How do jump drives really work?

[far-trader]

...We have to find a way to open the Jump point on caps, and find a use for fuel after the fact but before the ship enters said space. Hmmm...maybe the LHyd is used as reaction mass to enter the Jump Point because other types of thrust would disrupt the opening. the larger the jump the more umph needed.

Interesting idea. At least that would tie better to the displacement* and jump range memes. Still makes the Annic Nova a problem.

* which is the big argument against the whole jump bubble (GURPS?) idea, since a bubble to enclose the hull will always be bigger than the hull, and vary by hull form, yet the fuel is rated on displacement and not a bubble

 

[whartung]

So the process would be:

1. Ship uses power plant or capacitors to create a breach into JSpace.
2. The ship enters JSpace and "inflates" the bubble around the ship.
3. JSpace then collapses onto a protective cushion of hydrogen which surrounds the ship until the ship emerges again in normal space.

Drop tanks are thus valid in this case.

At what point are the drop tanks jettisoned through the jump bubble and moved 100D away from the ship?

 

[HG_B]

We have to find a way to open the Jump point on caps, and find a use for fuel after the fact but before the ship enters said space. Hmmm...maybe the LHyd is used as reaction mass to enter the Jump Point because other types of thrust would disrupt the opening. the larger the jump the more umph needed.

This was a solution to the problem of the jump grid needing a conductor from the grid to a sufficient distance away from the hull so that the opening was larger than the ship. H2 turned out to be the ideal conductor for the energy level and frequency...

 

[Blix]

So no, Capacitors should not be all that is needed to make a jump. They just are needed to jump start the Jump Point.

What are your guys takes on this? What am I missing?

Jump drives work however you say they work . Figure out a way that makes sense for you in your games, and go with that!

 

[Ronnke]

At what point are the drop tanks jettisoned through the jump bubble and moved 100D away from the ship?

After the ship has created the breach and formed the field/bubble, then the tanks are no longer needed and thus jettisoned before the breach closes. You do not need to be 100D from the drop tank as they are too small to interfere with a jump. Only objects larger and more massive than a ship requires attention to the 100D limit.

Also found this in the GURPS Traveller: Interstellar Wars book. (p170)

"Each jump requires a quantity of liquid hydrogen. Some of this hydrogen is converted into energy in the ship’s reactor, while some of it is used as reactor coolant. The rest of the fuel is expelled into jumpspace while the ship is in transit, to hold open the “bubble” of normal space that protects it."

 

[rancke]

Also found this in the GURPS Traveller: Interstellar Wars book. (p170)

"Each jump requires a quantity of liquid hydrogen. Some of this hydrogen is converted into energy in the ship’s reactor, while some of it is used as reactor coolant. The rest of the fuel is expelled into jumpspace while the ship is in transit, to hold open the “bubble” of normal space that protects it."

Two probelms with that quote: The aforementioned "hydrogen is a lousy coolant" problem and the likewise aforementioned "all the hydrogen is used up prior to entering jumpspace" problem.


Hans

 

[aramis]

Two probelms with that quote: The aforementioned "hydrogen is a lousy coolant" problem and the likewise aforementioned "all the hydrogen is used up prior to entering jumpspace" problem.


Hans

Not to forget the whole "GTIW also requires a gravity well at both ends of a jump" and "GTIW says jump exit is at the 100D limit" issue.

GTIW is at best a wholly isolated ATU, at worst, poorly researched and utterly inconsistent with Traveller.

 

[rancke]

Not to forget the whole "GTIW also requires a gravity well at both ends of a jump" and "GTIW says jump exit is at the 100D limit" issue.

That was an attempt to reconcile the CT account of the development of the Terran jump drive with the CT description of how the jump drive works (And with Imperium too, to be sure).

Sadly, as I realized a few weeks ago, it doesn't work. So the canonical CT account remains self-contradictory.


Hans

 

[rancke]

GTIW is at best a wholly isolated ATU, at worst, poorly researched and utterly inconsistent with Traveller.

GTIW is a very well-researched setting that fits quite well with the OTU, consistent with most previously published material. It has a few flaws, yes, but far fewer than most pre-GT Traveller material of comparable size.

And, yes, I meant to state this as a fact, not an opinion.


Hans

 

[Ronnke]

Not to forget the whole "GTIW also requires a gravity well at both ends of a jump" and "GTIW says jump exit is at the 100D limit" issue.

Not entirely correct. GTIW states that the mathematics of calculating a jump are far simpler when there is a large object at each end of the jump. It also implies that it's only during the IW period that Terran and Imperial navigators don't have the ability to plot jumps far from a massive object. I'm assuming the science of jump navigation has not progressed passed that limitation.

 

[rancke]

Not entirely correct. GTIW states that the mathematics of calculating a jump are far simpler when there is a large object at each end of the jump.

Sadly, in a normal jump, you're not aiming for a large object. You're aiming for a spot of empty space where you know a large object is going to be in 168 hours. If you were aiming for a large object, you'd arrive in empty space where that large object was seven days earlier. The implication is that if it simplifies the calculations to aim for a large object, you can just pretend that there is one in whichever empty spot you want to aim for.


Hans

 

[McPerth]

...and THEN the fuel is burned... somehow... using that energy from the capacitors, and that from the fuel...

I cannot believe all the jump fuel is burned, and let me show why (all those calculations are done in MT rules, but I don’t think they vary too much on HG. I don’t know other editions enough to talk about them)

In the black globe section of combat, they say the jump energy sinks are 0.05xVxJn. So a free trader has 0.005x2700x1=13.5 kl of sinks. It also says each kl can store 650 Mw (as we talk about energy, not power, I assume they are Mw hour), so it can store 135x650=8775 Mw hour.

Now, if we look at the PP section, a kl of PP produces 18 Mw (after efficiency) and consumes 0.005 kl of fuel/hour. So, 1 kl of fuel can produce energy for 200 hours, or 3600 Mw hour.

By the way, and to compare, we must take into account that the 3600 Mw h produced by 1 kl of fuel are the equivalent to 12960000 Mj, or the equivalent to a nuke of 3.097 kton. I think for such a thermonuclear bomb they use quite less hidrogen (I don't have those figures about nukes), so most of it isn’t burned by the PP.

To produce the 8775 Mw hour we need 2.4375 kl of fuel (at the rate of PP, so quite less is really burned). The free trader needs 270 kl of fuel, of which, as we have seen, less than 2.5 are burned (and uses the energy of a 7.5 kton nuke, you can calculate what is the equivalent for an Azhanti, or a Tigress). If all 270 kl were burned, the energy released (at PP rates) whould be 972000 Mw h, quite more than what the sinks can store, and the ship whould be vaporized.

I like the idea of using the rest as coolant. Sure there are better coolants, but none are so plentiful and easy to get, so it can be a good choice. It's stored as liquid, and by evaporating it I guess it can be quite a good coolant (more so in the amounts given here).

 

[whartung]

I like the idea of using the rest as coolant. Sure there are better coolants, but none are so plentiful and easy to get, so it can be a good choice. It's stored as liquid, and by evaporating it I guess it can be quite a good coolant (more so in the amounts given here).

I'll patiently await the armchair thermodynamics and fluid mechanics specialist to tell us how much heat the remaining LHyd consumed in the process would absorb, who knows, maybe it all balances out in the end . I never looked much at thermodynamics.

Oh, and McPerth, could you please make an effort to add blank lines between your paragraphs? It would make reading them much easier.

As an aside, if the vast amount of LHyd is used for cooling, then someone with eyes on the jumping ship would likely see some indication of the all the fuel being jettisoned prior to jumping.

 

[McPerth]

Oh, and McPerth, could you please make an effort to add blank lines between your paragraphs? It would make reading them much easier.

Done, sorry about that

 

[Ronnke]

The implication is that if it simplifies the calculations to aim for a large object, you can just pretend that there is one in whichever empty spot you want to aim for.

I'm assuming that navigators use the fact that they know in 7 days a large object will intersect their jump line. They rely on that object being there to actually precipitate them out of jump. If their calculations are wrong then they missed their target and suffer a misexit which has them appear at the 100D limit of some other random object in the system. Kind of like a shooter leading the shot on a moving target. If he misses, then the bullet eventually hits something else.

In keeping with the text, navigators of the Interstellar Wars era obviously don't know how to reliably pull a ship out of jump without the 100D limit intersecting their jump line. The science of stopping a bullet in flight without hitting something is still a mystery to them.

 

[ranger2261]

http://traveller.wikia.com/wiki/Jump_drive

 

[whartung]

In keeping with the text, navigators of the Interstellar Wars era obviously don't know how to reliably pull a ship out of jump without the 100D limit intersecting their jump line. The science of stopping a bullet in flight without hitting something is still a mystery to them.

Dunno how much sense that makes, since GTIW has Jump Masking as well. They need to plan and plot around the 100Ds in the system to not get screwed up.

 

[Ronnke]

Which is fine, they just need to hit a 100D to stop.

 

[rancke]

I'm assuming that navigators use the fact that they know in 7 days a large object will intersect their jump line.

First of all, that's not what the text says. It says that its easier to calculate if there is a solid body at both ends of the jump. Secondly, in a number of cases they don't know that for sure. It depends on how fast the planet they're aiming for moves compared to its 100 diameter limit. Some worlds move a lot more than that in the time the jump variation can cover.

Also, if you can aim close enough to be sure of at least hitting a planetary jump limit then you can aim close enough to an empty point in space to arrive within six to eight hours real-space travel. The implication of what GTIW says is clearly that having those solid bodies at both ends of jump makes the calculations a LOT more accurate. Without them, the inaccuracy must be several orders of magnitude greater.

They rely on that object being there to actually precipitate them out of jump. If their calculations are wrong then they missed their target and suffer a misexit which has them appear at the 100D limit of some other random object in the system. Kind of like a shooter leading the shot on a moving target. If he misses, then the bullet eventually hits something else.

As long as you hit the system, you're way ahead of the game if you're trying to cross a gap by jumping into an empty hex and then doing a second jump to a system.

In keeping with the text, navigators of the Interstellar Wars era obviously don't know how to reliably pull a ship out of jump without the 100D limit intersecting their jump line. The science of stopping a bullet in flight without hitting something is still a mystery to them.

You don't pull anything out of jumpspace. You put it into jumpspace and a week later it emerges willy-nilly. If you can aim close enough to hit the system, you can cross a gap. Which is the one thing that bit of background was created to explain why people of that period don't do.




Hans

 

[Ronnke]

Fair nuff.

You don't pull anything out of jumpspace. You put it into jumpspace and a week later it emerges willy-nilly. If you can aim close enough to hit the system, you can cross a gap. Which is the one thing that bit of background was created to explain why people of that period don't do.

If I'm not mistaken, you can be precipitated out of jump (1 week later) if your jump line is intersected by an unaccounted for 100D object.

eg. You make a jump to the next system, but as luck would have it, there is a rogue planet that has intersected your jump line mid way between systems. So you emerge from JSpace not at your intended destination but at 100D of the rogue planet, 168 hours +/- 10% from your departure.