Accuracy of Jump

[Bill Cameron]

Originally Posted by Drifter

Is there canon, or widely held opinion, about how accurate a Jump exit can be plotted?

As they others have already told you, Mr. Miller's essay in JTAS #24 puts the canonical accuracy of jump at +/- 3000 km per parsec jumped. What isn't as clear is where the jump exit point is actually measured from.

You see, many of the problems associated with jump physical accuracy disappear when a jump exit point is measured in reference to the departure system and not the destination system. Thus the exit point of a jump from Regina to Roup isn't measured as a certain distance from Roup but as a certain distance from Regina.

This means jumps are plotted in much the same way artillery is aimed. Forward observers relay aiming instructions to a gun in relation to the gun's position just as navigators plot their jump exit point in relation to the system they are departing from. And, because the destination system is moving relative to the departure system, navigators plot an exit point with their ship's travel time mind just as artillerymen plotted their aiming points against moving targets with their shell's flight time in mind.

Once you change your perspective of where jump distances are measured from a great many of the oddities surrounding jump no longer seem odd at all.

[johndallman]

Originally Posted by Bill Cameron

... Mr. Miller's essay in JTAS #24 puts the canonical accuracy of jump at +/- 3000 km per parsec jumped.

... because the destination system is moving relative to the departure system, navigators plot an exit point with their ship's travel time mind just as artillerymen plotted their aiming points against moving targets with their shell's flight time in mind.

It's a nice idea, but you're going to have to alter some numbers to make it fit together. Stars near the sun seem to have typical relative velocities of a few tens of kilometres/second. 3000km is enough to account for a minute or two of variation in jump time, rather than the larger variations of canon.

[Drifter]

Antares is a good, if extreme, example for all this.

Antares itself is shedding material, so its driving all its asteroids and other 'junk' out of the system. So there probably isn't an asterod belt within the 100D limit to house all those billions of people. Could there be stuff in the outer system, close enough in that B doesn't capture/disrupt it?

Maybe a zone of captured rock and ice, not quite a Kuiper belt. It would be transitory, on a geological time scale (well, astrological I guess), as the star sweeps up rubble as it moves along, eventually flinging it back out into deep space. But there long enough to house a subsector government.

And this avoids the insane 100D limit issue. That belt is going to be, probably well outside jump shadow.

[Fred Brackin]

Originally Posted by Drifter

(well, astrological I guess),.

Cosmological is probably the correct term.

[Bill Cameron]

Originally Posted by johndallman

It's a nice idea, but you're going to have to alter some numbers to make it fit together. Stars near the sun seem to have typical relative velocities of a few tens of kilometres/second. 3000km is enough to account for a minute or two of variation in jump time, rather than the larger variations of canon.

You still don't understand.

The exit point is measure in reference to the departure system thus the 3000km/parsec variation is also measured in reference to the departure system.

Using the Regina-to-Roup example again, the navigator plots an exit point which is up to one parsec from Regina and the vessel exits jump space within 3000 km of that point. Just as unlucky bomber would happen to be flying by the point where a gunner aimed his AA shell to explode, the Roup system happens to be "flying by" the navigator's Regina-referenced jump exit point.

Turning the Drifter's questions regarding real space vectors, the rules deliberately simplified that aspect of jump for ease of play. Vector matching between the departure and destination systems has been mentioned in adventures at least as far back as MT and vector matching as part of the rules is part of TNE.

Much like gravity effecting weapons ranges, vector matching is a bit of optional realism which a GM can decide to inflict or not inflict on his players.

[Drifter]

Originally Posted by Bill Cameron

As they others have already told you, Mr. Miller's essay in JTAS #24 puts the canonical accuracy of jump at +/- 3000 km per parsec jumped. What isn't as clear is where the jump exit point is actually measured from.

You see, many of the problems associated with jump physical accuracy disappear when a jump exit point is measured in reference to the departure system and not the destination system. Thus the exit point of a jump from Regina to Roup isn't measured as a certain distance from Roup but as a certain distance from Regina.

This means jumps are plotted in much the same way artillery is aimed. Forward observers relay aiming instructions to a gun in relation to the gun's position just as navigators plot their jump exit point in relation to the system they are departing from. And, because the destination system is moving relative to the departure system, navigators plot an exit point with their ship's travel time mind just as artillerymen plotted their aiming points against moving targets with their shell's flight time in mind.

Once you change your perspective of where jump distances are measured from a great many of the oddities surrounding jump no longer seem odd at all.

Yes, to an extent. An acceptable extent in my case, even if I'm giving it the 'eye'.

Mr. Laiho had early talked about reaching the proper vector, but the jumpspace article makes clear that you are at 'zero' speed when you reach your jump point. Zero relative to what? That has come up before, I know, in discussions about jump. To me the clear assumption is zero relative to the local star system. This implies that navigation is trying to drop out as many variables as possible - in this case the vector of the ship relative to the primary.

In the end I just want to know if the ship travels in a straight line in jumpspace, or curves around to reach its desired exit. Looks like it goes straight only.

[Hans Rancke-Madsen]

Originally Posted by Drifter

Mr. Laiho had early talked about reaching the proper vector, but the jumpspace article makes clear that you are at 'zero' speed when you reach your jump point. Zero relative to what? That has come up before, I know, in discussions about jump. To me the clear assumption is zero relative to the local star system. This implies that navigation is trying to drop out as many variables as possible - in this case the vector of the ship relative to the primary.

Simplification for game purpose again. What a departing ship actually is maneuver to achieve a zero vector relative to the destination world. But that's really difficult to calculate because we usually know zip about the vectors of the origin and the destination worlds relative to each other. So the rules substitute a calculation based on achieving a zero vector relative to the origin world, which in many cases is close enough for game purposes and in the cases where it isn't close, we overlook that anyway.


Hans

[jeff_wilson]

Originally Posted by Hans Rancke-Madsen

Simplification for game purpose again. What a departing ship actually is maneuver to achieve a zero vector relative to the destination world....

Can't we say that the vessel emerges at rest wrt the target object and its 100D sphere?

[Hans Rancke-Madsen]

Originally Posted by jeff_wilson

Can't we say that the vessel emerges at rest wrt the target object and its 100D sphere?

I just did.


Hans