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

[Grav_Moped]

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?

Because early on, they didn't think through the implications of the described capabilities of the air/raft.

They fixed this in HG'80 and LBB2'81, by changing the flavor of the technobabble.

Except they didn't totally fix it in LBB2'81, because they kept the fuel formula for backward compatibility while redefining what it meant.

 

[AnotherDilbert]

Except they didn't totally fix it in LBB2'81, because they kept the fuel formula for backward compatibility while redefining what it meant.

It's exactly the same formula for exactly the same reason: to produce power to power the ship including the m-drive.

Only now it lasts four weeks instead of one trip.

 

[mike wightman]

For it to be used as an energy weapon of factor 1-6 something must be being projected, therefore it is a high energy plasma or fusion exhaust.
As the ship gets larger a greater weapon rating is needed to get the same factor, so a 1000t m6 is the equivalent of 100 energy weapon points giving an energy weapon factor of 6.
A 10,000t ship would require1000 weapon points to get the same energy weapon factor of 6.

My explanation is that the m-drive consists of a field generator - this is based on nul-grav tech invented at TL8 and makes the air/raft available. The field generator lowers the mass of anything within the field (hence it is volume rather than mass based) and can have an acceleration compensation field component added by the installation of additional machinery along with the grav plates that produce artificial gravity.
You then have the thrust component that consists of a fusion drive that does have a high energy exhaust (which gets larger as the ship gets bigger thus the weapon factor remains the same).

 

[AnotherDilbert]

Since you bring up being influenced by later editions, ...

Note that I don't think we SHOULD be influenced by later editions, just that I can't help letting it colour my prejudice...

 

[Grav_Moped]

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.

It's a typical travel time for that distance, at 1G, not a time for a journey that is a typical one. 1 billion miles (from the table in LBB2'77 -- it's not kilometers) is about the current distance from Earth to Saturn (Jupiter is significantly closer). They didn't keep track of which orbit a gas giant was in until LBB6, so "1 billion miles" seems like it was meant as a proxy for "typical distance to a system's gas giant".

Again, the fuel allocation for almost exactly a week of thrust, combined with the "it's all burned every trip regardless of actual distance traveled" rule, is clearly a handwave to avoid having to track maneuver fuel use in starships. The "one-day either side of the Jump" trips get averaged out with the ones where it's necessary to spend over a week to get to a gas giant for wilderness refueling.

 

[kilemall]

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.





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...

Imperium predated Traveller by years and got retconned into the OTU.

For home brew I have missiles burning fuel at a greater rate under the idea that the smaller sub-dton frames cannot get rid of heat other than fuel dump. That’s my explanation but I am not confused that I went there for mechanics supporting results reasons.

 

[AnotherDilbert]

It's a typical travel time for that distance, at 1G, not a time for a journey that is a typical one. 1 billion miles (from the table in LBB2'77 -- it's not kilometers) is about the current distance from Earth to Saturn (Jupiter is significantly closer). They didn't keep track of which orbit a gas giant was in until LBB6, so "1 billion miles" seems like it was meant as a proxy for "typical distance to a system's gas giant".

Agreed, but apparently a ship was supposed to be able to do that, so not limited to a week of acceleration.

Again, the fuel allocation for almost exactly a week of thrust, combined with the "it's all burned every trip regardless of actual distance traveled" rule, is clearly a handwave to avoid having to track maneuver fuel use in starships.

Agreed, all of it's a handwave.

My point was that there is nothing special about a week, it's probably just a coincidence that a week is 1008 turns.

 

[Grav_Moped]

It's exactly the same formula for exactly the same reason: to produce power to power the ship including the m-drive.

Only now it lasts four weeks instead of one trip.

Disagree. The reason it lasted "one trip" was because "one trip" was "up to one week of full acceleration" (usually a lot less, but it could be a bit more if a gas giant visit was involved) and writing it all off each trip and averaging it over time was simpler than having to do the math every time.

It's the same formula -- one that disregards ship tonnage -- because the original maneuver fuel use rules disregarded ship tonnage in both small craft and starships/non-starships. HG rules adjust for ship tonnage and provide for 4 weeks fuel. LBB2'81 rules just changed "one trip" to "4 weeks" but excluded HG's adjustment for ship tonnage.

The giveaway is that LBB2'81 small craft (built under HG'80) use the HG fuel formula also -- but not the Standard Drives. They kept the old formula for those because changing it would distort legacy small ship designs and break the large ones.

From your subsequent post:

Agreed, but apparently a ship was supposed to be able to do that, so not limited to a week of acceleration.

Then why list it as "effectively unlimited" [emphasis added] at "at least 288 turns"? Why not have it literally unlimited with a time duration given? Edit to add: ...as in both versions of HG.

Edited to add my conclusion: The reason is that it wasn't literally unlimited, but wasn't intended to last for a specific duration -- but instead, for "long enough" to handwave the actual fuel consumption rate.

 

[AnotherDilbert]

Imperium predated Traveller by years and got retconned into the OTU.

They were both published in 1977, developed by the same people, and used the same combination of "jump" and "sublight" drives?

They must be connected on the idea level?

 

[Grav_Moped]

My point was that there is nothing special about a week, it's probably just a coincidence that a week is 1008 turns.

My point is that there is something special about a week. They could have set starship powerplant fuel requirements to any arbitrary value or proportion, but they chose to set them to almost exactly what the small craft fuel consumption rules would dictate for one week's acceleration.

 

[AnotherDilbert]

Disagree. The reason it lasted "one trip" was because "one trip" was "up to one week of full acceleration" (usually a lot less, but it could be a bit more if a gas giant visit was involved) and writing it all off each trip and averaging it over time was simpler than having to do the math every time.

There is no one week of acceleration, it's just a numerical accident.

It's one "trip", and don't worry about it.

Then why list it as "effectively unlimited" [emphasis added] at "at least 288 turns"? Why not have it literally unlimited with a time duration given? Edit to add: ...as in both versions of HG.

288 turns = 48 h is enough for a normal trip as in "Actually making a jump takes about one week of elapsed time, which includes navigational and pilot support, and normal preparation as necessary. Transit time to a point at least 100 planetary diameters out adds a total of approximately 20 hours to the whole trip."

The combat chapter does say "There is no restriction on the number of accelerations which may be made by a fuelled ship, ..."

Edited to add my conclusion: The reason is that it wasn't literally unlimited, but wasn't intended to last for a specific duration -- but instead, for "long enough" to handwave the actual endurance.

Quite, don't worry about it, it just works.

 

[AnotherDilbert]

My point is that there is something special about a week.

You believe so, I don't.

Ship power plant fuel is set to 10 t per trip.
Small craft m-drive fuel is set to 10 kg per turn.
A week happens to be 1008 turns. In LBB2'81 it was 605. In HG it was 504.
Coincidence.


A ship is supposed to able to accelerate for two days (288 turns, "normal jump"), or perhaps ten days ("1 billion miles"), or something undefined. Nowhere is a week of acceleration mentioned or implied.

Note that power from the power plant is not used for the m-drive alone, it's used for other purposed too, and that lasts the entire trip, not just while accelerating.

 

[Grav_Moped]

Note that power from the power plant is not used for the m-drive alone, it's used for other purposed too, and that lasts the entire trip, not just while accelerating.

Note that in '77, the "other purposes" were essentially token amounts -- to the extent that the XBoat didn't actually need a power plant.

 

[AnotherDilbert]

Note that in '77, the "other purposes" were essentially token amounts -- to the extent that the XBoat didn't actually need a power plant.

It had a lot of unspecified tonnage that might have included the batteries, and strictly limited endurance, unlike normal ships. It also didn't have any lasers, that presumably use some power.

The X-boat is a result of Rule 0, not really a good example of a regular ship.

 

[kilemall]

They were both published in 1977, developed by the same people, and used the same combination of "jump" and "sublight" drives?

They must be connected on the idea level?

Perhaps, may have been Imperium influenced the jump route concept, but the Vilani part wasn’t in the original game, if no other reason then there wasn’t an OTU then.

Could have sworn my Conflict Games edition had an earlier date then 1977.

 

[AnotherDilbert]

Perhaps, may have been Imperium influenced the jump route concept, but the Vilani part wasn’t in the original game, if no other reason then there wasn’t an OTU then.

It might not be the same TU, but the ship mechanics are more or less the same?

Could have sworn my Conflict Games edition had an earlier date then 1977.

I have no idea, I just looked at the wiki. My example is dated 1977 by Conflict Games, Normal, Illinois.

 

[Grav_Moped]

Ship power plant fuel is set to 10 t per trip.
Small craft m-drive fuel is set to 10 kg per turn.
A week happens to be 1008 turns. In LBB2'81 it was 605. In HG it was 504.
Coincidence.

Except that it's only in LBB2'77 that maneuver fuel expenditure rates are considered at all, so the length of a turn in later editions is irrelevant.

A ship is supposed to able to accelerate for two days (288 turns, "normal jump"),

"Two days" is the non-jump part of a normal jump flight, true. At 10kg/g-turn, that's only 2,880 kg/g-turns needed, not the 10,000kg/g-turn requirement specified by LBB2 for starship drives. This requirement is far too high to be consistent with small-craft fuel use rates -- why, then, not use small-craft drives or multiples thereof for maneuver, plus a power plant for intermittent use, instead?

or perhaps ten days ("1 billion miles"),

At 10kg/g-turn, that's 13.8Td fuel (that's stretching the fuel quite a bit there on the high end, but since we're mostly talking about starships, perhaps they can borrow part of the jump fuel reserve if it's not handwaved entirely -- which it was).

or something undefined.

They explicitly undefined it in HG and LBB2'81.

Nowhere is a week of acceleration mentioned or implied.

The implication is in that 10Td/G (that is, 10Td per Pn which equals Gs) is a week of maneuver fuel in the part of the spacecraft rules (small craft) where fuel use is tracked explicitly.

Addressing your subsequent post about the XBoat:

It had a lot of unspecified tonnage that might have included the batteries, and strictly limited endurance, unlike normal ships.

The "unspecified tonnage" was specified to be data banks.

It also didn't have any lasers, that presumably use some power.

It also had a Model/4 computer, that, when Traveller started caring about power use in LBB5'80, needed 2EP. LBB2'77 didn't care about power use.

The X-boat is a result of Rule 0, not really a good example of a regular ship.

It's valid in '77, or at least they thought it was valid enough to not require an explicit rule exception. LBB2'81 broke it, but that's outside the scope of fuel use in '77.

 

[AnotherDilbert]

"Two days" is the non-jump part of a normal jump flight, true.

Two days comes from the "at least 288 turns", it is at least mentioned in the rules.

The implication is in that 10Td/G (that is, 10Td per Pn which equals Gs) is a week of maneuver fuel in the part of the spacecraft rules (small craft) where fuel use is tracked explicitly.

I see no implication, just a coincidence. Nowhere in the rules is any specific importance or mention of a week.

While Pn is often the same as Mn, it does not have to be, e.g. if we want an oversized PP for Double Fire.

Addressing your subsequent post about the XBoat:

The "unspecified tonnage" was specified to be data banks.

It also had a Model/4 computer, that, when Traveller started caring about power use in LBB5'80, needed 2EP. LBB2'77 didn't care about power use.

Original version had a m1/bis (S7, p9) changed to a m/4 (S7, p10), presumably to look more compatible with LBB2'81.

The data banks have no defined size: "The standard bridge is complemented by a Model/4 computer, massive communicators, and message data banks."

But, OK, there is no mention of batteries, but "Power Plant: None. Jump drives carry power plant capacities and functions." (S7, p9)

It's valid in '77, or at least they thought it was valid enough to not require an explicit rule exception. LBB2'81 broke it, but that's outside the scope of fuel use in '77.

Depending on how literal you want to be:

LBB2'77, p11:
_ _ The Engineering Section: Each starship is fitted with a power plant (to provide internal power and power for the maneuver drive), a maneuver drive (for interplanetary travel), and a jump drive (for interstellar jumps). Each is essential to the definition of a starship.

S7, p9 also had a little note "Ship can function automatically without any crew." I would call that an exception to the crew rules?

 

[Grav_Moped]

Two days comes from the "at least 288 turns", it is at least mentioned in the rules.

And it's "close enough" to the normal-space flight time for a trip between two Size 8 worlds. It's noted as a minimum.

I see no implication, just a coincidence. Nowhere in the rules is any specific importance or mention of a week.

The two-week jump cadence (one in jump, one at a world) is canon. Therefore, a starship (except in rare circumstances) would not have time to use more than a week's acceleration fuel -- and burns the amount that would have been that much on every trip regardless. Similarly, it doesn't need more than a week's acceleration fuel for an in-system trip since jumping would be quicker.

This may be coincidental. However, since it fits two separate constraints (maximum plausible insystem flight time and maximum likely flight time between jumps), correlation appears to suggest causation.

While Pn is often the same as Mn, it does not have to be, e.g. if we want an oversized PP for Double Fire.

But having an oversized power plant does not (necessarily) increase the Pn and therefore the fuel requirement. Thus, the fuel requirement generally tracks the maneuver drive capability while not (necessarily) tracking the power plant size.

S7, p9 also had a little note "Ship can function automatically without any crew." I would call that an exception to the crew rules?

Sure. An unnecessary one, but it's there. It's also contemporaneous with legal jump torpedoes, so....

 

[infojunky]

Ever consider using the fuel use chart from Beltstrike?