LBB2 M-Drives in LBB5: When does it help?

[kilemall]

Nah.
That just creates more problems of intellectual inconsistency than it solves.

Simple? Sure.
USEFUL? Not so much ...

<shrug> I don’t know that inconsistency is such a problem, just seems to cover most of the translation of LBB2 classic ship designs to an EP system, particularly the small craft.

Or perhaps they have a short burst overgenerate potential, in the same way the jump drives can apparently be tuned for rough system unrefined fuel jumps.

 

[kilemall]

Spinward, the fuel waste heat paradigm is what I use for my HG missile design sequence, with the goal of having a similar fuel burn rate to the missile supplement while still having a micro fusion plant explaining the sustained power for those 1 hour plus maneuvers.

 

[Spinward Flow]

Spinward, the fuel waste heat paradigm is what I use for my HG missile design sequence, with the goal of having a similar fuel burn rate to the missile supplement while still having a micro fusion plant explaining the sustained power for those 1 hour plus maneuvers.

 

[Grav_Moped]

<shrug> I don’t know that inconsistency is such a problem, just seems to cover most of the translation of LBB2 classic ship designs to an EP system, particularly the small craft.

The small craft in 2nd Edition are in fact LBB5'80 designs...

 

[Grav_Moped]

The only difference then is ... how big is the hull you're installing that drive into?
Yes, you get "higher code" performance from the same drive in a smaller hull, but you also consume more fuel in a smaller hull ... so what gives?

"What gives?" is that it's the '77 small craft fuel burn rules scaled up far beyond where they'd make any sense whatsoever ('77 starship fuel rules, 1 week ("at least 288 turns" at 10 minutes each) of full power/thrust is 10,000kg per Pn; Pn=Gs) then simply re-labeled as "4 weeks" for the '81 rules.

 

[Grav_Moped]

Long reachback. (I'm bored. Sorry.)

Ships have a simple limit as well of 288 burns...

Also note one could use the fuel use from Beltstrike as well...

It's not the limit, it's the minimum -- at least 288 turns (which is just under a week of full acceleration).

That value, in context, means that however many turns it actually is, that number is large enough that no plausible combat maneuvering will cause a starship to run out of fuel. Thus, there's no need to track maneuver fuel use for starships.

What it actually is, in the RPG context (rather than the space combat rules context), is "enough to get to jump limit from the origin world, and to get from jump limit at the destination to the world itself". This is almost always less than 7 days of full acceleration (size 8 to another size 8, each outside its star's exclusion zone, takes about 2 days), but it's all expended regardless of actual acceleration used during the trip.

 

[mike wightman]

288 turns is 48 hours - a ship combat turn in LBB2 77 is 10 mins, 6 turns per hour.
288/6=48 hours

10,000kg/288=34.72kg of fuel per 10 min "burn"

 

[Grav_Moped]

288 turns is 48 hours - a ship combat turn in LBB2 77 is 10 mins, 6 turns per hour.
288/6=48 hours

10,000kg/288=34.72kg of fuel per 10 min "burn"

One "burn" under '77 small craft rules (each 1G increment for each 6-minute turn) expends 10kg fuel per G.
1000kg (which is 1Td by definition in the rules) fuel yields 100 "burns".
10,000kg per G (10Td per Pn, and Pn>=Gs) yields 1000 burns, or 166.67 hours, or 0.992 weeks (6.944 days).

Yeah, 10kg per G-turn starts looking like straight-up fantasy once you go over a few hundred Td of ship, but that gets lampshaded by the "it all gets used every trip, even though most of the time you would only use a little over a quarter of it" rule.

 

[mike wightman]

Smallcraft and a starships have different fuel burn rates:

Fuel is also used by the maneuver drives of non-starships. When used in such
vessels displacing under 100 tons (ship's boats, shuttles, pinnaces, etc) 10 kilograms
(1/100th of a ton) of fuel is sufficient for 1G of acceleration for 10 minutes.

Ships burn 34.72kg of fuel per turn per g.
Smallcraft burn 10kg of fuel per turn per g.

 

[Grav_Moped]

Smallcraft and a starships have different fuel burn rates:


Ships burn 34.72kg of fuel per turn per g.
Smallcraft burn 10kg of fuel per turn per g.

Not quite. As noted above, the stated 288 turns is the minimum, not a maximum. That had me tripped up for a long time too.

There are two separate values that need to be reconciled: the 10Pn is from the build rules for starships, and the "at least 288 turns" is from the combat rules for starships. They're not quite saying the same thing.

From the build rules, ships burn 10,000kg per G (or rather, per Pn, but in '77 they're basically equal) per flight of any reasonable distance, and over the course of two weeks -- one of which is spent in Jump. This says nothing about how much gets burned per G per turn.

From the combat rules, the "at least 288 turns" is just to place that in the context of those rules: however much it might actually burn per G per turn, there's enough in the tanks that a starship is unlikely to run out of fuel during an engagement.

This isn't to say that they can't have different burn rates, but that minumum burn duration isn't actually saying that they are different.

 

[mike wightman]

The rule states that they are different.

The 288 burns minimum is the 10tons of power plant fuel, 10,000kg, of fuel which is the minimum.
You can carry more power plant fuel than the 10tons for more burn duration.

I reconcile it my having the m-drive include a null grav component that lowers the mass of a given volume of ship, which is why bigger drives in bigger ships still only require 10t of fuel per g.

 

[AnotherDilbert]

There are two separate values that need to be reconciled: the 10Pn is from the build rules for starships, and the "at least 288 turns" is from the combat rules for starships. They're not quite saying the same thing.

Not quite, they are from the same section, LBB2'77 p5: Operating Expenses:

_ _ 1. Fuel. Starship fuel costs CR 500 per ton (refined) or CB 100 per ton (unrefined), at most starports. Fuel consumption is based on formulae related to the size of the starship power plant and the jump drive.
_ _ A power plant, to provide power for one trip (internal power, maneuver drive power, and other necessities) requires fuel in accordance with the formula: 10Pn.
Pn is the power plant size rating, determined from the maximum drive potential table by cross-referencing power plant letter and hull size. The formula indicates amount of fuel in tons, and all such fuel is consumed in the process of a normal trip. A fully fuelled power plant will enable a starship an effectively unlimited number of accelerations (at least 288) if necessary to use the maneuver drive during the trip (as when miniatures combat is used to resolve a ship to ship encounter).
_ _ A jump drive requires fuel ...
_ _ Fuel is also used by the maneuver drives of non-starships. When used in such vessels displacing under 100 tons (ship's boats, shuttles, pinnaces, etc) 10 kilograms (1/100th of a ton) of fuel is sufficient for 1G of acceleration for 10 minutes.

Note that power plant fuel is explicitly to produce power for ship's uses, including the M-drive. No mention of propellant or reaction mass is made.

Neither the Travelling chapter nor the Combat chapter mentions any limitations to accelerations for ships.
LBB2'77, p26: Starship Combat, Movement:

There is no restriction on the number of accelerations which may be made by a fuelled ship, but the total acceleration in a turn in inches, may not exceed the size rating of the M-Drive.

Only small craft manoeuvre drives explicitly uses "fuel" directly, perhaps as propellant.

 

[Grav_Moped]

Not quite, they are from the same section, LBB2'77 p5: Operating Expenses:

I really need to get a copy of the '77 rules.

Note that power plant fuel is explicitly to produce power for ship's uses, including the M-drive. No mention of propellant or reaction mass is made.

Adding emphasis:

_ _ A power plant, to provide power for one trip (internal power, maneuver drive power, and other necessities) requires fuel in accordance with the formula: 10Pn.
Pn is the power plant size rating, determined from the maximum drive potential table by cross-referencing power plant letter and hull size. The formula indicates amount of fuel in tons, and all such fuel is consumed in the process of a normal trip.

How much is consumed in a non-normal trip? Not stated. What constitutes a non-normal trip? Also not stated. This is explicitly hanging a lampshade on the issue.

Again adding emphasis:

A fully fuelled power plant will enable a starship an effectively unlimited number of accelerations (at least 288) if necessary to use the maneuver drive during the trip (as when miniatures combat is used to resolve a ship to ship encounter).

Which was my point -- fuel expenditure from maneuver is at worst about triple that for small craft (34.72kg/g-turn, taking the 288 as a maximum, which it is not), but can be much lower (as in a worst-case under LBB2 of sequential wilderness refueling from gas giants, since stellar jump blocking wasn't considered at the time).

Neither the Travelling chapter nor the Combat chapter mentions any limitations to accelerations for ships.
LBB2'77, p26: Starship Combat, Movement:

The limitation is how much a ship can plausibly accelerate during a normal trip (during which, it burns the entire power plant allocation). The worst case (assuming the normal two-week jump cadence) is literally one week (3.5 days out, 3.5 days in, 7 days in Jump, zero layover) because if it took longer, it would break the cadence.

By what is undoubtedly pure coincidence, that's almost exactly how much the 10Pn allocation would enable, using the small craft fuel consumption rate.

Only small craft manoeuvre drives explicitly uses "fuel" directly, perhaps as propellant.

Explicitly, yes.
Implicitly? As I noted above, it looks very much like they did use the small craft fuel consumption rate for starships, but concealed that this was what they did -- likely because it does get silly for ships larger than 200Td or so, and downright unbelievable in the over-1000Td range.

 

[whulorigan]

I really need to get a copy of the '77 rules.

The CT CD from FFE has all versions of the CT rules on it, including CT'77 and HG'79.

 

[Silverhawk]

The CT CD from FFE has all versions of the CT rules on it, including CT'77 and HG'79.

Good to know.

 

[AnotherDilbert]

The limitation is how much a ship can plausibly accelerate during a normal trip (during which, it burns the entire power plant allocation). The worst case (assuming the normal two-week jump cadence) is literally one week (3.5 days out, 3.5 days in, 7 days in Jump, zero layover) because if it took longer, it would break the cadence.

By what is undoubtedly pure coincidence, that's almost exactly how much the 10Pn allocation would enable, using the small craft fuel consumption rate.

According to Travelling (LBB'77, p2) a "Typical Travel Time" is 9.6 days for 1 billion km under constant acceleration, so by that logic a ship would use less fuel than a smallcraft. I'm not quite buying that a 5000 Dt (or 100 Dt) ship uses less fuel than a 50 Dt smallcraft for the same acceleration...

Yes, there are 1008 turns in a week, but I wouldn't read too much into that, I guess that is more happy coincidence than cunning calculation.

A ship is not normally accelerating for several days and jumping in the same trip, a "normal" interstellar trip is acceleration for a few hours (normal 100 D limit), jump for a week, and acceleration for a few hours. Stellar 100 D limits were not considered in LBB2'77.

Explicitly, yes.

Implicitly? As I noted above, it looks very much like they did use the small craft fuel consumption rate for starships, but concealed that this was what they did -- likely because it does get silly for ships larger than 200Td or so, and downright unbelievable in the over-1000Td range.

Or they just grabbed an arbitrary number that sounded good for small ships (10Pn) and another arbitrary number that seemed to work for smallcraft (10 kg/G/turn).

What they actually said is that ships use fuel to produce power that is fed to the "manoeuvre drive", but smallcraft use fuel directly in the "manoeuvre drive". To me (probably influenced by later editions) that does not sound like the same technology, more like magical power-to-thrust machines in ships, and magically fuel-efficient rockets in smallcraft. I suspect they started with rockets, but removed it as too much faff, replaced with "don't worry about it, it just works". It should probably not be taken all that literally, or assumed to be all that perfect: It's just a small part of a game.


In the game Imperium (developed concurrently with Traveller?) ships could accelerate to about 85% of lightspeed to travel between stellar systems, that would take a year or so of acceleration at 1 G. I would not take that to mean that all ships can routinely accelerate for years with standard amounts of fuel...

 

[mike wightman]

In Imperium it is "80 to 90 percent" while in Dark Nebula (which uses basically the same ruleset as Imperium) it is 90%

Since you bring up being influenced by later editions, the next rulebook to give us more details was HG79, where we learn all about acceleration compensation being a limit and that the m-drive can be used as an energy weapon.
An energy weapon - plasma or fusion gun - that has a factor of m-drive rating regardless of the size of ship.

 

[AnotherDilbert]

In Imperium it is "80 to 90 percent" while in Dark Nebula 9which uses basically the same ruleset as Imperium) it is 90%

Yes, about 85% ≈ 85%±5% ≈ 80-90%, somewhere around there, but not exactly...

Since you bring up being influenced by later editions, the next rulebook to give us more details was HG79, where we learn all about acceleration compensation being a limit and that the m-drive can be used as an energy weapon.
An energy weapon - plasma or fusion gun - that has a factor of m-drive rating regardless of the size of ship.

And also says:

LBB5'79, p17:
MOVEMENT
_ _ Starships move through normal space using maneuver drives as described in Book 2, page 1 under Interplanetary Travel. Power for the maneuver drives is provided by the starship's power plant, which must have a drive number equal to or exceeding the drive number of the maneuver drive. Tech level requirements for maneuver drives are imposed to cover the grav-plates integral to most ship decks which allow high-G maneuvers while the interior G-fields remain normal. Fuel consumption for starships is inconsequential, and assumed to be part of the power plant consumption, regardless of the degree of maneuver undertaken.

Artificial gravity and inertial compensation is new, but just as in LBB2'77 the m-drive uses no noticeable fuel or propellant just a lot of power from the power plant.

And it's a fusion torch (i.e. uses a lot of propellant).

OK, it's a reaction drive that does not use any reaction mass, got it. I have no idea what that is, the best guess I can come up with is an extremely high powered ion drive that accelerates a minuscule amount of reaction mass to extreme velocity. But where does fusion come into it, except as an exiting buzzword? It's certainly not a Nivenesque fusion torch, as that would use a lot of propellant.

Sorry, I don't see much except a pile of random buzzwords here. Early CT never tried to explain how it worked, it just did. Trying to divine the exact nature of "manoeuvre drives" from the few oracular pro-nouncements in the LBBs seems futile. (It's rather amusing that the word pronouncement is censored, quite Victorian!)


But why are we faffing about with dangerous fusion drives when we have perfectly usable grav drives (magical machines that turns power into thrust?) such as in the air/raft?

 

[Grav_Moped]

(Do we really have to censor the word ⌧ouncement?)

Yes, yes we do*. If you want to work around it, sneak an italics or bold instruction of zero length <i></i> (but use square brackets of course) into the middle of the part of the word that would be prone** to targeting by the text-substitution macro. This has to be done in manual coding mode, not WYSIWYG mode, or it gets corrected (simplified) out.

-----------
*may not be completely true.
**see what I did there?

 

[Grav_Moped]

An energy weapon - plasma or fusion gun - that has a factor of m-drive rating regardless of the size of ship.

Yeah, that kind of nails it down. If weaponized maneuver drive damage was meant to be based on maneuver drive output, the effect would scale by ship size (larger ships would have had more batteries of factor 1-6). Since it didn't, it's a carry-over from LBB2 '77.