LBB2 '81 Jump Drives are too big; HG power plants are bonkers!

[Grav_Moped]

I have argued for decades that the authors of HG got the maneuver drive and jump drive tables flipped somehow.

IMO it was a deliberate flip that they didn't think through [ETA: or explain]. Adding [ETA: the requirement for] Pn=Jn -- which happened in HG '80 before it did in LBB2 '81 -- means tech level affects the tonnage needed for Jump too.

In LBB5, the power plant is a big chunk of the drive bay, especially at lower TLs.

Big Eureka! energy here: This is where the idea for the power plant burning all the jump fuel instead of the jump drive itself doing so, originated. Unlike LBB2 '77 jump drives, the small jump drives of LBB5 are meant to be just the field generators and not include the hot/inefficient power plant inside the jump drives of the LBB2 '77 rules (and carried forward into the '81 rules for backward compatibility).

Which means that (despite what the rules say), a HG power plant can run in overload mode for up to two turns (40 minutes), and in each of those turns put out half the energy needed to charge the jump capacitors for a max jump (assuming the design Pn=Jn), which is 18EP per Jn per 100Td. It burns 5% of the ship's tonnage in fuel per Pn in each of those turns while doing so.

After that, it needs a lot of time to cool down before doing it again (probably not a whole week, but if you're doing it to jump, you have that week).

In short: Overload mode allows a power plant to, for up to two turns, produce 18 times its normal output, by burning 5% of the ship's tonnage in fuel each turn. Doing so precludes the ship Jumping for [some duration that needs to be worked out] unless it can generate the necessary 36EP/Jn/100Td without having used overload mode for more than two turns including the Jump power-up. (Example: a J2 ship with Pn=2 needs only one turn in overload mode to do a J-1.)

This may require an engineering check, similar to that needed for Jump, in rulesets that require one.

 

[Grav_Moped]

To expand on the first part of the thread title:

Once the power generation function is moved out of the Jump Drive into the power plant (as it was in LBB2 '81 compared to LBB2 '77), the Jump Drive should be reduced in size to reflect that (as HG '79 and '80 did, but which LBB2 '81 failed to do for backwards compatibility reasons).

 

[AnotherDilbert]

As per JTAS#24 the power plant explicitly runs in "overdrive" to power the jump.

When the jump drive is activated, a large store of fuel is fed through the ship power plant to create the energy necessary for the jump drive. In the interests of rapid energy generation, the power plant does not work at full efficiency, and some of the fuel is lost in carrying off fusion by-products, and in cooling the system.

Which means that (despite what the rules say), a HG power plant can run in overload mode for up to two turns (40 minutes), and in each of those turns put out half the energy needed to charge the jump capacitors for a max jump (assuming the design Pn=Jn), which is 18EP per Jn per 100Td. It burns 5% of the ship's tonnage in fuel per Pn in each of those turns while doing so.

Your assumptions are incomplete: You need the stated power plus burning the jump fuel for power, the jump fuel does not produce the stated power.

As a basic approximation the jump fuel used as regular power plant fuel would produce the full regular power for 40 weeks, so a 1000 Dt J-1 ship would produce something like 10 EP per turn for 3 × 24 × 7 × 40 = 20160 turns or 201600 EP, round it down to ~100000 EP because inefficiencies for simplicity.

A Scout or Free Trader would produce in the order of 20000 EP when it jumps...

 

[infojunky]

Note further editions of Traveller also used the small Jump Drive model.

 

[Grav_Moped]

As per JTAS#24 the power plant explicitly runs in "overdrive" to power the jump.





Your assumptions are incomplete: You need the stated power plus burning the jump fuel for power, the jump fuel does not produce the stated power.

As a basic approximation the jump fuel used as regular power plant fuel would produce the full regular power for 40 weeks, so a 1000 Dt J-1 ship would produce something like 10 EP per turn for 3 × 24 × 7 × 40 = 20160 turns or 201600 EP, round it down to ~100000 EP because inefficiencies for simplicity.

A Scout or Free Trader would produce in the order of 20000 EP when it jumps...

Baseline power generation is 1EP per turn per Pn per 100Td (LBB5 EP, not MongT EP).

Jump power is "full jump-caps" (that is, at 0.5% ship tonnage per Jn, and 36EP/Td, is 18EP per Jn per 100Td).

Energy needed from power plant is 2EP per Jn per 100Td, delivered in either 1 or 2 turns (a powerplant of Pn=Jn takes two turns).

This leaves 16EP per Jn per 100Td that can only be coming from the Jump fuel burn because nothing else is producing anything close to that energy. It's horribly inefficient, but it's the only practical way to get that much energy at once (you'd need Pn=18Jn to do it without supercharging the power plant).

It's extremely inefficient. Instead of 5 tons of fuel yielding 1EP for 20 weeks, it's instead yielding 18EP for 20 minutes.

 

[AnotherDilbert]

Note further editions of Traveller also used the small Jump Drive model.

But disconnected them from the power plant, so they burn the jump fuel directly, e.g. MT & TNE.

 

[AnotherDilbert]

Jump power is "full jump-caps" (that is, at 0.5% ship tonnage per Jn, and 36EP/Td, is 18EP per Jn per 100Td).

No, you need the 18 EP plus the energy from the jump fuel:

LBB5, "The Black Globe", p43:
If a ship absorbs enough energy to make a jump, and is supplied with sufficient fuel, it may jump at the end of the turn.

You still need to burn the fuel, regardless how much energy you have in the buffers. Otherwise all you would need to jump would be a black globe and some nukes...

 

[mike wightman]

I think the best explanation I have read is that full capacitors are the spark, you still need to fuel the piston...
or a starter motor analogy - you need the capacitors full to initiate the jump procedure, but you still need a lot more energy for the jump itself.

 

[AnotherDilbert]

I believe the capacitors are just a buffer, regulating the flow of energy from the power plant to the jump process. The total amount of energy involved is vastly larger than the capacity of the capacitors.

 

[Condottiere]

Don't they go BOOM! if they absorb one too many energy points?

 

[Grav_Moped]

No, you need the 18 EP plus the energy from the jump fuel:


You still need to burn the fuel, regardless how much energy you have in the buffers. Otherwise all you would need to jump would be a black globe and some nukes...

The requirement for Jump from the power plant is only 2EP/Jn/100Td. The capacitors hold 18EP/Jn/100Td, and need to be fully charged to Jump. Those extra 16EP/Jn/100Td have to come from somewhere, and the only plausible energy source is the jump fuel burn (or input from a black globe, if present).

The nominal requirement for the Jump fuel may just be that if you're charging the caps from a black globe instead of overdriving the power plant, you still need to dump that fuel through the drives as a total-loss cooling method to keep things from going boom. Perhaps it's not absolutely necessary to do this, but nobody's tested to find out exactly how little fuel is actually needed for cooling. Each failed attempt requires expending a difficult-if-not-impossible-to-replace black globe generator, after all.

It's not consistent with Collector-Drive powered Jump Drives though. Maybe those use the canopy as a heat sink/radiator, explaining why you can't just unplug the accumulator and leave the canopy behind? //handwaves frantically because Collectors already break physics under most rule sets after 1977//

 

[Grav_Moped]

I believe the capacitors are just a buffer, regulating the flow of energy from the power plant to the jump process. The total amount of energy involved is vastly larger than the capacity of the capacitors.

I think the 36EP in the capacitors is all that's needed to get into jumpspace, and the jump fuel expenditure is then about 1/2000th as efficient as normal power plant fuel use. Now, this isn't to say that it uses a 2000-times-less-efficient reaction, but instead that a power plant running at 18 times normal output needs significantly more cooling capacity when being pushed that hard. Also, pushing 18EP through no more than 3Td of machinery (J-1 Jump Drive for 100Td, the best case) is going to make it pretty warm -- and it's mostly concentrated in the 1/2-ton of jump capacitors! So, dumping a lot of fuel past/through the power plant and jump drive as a total-loss cooling method makes some sense there too. Admittedly, liquid hydrogen is probably not the best working fluid for this purpose, but it's already on hand for reactor fuel so why not?

So, a less fuel-efficient reaction combined with more fuel wasted for cooling, gives you the insanely high relative fuel consumption rate for the jump fuel burn. And you need the cooling for the jump drive even if you're not running the reactor in overload mode.

 

[Grav_Moped]

It's not consistent with Collector-Drive powered Jump Drives though. Maybe those use the canopy as a heat sink/radiator, explaining why you can't just unplug the accumulator and leave the canopy behind? //handwaves frantically because Collectors already break physics under most rule sets after 1977//

Wait. That makes too much sense. You need to minimize volume to get into Jumpspace efficiently, but once there the canopy can be extended (because the canopy material has the properties of a hull's jump grid in addition to its ability to pull energy out of nowhere) and used as a radiator. So you can't use just the "magic particle tank" as a small replacement for the normal jump fuel load.
Reposting on the Collector Discussion thread.

 

[kilemall]

This looks like a power up for ships in battle, particularly battle riders where the extra fuel would just be a weapon/armor trade off for the emergency capacity.

 

[Grav_Moped]

This looks like a power up for ships in battle, particularly battle riders where the extra fuel would just be a weapon/armor trade off for the emergency capacity.

And that raises a good point that I didn't mention: Do non-starship and small craft power plants also have this capability?