traveller sources I see astrogation and jump plotting involves vectoring the vessel before entering jumpspace. Vectoring is a combination of direction and speed for the uninitiated. No speed means no vector. Jumpspace is a time and or distance distortion but does not itself convey the vector. The vessel points and moves then enters jumpspace. The vessel's speed has no bearing per se since it always takes one week to get to the exit. Therefore a vessel can impart a minimal velocity other wise you would enter jumpspace for a week and come out right where you started!

And you would not want a lot of speed when first entering normal space. No matter how accurate you think your calculations are Murphy is never far away. You will survey your entry point, establish actual location then correct vector to your final goal. You really don't want to be moving fast especially around the 100d horizon of a heavily trafficked mainworld.

 

[DFW]

Reading various Traveller sources I see astrogation and jump plotting involves vectoring the vessel before entering jumpspace.

Actually, no where in the rules is any speed or, direction in normal space required.

 

[phavoc]

Reading various Traveller sources I see astrogation and jump plotting involves vectoring the vessel before entering jumpspace.

Actually, no where in the rules is any speed or, direction in normal space required.

DFW is correct. The rules never expound upon the nuances of jump space, vectors, intertia and the like.

You need to get a copy of The Journal of Traveller's Aid Society #24. In there Mark Miller wrote a long essay on what jump space is, how it worked, and the 'science' around it.

In the article he talks about how your jump calculations have to take into account the relative direction and velocity of the solar system you are jumping from and the one you are jumping in to in order to not have speed and direction placed upon your ship as you exit jumpspace. Most civilian ships will enter a new system at zero KPH relative, and then begin thrusting towards their target. It's a very interesting read if you are looking to have a better understanding of the underlying mechanics.

I heartily reccomend getting the compilation CD for FFE, as there are many, many articles in there that are quite good.

 

[far-trader]

...In the article he talks about how your jump calculations have to take into account the relative direction and velocity of the solar system you are jumping from and the one you are jumping in to in order to not have speed and direction placed upon your ship as you exit jumpspace. Most civilian ships will enter a new system at zero KPH relative, and then begin thrusting towards their target.

Which goes contrary to the stated random arrival time and position. You can't have both in my opinon.

And which, unfortunately hints at being able to apply a vector upon emergence...

Such as the good idea of saving time and fuel by not coming to a relative zero vector before jumping, and arriving with an economical vector towards your destination.

And the evil idea of applying a massive vector for arrival without any need of building it up before departure. Congratulations, you've just improved on near-C rocks popping out of jump space.

The article creates more questions and problems than it answered Again imo (and albeit from a foggy recollection of it, I should really re-read it).

 

[rust]

Which goes contrary to the stated random arrival time and position. You can't have both in my opinon.

Yes and no.

The arrival time does not make a difference concerning the velocity and
vector of the destination system, but a huge difference concerning the
velocity and vector of the destination planet.

Therefore it would make sense to arrive with a velocity and vector which
are identical to that of the destination system's star, and then to locate
the destination planet and accelerate or decelerate towards it.

 

[phavoc]

...In the article he talks about how your jump calculations have to take into account the relative direction and velocity of the solar system you are jumping from and the one you are jumping in to in order to not have speed and direction placed upon your ship as you exit jumpspace. Most civilian ships will enter a new system at zero KPH relative, and then begin thrusting towards their target.

Which goes contrary to the stated random arrival time and position. You can't have both in my opinon.

And which, unfortunately hints at being able to apply a vector upon emergence...

Such as the good idea of saving time and fuel by not coming to a relative zero vector before jumping, and arriving with an economical vector towards your destination.

And the evil idea of applying a massive vector for arrival without any need of building it up before departure. Congratulations, you've just improved on near-C rocks popping out of jump space.

The article creates more questions and problems than it answered Again imo (and albeit from a foggy recollection of it, I should really re-read it).

Actually, the article states that you do retain heading and velocity upon re-entry into the new starsystem. It talks about military ships and couriers accelerating on the vectors that they want to be on upon arrival, then jumping, and up re-entry they have retained that in the new system.

Now, as I understand it, the jump calculations allow you to disregard the relative movement speeds of the two separate star systems, so for navigation it's essentially a non-issue.

 

[BFalcon]

Quite frankly, having read this thread, it sounds like every source contradicts the others...

Possibly you could look at the age of the article and disregard the oldest, on the grounds that they use more primitive science as their foundation while the latest ones use more up-to-date theory as their basis... but that would be slightly spurious...

I think it's going to be something that we can discuss forever, so it comes down to this: What do you happen to prefer for your Traveller universe? Whatever you decide, just don't assume that other people will use the same.

It is a game, after all, so storytelling far exceeds the actual science it's based on (with varying strengths of necessity for scientific accuracy from group to group - some won't care, while others (looking at you here, rust) have to put up with groups that sound like they would prefer it if they could get Stephen Hawking to sign off on every theory...

 

[rust]

... some won't care, while others (looking at you here, rust) have to put up with groups that sound like they would prefer it if they could get Stephen Hawking to sign off on every theory...

I am not fully convinced that they would accept him as competent enough
to trust his judgement. :roll:

 

[BFalcon]

LOL you have my sympathy...

 

[Prime_Evil]

Quite frankly, having read this thread, it sounds like every source contradicts the others...

That's a common problem for any shared universe that has developed over a couple of decades. Keep in mind that when Traveller was originally written the world was a very different place and the kinds of assumptions that were made about how things work reflect that - for example look at the way the original LBBs depict computer technology in the far future. It's hard to believe that those books were written before the personal computer or the Internet.

Personally, I suspect that the way that jump drive was described has less to do with scientific plausibility and more to do with the feel that the game designers wanted to capture. In order to justify a feudal setting modelled on classic 1950s SF it was necessary to have interstellar travel work in a particular way. In addition, the desire to have gunboat diplomacy along the frontiers of the kind practiced by the British Empire in its heyday, it was necessary to assume that space travel was an analogue of sea voyages in the 18th and early 19th centuries.

Possibly you could look at the age of the article and disregard the oldest, on the grounds that they use more primitive science as their foundation while the latest ones use more up-to-date theory as their basis... but that would be slightly spurious...

The hard SF boom of the late 1990s means that authors nowadays are far more careful about how they depict interstellar travel. Even many space opera authors nowadays are careful to provide some sort of coherent explanation regarding the mechanism used for interstellar travel. There has been a real shift in sensibilities here since Traveller was first published.

I think it's going to be something that we can discuss forever, so it comes down to this: What do you happen to prefer for your Traveller universe? Whatever you decide, just don't assume that other people will use the same.

Agreed. But it can be *fun* to discuss how stuff might work - that's why we're fans

It is a game, after all, so storytelling far exceeds the actual science it's based on (with varying strengths of necessity for scientific accuracy from group to group - some won't care, while others (looking at you here, rust) have to put up with groups that sound like they would prefer it if they could get Stephen Hawking to sign off on every theory...

In my experience, most gaming groups have at least one player who will seek to identify and exploit any inconsistencies in the way that the technology is depicted. Sometimes these players will approach the subject matter with an eye on scientific plausability and sometimes they won't. At the end of the day, it's not scientific plausibility that's important - it's internal narrative consistency. You can get away with handwaving a lot of this stuff, so long as you are careful not to contradict yourself at any point.

 

[Prime_Evil]

I am not fully convinced that they would accept him as competent enough to trust his judgement. :roll:

I wonder if Stephen Hawking is a power gamer

 

[DFW]

Quite frankly, having read this thread, it sounds like every source contradicts the others...

Possibly you could look at the age of the article and disregard the oldest, on the grounds that they use more primitive science as their foundation while the latest ones use more up-to-date theory as their basis...

Which is why I wrote this thread and updated the "tech" of the rules...

 

[hdan]

Quite frankly, having read this thread, it sounds like every source contradicts the others...

Possibly you could look at the age of the article and disregard the oldest, on the grounds that they use more primitive science as their foundation while the latest ones use more up-to-date theory as their basis...

Which is why I wrote this thread and updated the "tech" of the rules...

I'm glad you did - the "come to rest relative to the frame you are leaving" approach solves many problems, (and gives some parameters for how X-boats must work - they must have at least some simple chemical attitude and "docking maneuver" type jets to stabilize themselves, but would not be able to carefully compute a pre-jump vector that would let them aerobrake into orbit around the destination world. Thus, they require a tender.)

It also suggests another reason for the 100d limit - as a rule of thumb, perhaps at 100d your vector won't be perturbed by gravity enough to matter in the amount of time it will take to activate the jump drive.

(Which if you really want to worry about such things, could be used to suggest a duration for the process of slipping into jumpspace, once you choose a maximum acceptable delta-V....)

 

[Ishmael]

..I have a different take on this.

I feel that a ship maintains its momentum relative to the universe while in jump space. It also retains that momentum upon exit. ... or tries to.

..The frame of reference would be the universe as the sum of all possible frames corresponding to all possible observers within the universe. The speed and direction and mass of the jumping ship is set at the jump entry and must be the same upon jump exit in order to maintain conservation of momentum.

..If the ship re-enters normal space on a slightly different vector, as from a misjump ( a controlled change of vector is not possible in jump ), the ship's momentum with respect to the normal-space frame changes putting stress on the ship's structure. If this stress is great enough, it rips the ship apart.. The same can occur should the ship change its mass in jump-space, perhaps from dumping cargo, fuel or other mass while in jump.

..Jump drives cannot allow for 'perfect' entry or exit from jump-space. The calculations involve complex and irrational numbers, so a 'perfect' answer for jump-space calculations are not possible; only approximations from the jump energizing/timing sequences can be worked out. Difference between a 'perfect' jump-calc and the capabilities of the machinery in timing energy sequences causes errors in the jump with are chaotic in nature. Should the error be too large, a misjump occurs. This is also the cause for the randomness of jump exit locations and times.

..Even so, the calculations are almost always more accurate that the machinery and electronics can duplicate due to small differences in current flow, mass loading, switching rates, etc. such as might be caused by differences in temperatures or even age of components.

..It is the differences in precision between what the calculations require and what the machinery is capable of acting upon that cause misjumps and exit vector changes. should the exit vector errors be large enough, the ship might be ripped apart by its own momentum.

...The differences in precision between the calculations and machinery's capabilities cause the the jump exit to vary in a chaotic fashion which is unpredictable for the range of numbers involved.

..On very rare occasions, the machinery's precision matches a calculation that would have fit a jump of 10, 20 or more parsecs distance, but beyond that, the most likely outcome is a shredded ship due to a bad exit.

..The same stresses acting upon a person's body is the cause of jump sickness and the disorientation felt by some people.

..Ships generally enter jump with a vector of low speed in order to minimize any stresses that might occur upon exit from this effect.