From Port to Jump Point

[Supplement Four]

I'm reading Leroy Guatney's excellent article in JTAS-22 (same title as this thread).

I've often toyed with making jump exits dependent on jump points (jump "spheres" really) around massive stellar bodies.

This would mean that a ship really couldn't exit anywhere it wanted to--out in deep space, for instance. At least, that's the way I'm reading his article, with the J points being tied to the biggest masses in a star system.

I'm thinking of going with this dude's "definition" of Jumpspace. It'll put some "logic" into jumping, and give the pilot and navigator something to think about. I especially like his idea for micro-jumps.

 

[Supplement Four]

I'm reading Leroy Guatney's excellent article in JTAS-22 (same title as this thread).

I've often toyed with making jump exits dependent on jump points (jump "spheres" really) around massive stellar bodies.

This would mean that a ship really couldn't exit anywhere it wanted to--out in deep space, for instance. At least, that's the way I'm reading his article, with the J points being tied to the biggest masses in a star system.

I'm thinking of going with this dude's "definition" of Jumpspace. It'll put some "logic" into jumping, and give the pilot and navigator something to think about. I especially like his idea for micro-jumps.

 

[Plankowner]

What did he base the radius of the sphere on? Mass of the star or size (like traveller).

Either way you look at it, the interference of the star with nearer planets can cause all kinds of problems that were never discussed in any of the LBBs that I am aware of.

For example...
Use the standard 100D limit for Jumping. From Earth (diameter 12,750km) would require a standoff of 1.275 Mkm (just under twice the orbit of the moon).

The sun has a diameter of 1.4Mkm, so 100D would be 140Mkm which is just under 1 AU. So from Earth, you are OK to jump at 100D.

BUT, now look at a K5v star (0.566 Sol = 792Kkm) so the 100D is 79.2Mkm (about 0.5AU).

The prime habitable zone of a K5v star is about 0.3AU, so for these smaller stars, you will not be able to use the 100D limit of the Main World, you will have to use the star.

All my numbers for the K5v star were taken from LBB6, so they are Traveller's own numbers.

Using mass instead of size gives you slightly different numbers, but the same problem.

For a while I tried using stellar mass and a 10AU limit (at 1.0 Solar Mass), but it threw off my travel times and really messed up my STL endurance, so that didn't work either.

If you use Jump Points (similar to Lois McMasters Bujold's Vorkosigan books), you run into the problem of having choke points in every system that make it easy to defend. That REALLY changes your naval tactics. BUT, it adds that some systems are MUCH more valuable because of their number/location of jump points than they are for the planets, which can be used to explain why population and habitability are decoupled in the UWP generation system. Bad systems with lots of good jump points become economic power houses where good systems with bad Jump Points can stay backwaters.

 

[Plankowner]

What did he base the radius of the sphere on? Mass of the star or size (like traveller).

Either way you look at it, the interference of the star with nearer planets can cause all kinds of problems that were never discussed in any of the LBBs that I am aware of.

For example...
Use the standard 100D limit for Jumping. From Earth (diameter 12,750km) would require a standoff of 1.275 Mkm (just under twice the orbit of the moon).

The sun has a diameter of 1.4Mkm, so 100D would be 140Mkm which is just under 1 AU. So from Earth, you are OK to jump at 100D.

BUT, now look at a K5v star (0.566 Sol = 792Kkm) so the 100D is 79.2Mkm (about 0.5AU).

The prime habitable zone of a K5v star is about 0.3AU, so for these smaller stars, you will not be able to use the 100D limit of the Main World, you will have to use the star.

All my numbers for the K5v star were taken from LBB6, so they are Traveller's own numbers.

Using mass instead of size gives you slightly different numbers, but the same problem.

For a while I tried using stellar mass and a 10AU limit (at 1.0 Solar Mass), but it threw off my travel times and really messed up my STL endurance, so that didn't work either.

If you use Jump Points (similar to Lois McMasters Bujold's Vorkosigan books), you run into the problem of having choke points in every system that make it easy to defend. That REALLY changes your naval tactics. BUT, it adds that some systems are MUCH more valuable because of their number/location of jump points than they are for the planets, which can be used to explain why population and habitability are decoupled in the UWP generation system. Bad systems with lots of good jump points become economic power houses where good systems with bad Jump Points can stay backwaters.

 

[Black Globe Generator]

Originally posted by WJP:
This would mean that a ship really couldn't exit anywhere it wanted to--out in deep space, for instance. At least, that's the way I'm reading his article, with the J points being tied to the biggest masses in a star system.

I don't have my reprints handy at the moment, but what I took away from the article was the idea that these are the most commonly used jump points, rather than the only places in space where ships can enter or exit jump space.

IMTU the j-points described in the article are navigational points for which you can buy jump tapes - other than that, there are no restrictions on where a ship can jump other than effect of the 100d limit.

 

[Black Globe Generator]

Originally posted by WJP:
This would mean that a ship really couldn't exit anywhere it wanted to--out in deep space, for instance. At least, that's the way I'm reading his article, with the J points being tied to the biggest masses in a star system.

I don't have my reprints handy at the moment, but what I took away from the article was the idea that these are the most commonly used jump points, rather than the only places in space where ships can enter or exit jump space.

IMTU the j-points described in the article are navigational points for which you can buy jump tapes - other than that, there are no restrictions on where a ship can jump other than effect of the 100d limit.

 

[Supplement Four]

Originally posted by Plankowner:
What did he base the radius of the sphere on? Mass of the star or size (like traveller).

Sorta.

I like what he did.

In a nutshell, he says that a ship's jump drive not only designates how far it can jump but also how accurate it is in fine-tuning the jump exit.

There are six primary jump exit points in a system. All Jump-1 vessels exit on a point on the sphere created by 100 diam's of the system's star (provided that point isn't masked).

Jump-2 vessels can "fine-tune" their exit so that the ship re-enters N-Space at either the J-1 point or the J-2 point. The J-2 point is 100 diams from the next largest stellar body in the system.

So, a Jump-2 ship, exiting in the Sol system, would have a choice of exiting 100 diams from Sol, or 100 diams from Jupiter.

The J-3 point is based on the next biggest body in the system, and so on.

He lists some special rules for micro-jumps and binary/trinary systems, but you get the idea.

I like how he's made a roadway, or "jump path" in space. Instead of just saying, "OK, you jumped to the next system...now...", the players can put some thought/strategy/tactics into where they will enter the system.

"If we enter here, our journey will take X days, but if we enter here, we can refuel at the GG, then do a micro jump to here, where we want to be."

Or, something like that.

I like how this will sometimes put the ship a distance from the destination world--not always 100 diams out.

The idea of working jump like this lends itself to creating unique star systems, too....which may explain some of those unique UWPs we see at times.

"Man, I like that planet, but it's a bitch getting there...".

 

[Supplement Four]

Originally posted by Plankowner:
What did he base the radius of the sphere on? Mass of the star or size (like traveller).

Sorta.

I like what he did.

In a nutshell, he says that a ship's jump drive not only designates how far it can jump but also how accurate it is in fine-tuning the jump exit.

There are six primary jump exit points in a system. All Jump-1 vessels exit on a point on the sphere created by 100 diam's of the system's star (provided that point isn't masked).

Jump-2 vessels can "fine-tune" their exit so that the ship re-enters N-Space at either the J-1 point or the J-2 point. The J-2 point is 100 diams from the next largest stellar body in the system.

So, a Jump-2 ship, exiting in the Sol system, would have a choice of exiting 100 diams from Sol, or 100 diams from Jupiter.

The J-3 point is based on the next biggest body in the system, and so on.

He lists some special rules for micro-jumps and binary/trinary systems, but you get the idea.

I like how he's made a roadway, or "jump path" in space. Instead of just saying, "OK, you jumped to the next system...now...", the players can put some thought/strategy/tactics into where they will enter the system.

"If we enter here, our journey will take X days, but if we enter here, we can refuel at the GG, then do a micro jump to here, where we want to be."

Or, something like that.

I like how this will sometimes put the ship a distance from the destination world--not always 100 diams out.

The idea of working jump like this lends itself to creating unique star systems, too....which may explain some of those unique UWPs we see at times.

"Man, I like that planet, but it's a bitch getting there...".

 

[Supplement Four]

Originally posted by Plankowner:
If you use Jump Points (similar to Lois McMasters Bujold's Vorkosigan books), you run into the problem of having choke points in every system that make it easy to defend. That REALLY changes your naval tactics.

True in one sense. Not so true in another.

I'm not so sure any point on the 100 diam sphere of a system's star is easy to defend without a large fleet. We're talking about a lot of distance there, even if your ship can pull 6Gs.

So, choke points will occur, but those choke points are damn big (your acutal entry point is any point on the 100 diam sphere of the system's star).

You'd think this would preclude attacks by pirates and things.

Not so (or true only in some systems). Low Tech systems (most in the Spinward Marches, for example) without Naval Bases won't typically have system defense.

So, let's say a Low-TL world on the Spinward Main doesn't have a Naval or Scout base. A J-1 ship jumps in at 100 diams from the star, and it's a 2.83 day journey to the system's main world.

There's a lot that can happen in that three days the ship will be speeding off to the main world...plenty of room to throw some action on the players.

 

[Supplement Four]

Originally posted by Plankowner:
If you use Jump Points (similar to Lois McMasters Bujold's Vorkosigan books), you run into the problem of having choke points in every system that make it easy to defend. That REALLY changes your naval tactics.

True in one sense. Not so true in another.

I'm not so sure any point on the 100 diam sphere of a system's star is easy to defend without a large fleet. We're talking about a lot of distance there, even if your ship can pull 6Gs.

So, choke points will occur, but those choke points are damn big (your acutal entry point is any point on the 100 diam sphere of the system's star).

You'd think this would preclude attacks by pirates and things.

Not so (or true only in some systems). Low Tech systems (most in the Spinward Marches, for example) without Naval Bases won't typically have system defense.

So, let's say a Low-TL world on the Spinward Main doesn't have a Naval or Scout base. A J-1 ship jumps in at 100 diams from the star, and it's a 2.83 day journey to the system's main world.

There's a lot that can happen in that three days the ship will be speeding off to the main world...plenty of room to throw some action on the players.