The Compleat LBB2 Ship Design

[mike wightman]

So with TL9+ doable? I wonder if there is some combination of gravitics and electromagnetic thrust going on here... (and no I don't mean my daft inertial handwave), something we could explain with Traveller tech assumptions.

 

[AnotherDilbert]

To accelerate 15 tonnes of mass to ~25 000 km/s would take

E = mv²/2 = 15000 × 25000000² ≈ 9.4 × 10¹⁸ J

over 225000 s that is about 4 × 10¹³ W ≈ 42 TW, roughly twice the Earths current capacity?

 

[AnotherDilbert]

So with TL9+ doable?

No...

Ignorance is bliss, better not think about it.

Accelerating spacecraft by several Gs for weeks on end is firmly in the Fiction part of SciFi.

 

[mike wightman]

Isn't real physics fun

I have had a good deal of enjoyment from discussing things like this with you.

 

[AnotherDilbert]

https://www.iter.org/sci/FusionFuels

While a 1000 MW coal-fired power plant requires 2.7 million tonnes of coal per year, a fusion plant of the kind envisioned for the second half of this century will only require 250 kilos of fuel per year, half of it deuterium, half of it tritium.

Fusion: 1000 MW [1 GW] takes 250 kg/year.
42 TW = 42000 GW takes 250 / 1 × 42000 ≈ 10 000 000 kg ≈ 10 000 tonnes per year or ~1 ton/hour.
375 turns is 62.5 h so it would take ~65 tonnes of D & T to accelerate the reaction mass.

At about 0.05% rate of natural hydrogen, that would be 65 / 0.0005 ≈ 130 000 tons of hydrogen (unrefined skimmed fuel).

 

[AnotherDilbert]

Perhaps if golden age sci fi had been a little more scientifically rigorous in its description of magical ship drives we could have got a 'harder science' drive for Traveller, I have toyed with making the jump fuel requirement the M-drive fuel.

It would have been all about near earth, or perhaps months long expeditions to Mars, not very exiting...

Going somewhere requires ignoring physics, so ignored it was...

 

[AnotherDilbert]

Isn't real physics fun

I have had a good deal of enjoyment from discussing things like this with you.

It certainly leads to unexpected places...

 

[mike wightman]

It does indeed, which leads to new ideas and insights, or at least consistent handwavium

So how do we explain the legacy to current versions of the M-drive?

reaction drive -- huge energy requirement, little reaction mass (nowhere near enough of either)
HEPlaR -- as above but with a much larger though still inadequate reaction mass
reactionless thrusters -- the more modern approach
MT - thruster, or take every bit of Traveller technobabble, ignore any real world science and wave hands vigourously
T5 - thruster but handwavium gravitcs
MgT - as above

The modern take on the reactionless drive - put electricity in, it moves a volume rather than a mass, it doesn't require anywhere near as much energy as if you are moving the mass of the ship.

So some sort of gravitic bubble warp drive sort of thing.

 

[AnotherDilbert]

It's all simplifications on top of simplifications, except perhaps Striker and FFS that was only one layer of simplifications...

I consider Traveller reality is somewhere about what FFS described (no HEPlaR, it has thrusters as alt-tech), you accelerate mass, thrusters and anti-grav just provide thrust by gravitonic jiu jitsu to get the local gravity field accelerate you in one direction and the local star system in the other direction.

There is obviously not even remotely enough energy or fuel involved to accelerate either grav vehicles or spacecraft as described in Traveller.

HEPlaR is more trouble than it's worth.

 

[whulorigan]

...

So how do we explain the legacy to current versions of the M-drive?
...
reactionless thrusters -- the more modern approach
MT - thruster, or take every bit of Traveller technobabble, ignore any real world science and wave hands vigourously
T5 - thruster but handwavium gravitcs
MgT - as above

I am always careful about the term "Reactionless Thruster". Just because a drive does not expel reaction mass does not necessarily make it "reactionless". Gravitic Drives can be reaction drives by interacting with the other bodies in the star system via the gravitational/pseudo-gravitational interaction, the ship gaining momentum, and the other bodies losing a commensurate amount.

The DGP/MT Thruster is the only one I remember specifically as truly "reactionless", "pushing-off" of its own Thruster plates thru the Strong Nuclear Force in some way (per SOM, Vol. 1).

The modern take on the reactionless drive - put electricity in, it moves a volume rather than a mass, it doesn't require anywhere near as much energy as if you are moving the mass of the ship.

So some sort of gravitic bubble warp drive sort of thing.

The flavor text in T5 (and T4 ?) seems to imply some sort "gravitic bubble warp drive" for its interpretation of a grav-based M-Drive.

 

[AnotherDilbert]

I am always careful about the term "Reactionless Thruster". Just because a drive does not expel reaction mass does not necessarily make it "reactionless". Gravitic Drives can be reaction drives by interacting with the other bodies in the star system via the gravitational/pseudo-gravitational interaction, the ship gaining momentum, and the other bodies losing a commensurate amount.

Agreed.

The flavor text in T5 (and T4 ?) seems to imply some sort "gravitic bubble warp drive" for its interpretation of a grav-based M-Drive.

T4 is just like TNE, except "thruster plates" is the default and HEPlaR is an alternative.

T5 does not say anything specific:

Maneuver drives interact with gravity to move spaceships. Parts of the drive reach out and grab the gravity of a world or a star and push against itto make the ship move. Isn’t that neat?

Sounds much like TNE and MT to me? I.e. no bubbles, just thrust accelerating mass in the normal manner.

 

[AnotherDilbert]

FFS is also more trouble than it's worth, except as mathematics homework. It's proof that complexity requires a lot of effort to contain and describe, and then the bar is raised on the user base to use it.

Absolutely, but it's a description of how things work, slightly less simplified.

Which is fine, except Traveller as a game does not require that level of sophistication. Don McKinney was fond of saying that "starships are just boxes that transport you to the next adventure." And while that offended my sensibilities, there's a sense in which he was right.

Agreed, the default ships are good enough to play, and everyone use the Scout and Free Trader...

 

[mike wightman]

By simplifying the description to:
"It interacts with gravity sources to produce vectored movement"
it opens up a lot of wiggle room for refs to handwave.

For example the M-drive is good to 1000D from a star or planet, while the G-drive is limited to 10D, and then the NAFAL-Drive works everywhere (possibly using the gravity of the galaxy as its interaction)

 

[AnotherDilbert]

Traveller has lots of things going on. Maneuver drives, regardless of reaction noises, have really only ever been gravitic magic, and HEPlaR seems the right kind of fusion rocket for the rest of Traveller.

Agreed, M-drives are just magic.

HEPlaR isn't a rocket, TNE of course has fusion rockets in addition...

 

[mike wightman]

Fusion rockets also made an appearance in the MT Hard Times design sequence, I would have to go back through decades old notes but if I recall correctly, they were a better way of moving a ship than the thruster/power plant combo (because of the mess they made with converting Striker to ship power plant scale).

 

[AnotherDilbert]

By simplifying the description to:
"It interacts with gravity sources to produce vectored movement"
it opens up a lot of wiggle room for refs to handwave.

It tells me too little. What I want defined is how it works with newton, so something like
"M-drives magically produce thrust"
work for me. Then I can do simple calculations and derive the travel time formulæ.

For example the M-drive is good to 1000D from a star or planet, while the G-drive is limited to 10D, and then the NAFAL-Drive works everywhere (possibly using the gravity of the galaxy as its interaction)

TNE is a toolbox for explanations, T5 for ideas...

I can't really be bothered with different drives, but OK, grav drives only work close to planets, and M-drives close to stars, and are much less efficient far away.

 

[robject]

TNE is a toolbox for explanations

That is exactly right.

FFSx and its kin, as well as orbital mechanics and worldbuilding science, are extremely useful for people who will use it. GURPS has a version of it as well.

They are not binding on Traveller. So, the rulebooks are a check or corrective; for instance when creating power plants using Fire, Fusion, and Steel _2_. If FFS2 says a one-ton power plant can power a Tigress for a year without refueling, then who is say that's wrong? Answer: the rules. If FFS2 says you can build a man-portable weapon capable of shooting a starship out of the Moon's orbit from the ground, who is to say otherwise? Answer: the rules. I refer you to Ditzie Spofulam, the River-Tam-like child physicist-engineer-scientist-designer-inventor who should not be allowed to design weapons.

Also, I find it intolerably like doing math homework. But, some people really enjoy it.

Hence -- have at it and cheers! Just don't expect me to read stat blocks with high-technical specs and more than two places of precision.

I called Shane on it with his Alien Suns 01. Possibly unrealistic precision in some places. He eventually kept some of the detail for verisimilitude, which I admit is understandable from a "chrome" point of view.

 

[AnotherDilbert]

FFSx and its kin, as well as orbital mechanics and planetary (worldbuilding) science, are extremely useful for people who will use it. GURPS has a version of it as well.

Regular plain old physics is how the universe works in Traveller, with some specific exceptions. You can gloss over the details, but that forms the basis for the simplified systems.

So, orbital mechanics is binding for Traveller, but with magical drives with near-infinite ∆v it's not much of a practical concern.

It is not binding on Traveller, however. It is a tool, not a rule. The rules serve as a check or corrective; for instance when creating power plants using Fire, Fusion, and Steel _2_. If FFS2 says a one-ton power plant can power a Tigress for a year without refueling, then who is say that's wrong? Answer: the rules. If FFS2 says you can build a man-portable weapon capable of shooting a starship out of the Moon's orbit from the ground, who is to say otherwise? Answer: the rules.

What rule? The rule in T4 is what FFS2 says it is.

But it is not binding for other editions.

 

[whartung]

I stand by my interpretation - that and the authors flat out stated that the M-drive was intended to be a reaction drive when HEPlaR was introduced for TNE.

If you want what the "authors intended", look to MT.

MT is CT refined. It's CT with AHL combat, and a Striker-esque design system.

But the vast bulk of the "universe" that is Traveller is there, with larger books and more room for discussion.

Unlike TNE, which IS a "do over", MT was not. It's a refinement of CT.

They took all of the LBB, the JTAS, and other expansions and coalesced it into a more singular form. CT was the Big Bang, MT was the after the stars had started to form and the worlds were cooling.

In MT they had every opportunity to clarify whatever they hinted on in CT.

Given that:

The fourth significant development came from the search for a starship maneuver drive that did not lose efficiency when away from a strong gravity well. Artificial gravity and damper technology led to yet another sub-atomic force-based technology. This new, artificially generated force pushes against a vessel’s “thrust plates’’ themselves, which make true reactionless thrusters a reality for starship sized vessels.

That's from p56 of the Referee's Manual for MT. That's pretty black and white.

 

[McPerth]

Fusion rockets also made an appearance in the MT Hard Times design sequence, I would have to go back through decades old notes but if I recall correctly, they were a better way of moving a ship than the thruster/power plant combo (because of the mess they made with converting Striker to ship power plant scale).

In fact, they were not better than thruster plates, but they were better than gravitic M-drive (TL9-11)...

In MT, the drives where gravitic, but while gravitic M-drives lost efficiency when far from a large mass (so he fusion rocket was better at TL 9-11), the thrusters (TL12+) did not depend on thsoe large masses.

Also in MT the fusion rocketd did not have the irradiated exhaust problems TNE ones had...

And BTW, the same rules where they appeared in HT (One Small Step, for pre-gravitic spacecrafts) where also publisched in Challege magazine,