OTU Only: A Funny Thing Happened on the Way from Collace

[AnotherDilbert]

Beltstrike: Belter's Handbook, p11:

That is clearly incompatible with LBB2, LBB5'79, TCS, and the optional rules in JTAS#14.


For a third incompatible system we can look at Striker, where a 500 MW (2 EP) fusion plant for a vehicle would require 500 × 1.5 × 24 × 7 × 4 = 504000 l = 504 m³ ≈ 36 Dton fuel for full output for four weeks.

 

[Grav_Moped]

Something was ferreting away at the back of my mind and here it is, from the CT boxed adventure Beltstike and applies to LBB2 designed ships:
...

That's precisely the level of detail I'm looking for! CT (especially 2nd Ed.) actively moved away from that kind of detail so as to simplify gameplay. Reasonably so, because keeping track of fuel and calculating travel times would have been a hassle back before everyone owned a calculator, let alone a computer that could do spreadsheets.

Doing it on a fleet level (HG, TCS) would have been -- and honestly, still is -- slightly absurd.

 

[Grav_Moped]

There are no universe-defining constants defined in CT ship design, only gamey game rules.

There are no definitions of what a power plant is or how it works, just that it is a black box that consumes fuel (hydrogen) and produces power. You might assume fusion is involved, but the rules can neither confirm nor deny.



There is no definition of how much fuel is consumed per hour or week under different conditions in CT, only a hard game rule that says that you need a specified amount of fuel tankage and that "The stated fuel tonnage supports four weeks cruising (including time spent in jump space) before refuelling is necessary" or "Power plant fuel under the formula (10Pn) allows routine operations and maneuver for four weeks", i.e. normally the fuel lasts four weeks, but under unusual usage conditions it might last longer or shorter.

....
I would say it is likely that the fuel will run out before the fourth jump is complete, and that the ship will emerge with the crew cold, dark, and gasping for air, or perhaps dead...

Three jumps are probably OK though.
...

That's a more favorable answer than I expected.

It looks like there's enough powerplant fuel left at that point to start the 4th jump and run the powerplant for at least part of the Jump.

Two and a half days into it, maybe?

If so, that makes the burn rate during Jump 20% higher (28 days/23.5 days=1.2) than the monthly average burn rate. I still figure the monthly average is a better metric, but 20% higher seems reasonable.

You see where I'm going with this, right?

XBoat pilot only gets a half-stateroom (saves 2 tons). This allows fuel capacity to be 52 tons (from 50).
40 tons get used in the J4, leaving 12 tons for the powerplant. That's 20% more than 1 week of typical monthly average use (10 tons), so it's enough.

Oh, and if the burn rate is no more than 30% higher than the monthly average (that is, if the example rift-jumping Free Trader exited its third jump with even just 0.3 tons of fuel left over), I can still make it work by changing the XBoat's computer to a Model/3bis* to free up one last ton for fuel.




*No, it's not on the computer table. But look at the table and you can figure out what the Mod/3bis should be. Then compare the price to a Mod/4 to see why they left it off...

#bis computers:
- 1 TL higher than base model
- Same tonnage as base model
- CPU=storage of base model, but no storage
- Can control a jump one number higher than the base model
- Cost is twice that of the base model

 

[mike wightman]

bis models of every computer model are allowed in HG79 edition, and the placeholder USP factors are still there in HG80 - if you have just made up their stats well done it matches what it says in HG79 except bis computers have twice the CPU capacity of the base model.

 

[Grav_Moped]

Quick thought on fuel use (this is just a placeholder unless I can't get back to it before the edit window expires):

A normal month's operations include two jumps and two planetfalls.

Powerplant fuel demands will come from:
1. two jumps (14 days)
2. two mainworld-to-100D runs (about 2 days total but I need to do the math)
3. two 100D-to-mainworld runs (also about 2 days, likewise)
4. 10 days in port, powered down (waiting for cargo/pax).
Combined, these will come to 100% of the 4-week fuel allocation.

Assumptions:
- Real-space transit is at max powerplant output.
- Jump may be at max powerplant output.
- (maybe, but it's sort of implied by the fact that non-starships have the same fuel consumption as starships) real-space transit fuel use is equal to jump fuel use.
-- One week of normal use of a non-starship (which is more than the one sortie per week of a starship) has the same fuel consumption as one Jump.
--- We just need to figure out how much its life a typical non-starship spends in flight...

- there may be more. As noted, this is a placeholder.

 

[Grav_Moped]

bis models of every computer model are allowed in HG79 edition, and the placeholder USP factors are still there in HG80 - if you have just made up their stats well done it matches what it says in HG79 except bis computers have twice the CPU capacity of the base model.

I KNEW IT!

I thought I'd seen it somewhere -- my ref back in the '80s had the first editions, I had second editions. Over the passage of decades, I was half-convinced it was one of his house-rules....

(And oh boy did he have house rules. Tons were different -- maybe 30ft^3 Register Tons? -- and starship fuel/power was from what amounted to nuclear batteries. Very H. Beam Piper.)

Thanks!

 

[AnotherDilbert]

If so, that makes the burn rate during Jump 20% higher (28 days/23.5 days=1.2) than the monthly average burn rate. I still figure the monthly average is a better metric, but 20% higher seems reasonable.

Nowhere did I try to imply that fuel is burned faster in jump space.

I pointed out that a few jumps probably take longer than 7 days each with overhead, and that 4 weeks (28 days) fuel probably don't last for a 4 × (perhaps) 8 days ≈ 32 day trip.

XBoat pilot only gets a half-stateroom (saves 2 tons). This allows fuel capacity to be 52 tons (from 50).
40 tons get used in the J4, leaving 12 tons for the powerplant. That's 20% more than 1 week of typical monthly average use (10 tons), so it's enough.

It does not matter if you have 5 or 15 Dtons of power plant fuel, the rules still require 40 Dtons.



If you house-rule it you can do whatever you want, of course, but you did mark this thread "OTU".



If the X-Boat can make do with ~10 days fuel, why would any ship carry more than, say, two weeks fuel? The Scout and Far Trader could certainly use the 10 Dtons suddenly freed up. Reasonably all standard ships should be redesigned to these new rules?

 

[mike wightman]

In CT 77 edition all power plant fuel was used per trip just like jump fuel was all used per jump - there was no four week duration to cause confusion.
Which of course begs the question how much fuel reserve do you have as you are on approach to the planet you have jumped to?

 

[AnotherDilbert]

In CT 77 edition all power plant fuel was used per trip just like jump fuel was all used per jump - there was no four week duration to cause confusion.

It's even worse, since all power plant fuel is consumed in a normal trip and the Travelling chapter describes a trip as usually two weeks, including time in port.

Hence the fuel can only be expected to last 10-14 days?

 

[boomslang]

Beltstrike: Belter's Handbook, p11:

That is clearly incompatible with LBB2, LBB5'79, TCS, and the optional rules in JTAS#14.

This table is a fundamental part of MTU.

Simply because it is logical and scalable and does not necessarily contradict anything else in most versions of CT about the rate at which power plant fuel is actually consumed during operations.

I resist the notion that it is "clearly incompatible" with LBB2, for instance. LBB2 describes 10Pn dtons as "sufficient" for four weeks of operations. Of course it is; in many cases it is much more than merely sufficient, since the vessel can function quite well under many circumstances (picket duty, for example) using significantly less than its full power plant load every 28 days.

I read CT's 10Pn dtons as a regulatory/safety requirement for basic spaceworthiness. Inadequate tankage as per the regs = no certificate from the port inspector at overhaul time. (And a recurring Adventure Hook, perhaps.)

The issue of fuel use versus fuel tankage requirements always comes back to the aftermarket modifications that give us S7 Type J...

 

[Grav_Moped]

This table is a fundamental part of MTU.

Simply because it is logical and scalable and does not necessarily contradict anything else in most versions of CT about the rate at which power plant fuel is actually consumed during operations.

I resist the notion that it is "clearly incompatible" with LBB2, for instance. LBB2 describes 10Pn dtons as "sufficient" for four weeks of operations. Of course it is; in many cases it is much more than merely sufficient, since the vessel can function quite well under many circumstances (picket duty, for example) using significantly less than its full power plant load every 28 days.

I read CT's 10Pn dtons as a regulatory/safety requirement for basic spaceworthiness. Inadequate tankage as per the regs = no certificate from the port inspector at overhaul time. (And a recurring Adventure Hook, perhaps.)

The issue of fuel use versus fuel tankage requirements always comes back to the aftermarket modifications that give us S7 Type J...

I don't have S7, just S4 -- and all it says is that the Type J has "...increased cargo space... at the cost of less recreation room" (but not by how much), J2 and I think it used to say 1G.

I erased whatever was there and wrote in 2G decades ago, assuming it was a typo because a Size A M-Drive yields 2G in 100Td and it's impossible under either LBB2 or LBB5 to get 1G (max) out of 1Td of M-Drive (the space a Size A drive occupies) in a 100Td hull.

I'm guessing in hindsight that the "...and 1G capabilit[y]" was intentional, and resulted from trading some of the power plant fuel allocation for cargo space. And that they thought that was acceptable because in LBB2 '77 the ship didn't need Pn 2 even for Jump -- and never revisited it after the '81 changes.

Why you can't get 1G in 100Td from a 1Td drive (formula weirdness):

Spoiler:

LBB2's M-Drive tonnage formula doesn't work below Size A. It's Td=(Lx2)-1 where L is the ordinal value of the drive letter (A=1, B=2, C=3... with the breaks at I and O because it's Traveller). Below Size A, it results in maneuver drives with negative tonnage.

LBB5's formula doesn't produce a maneuver drive smaller than 2Td in a 100Td hull, and there'd be no reason to replace a drive that would do 2G with a bigger one that would only do 1G. It's possible to rework the formula to solve for Gs per %Td rather than %Td per G, but it gets weird below 1G, converging on 0.33G for a 0.0%Td M-Drive.

 

[Grav_Moped]

Nowhere did I try to imply that fuel is burned faster in jump space.

I pointed out that a few jumps probably take longer than 7 days each with overhead, and that 4 weeks (28 days) fuel probably don't last for a 4 × (perhaps) 8 days ≈ 32 day trip.

Same effect -- 14% longer duration requires 14% more powerplant fuel (in this case, 1.4 Td per J4 in an XBoat). Pilot in double occupancy frees up 2 Td. Still works.

It does not matter if you have 5 or 15 Dtons of power plant fuel, the rules still require 40 Dtons.



If you house-rule it you can do whatever you want, of course, but you did mark this thread "OTU".



If the X-Boat can make do with ~10 days fuel, why would any ship carry more than, say, two weeks fuel? The Scout and Far Trader could certainly use the 10 Dtons suddenly freed up. Reasonably all standard ships should be redesigned to these new rules?

There are reasons you'd want more fuel than the average case calls for. The first is if you need to detour to a gas giant to refuel before or after going to the mainworld. Another is if you expect to have to travel to multiple points on the mainworld or in-system, requiring multiple hops during the 10 days you're there. The biggest one, though, is if the mainworld orbits inside its star's 100D limit -- it may take days or even weeks to get from the star's 100D limit to the mainworld. (This happens with big, cool stars -- Judice/District 268 is one such. Somewhere on the boards there's a list of them.)

Out-of-universe (for game play reasons), a ship needs 4 weeks of fuel because it's enough that you only have to think about Jump fuel and can mostly ignore powerplant fuel. I expect that's all the though the writers gave it, and that's all they needed to do.

In-universe, ships will be designed to deal with the worst-case situations listed above unless they will either never encounter them (XBoat) or accept that some destinations will be either awkward to reach or completely unreachable despite having the requisite Jump range. Hence, the in-universe reason for a 4-week supply.

I'm fine with a Type S having extra fuel and have said so several times. If you use the TCS power-down rule and flat-rate PP fuel consumption, the Type S can do a J2 and a J1 back-to-back if they're careful and circumstances permit. I think it's a great in-universe explanation for that ship's ludicrously-huge fuel tank. I get that you don't buy that, and that's ok.

Why I think it works for the average case:

Spoiler:

1/2 week at Pn 1, 1G from origin world to 100D limit uses 1.25 tons fuel. 37.5 tons remain.
1 week at Pn 2 for J2 and the Jump fuel burn itself, uses 5+20 tons fuel. 12.5 tons remain.
1 week at Pn 1 for J1 and the Jump fuel burn itself use 2.5+10 tons fuel. 1.25 tons remain.
1/2 week at Pn 1, 1G from 100D limit to destination world uses 1.25 tons fuel. 0 tons remain at arrival.

The 1/2 week is more time than would actually be spent in flight between a world and its 100D limit, so there's a little wiggle room. On the other hand, this doesn't work for the worse-than-average cases I described above.

Far Traders?

The A2 from A3: Twilight's Peak has 60 Td fuel; an '81 design. The maneuver drive rating is not stated, but if built under LBB2 '81 it would end up being 2G. All listed components and cargo total 200Td if it has a Mod/2 computer, MD B, and has 1Td set aside for a second turret.

It could run at 1G, but wouldn't. It lives on spec cargo and time is money... also, they're not going to settle for "we can't get there from here" and risk missing out on a profitable cargo run.

The one from DA 6: Night of Conquest has 50Td fuel, but it's a '77 design and probably J2/1G/Pn 1.

 

[Grav_Moped]

What does the powerplant do for Jump?

Here's my interpretation of why a powerplant of Pn=Jn is required. It's not incompatible with the rules or existing explanations.

Per LBB5, a Jump Drive contains Jump Capacitors that hold 18*M*Jn EP. Also per LBB5, these capacitors need to be provided with 2*M*Jn EP over 1 or 2 turns (20-40 minutes). That leaves 16 EP*M*Jn unaccounted for, and these have to come from the "overclocked power plant" part of the Jump Drive.

Here's where my interpretation comes in. The Jump Drive, if it gets the maximum energy out of its powerful-but-inefficient fuel burn, would actually generate all 36 EP*M*Jn for the capacitors. However, the Jump Drive fusion reaction doesn't generate a stable or predictable amount of energy -- it can be up to 11% lower than its theoretical maximum output. The powerplant is there to make up the shortfall. If it can't do it in one turn (20 minutes), it has to run longer to finish "topping off" the capacitors.

You can't build a Jump Drive to have the additional capacity to make up that margin because it can't be controlled precisely enough -- it will inevitably overcharge the capacitors, destroying the ship.

That's the first part of the interpretation. The second part is what happens in Jumpspace. Jump, despite Humaniti's thousands of years of experience with it, is still not well understood according to canon. Experiments have found that the Jump Drive should have external power applied to maintain the Jump Bubble. This power is applied for 158.2 hours, at which point it is safe to allow the Jump Bubble to collapse. For a normal Jump this may happen immediately or take up to 33.6 hours to happen. The time distribution of Jump Bubble collapse approximates a bell curve centered on 168 hours from Jump initiation.*

While there have been rare instances of ships staying in Jumpspace for the expected week even after suffering a power plant failure immediately after Jump, the usual consequence is loss of the ship. The likelihood of a mishap increases the longer the Jump Drive is unpowered before the 158.2 hour mark.

Powering the Jump Drive for longer than 158.2 hours does not appear to have any effect on the timing of Jump Bubble collapse. Neither does providing more power to the Jump Drive.**


No, I don't have any idea how much power the Jump Drive needs to keep the Jump Bubble stable.


*For reasons unknown to science, this is actually a pyramid rather than a bell curve. (Science doesn't know that it's a modified 2D roll. )

**Theoreticians suspect that if the rules of the Universe were slightly different, it would be possible to bias the timing of Jump Bubble collapse closer to precisely 168 hours by careful adjustments to the Jump Drive. (These theoreticians may or may not have access to rules published after 1981.)

 

[AnotherDilbert]

This table is a fundamental part of MTU.

You do as you wish in YTU, of course.

I resist the notion that it is "clearly incompatible" with LBB2, for instance.

Not that it matters to YTU, but let me explain why I believe it's incompatible:
A Free Trader must have 10 Dt power plant fuel. Basic power for four weeks would consume 2 × 0.05 × 4 = 0.4 Dt fuel. A week of acceleration would consume 2 × 0.35 = 0.7 Dt fuel. With a bit of margin the Trader would only need 1 Dt fuel, or perhaps 2 Dt for extremely extended operations. Having 10 times that is simply silly, another 8-9 Dt payload would be much more useful.
An Akerut Hercules-class freighter (TTA, 5000 Dt, PP-1) must have, and has, 10 Dt power plant fuel. Basic power would consume 50 × 0.05 × 4 = 10 Dt, leaving no fuel at all for acceleration. Even two days acceleration (one day out, one day in) would need an additional 50 × 0.05 × 2 = 5 Dt fuel it does not have.

Simply put a fuel consumption proportional to hull tonnage does not work with the fixed tonnage fuel requirements in LBB2.


LBB5'79, TCS, and JTAS#4 allows you to power down the PP to a PP-1 equivalent, but it specifically uses the full fuel requirement for a PP-1 every four weeks, i.e. A Scout would use at a minimum 10 Dt fuel per four weeks.

 

[AnotherDilbert]

I don't have S7, just S4 -- and all it says is that the Type J has "...increased cargo space... at the cost of less recreation room" (but not by how much), J2 and I think it used to say 1G.

It's detailed in S7. It keeps the drives, of course, but takes two staterooms and 10 Dt fuel tankage to turn into two 10 Dt ore bays.

It is noted that it is reduced to J-1 with the reduced fuel tankage (30 Dt), but can do J-2 with a 10 Dt demountable tank in one of the ore bays.

Since it still has a PP-2 it requires 20 Dt power plant fuel.

 

[Grav_Moped]

...

Simply put a fuel consumption proportional to hull tonnage does not work with the fixed tonnage fuel requirements in LBB2.

The fixed tonnage fuel requirements in LBB2 don't even work with themselves. Hang a 100-ton drop tank off a Type S and its fuel consumption rate drops by half. (... and it suddenly needs a Navigator, too.)

LBB5'79, TCS, and JTAS#4 allows you to power down the PP to a PP-1 equivalent, but it specifically uses the full fuel requirement for a PP-1 every four weeks, i.e. A Scout would use at a minimum 10 Dt fuel per four weeks.

I just mentioned that upthread.

Wait, it's in some version of HG too?!

All I get out of HG is that power plants use 1%M*Pn, not that they can be powered down.

It also states that "Fuel consumption of maneuver drives is inconsequential, and is assumed to be part of the power plant consumption, regardless of the degree of maneuver undertaken." (HG '81, p. 17, Para. 2). Then again, this is in the context of power plant factors that need letters instead of digits...

 

[AnotherDilbert]

Out-of-universe (for game play reasons), a ship needs 4 weeks of fuel because it's enough that you only have to think about Jump fuel and can mostly ignore powerplant fuel. I expect that's all the though the writers gave it, and that's all they needed to do.

Probably, but they phrased the rule clumsily, and that is what we are left with.

In-universe, ships will be designed to deal with the worst-case situations listed above unless they will either never encounter them (XBoat) or accept that some destinations will be either awkward to reach or completely unreachable despite having the requisite Jump range. Hence, the in-universe reason for a 4-week supply.

You might imagine so, but the rules are blunt and does not give any reason.

 

[AnotherDilbert]

Here's my interpretation of why a powerplant of Pn=Jn is required. It's not incompatible with the rules or existing explanations.

Read JTAS#24: "Jumpspace" by MWM, at least technically part of CT.

"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. "

 

[AnotherDilbert]

The fixed tonnage fuel requirements in LBB2 don't even work with themselves. Hang a 100-ton drop tank off a Type S and its fuel consumption rate drops by half.

The whole lettered drive system is ridiculous, yet it is RAW. Yes, a Power Plant-A in a 100 Dt hull requires 20 Dt fuel, the same power plant in a 110 Dt hull requires 10 Dt fuel.

All I get out of HG is that power plants use 1%M*Pn, not that they can be powered down.

The 1%, i.e. as for PP-1, is a minimum consumption:

A power plant uses fuel equal to 1% of the ship's tonnage every four weeks, regardless of actual power drain; this usage is primarily to maintain the fusion bottle and other housekeeping functions.

Power plant fuel is computed at 1% of the ship tonnage per power plant number; a 10,000 ton ship with power plant-6 requires 600 tons of fuel tankage for its power plant.

At a guess this is where the TCS powering down rules come from.

 

[mike wightman]

I find it remarkable that GDW managed to come up with four published ship design systems that look similar but are in fact very different, and that's before taking into account bespoke designs such as the Annic Nova and the Gazelle.