Jump accuracy in ANY Traveller System

[Hal]

I had an internally consistent model for jump which included both masking and shadows. I developed it for my TML Newbie Essay and even had someone who taught logic at Brown University check it over for holes.

T5 killed it.

Now I'm back at square one.

Mind sharing it? If not here, then privately works for me.

 

[Whipsnade]

It was the "Bead-on-a-wire" model, Hal. The TML posts were titled something like "Lines and Limits, Masks and Shadows".

The model proposed that :

• That ships moved through jump space, moved and not maneuvered.
• That a course plotted through jump space was best represented as a straight line through normal space.
• That a ship in jump space existed on a specific point at any given time during it's jump.
• That movement in jump space translated directly to displacement in normal space.
• That each jump space dimension act as a "multiplier" of sorts with the movement occurring within it being multiplied with regards to normal space.

When T5 introduced the blockage and vector changes in jump, my Bead-on-a-wire model fell apart. Blockage was especially damaging because it can applied to a ship's jump course, or line in T5, at any time and point during the jump.

I'd developed with an eye towards preventing exactly what T5 calls "blockage". In my model, a sufficiently large object would only interfere with a vessel in jump if it was located on that vessel's jump course at the time the vessel arrived at that point, that's the "... specific point at any given time..." bit.

In T5, you can park a sufficiently large object on a vessel's jump entry point at any time during the 168 hour period and prevent the ship from leaving. The vessel in jump will basically exit where it entered a week earlier.

My model was designed to preclude that while still keeping jump masking and jump shadows in the mix.

 

[Hal]

Gotcha. I can see what you mean by "blew it apart".

 

[aramis]

T5 is more a Bead on a Quantum Uncertainty Rubber Band...

Nothing before prohibited changing your vector in jumpspace... just nothing explicitly allowed it. Note also, changing your vector while in jumpspace has no effect on the jump, either, in T5. Just which way you'll be going in n-Space once you exit. It's a handwave to allow less concern about the (IRL surprisingly high) relative velocities of the stars.

You still cannot change the jump course.

Oh, and looking in T5.09 (which, Bill, if you haven't grabbed, you should)...

Page 341 -

BLOCKAGE and SCATTER
Blockage terminates a courseline short of the destination. Scatter shifts the end of the courseline away from the intended destination.
Blockage
A planned jumpline may be blocked (at any point along the course, at the moment jump begins) by an intervening gravity source (larger than the ship in jump). The ship exits from jump at 100 diameters from the gravity source. The effect mimics quantum mechanics wave function collapse.​

Underline added for emphasis; bold original
Your Bead on a wire has been restored. Somewhat.

My argument to Marc boiled down to Blockage at any point other than entry results in only mega-freighters being able to jump on a regularly used route... anything smaller that left within a week on the best vector matching course winds up back where it started under the T5.0 model...

 

[Lycanorukke]

A planned jumpline may be blocked (at any point along the course, at the moment jump begins) by an intervening gravity source (larger than the ship in jump). The ship exits from jump at 100 diameters from the gravity source.

In that case what happens if the gravity source acting as the blockage is mobile (well, mobile with respect to the system it is in)?

Eg: MSV Trashcan jumps, but at the moment of jump ISV Megabig cruises through the proposed jump line a few AU away.

When Trashcan pops out of jump, does it appear where the Megabig was at the time of jump, or does the jump exit follow Megabig's gravity well around? What if Megabig itself jumps before Trashcan emerges?

 

[aramis]

In that case what happens if the gravity source acting as the blockage is mobile (well, mobile with respect to the system it is in)?

Eg: MSV Trashcan jumps, but at the moment of jump ISV Megabig cruises through the proposed jump line a few AU away.

When Trashcan pops out of jump, does it appear where the Megabig was at the time of jump, or does the jump exit follow Megabig's gravity well around? What if Megabig itself jumps before Trashcan emerges?

T5.09, nothing. Nothing at all. It's only at the moment of jump that it matters.

 

[Hal]

Keep in mind too, the blocking source, as far as ships are concerned, has to be larger than the jumping ship to affect it. It still causes problems of sorts unless...

The issue never arises due to not only planetary motion - but also stellar and Galaxy motion. Technically speaking, a ship leaving the same geostationary location over a fixed spot on a planet will never be within 100 diameters of a ship that left that same geostationary spot an hour ago. Just the velocity of the star itself should move the world away from that point in a miles per second velocity.

 

[Lycanorukke]

Keep in mind too, the blocking source, as far as ships are concerned, has to be larger than the jumping ship to affect it.

If the PCs are putting around in a Free Trader or Scout (by far the most common ACS's PCs use), almost anything can block them. Just about everything is bigger than them - forget megafreighters, a SDB in the wrong spot in the outer system can cause problems (a minisucle chance given the size of ships vs size of space, but still there). If flight lanes are used to/from the planet the chance increaes considerably as traffic is funneled.

Sure you can't 'step on their tail' anymore as was possible in T5.0, but if at the _instant_ ship A jumps, ship B is causing a block (regardless of location or velocity differences), where does ship A end up?

 

[aramis]

If the PCs are putting around in a Free Trader or Scout (by far the most common ACS's PCs use), almost anything can block them. Just about everything is bigger than them - forget megafreighters, a SDB in the wrong spot in the outer system can cause problems (a minisucle chance given the size of ships vs size of space, but still there). If flight lanes are used to/from the planet the chance increaes considerably as traffic is funneled.

Sure you can't 'step on their tail' anymore as was possible in T5.0, but if at the _instant_ ship A jumps, ship B is causing a block (regardless of location or velocity differences), where does ship A end up?

100 diameters of the block from where the block is at exit time.

 

[Lycanorukke]

100 diameters of the block from where the block is at exit time.

Yes, but if ship 'A' is now 'jump exit attached' to ship 'B', in 7 days time when jump exit occurs will 'A' exit 100 diams from where 'B' is _now_, or 100 diameters from where 'B' _was_ when it was blocking.

If 'A' exits where 'B' is now, 'A' could potentially be trying to exit jump onto a planets surface (though the planets 100D would force them out before they got that close), into Jump space (1 day after the block occurs 'B' jumps to another system and is intransit when 'A' tries to exit) or even a different system altogether ('B' completed its Jump before 'A' due to time variation).

On edit: Hope I am explaining it better this time

 

[Adam Dray]

Note also, changing your vector while in jumpspace has no effect on the jump, either, in T5. Just which way you'll be going in n-Space once you exit. It's a handwave to allow less concern about the (IRL surprisingly high) relative velocities of the stars.

So if two stars are careening towards each other at 0.5c, and your starship before jump is moving at some small, non-relativistic speed, you need to add 0.5c to your vector after your jump to match velocity with the system.

Or you don't, and you aim yourself at the downport, smashing your 500k dT ship into the planet at 0.5c. I assume this is a thing in Traveller?

 

[whartung]

So if two stars are careening towards each other at 0.5c, and your starship before jump is moving at some small, non-relativistic speed, you need to add 0.5c to your vector after your jump to match velocity with the system.

Or you don't, and you aim yourself at the downport, smashing your 500k dT ship into the planet at 0.5c. I assume this is a thing in Traveller?

In theory, yes, this is a "thing".

In "reality", it's not that big of a deal. The systems all tend to be orbiting the galactic center, not careening randomly in space, so in effect, especially systems that are "close" together, their relative velocities are more than manageable with the Traveller drives, even in TNE where fuel counts.

So, since in "reality" it's "not a big deal", in practice, it's pretty much ignored entirely.

 

[whartung]

Page 341 -

BLOCKAGE and SCATTER
Blockage terminates a courseline short of the destination. Scatter shifts the end of the courseline away from the intended destination.
Blockage
A planned jumpline may be blocked (at any point along the course, at the moment jump begins) by an intervening gravity source (larger than the ship in jump). The ship exits from jump at 100 diameters from the gravity source. The effect mimics quantum mechanics wave function collapse.​

Underline added for emphasis; bold original
Your Bead on a wire has been restored. Somewhat.

My argument to Marc boiled down to Blockage at any point other than entry results in only mega-freighters being able to jump on a regularly used route... anything smaller that left within a week on the best vector matching course winds up back where it started under the T5.0 model...

How does this occur a "week later"? Are ships in jump still considered a gravity source? Why is this not a traffic issue of simply directing ships out in to jump lanes to facilitate transit?

I can see how a larger ship can interdict a smaller ship that they a nearby at the moment of jump (thus allowing a large ship to trap a smaller ship if it cares to continue to match vectors). But not sure how this affect anyone after the larger ship jumps.

 

[flykiller]

In theory, yes, this is a "thing".

In "reality", it's not that big of a deal.

I calculated it out one day, even a m1 ship can compensate for the most extreme known vector differentials in less than an hour. easily done on the transit out to jump.

now there are a few systems that are not part of the milky way galaxy - in particular there is one known to be from the magellanic cloud that is whipping through this one on a non-member vector - but even this is easily matched.

.5c differential is right out.

 

[Adam Dray]

.5c differential is right out.

Even if you want .5c differential to make your ship into a megatorpedo?

I know there are some rogue stars out there moving at weird velocities.

 

[whulorigan]

Even if you want .5c differential to make your ship into a megatorpedo?

I know there are some rogue stars out there moving at weird velocities.

But none approaching one another at relativistic speeds.

 

[flykiller]

I know there are some rogue stars out there moving at weird velocities.

yeah, "weird" in that they obviously are not from this galaxy and are heading in a different direction, not "weird" meaning .5c vd. a star moving that fast probably would look like a rocket as it fused all the stray hydrogen in its bow wave.

 

[aramis]

In theory, yes, this is a "thing".

In "reality", it's not that big of a deal. The systems all tend to be orbiting the galactic center, not careening randomly in space, so in effect, especially systems that are "close" together, their relative velocities are more than manageable with the Traveller drives, even in TNE where fuel counts.

So, since in "reality" it's "not a big deal", in practice, it's pretty much ignored entirely.

In reality, it tends to be variant by up to 100 kps in velocity relative to the galaxy and frequently difference in directionality of movement, of a roughly 299,792.5 kps speed of light. for up to about 200kps relative to each other.

A very small portion exceed that, in the 100-1000 km/s speeds, for up to about 0.3 C relative. 1000 km/s is roughly 28:20:41 at 1G. And it is also only a tiny fraction of systems 0.000001 of all systems are in this category - called "hypervelocity"...

If you can use gravitic drives to change your exit vector relative, then it's trivial to account for the difference in vector. 28 of 168 hours.

 

[esampson]

I calculated it out one day, even a m1 ship can compensate for the most extreme known vector differentials in less than an hour. easily done on the transit out to jump. . .

Or, one would assume that clever navigators simply make sure that the vector is already compensated for as they jump. This is something a lot of people don't get.

As an example, Planet A is moving 'west' from Planet B at a relative speed of 100 km/s (or at least in one week it will be moving 'west' at a relative velocity of 100 km/s from Planet B's current velocity since the orbit of Planet A will slightly alter its vector during the week). Planet A and Planet B are both Earth sized planets and the ship is capable of 1 G of acceleration.

Ideally the pilot launches from Planet B at a heading of '341.5 degrees'. It will take 4 hours and 28 minutes for the ship to reach 100D from the planet. At this moment the ship is traveling at a heading of 341.5 degrees from Planet B with relative velocity of 157.6 km/s and the ship jumps.

Exactly one week later the ship precipitates from jump space with a vector of 18.5 degrees relative to Planet A and a relative velocity of 157.6 km/s. As a result the ideal landing point is exactly 100D away from planet B at 198.5 degrees relative to Planet B.

This means that Planet B is 18.5 degrees relative to the ship and the ship his heading directly toward the plant. By aiming the ship at a relative heading of 198.5 and firing the maneuver drives at full power the ship will come to a complete stop relative to Planet A in 4 hours and 28 minutes, during which time it will cover exactly 100D and end touching down on the surface.

This is a 'textbook' flight in the sense that you would only encounter such a situation in a textbook. In real life the exact launch and landing positions would be factors that would cause some slight alterations in the flight plan and safety margins would need to be built in to deal with temporal and positional scattering. Additionally other angles can be used for launch and arrival which could prove very important depending upon exactly what the jumpline might pass through. (if you took the point located at 100D from Planet and rotated it around the X axis of the planet it would draw a circle in space. Launching toward any point on that circle would suffice just as well).

Two things that it would be good to take away from this. First, even at the relatively high difference of 100 km/s and with a slow 1 G ship there was no need to spend any time in jumpspace countering the difference and this would hold true all the way up to 315.1 km/s. Just the normal acceleration and deceleration necessary to reach/return from 100D will generate enough velocity to counter the relative differences in a well planned jump.

The second thing to take away is that the departure vector for the ship has absolutely nothing to do with the relative position of the planets. It is mostly a factor of the relative vectors of the planets. Planet A could have been 'west' of Planet B and you could use the exact same heading of 341.5 degrees. The image of the ship pointing its nose toward its target before jumping is a myth.

 

[Condottiere]

Outside of Ceti Alpha Five, few planets actually change their orbit in the short term.