Jump Space Astrogation

[Hal]

Hello Folks,
While discussing things elsewhere, I got to thinking about one of my pet peeves with Traveller - variable duration jumps.

Marc Miller wrote in a JTAS article that jumping is accurate to 3,000 kilopmeters per parsec travelled. The variable time duration aspect means that a ship can't possibly be accurate to within 3,000 Kilometers per parsec - the time duration of Jump space alone makes this impossible.

Or does it?

I got to thinking a while back about what I need to do to be able to play Traveller using Vectors. I decided that I would use the Polar Co-ordinate system and use two frames of reference. The first is that of the Primary Sun of that star system. All things are recorded relative to the sun's position. The second is relative to the ship/planet itself - and that is the vector of movement relative to that point of reference.

What if Marc's vision IS compatable with both a universe in motion and Traveller the game as we've come to enjoy it?

The exit point from Jump space is accurate to +/- 3,000 kilometers. The real variable is the time duration. Since other objects in motion will have moved in the variable time - and astrogators can't predict just how much time it will take for the jump - that is the TRUE problem of interstellar navigation.

But what if we look at things a little differently? Suppose you aim for a spot that is at 42 degrees, with a radius of 93,100,000 miles? This is 100,000 miles outside of the Earth's orbit - but that 42 degrees will be precisely 42 degrees. Whether you get there 16.8 hours early, 10 hours early, 20 minutes early, 20 minutes late, 10 hours late, or 16.8 hours late - doesn't MATTER. You still hit the point 42 degrees - 93,100,000 miles +/- 3,000 kilometers (I know, I'm mixing measurement units - sorry).

So how does an astrogator plan for this? It all depends on what the captain wants. If he wants the navigator to plan on being more or less on time and the captain doesn't care if he's got a stern chase type of thing (ie chasing the planet he's trying to land on) no problem. If the captain wants a least fuel (For TNE universes) then he is always going to want to arrive just ahead of the planet in question such that it will catch up to him rather than require that he chase IT.
Therein lies the secret to solving the issues involved with Traveller's variable jump space navigation. Astrogators tend to plot for a place ahead of the planet such that even if they arrive from jump space some 196 hours rather than 168 hours - they will STILL be ahead of the planet. In fact? Navigators might PREFER to spend 196 hours in jump space because it means they are closest to the planet when they emerge from Jump space. At 168 hours - they will be a little ahead of the planet, and if they spend only 150 hours in jump space, they will be WAY ahead of the planet (the farthest from the planet that is possible).

 

[Hal]

Suppose you have a situation where you, the navigator, has plotted to arrive directly in the path of an oncoming planet. Due to the vaguarities of when the ship pops out of jump space, the ship may be coming out of jump space well before the planet arrives, well after the planet arrives, or perhaps within 100 diameters of the planet itself when it pops out.

Question:
Does the 100 diameter limit pop you out WHEN you are at the 100 diameter timewise as plotted to "where" you come out, or does the jumpspace planned exitpoint itself get shifted to the 100 diameter limit

Example:
Suppose you intend to come out at point X from your jump. If you came out precisely at X after being in jump space for 168 hours, you will be 10,000 distance units ahead of the planet. If however, you arrive 16 hours earlier, you will be 20,000 distance units away. But if you arrive 16 hours later - you'd be ZERO units away. For the sake of argument, lets say that your ship is about to arrive 16 hours late. If you exit at your exit point, you are in violation of the 100 diameter limit.
Method 1:
Would you be precipitated out earlier than the 16 hours you would have been late such that instead, you are only 15.5 hours late?

Method 2:
Would you arrive out of jump space 16 hours late, and your jump exit point gets forced to move until it is precisely 100 diameters away?

Method 1 is a Time displacement that forces the ship to be precisely 100 diameters away, while method 2 is a physical displacement. Method one assumes a temporal adjustment while physical remains unchanged - method 2 assumes a phsyical displacement while the temporal remains unchanged...

Hmmmm

 

[mike wightman]

Method 2 sounds the most like how I think it works.

 

[FlightCommanderSolitude]

Method 2 is correct, in my opinion. There is no correlation between time and space in jumpspace [1], so you arrive when you arrive, and then your position is adjusted if necessary so as not to violate 100-diameter limits.

[1] or rather, they do not have the same correlation as they do in normal space.

 

[Keklas Rekobah]

"Method 1 assumes a temporal adjustment while physical remains unchanged - method 2 assumes a phsyical displacement while the temporal remains unchanged..." - Sigg Oddra.

Have you considered a third alternative?

Temporal and physical parameters remain unchanged, while the probablistic parameter comes into effect.

Your ship comes out of jump in a universe with a slightly different history; perhaps one in which your character never existed, or wherein the Third Imperium started a few hundred years later, or one in which something a simple as your ship's Transponder ID code was entirely different...

"... I'm sorry sir, but we'll have to impound your ship and cargo until we get this matter cleared up... strange... the transponder hasn't been tampered with, and yet you ID as an Azhanti High Lightning class vessel..."

 

[aramis]

I've always kind of assumed the exit point is defined by a particular gravimetric well, and gets fixed at jump-time; no matter how long, the exit point is dragged relative to the target gravity well and it's most significant secondary well... and maybe tertiary well, as well...

Which also means that large moons cn throw the whole works askew.

I also assume momentm is preseved relative to same.

Now, if you intentionally plot into a gravity well, too deep, the violent exit is the sudden kink in the tunnel your bubble of N-Space is forced through.