JUMP - bearing and speed

[atpollard]

It is possible to interpret the time variability in a jump as simply meaning that all jumps are not of the same time length, but that the duration of any specific jump is precisely known before entering jump space (roll the +/- 10 percent while performing the jump calculations and before pressing the big "ENGAGE" button). There is some official data that contradicts this and some official data that supports this.

Consider it a possible alternative that eliminates most of the difficulties without completely throwing away the time variability aspect of jumps.

 

[far-trader]

It is possible to interpret the time variability...

And distance, don't forget the random per parsec distance from emergence point Marc added in some article or other. Or maybe that's optional, I can't recall.

in a jump as simply meaning that all jumps are not of the same time length, but that the duration of any specific jump is precisely known before entering jump space (roll the +/- 10 percent while performing the jump calculations and before pressing the big "ENGAGE" button). There is some official data that contradicts this and some official data that supports this.

Consider it a possible alternative that eliminates most of the difficulties without completely throwing away the time variability aspect of jumps.

Precisely the way I've long done and explained it

 

[atpollard]

And distance, don't forget the random per parsec distance from emergence point Marc added in some article or other. Or maybe that's optional, I can't recall.

Happily, I must have missed that and have enjoyed blissful ignorance of yet another silly "problem".

My plan is to just aim for the center of mass and precipitate out at the 100 diameter limit. It works for me.

 

[BetterThanLife]

Happily, I must have missed that and have enjoyed blissful ignorance of yet another silly "problem".

My plan is to just aim for the center of mass and precipitate out at the 100 diameter limit. It works for me.

But the issue becomes, within 100D of what? Come out right at the edge of a Lagrange point and see how long that ship will last.

No I am not about to get that complex in any game I run. IMTU: The Jump in with BG on and drift to the target zone, will not be a fleet maneuver and will be no more than a plot device for me. Further I am going to assume, unless circumstances dictate otherwise, that the normal procedure is to come to rest relative to the star you are leaving from and arrive at rest relative to the star you are going to. Anyone that is going to be doing a jump with a velocity is going to come in above or below the ecliptic, be treated as a crash jump and come in with a vector away from the system. (Usually only going to happen in emergencies.)

 

[far-trader]

Happily, I must have missed that and have enjoyed blissful ignorance of yet another silly "problem".

My plan is to just aim for the center of mass and precipitate out at the 100 diameter limit. It works for me.

It's what I do too I can never remember it it's 1000k per parsec or 10,000k per parsec or something else And I don't think it was ever clarified if it was up, down, sideways, closer or further or some combination of :file_22:

I like BTL's way just above too, I've always been a zeroed vector for safe jump advocate. Never thought of making jumps with velocity a kind of misjump, nice treatment.

 

[BetterThanLife]

It's what I do too I can never remember it it's 1000k per parsec or 10,000k per parsec or something else And I don't think it was ever clarified if it was up, down, sideways, closer or further or some combination of :file_22:

A Parsec is 3.26 light years. Since light travels at 3x10^8 m/second, that would make it 300,000 Km per second. 1 Parsec would be equal to (approximately) 9.46x10^12 Km. or 9,460,000,000,000 Km.

 

[far-trader]

You misunderstood my confusion BTL I know what a parsec is, I can't recall what the jump displacement error was from the Marc Miller article. In fact I can't recall where the article was published for sure (JTAS I think) or if it was ever included in an official rules set.

 

[BetterThanLife]

You misunderstood my confusion BTL I know what a parsec is, I can't recall what the jump displacement error was from the Marc Miller article. In fact I can't recall where the article was published for sure (JTAS I think) or if it was ever included in an official rules set.

Ooops! I don't even want to think about adding that to the equation. And people think that Computers in Traveller are too big? To do that calculation, with that many fudge factors they are entirely too small.

 

[far-trader]

Ooops! I don't even want to think about adding that to the equation. And people think that Computers in Traveller are too big? To do that calculation, with that much fudge factor they are entirely too small.

You may be onto something there :file_22: Maybe Marc wrote the article and invented the jump displacement error as a justification for massive computers

 

[Andrew Boulton]

3000km/parsec.

 

[far-trader]

3000km/parsec.

Ah, thanks Andrew!

 

[BetterThanLife]

OK so we are looking at the following input into our calculations for Jump.

1. Current vector of starship, relative to starting starsystem.
2. Vector of target starsystem, relative to starting starsystem.
3. Vector of target heavenly body within target system, relative to target starsystem.
4. Vector of any nearby, in respect to target heavenly body, heavenly bodies relative to target starsystem.
5. Ideal location of jump emergence point, relative to target starsystem.
6. Ideal vector of starship at emergence, relative to target starsystem.
7. Vector of any other heavenly bodies or other objects that may cause the ship to precipitate out of jump because the path of the ship within Jump space passed within 100 diameters of it.

Account for the following errors:
Arrival time is +/- 16.8 hours
Location of arrival is +/- 3000 KM
Accuracy of charts for target starsystem.
Arrival vector is +/- 5 degrees in each plane.
Arrival speed is +/- 10% from current speed. (The last two are not in the rules but based on everything else being inaccurate valid implied errors.)
Rogue Comets, Asteroids, planetoids, moons that may change things either at the time of arrival or before arrival.
Space traffic at the time of arrival.
Arrivals from this or other destinations in the same target jump emergence point.
Lurking ships at the target jump emergence point.

We're talking about, what, 7 unrelated differential equations? All of them dealing with 3D vectors, orbital mechanics and gravitational forces. And adding in 9 unrelated uncertainty factors to each of them? And we are going to make these calculations in under a half hour?

YIKES!

And that is just for a Jump-1.

 

[Icosahedron]

Imagine you are stirring a fruit cake mix and a fly lands in it.

No, this is not a Trader Jim problem.

It depends on how you see space. In the stirred mix analogy, although different parts of it are moving at different speeds relative to each other, a fly taking off from one raisin and landing on another will always be at rest relative to the local medium. Any speed differential is absorbed in the flight, which takes place in a dimension that is separate from the mix surface.

Conservation of vector is the referee's choice. It could be conserved, or it could be absorbed by Jump Space so that no matter what your start vector, you always arrive at rest relative to the local G field.

IIRC, the cake mix has closer ties with General Relativity than the idea of an absolute, empty space having things whizzing through it with different vectors.

 

[BetterThanLife]

Even scarier people want to do this with Black Globes up, coasting blind into a target zone, without hitting anything, with a squadron that is going to be scattered in space and time at the jump emergence point? Good luck with that.

 

[aramis]

16.8 hours
x60 minutes
x60 seconds
x10 km/s stellar speed differential..

produces up to about 600,000 km (6E8 m) off course.just from variability.
Add 3000km per parsec, and that's a pittance...

And I do believe 10km/s to be low for star-to-star vector difference. Each 10km/sec is a G-burn to compensate (0.5G-hours). And THEN you have to accomodate both the difference in current position AND the motion while recovering... so you'll need at least 3 g-burns to make up for it, and at 1G, it's up to 7 Gburns... well more than TNE merchants can spare... to be reasonably close to the official schedule, which includes 5 days dirtside.

Don't forget, either, that the planets you're aiming for are ALSO moving within the system, so if you miss, you may wind up nearer them, or farther than that...

 

[flykiller]

And I do believe 10km/s to be low for star-to-star vector difference.

http://csep10.phys.utk.edu/astr162/lect/motion/space.html

 

[BetterThanLife]

16.8 hours
x60 minutes
x60 seconds
x10 km/s stellar speed differential..

produces up to about 600,000 km (6E8 m) off course.just from variability.
Add 3000km per parsec, and that's a pittance...

And I do believe 10km/s to be low for star-to-star vector difference. Each 10km/sec is a G-burn to compensate (0.5G-hours). And THEN you have to accomodate both the difference in current position AND the motion while recovering... so you'll need at least 3 g-burns to make up for it, and at 1G, it's up to 7 Gburns... well more than TNE merchants can spare... to be reasonably close to the official schedule, which includes 5 days dirtside.

Don't forget, either, that the planets you're aiming for are ALSO moving within the system, so if you miss, you may wind up nearer them, or farther than that...

Nearer is not necessarily a good thing.

 

[BlackBat242]

All of this discussion just confirms my decision back in the day not to convert to "Mangled Traveller":file_28:... much less "Traveller's New Errors":frankie:.

No need to worry about random, unpredictable "russian roulette" jumps, and more than 48 hours of maneuver fuel aboard when exiting jump.



Of course, with all of this agonizing about "jump out at rest to the system you are leaving" vs "jump in at rest to the system you are entering", vs "jump out at some retained vector and wonder how it will effect your jump exit", and discussion of system vector vs galactic vector, you all seem to have missed a better compromise...


Jump out at rest compared to the local galactic vector, and you will exit jump the same way.

That way you will NOT have to calculate relative system vectors, etc... your navigation charts will have system vectors relative to the local galactic vector, along with system orbit data (to calculate what is where in your destination system), and that's all you need to have to calculate your safe jump.


Of course, that would mean no one could calculate your destination from your jump vector, but we don't like tailgaters anyway.

Of course, getting fancy makes things harder... and jumping into an incompletely charted system is even more fun... just ask the scouts.

 

[Fritz_Brown]

1) That's why (after all the math here) the smart merchant pops in and out above or below the system ecliptic. There's a lot less stuff (well, except for the ships) whizzing about up there, and a small error is less likely to put you stepping off the curb in front of a cometary bus.

2) Cherryh's Chanur novels are great for relating the terror of coming into a system (especially a very dirty one like Urtur) with some relativistic speeds because of your "jump". (Her drive is not the same as Traveller's.) It's why I would want (no matter your take on rules) to come in with a relative 0 velocity.

3) So long as its consistent in YTU, and it provides the right plot hooks, just do it.

 

[TheEngineer]

What about the "running against the gravity well" thing ?
I don't know any rules, which say that it hurts....