Jump drive

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EDG
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Jump drive

Postby EDG » Thu Dec 13, 2007 4:19 am

Jump travel is the only known means by which a vessel may travel faster than the speed of light. To jump, a ship creates a bubble of hyperspace by means of injecting high-energy exotic particles into an artificial singularity. The singularity is driven out of our universe, creating a tiny parallel universe which is then blown up like a balloon by injecting hydrogen into it. The jump bubble is folded around the ship, carrying it into the little pocket universe.

This new universe is short-lived, and will eventually collapse, precipitating the ship back into normal space several light-years from its original position.
Er, is that actually how OTU jump drives are supposed to work? The bold part is news to me.

Gravity can cause a jump bubble to collapse prematurely, bringing a ship back into normal space early (so if a ship tried to jump from Earth to Mars when the Sun was between the two, the vessel would fall out of jump space as soon as it came within one hundred diameters of the Sun.
Oo, that's going to upset the purists ;). Jump Shadowing/Masking has always been controversial in Traveller - though personally I think it's internally consistent with how jump is supposed to work.

Also leads to interesting situations around Giant or Supergiant stars like Antares, where the 100D limit can be up to 1000 AU wide...
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Postby AKAramis » Thu Dec 13, 2007 6:20 am

Agreed: jump masking by stars is controversial. Which is a good reason to have the "generic traveller" have it defined, but then to put an option in.

It does, however, run counter to prior explanations of jump. Not that they are any more viable...

but, by the same token, defining the process is going to raise hackles no matter what.

I like the explanation.
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Postby EDG » Thu Dec 13, 2007 6:35 am

AKAramis wrote:Agreed: jump masking by stars is controversial. Which is a good reason to have the "generic traveller" have it defined, but then to put an option in.

It does, however, run counter to prior explanations of jump. Not that they are any more viable...
IIRC jump masking/shadowing came from an article Marc Miller wrote in JTAS.

Either way, I think it's best if MongTrav explicitly defines what can and can't block jump and how it does it.

e.g.
1) can you ever arrive within 100D of a target?
2) Are you generally automatically precipitated out of jump at the 100D limit of your target?
3) Can you ever jump out from a system within 100D of an object?
4) Is there a minimum radius/mass for an object to have a 100D limit?

I think the canonical answers to those questions are:
1) No (unless as a consequence of a misjump, which is going to be rough).
2) If you attempt to precipitate within it (without a misjump), then you will always be dropped at the 100D limit. But you can deliberately choose to arrive anywhere beyond a 100D limit if you want.
3) Yes, but then you increase your chance of misjump/damage.
4) It's implied that spacecraft don't ever have 100D limits. The implication is that you need at least a 1km-radius asteroid before you have a 100D limit.


Mention of an alternative gravity/tidal-based method would be nice too, since that's quite popular in the ATUs out there. The way I do it myself is to say that the limit is where gravity drops to a certain value (e.g. 0.01 m/s2) - this has the advantage of being tied to a real property (mass) and not something as tenuous as radius, and also means that red giant stars don't have ridiculously huge 100D limits (in fact, the aforementioned gravity-based limit is inside the star).
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Postby AKAramis » Thu Dec 13, 2007 7:59 am

EDG wrote: IIRC jump masking/shadowing came from an article Marc Miller wrote in JTAS.
Yes. But I was usng stellar blocking before ever seeing the article. Not consistently, and not based upon any reliable figures... just as a story element.
EDG wrote:Either way, I think it's best if MongTrav explicitly defines what can and can't block jump and how it does it.

e.g.
1) can you ever arrive within 100D of a target?
2) Are you generally automatically precipitated out of jump at the 100D limit of your target?
3) Can you ever jump out from a system within 100D of an object?
4) Is there a minimum radius/mass for an object to have a 100D limit?
My understanding of the OTU for these is:
1) No. Never.
2) Yes. Always. The deeper your exit point, the more violently.
3) Yes. (CT and MT both make it possible at anything over 10 diameters)
4) I used a 100d limit for anything over 100 Td.... presuming that if it was too small to hold a bubble, it was too small to affect one. Some GM's set it at a kilo, others at a ton. Until (IIRC) T4, there was no threshold formally set. Many seem to set it at the lower bound of a Size S world.

I do agree it would be nice to have explicit limits IF the methodology is being defined as well.

As to the tidal method, what is the smallest spheroid ship at "default" 15Tm /Td to generate the minimum tide you mentioned (e.g. 0.01 m/s2)?

I think it's a good alternative method, but it's not as simple. Agree it would be a good sidebar.
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Postby EDG » Thu Dec 13, 2007 8:41 am

AKAramis wrote:1) No. Never.
Aw, but then that removes the possibility of coming out of jump suddenly with a planet filling the whole viewscreen and expanding rapidly ;).
2) Yes. Always. The deeper your exit point, the more violently.
Really? So coming out at 100D is actually pretty rough, but further is smoother?
3) Yes. (CT and MT both make it possible at anything over 10 diameters)
Yep, that was my understanding too, but between 10 and 100D the misjump chances are considerably higher.
4) I used a 100d limit for anything over 100 Td.... presuming that if it was too small to hold a bubble, it was too small to affect one. Some GM's set it at a kilo, others at a ton. Until (IIRC) T4, there was no threshold formally set. Many seem to set it at the lower bound of a Size S world.
That's the problem with setting it using radius as a limit, rather than mass - you could theoretically make multi-kilometre-scale 'barrage balloons' in space made of solar sail foil and trivial mass that might (if you're lucky) have a 100D limit that blocks ships.
As to the tidal method, what is the smallest spheroid ship at "default" 15Tm /Td to generate the minimum tide you mentioned (e.g. 0.01 m/s2)?
Oh, lordy knows - very small, since even the biggest ships won't generate that much gravity based on their own actual material mass :). (and note, my example used actual gravity, not tidal forces). Though there is the generally unstated problem of the g-field produced by their artificial gravity... I guess everyone just assumes that the artificial gravity stops at the ship hull somehow (gravity dampers in the hull maybe??).
I think it's a good alternative method, but it's not as simple. Agree it would be a good sidebar.
Could be simple if it was just done as a table. You'd just need average gravities and the corresponding limits for the major star types, planets, and brown dwarfs listed there.
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Postby AKAramis » Thu Dec 13, 2007 6:56 pm

No, coming out at 100D is smooth; if your target was at 0D that displaced energy goes somewhere... IMU, it's a violence at exit.

And it doesn't preclude the compensators from failing on a misjump and leaving the interstellar relative velocities uncorrected for... "Hey, we're 10min out from that world!"
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Postby Allensh » Thu Dec 13, 2007 7:08 pm

I think Mongoose's explanation for how jump drive works is as good as anything else I've ever seen in Traveller..which means its complete hooey, but then so is Jump Drive in general :)

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Postby Rikki Tikki Traveller » Thu Dec 13, 2007 9:25 pm

Mongoose's explanation also eliminates Hyperspace or Jumpspace. Now everything is pocket universes.

Also, we now know what happens to the Jump Fuel! It all gets expended at the beginning of the jump and is what keeps the bubble open until you exit.
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Postby Mongoose Gar » Thu Dec 13, 2007 9:31 pm

I suspect my little pocket universe explanation is going to get folded away into a sidebar along with alternate FTL drives.
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Postby captainjack23 » Thu Dec 13, 2007 9:37 pm

Mongoose Gar wrote:I suspect my little pocket universe explanation is going to get folded away into a sidebar along with alternate FTL drives.
Okay, so based on this, and your request for "comment on jump and the ramifications" post, you want us to post our actual jump theory/rationalizations/handawaves for how it works ?


....cool.

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Postby Rikki Tikki Traveller » Thu Dec 13, 2007 9:59 pm

Well, one of the sticky issues has always been the Jump Grid.

If the hull of the ship needs a special coating/matrix whatever to be able to jump? Some versions/designs seemed to imply that you needed one and others didn't.

Personally, I don't like the idea of the entire ship having to be enclosed in a grid of some kind (usually handwaved as a Lanthanum grid) since hull damages would damage your Jump capability.

Another topic is Jump Accuracy. Marc Miller claimed a long time ago that jumps were accurate to about 3000 km. That is DAMN accurate over 6 parsecs, or even 1 parsec. Perhaps the Effect Die roll of the Navigator would give you the accuracy. Given that the TIME of the jump has 6d6 variation (+08%), having a distance accuracy of (+0.00000001% seems a bit rediculous without some kind of explanation. But, if you make the accuracy of the same order of magnitude as the time variation, then you are quite likely to miss the entire solar system when you try to jump.

I can accept the accuracy for game purposes, but then you need to explain why there is a variation in the time. Don't just tell us it is 148+6d6; tell us WHY.
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Postby Allensh » Thu Dec 13, 2007 10:20 pm

Pocket universes are not completely unknown in Traveller...Yaskodray, for example.

It works as good as any other explanation.

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Postby GamerDude » Fri Dec 14, 2007 5:34 am

actually, I can't remember if it was CT, MT, or GURPS:Traveller which described the 'jump bubble' being like a pocket universe.

In Jump, through the windows you can't see anything outside but pure black, lightning arcing from the hull to the 'bubble' due to the charges building up on the hull while in Jump.
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Postby AKAramis » Fri Dec 14, 2007 7:32 am

ParanoidGamer wrote:actually, I can't remember if it was CT, MT, or GURPS:Traveller which described the 'jump bubble' being like a pocket universe.

In Jump, through the windows you can't see anything outside but pure black, lightning arcing from the hull to the 'bubble' due to the charges building up on the hull while in Jump.
Such a description is in MT's Starship Operator's Manual, by DGP.

Some elements wound up in the description in (IIRC) TNE's Regency Sourcebook.

There are hints of it in several places in CT, but nothing explicit.
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Postby Lane Shutt » Mon Dec 17, 2007 6:09 pm

Rikki Tikki Traveller wrote: Another topic is Jump Accuracy. Marc Miller claimed a long time ago that jumps were accurate to about 3000 km. ... Given that the TIME of the jump has 6d6 variation (+08%), having a distance accuracy of (+0.00000001% seems a bit rediculous without some kind of explanation.
IMHO the accuracy of 3000km should be an average value.
Accuracy could be something like 2D6-(effect die) x 1000km, values <1 divide by 10 ie. 0x1000 = 100, -1x1000=100.

The timing variation could be explained by the specifics of the jump insertion and exit points. A jump 3 from system X to Y would differ from jumps X to Z or Y to Z. They may even differ greatly based on where in the system and position of planets.

Jump times should be modified by effect die.
There should also be an option for jump beacons/ markers. These would be used for traffic control in a system and also provide a bonus on timing to specified destinations. Jump points A-D would give lower times to system X because the jump was well known, only variations in ship and drive affect the timing. Other Jump markers would correspond to different systems or used for incoming traffic.
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Postby pasuuli » Mon Dec 17, 2007 8:57 pm

Rikki Tikki Traveller wrote:Mongoose's explanation also eliminates Hyperspace or Jumpspace. Now everything is pocket universes.
It's a neat way of tying in uber-high technology into "typical" interstellar terms, too.
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My comments

Postby barasawa » Thu Dec 20, 2007 2:31 am

Hiya, I just had to lay down my 2Cr here.

FTL is possible. At least in the Traveller Universe, otherwise it wouldn't be much of an interstellar game... (Possibly in the real world, but we havent' figured out how. And to those who want to argue physics, just assume the physics are still wrong and have fun.)

Don't have my old sourcebooks these days, but I recall it being stated that jumpspace (the place where the ship exists when jumping. Heck, you could call your bedroom sleepspace for that matter.) is completely unable to interact with energy or matter in n-space. That actually fits very nicely with a pocket dimension. Also, it fits with the modern concepts of a warp drive. (NOT Star Treks version.) It wraps a bubble of space around itself and moves the bubble, not the ship.

With that in mind, perhaps the radius limit is actually due to the gravity well trashing or destabilizing the bubble. (Whether it's a true pocket dimension, or a space/time cocoon doesn't matter.) In that case, the radius issue is simply a game mechanic to simplify the rules. After all, a size 9 world has a radius of 9000, you don't have to know what it's density is, or how to calculate the mess that is a gravity well. You don't want to scare away players by throwing calculus at them. (Actually I think an algebraic formula would work, but who cares, I don't want to do that kind of math in my games either.)

As to dumping hydrogen into the bubble to keep it open, it seems that it doesn't really matter what you use. But we know that unprocessed hydrogen runs the risk of a misjump. Now why would that be?
*How about this. The hydrogen is used to not only produce an expansion pressure, but it acts as a frequency conduit/medium for the field that creates/controls the bubble. As such, any non-hydrogen, or hydrogen isotopes could muck with the carefully calibrated frequency needed, thus causing a misjump.

This idea also explains why you can't just use the contragravity systems to blow up the bubble. That just deals with negative gravity, not frequencies. Also, it doesn't allow use of contragravity to allow close in jumps either. It would be like trying to get a smooth ride on a road with pillars and potholes.

(As long as I'm mentioning Contragravity, I saw some people wondering why shipboard gravity didn't cause issues. I would guess that would be because of the contragravity system preventing it from exiting the hull. For that matter, when combined with inertial dampers, I wouldn't even let it effect more than a single deck at a time, under normal circumstances.)

One concept is that this could be interpreted to allow for an Emergency Jump. A quick omgsos that results in an automatic misjump, but happens faster, possibly with significantly less hydrogen as well.

In my opinion, these ideas do not in any way eliminate the concept of jumpspace. It just changes it from being something that is seperate and complete at all times, to nothing more than a psychological result of an artificial isolation. (An old spacer once told me, "We call it jumpspace" not cause we go to someplace else, but rather cause we ain't here, and we got no place we can go when we're there.".)

Just a bit more. If you are not going into another reality, why do misjumps go so wacky? If it's true that our 3 dimensional universe is just the skin of an 8 dimensional structure, you can probably assume that anything able to divest itself from the surface matrix would have to navigate 8-dimensionally. In which case, you forget to carry the one, and you bounce too close to a supernova... Or you get turned into a modern art klein bottle or something...)

Ok, I've thrown enough ideas and concepts (not to mention opinions) out there, time for more of yours. Thanks for reading.
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err... typo/error

Postby barasawa » Thu Dec 20, 2007 2:38 am

err, I think I goofed on the planet size stuff. First, I think that was supposed to be diameter. And second, I think there was a chart, not a super simple formula. Wish I hadn't lost my Traveller books in the 90s.
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