Cargo Capacity and volume and mass

[AnotherDilbert]

So, I reworked my old 20,000-ton hauler (with the 13,650 d-ton hold) with the 10-tons per d-ton assumption for all the non-fuel bits, and ran the numbers to see what I could get in the cargo bay while keeping the overall ship to 200,000 mass-tons.

There is no mass for LBB5 ships, only volume.

A PP-1 at TL-15 is 200 Dt = 2800 m³, mass unknown.
A 10 000 Dt cargo hold is 140 000 m³, mass unknown.


If we peek ahead at MT we do get masses specified for different components, but mass isn't really used, except for vehicles.
Something like this (MT uses 1 Dt = 13.5 m³):
A 20 000 Dt J-2, M-2 freighter, with a volume of 270 000 m³, empty mass of ~180 000 tonnes, loaded mass of ~343 000 tonnes

Note that the drives are still calculated as percentages of volume.

 

[Badenov]

LBB5 never deals in or mentions mass.

This makes my head hurt so much. Also, why even call it 'tons' if it's not about mass? Just call it 'displacement' rather than 'displacement tons'

It's a simplification. Mass is hand-waived everywhere.
Whats the mass of the power plant? Who cares, we know the volume and cost.



Traveller uses plain old physics, except for a few explicit exceptions.
Ships obey Newton's Laws. M-drives produce thrust in the drive itself, that propels the ship by F=ma.
Generally that is simplified, in FF&S it's explicit.

I think it's better to say Traveller ignores plain old physics, mass is the 'm' in F=ma. Ships blithely ignore Newtons laws as their a is controlled by their F regardless of m.

 

[AnotherDilbert]

This makes my head hurt so much. Also, why even call it 'tons' if it's not about mass? Just call it 'displacement' rather than 'displacement tons'

Presumably tradition, LBB2'77 was in mass only, volume unspecified.

I think it's better to say Traveller ignores plain old physics, mass is the 'm' in F=ma. Ships blithely ignore Newtons laws as their a is controlled by their F regardless of m.

The underlying physics is F=ma, the simplification is constant acceleration.


The vehicle design and operation system for CT: Striker was explicitly Newtonian:

CT Striker, B3, p8:
A grav vehicle requires grav generators installed in its chassis. Each .02 m³ of grav generators produces 1 ton of thrust and requires .1 megawatts of power from the power plant. They weigh 2 tons and cost Cr100,000 per m³.

Divide thrust in "tons" by mass of the vehicle in tons to get the thrust-to-mass ratio.

 

[Badenov]

Presumably tradition, LBB2'77 was in mass only, volume unspecified.

This actually makes more sense than the other way.

The underlying physics is F=ma, the simplification is constant acceleration.


The vehicle design and operation system for CT: Striker was explicitly Newtonian:

Divide thrust in "tons" by mass of the vehicle in tons to get the thrust-to-mass ratio.

CT: Striker shares that in common with Mongoose Supplement 6 Military Vehicles, which also tracks volume and mass separtately.
Of course you still can't build a truck that carries a ship's cargo because that's only in d-tons, with the conversion apparently varying between versions. Rather than thrust to mass, though, there was a bit more complication. Engine power was engine power, and the amount of go you got was partly based on what sort of drive you had: wheels, jets, props, tracks, grav, etc, and the engine power, and the vehicle mass.

 

[TamsinP]

This makes my head hurt so much. Also, why even call it 'tons' if it's not about mass? Just call it 'displacement' rather than 'displacement tons'

It's because, as noted in my first post on p1 of this thread, Traveller dTons are the equivalent of Gross Register Tons/Gross Tons used for "wet" ships.

As a note, when discussing "wet" ships, displacement is the mass of the ship

 

[kilemall]

In theory, steel is cheap and air is free (and somewhat weightless).

In the end, hull armour and engineering would probably be the most mass intensive components, assuming spinal mounts are a series of tubes.

Like the internet?

 

[kilemall]

This is one of those things where I ignore mass until it becomes a plot point.

 

[AnotherDilbert]

This actually makes more sense than the other way.

Volume make it easier to draw deckplans.

CT: Striker shares that in common with Mongoose Supplement 6 Military Vehicles, which also tracks volume and mass separtately.
Of course you still can't build a truck that carries a ship's cargo because that's only in d-tons, with the conversion apparently varying between versions. Rather than thrust to mass, though, there was a bit more complication. Engine power was engine power, and the amount of go you got was partly based on what sort of drive you had: wheels, jets, props, tracks, grav, etc, and the engine power, and the vehicle mass.

Sounds about the same. Grav vehicles ignored the whole transmission, suspension, and ground pressure thing.

 

[Condottiere]

I would think the difference between a starwarship and a megafreighter, is that while both are inclined to stuff themselves, the starwarship has a lot of moving parts that need buffer space, and weapon systems probably aren't solid state right through.

The freighter, at least an efficient one, will have somewhat accessible standard sized containers, which may or may not be completely stuffed.

 

[Carlobrand]

Let's play with it from the other direction, and someone will have to let me know if I make a mistake because - well, I do that sometimes.

So, a power plant 1 produces 1 EP in a 100 dTon craft. MegaTraveller calls 1 EP 250 megawatts - 250 million joules per second. 1 EP can accelerate a 100 dTon craft at 1G. 250 million joules per second is the energy of 5,000 tons moving at 10 m/s. Every second that plant is adding another 10 m/s to the craft's velocity. Ergo, the mass of a 100 dTon craft is equal to or less than 5000 metric tons - depending on how much energy is being lost in the course of the drive operating.

I hope I didn't screw that up.

 

[Carlobrand]

I'm going to add to that:

We can infer from this that the 1g maneuver drive in this case can, through some sort of far future science-magic, accelerate a volume of 100 dTons, and no more than 100 dTons, by 10 meters per second square, provided the volume contains no more than 5000 metric tons less whatever energy is being lost due to inefficiency. (Traveller rarely considers inefficiency but we've got some leeway to do so here if we wish.) The maneuver drive will simply fail to operate if asked to move more than 100 dTons or 5000 metric tons (less blahblahblah). It is in essence creating and accelerating a bubble.

Unless I screwed that up.

 

[chipla]

Maybe it’s only the volume that matters for the acceleration?

 

[AnotherDilbert]

So, a power plant 1 produces 1 EP in a 100 dTon craft. MegaTraveller calls 1 EP 250 megawatts - 250 million joules per second. 1 EP can accelerate a 100 dTon craft at 1G. 250 million joules per second is the energy of 5,000 tons moving at 10 m/s. Every second that plant is adding another 10 m/s to the craft's velocity.

Now do the calculation over a minute or an hour instead...

a = 1 G ≈ 10 m/s²
v = at
E_k = mv²/2

After 100 s we have an kinetic energy of m(10×100)²/2 = 1 000 000 m/2 J.
If mass is ~1000 tonnes = 1 000 000 kg, E is 500 GJ.

Over 100 s the power plant put out 250 MW × 100 s = 25 000 MJ = 25 GJ, not even remotely enough.

The only conclusion is that the power plant can't produce enough power to accelerate the ship. Essentially, the power is used to extend the thumb, and the universe gives us a lift...

MT RM, p58:
The second major breakthrough is artificial gravlty. Created by manipulating subatomic forces, artificial gravity is not anti-gravity but is instead a unique force that acts upon the natural gravity field created by all matter. Artificial gravity can be made to either push or pull.

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.

 

[mike wightman]

The gravitcs borrow energy from a local gravity well or even the univeral gravity wave background. The EPs that go to the m-drive are to create the field and potential energy borrowing mechanism.
Nope. I have no idea how this magic works either.

 

[Condottiere]

Gravity provides a deep enough well to paddle around in.

Once in the shallow end, you can only tiptoe through the tulips.

 

[AnotherDilbert]

The gravitcs borrow energy from a local gravity well or even the univeral gravity wave background. The EPs that go to the m-drive are to create the field and potential energy borrowing mechanism.
Nope. I have no idea how this magic works either.

Quite, thrust is produced by sheer magic, neatly giving us the pure Newtonian movement system in LBB2.

 

[infojunky]

Quite, thrust is produced by sheer magic, neatly giving us the pure Newtonian movement system in LBB2.

Though to be honest Book2 drives where a flavor of torch drives at the begining.

 

[Marcatlas]

So, something that has been bothering me for a while are dTons.

DTons is ONLY a volume measurement in regards to ship design and capacity. NOT mass. Therefore, 1 dTon of lead takes up the same volume as 1 dTon of feathers. Nothing to do with mass or weight.

 

[Marcatlas]

Maybe it’s only the volume that matters for the acceleration?

Mass doesn't play into it. This is explained in game version rules that state the M-drive is gravitic in nature. A dTon of lead falls into a gravity well at the same acceleration as a dTon of feathers.

For those rule sets where the M-drive is based on something that operates using the 3rd law of motion, like a rocket, mass must be considered when calculating acceleration available from any given M-drive.

 

[AnotherDilbert]

Though to be honest Book2 drives where a flavor of torch drives at the begining.

Yes, there were low-key reaction drives in LBB2'77 and LBB5'79. That was gone in LBB5'80 and LBB2.81, in favour of no specified flavour. The narrative became gravitic M-drives with time, firmly entrenched in MT.