Jump fuel, L-Hyd droptanks and Battle Tenders

[jwpacker]

If you can have external tanks on a ship that contain fuel for the jump, and you drop the tanks before you pull the trigger, thus saving internal space for more interesting things than liquid hydrogen, why couldn't you have a battle tender feeding a modified battle rider, with a jump drive but no extra fuel, do the same thing?

Is there some sort of assumption that you blow the L-Hyd tanks mere seconds before you jump, and the "jump field" would theoretically detroy the tender?

 

[Jeraa]

From High Guard:

risk. Jumping is a delicate procedure, which is greatly complicated by having big empty fuel tanks flying around in close proximity to the jump bubble.

Jumping using a drop tank applies a –(15–TL) DM to the roll for misjumping (see page 141 in the core rulebook).

When a drop tank is used, roll 2d6. On an 8+, the tank survives the ejection process and can be retrieved and reused. Otherwise, it is destroyed by the expanding jump bubble or warped by the jettison explosion. At TL14 the use of drop tanks has been improved to such a degree that drop tanks designed at this tech level or above will automatically survive use.

If a small drop tank interferes with the jump drive enough to potentially cause a misjump, so will a large tender. And there is a good chance the drop tank (and so potentially the tender) is destroyed when you jump, unless the tank is built to TL 14 specs or higher. (Or the drive is TL 14. Something must be TL 14, its not too clear which one.)

The tactic probably won't be used until TL 14 at the earliest (thats when you no longer have the chance to destroy the tank/tender). I doubt it would be in regular use then because of the greater risk of misjumping.

 

[jwpacker]

Nicely summarized. I can see that being a one-off or prototype at TL15, but the beancounters would likely balk at anything more risky than that...

 

[far-trader]

There is one more aspect to consider re jump tenders as drop tanks:

A ship can only safely Jump when it is more than one hundred
diameters distant from any object.

Presumably this is part of the reason drop tanks are made so lightweight (so as not to impose a 100D restriction/hazard, as it's not mentioned). However, a jump tender per the idea wouldn't have that edge. It would impose the 100D restriction/hazard, at the larger of the 100D of the ship itself or the tender. I don't think there'd be time to "clear" the area. The drop tank usage certainly seems to imply that the tanks are in the immediate area.

I think I would 'allow' the practice but with the misjump penalty for being within 100D, applicable to both the ship and the tender (though with the only result possible for the tender being "destroyed"). So while possible, it certainly wouldn't be safe and is probably never going to be done except in an extreme emergency scenario.

Like being in the middle of being refueled when an attack is launched, and the ship makes a desperate emergency jump treating the tender as a drop tank (and very possibly sacrificing it, though it would probably be lost in the attack anyway).

 

[phavoc]

Depending on how you wanted to do the rule, you could simply have the external tanks self-destruct once the fuel was used up. Small, hell, even big, explosive charges ripping the tanks to shreds is not going to hurt starship hull plating. If a PGPM-15 won't hurt you, then the equivalent(s) blasting the tank to shards won't either.

Or, conversely, have them composed of some material that easily expands as hydrogen is dumped in the fuel bladder and contracts as it gets emptied. There's no reason why a 100Dton fuel bladder needs to take up all 100Dtons of space as you are draining it.

Finally, remember the 100diameter rule. It's all about mass. If the mass of your tank is 10Dtons when its empty, and you are in a 400Dton freighter, the distance you need to get away from your tank is quite small. And if you are traveling at 1G for a few hours, that tank will be 1,000's of meters behind you once you drop it.

 

[Captain Jonah]

Drop tanks do the job so I'm not sure why you would want to use a tender for the same thing.

You can build J1 battleriders with 1 jump of onboard fuel, carry them on a tender that jumps to one parsec from the target. Launches the riders and fits them with drop tanks.

The riders jump leaving the tanks behind, hit the target and jump back afterwards.

The tender meanwhile recovers and refills the tanks ready for the next attack.

Drop tanks are explosively ejected to get them far enough away so that they do not interfere with the jump field, its going to be hard to do that with a tender :lol:

 

[jwpacker]

All valid points - I was thinking of CT, where there was explicit text that said that the jump fuel was burned to put power into capacitors - these capacitors could thus be filled and held, I was thinking, to give enough time to get 100 diameters (not that terribly far) away before the jump was initiated.

I don't know that any such language is included in MgT.

 

[far-trader]

All valid points - I was thinking of CT, where there was explicit text that said that the jump fuel was burned to put power into capacitors - these capacitors could thus be filled and held...

If it's only the power in the capacitors that matter for jump then you can power your jump a myriad other ways. Solar collectors, Starport power stations prior to departure, etc...

However we know that the power itself is not enough, from CT HG (and in the OTU) at least, wherein even if the capacitors are filled you still need the required fuel to jump. In that instance it's not the power that is the bottle neck, it's something to do with processing the fuel rapidly (instantly imo).

I think it's a creation of a highly charged plasma stream under very specific controlled conditions using the jump fuel that rips a hole into jump space that will precipitate you where you want to go. The capacitors simply create the protective shield to see you through jump, and are maintained by the power plant after being created (usually with and by the jump fuel burn). And my "jump bubble" is not inflated with the fuel or filled with plasma. I don't even call it a bubble. It is simply a field effect of the hull.

 

[Hans Rancke]

However we know that the power itself is not enough, from CT HG (and in the OTU) at least, wherein even if the capacitors are filled you still need the required fuel to jump. In that instance it's not the power that is the bottle neck, it's something to do with processing the fuel rapidly (instantly imo).

Well, not instantly. In 40 minutes. If you can generate the power to fill the capacitors in two combat turns, you can jump; otherwise you have to abort.

The problem with that is that you can move a LOT of ship diameters in 40 minutes...


Hans

 

[far-trader]

However we know that the power itself is not enough, from CT HG (and in the OTU) at least, wherein even if the capacitors are filled you still need the required fuel to jump. In that instance it's not the power that is the bottle neck, it's something to do with processing the fuel rapidly (instantly imo).

Well, not instantly. In 40 minutes. If you can generate the power to fill the capacitors in two combat turns, you can jump; otherwise you have to abort.

The problem with that is that you can move a LOT of ship diameters in 40 minutes...


Hans

Yes, perhaps I wasn't quite clear. The power can be generated over time and from sources other than the jump drive, we agree on that.

I'm saying it is the fuel dump/burn that is the bottleneck. That is the part I think happens pretty dang fast, if not instantly, with little or no time to get completely clear of the drop tanks (or allow other ideas to work cleanly). It's my feeling that it is "all and now" for the fuel to jump. Your commitment point is when you pull the big lever that dumps the entire jump fuel into the drive and spits it out almost instantly in a plasma flare. Why yes, it would make a dandy weapon, but only at rock throwing range, and it would also damage the ship, if not destroy it outright in a critical jump failure.

 

[phavoc]

However we know that the power itself is not enough, from CT HG (and in the OTU) at least, wherein even if the capacitors are filled you still need the required fuel to jump. In that instance it's not the power that is the bottle neck, it's something to do with processing the fuel rapidly (instantly imo).

Well, not instantly. In 40 minutes. If you can generate the power to fill the capacitors in two combat turns, you can jump; otherwise you have to abort.

The problem with that is that you can move a LOT of ship diameters in 40 minutes...


Hans

That method of jump operation is pre-Mongoose. Now you have to use the jump fuel to create exotic particles to create a jump bubble around your ship.

Which gets me thinking, how can you create a bubble of exotic particles around your ship (and remain at the center) if you are moving? Wouldn't you need to come to relative zero velocity in order to stay in the center of your jump bubble? I wonder if this was thought about before the rule change?? It certainly makes it impossible to jump while another ship is in pursuit of you.

 

[hdan]

Which gets me thinking, how can you create a bubble of exotic particles around your ship (and remain at the center) if you are moving? Wouldn't you need to come to relative zero velocity in order to stay in the center of your jump bubble? I wonder if this was thought about before the rule change?? It certainly makes it impossible to jump while another ship is in pursuit of you.

Easy enough as long as you're not accelerating at the time you form the bubble. And if they're exotic, maybe they can be channeled with a magnetic (or gravitic?) field.

 

[phavoc]

Easy enough as long as you're not accelerating at the time you form the bubble. And if they're exotic, maybe they can be channeled with a magnetic (or gravitic?) field.

Doh! True enough. Once you stopped acceleration the particles you ejected from your ship would have the same velocity that you would.

So I suppose the unwritten rule is that you jump while under acceleration.

Next question would be how long it took to actually create the jump bubble.