Is it time for Jump-7 drives in Traveller?

[mike wightman]

If pumps can move fuel from drop tank to jump engine or from demountable tanks to jump engine then there is no reason said pumps can not manage to move the fuel from a tanker.

And it is not water, it is liquid hydrogen.

 

[daryen]

If pumps can move fuel from drop tank to jump engine or from demountable tanks to jump engine then there is no reason said pumps can not manage to move the fuel from a tanker.

And it is not water, it is liquid hydrogen.

It can still make quite the difference.

The drop tanks require pumps, but no tubes. Since the surface area of contact is so large, many connection points can be had. Plus, since there is direct contact, there is no transit time. With a distant tank, you have fewer contact points and non-zero transit times. Depending on how fast the fuel must be transferred, it is not that difficult to come up with reasons that drop tanks work, but a distant tank does not.

 

[Grav_Moped]

It can still make quite the difference.

The drop tanks require pumps, but no tubes. Since the surface area of contact is so large, many connection points can be had. Plus, since there is direct contact, there is no transit time. With a distant tank, you have fewer contact points and non-zero transit times. Depending on how fast the fuel must be transferred, it is not that difficult to come up with reasons that drop tanks work, but a distant tank does not.

It's also possible that the tanker can separate from the jumping ship at a minimum of 10m/sec² under Traveller rules, which makes getting to 100D (of either the jumping ship or the tanker or both) promptly, a trivial issue; and therefore, any stand-off distance during fuel transfer a moot point.

 

[spank]

I hate to point this out but in the MT and TNE universes the 10% per jump number was not the constant.

It wasn't even a constant, it was 5%+%5 per JN, so J-1 = 10%, J-2 = 15%, J-3 =15% J4 = 20%, etc,
that meant the "wall" was alot further out, and jumps got cheaper as tech progressed. And there were two progressions built in, one from the 5% plus 5% per JN, and one from the reduction above TL 16.
TL 17 J-8 would have been cheaper at 36% than TL 16 J-7, at 40%.

 

[Spinward Flow]

Do Collectors help you get around the Jump-7 fuel limit adequately in "rocket equation" terms for remaining payload fraction beyond the jump drive (and supporting displacement)?

 

[spank]

Do Collectors help you get around the Jump-7 fuel limit adequately in "rocket equation" terms for remaining payload fraction beyond the jump drive (and supporting displacement)?

Yes, but.
Yes,
A collector will use less space to fuel a give jump. For a 1000 ton ship it will use 360 tons for a collector big enough to fuel a J -7 drive, So a savings of 40%
And your total J-drive/powerplant/collector is only 654 tons, so better than a standard J-6 drive.
But,
Collectors will only be at C-3 @ TL-16, it will be TL 20 before they can support a jump 7. And Hop will be available at TL 17. ---Why use J-7 When you can Hop-10?

 

[Grav_Moped]

Yes, but.
Yes,
A collector will use less space to fuel a give jump. For a 1000 ton ship it will use 360 tons for a collector big enough to fuel a J -7 drive, So a savings of 40%
And your total J-drive/powerplant/collector is only 654 tons, so better than a standard J-6 drive.
But,
Collectors will only be at C-3 @ TL-16, it will be TL 20 before they can support a jump 7. And Hop will be available at TL 17. ---Why use J-7 When you can Hop-10?

Well, according to MWM's retcon explaining/justifying the dual-drive setup on Annic Nova, there was once a way to get J-8 or J-9 out of that ship, and in principle to build ships with J-27 or more at incomprehensibly higher tech levels. There's no indication that it's still possible for Annic Nova as presented in DA1 (or open to discovery by PCs or anyone else) though, or that the loophole it exploited to do so is possible for non-Collector Jump drives.

 

[Condottiere]

There's one written, not implied, restriction on fuel tank options.

You can't directly transfer fuel from the rubber bladder directly to the jump drive.

Also, consider the time window that any particular edition will insist that transfer takes place.

So, throughput and suction.

 

[mike wightman]

Since when is a drop tank a rubber bladder?

<Reads the rules again>
A:5 TCS

Other Types of Fuel Tankage: There are four varieties of fuel tankage which are
not integral to a ship, each with its advantages and disadvantages. These are collapsible
tanks, demountable tanks, exterior demountable tanks, and drop tanks.

Demountable tanks operate in the same manner as normal fuel tanks, and their
fuel is available for use by the drives immediately.

So the demountable tank 9(either interior or exterior) must contain the pumps and pipework to get the fuel to the jump engine as needed for the jump.

The next logical step is to move the demountable tank to another ship and have a long hose the same diameter as the pipework that allows such rapid movement of fuel. The 'oiler' should have a fast m drive so it can get out of the 100D window.

 

[Condottiere]

1. I think this is going to be very dependent on what each edition says about transferrable volume within a hundred diameters of a jump drive.

2. 'Cos even exterior empty hoses take up volume within the physics of Traveller hull calculations.

3. Dropped drop tanks have never been counted as part of the transferrable volume, mostly I suspect because writers saw them as legacy, and never really thought of the actual implications of having that empty volume near a jump drive, after the rules got revised. A lot of text tends to get copy pasted.

4. To be fair, neither did I until ten minutes ago.

5. Personally, I'd allow a one percent variation in volume, without adding that to the misjump algorithm.

6. How far would the tanks have to travel to clear the jump zone?

7. How much time would they have to clear the jump zone?

8. Maybe that's the real advantage of the lanthanum grid, no jump zone.

9. Speaking of time and space, conceivably external tanks are pretty near the jump drive.

A. Add an extended connection, even at the same throughput, and you add additional transfer time.

 

[mike wightman]

Note - the original write up of drop tanks had then as non-recoverable after their use 'dropped'.

It was only later the idea of recovering and reusing dropped tanks started to develop the schism.

 

[Condottiere]

Note - until today I never questioned these assumptions.

Without extensively ploughing through the rule books, I think survivable and reusability depended on technological level, whether of the drop tanks, hull, jump drive or shipyard, I don't recall.

 

[whulorigan]

Per T5, the "jump-bubble" (for those ships equipped with that mode of Jump-readiness) is a roughly spherical region whose diameter corresponds to 100x the dimensions (i.e. "diameter") of the ship. Anything within that volume can potentially be "dragged along" by the jump field. Any Jump "mishap" that occurs as a result will happen to the smaller object(s) by volume (ship or object(s)).

Thus a drop tank will need to be blown clear of that volume in order to survive undamaged.

Also note that a drop-tank equipped vessel will not be able to use the grid-option for jump readiness if the drop tanks are attached externally and the ship intends to carry mounted drop-tanks with it thru jump (like a Gazelle in some configurations), because the drop tanks will not be connected to the ship's jump-grid.

 

[coliver988]

Per T5, the "jump-bubble" (for those ships equipped with that mode of Jump-readiness) is a roughly spherical region whose diameter corresponds to 100x the dimensions (i.e. "diameter") of the ship. Anything within that volume can potentially be "dragged along" by the jump field. Any Jump "mishap" that occurs as a result will happen to the smaller object(s) by volume (ship or object(s)).

Thus a drop tank will need to be blown clear of that volume in order to survive undamaged.

Also note that a drop-tank equipped vessel will not be able to use the grid-option for jump readiness if the drop tanks are attached externally and the ship intends to carry mounted drop-tanks with it thru jump (like a Gazelle in some configurations), because the drop tanks will not be connected to the ship's jump-grid.

personally I was never a fan of drop tanks for a variety of reasons.

but as to the last point about jump grids: wonder if a grid could be extendable such as the jump net from supplement 9. Of course, a lot of early stuff was pretty loose (and I am personally pretty loose about jumps as well and don't even try to explain them). But a grid could be programmatically extended to the existing jump grid would be my assumption. though I may add DMs for the jump based on just how much extra you were carrying/extending. Sort of like those trucks that have multiple trailers - a bit more difficult to drive I assume.

from supplement 9:
The jump ship is designed to provide maximum flexibility in interstellar transportation. As built, it is capable of jump-6 and 1-G. Special field cables attached to the rear of the ship extend the ship's jump field to include this additional cargo.

edit: and also not a personal fan of this idea either - I always had to keep things inside the ship: things attached to the outside would have bad things happen to them. Just my interpretation of the rules.

 

[whulorigan]

but as to the last point about jump grids: wonder if a grid could be extendable such as the jump net from supplement 9. Of course, a lot of early stuff was pretty loose (and I am personally pretty loose about jumps as well and don't even try to explain them). But a grid could be programmatically extended to the existing jump grid would be my assumption. though I may add DMs for the jump based on just how much extra you were carrying/extending. Sort of like those trucks that have multiple trailers - a bit more difficult to drive I assume.

from supplement 9:
The jump ship is designed to provide maximum flexibility in interstellar transportation. As built, it is capable of jump-6 and 1-G. Special field cables attached to the rear of the ship extend the ship's jump field to include this additional cargo.

I think that would be workable.

 

[whartung]

because the drop tanks will not be connected to the ship's jump-grid.

Why not? Why can't they be "grid enabled" and part of the mounting process is wiring them up properly in a way that grid integrity is maintained whether they're connected or not.

 

[whulorigan]

Why not? Why can't they be "grid enabled" and part of the mounting process is wiring them up properly in a way that grid integrity is maintained whether they're connected or not.

I suppose it would be a referee's call as to whether or not a sufficiently suitable and robust connection can be made between the ship's jump-grid and a grid installed on a drop-tank (i.e. grid-contiguity, etc).

The other question would concern the expense necessary to embed a grid in a disposable drop-tank hull; if embedding a grid is trivial, then it might be financially viable, but if it is a complex and expensive process it may be possible but uneconomical for a disposable resource.

As a touch-point for discussion: T5 suggests that repairing grid-damage on a grid-enabled hull is difficult (which is why bolt-on plates are often used to cover breaks in a hull-grid).

 

[Grav_Moped]

Per T5, the "jump-bubble" (for those ships equipped with that mode of Jump-readiness) is a roughly spherical region whose diameter corresponds to 100x the dimensions (i.e. "diameter") of the ship. Anything within that volume can potentially be "dragged along" by the jump field. Any Jump "mishap" that occurs as a result will happen to the smaller object(s) by volume (ship or object(s)).

Thus a drop tank will need to be blown clear of that volume in order to survive undamaged.

Also note that a drop-tank equipped vessel will not be able to use the grid-option for jump readiness if the drop tanks are attached externally and the ship intends to carry mounted drop-tanks with it thru jump (like a Gazelle in some configurations), because the drop tanks will not be connected to the ship's jump-grid.

I'll need to re-read this, but I'm pretty sure the jump bubble rule you reference isn't that the bubble is 100 ship diameters in radius (as in, everything within 100D of the ship gets dragged along for the ride), but that the 100D jump preclusion zone is defined not only by the size of nearby foreign objects (typically a planet, but drop tanks or drop tank fragments would do it too), but also by 100 times the "diameter" of the starship executing the jump.

 

[Grav_Moped]

Note - the original write up of drop tanks had then as non-recoverable after their use 'dropped'.

It was only later the idea of recovering and reusing dropped tanks started to develop the schism.

Makes sense, in that if you want to guarantee the tanks aren't within 100 tank diameters of the ship at go-time, simply blow them to smithereens to make the individual tank fragment diameters a LOT smaller.

This ignores the amazing acceleration capability (at least 10m/sec²) that most ships include by default, but it's a good fallback if something goes wrong with the maneuver drive at the wrong moment.

It's also superseded by the T5 ruling that the ship's own diameter counts for establishing 100D separation.

 

[Condottiere]

1. Specifically to drop tanks, if it works for dispersed structure, it should work for them.

2. If not, jump tiles should create enough of a buffer to utilize.

3. Then, of course, draping over a jump net.

4. One solution, is for the dropped drop tanks to disintegrate.

5. Or just fall apart, since then only the mass of the walls would matter.

6. And zero armour factor is basically zero mass.