Cargo Capacity and volume and mass

[AnotherDilbert]

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.

It's just a simplification, a shortcut, to make ship design easier.

The most detailed system, TNE FF&S, described it thus:

TNE FF&S, p73:
Each cubic meter of installed thruster plate drive generates 40 metric tonnes of thrust, masses 2 tonnes, requires 1 MW of power, and cost MCr1.

Yes, a freighter will have higher acceleration when unloaded, but generally not all that much. Probably 1.something, instead of 1.0 loaded.


This contrived TNE Free Trader with almost 70 Dt cargo:

Thrust: 56.4 × 40 = 2256 t.
Mass: 2256 t / 1206 t.

So, acceleration = 2256 / 2256 = 1 G loaded, and acceleration = 2256 / 1206 = 1.87 G empty.


I have tried making a completely mass-based system, based on MT, but the end results are too similar to MT to bother with.

 

[whartung]

I have tried making a completely mass-based system, based on MT, but the end results are too similar to MT to bother with.

I'm guessing that the designers did the same thing.

The consequences in the large of "1.x" vs "1.0" are not tangible enough to require the bookkeeping.

With TNE, the data is there if you want it, but in the big picture, it's mostly meaningless.

 

[Badenov]

With all this discussion in mind, I have designed (in Mongoose 2008, sorry) a freighter ship of 100,000 tons. The vanilla version has nearly 69,000 tons of cargo space. But this thread implies mass kind of doesn't matter? It's just about the volume? If mass does matter, an alternate version has much larger engines, cutting the cargo space to 20,000 tons, but giving it an extra 200,000 tons of mass capacity, so it can haul denser cargoes like metals and radioactives. It seems like the bottom line is I am being told 'Forget physics, this is space magic, press the "I believe" button and do what the book says.'?

 

[kilemall]

With all this discussion in mind, I have designed (in Mongoose 2008, sorry) a freighter ship of 100,000 tons. The vanilla version has nearly 69,000 tons of cargo space. But this thread implies mass kind of doesn't matter? It's just about the volume? If mass does matter, an alternate version has much larger engines, cutting the cargo space to 20,000 tons, but giving it an extra 200,000 tons of mass capacity, so it can haul denser cargoes like metals and radioactives. It seems like the bottom line is I am being told 'Forget physics, this is space magic, press the "I believe" button and do what the book says.'?

Maybe others, I would tell you do what you want that works for your table.

You don’t eat meat RAW, why would you prepare your games the same way?

 

[Marcatlas]

With all this discussion in mind, I have designed (in Mongoose 2008, sorry) a freighter ship of 100,000 tons. The vanilla version has nearly 69,000 tons of cargo space. But this thread implies mass kind of doesn't matter? It's just about the volume?

In Mongoose 1st edition rules it is a gravitic type drive so mass doesn't matter. Only volume

 

[Badenov]

In Mongoose 1st edition rules it is a gravitic type drive so mass doesn't matter. Only volume

Why would volume matter, though? I suppose to enclose a jump bubble, but not for M-Drive. And what about chemical/reaction m-drives? Those need whole new tables, the current timing tables are accelerate halfway there, decel the rest tables. (I was bored and checked the math. They assume thrust 1 is 10m/s^2, and munged up a couple columns, but it's pretty much right.) Reaction drives need to get you to orbital altitude and up to orbital speed. But it's a way different number than the accel half/decel half.

 

[Marcatlas]

Why would volume matter, though?

If the grav field created by the drive can only encompass a certain area it would matter. A huge ship would require a correspondingly huge field to affect the ship.

 

[Badenov]

If the grav field created by the drive can only encompass a certain area it would matter. A huge ship would require a correspondingly huge field to affect the ship.

So, if I understand correctly, and I feel like I don't, a rating 1 drive for a certain volume, rated in d-tons, will move any mass contained by the volume rating of the drive? That implies so many things that make my head hurt. Portable black holes? We deliver.

 

[Marcatlas]

So, if I understand correctly, and I feel like I don't, a rating 1 drive for a certain volume, rated in d-tons, will move any mass contained by the volume rating of the drive?

No. It will move the ship the drive is installed in and thus anything inside the ship.

 

[Condottiere]

If enclosed volume was a specific issue for gravitic based drives, I'd say this would have more to do with the inertial compensation field, rather than pseudo mass.

 

[Badenov]

No. It will move the ship the drive is installed in and thus anything inside the ship.

That's what I was trying to say. So, portable Dyson spheres, this is an up and coming thing. Also, should this same thing be applied to reaction drives? Or are they best left ignored and un-dealt with?

 

[Marcatlas]

That's what I was trying to say. So, portable Dyson spheres, this is an up and coming thing. Also, should this same thing be applied to reaction drives? Or are they best left ignored and un-dealt with?

Dyson spheres have nothing to do with this. Reaction drives are like rockets. Newton's 3rd Law off motion applies to them and how they propel mass.

 

[Badenov]

Dyson spheres have nothing to do with this. Reaction drives are like rockets. Newton's 3rd Law off motion applies to them and how they propel mass.

I'm suggesting that a Dyson Sphere may be able to collect sufficient energy to power an spacecraft engine mounted to it. If the mass doesn't matter, why would you not be able to move a star if you could enclose it, which is the point of a Dyson sphere. Alternately, would the star itself be considered a giant fusion power plant?

So, if reaction drives use normal physics, I think I actually know how to do this: I can build a vehicle with Supplement 6: Military Vehicles (I think the CT equivalent book may be CT Striker, but not sure) that tracks mass and volume separately. I can seal it against vacuum and put in life support and all that, and I can make a vehicle that can fly to, and in, space.

 

[mike wightman]

The Ancients, and other advanced races, could move planets and stars.

 

[McPerth]

My assumption is that, until MegaTraveller, the authors decided to ignore mass and just use the volume to keep things simple.

And even in MT the gravitic/Thruster M-drives ignored mass, being only volume dependent. Mass was used for Agility and reaction M-drives (rockets), appearing in HT and Challenge under the name og One Small Step

But this thread implies mass kind of doesn't matter? It's just about the volume?

Basically, yes. No matter if you hold is fileld with L-Hyd or with superdense materials, the ship m-Drives wil lgive it the same acceleration.

So, if I understand correctly, and I feel like I don't, a rating 1 drive for a certain volume, rated in d-tons, will move any mass contained by the volume rating of the drive? That implies so many things that make my head hurt. Portable black holes? We deliver.

From another thread:

My excuse to handwave it (I claim it not to be anything more) is that, as drives are gravitic and use gravitic force, adding mass also adds gravitic force, so overcoming the effects of this increased mass

 

[mike wightman]

77 mass displacement not defined, 1000kg of cargo is one ton
This infers a 100mdt ship is indeed 100tonnes.
81 mass displacement tonnage is defined as the 14 cubic metre volume of one ton of liquid hydrogen, 1000kg of cargo is still one ton - so cargo and fuel mass 1tonne per 1mdt.

 

[AnotherDilbert]

Nothing to be sorry about, MgT1 (Mongoose 2008) is just as good as any other edition.

With all this discussion in mind, I have designed (in Mongoose 2008, sorry) a freighter ship of 100,000 tons. The vanilla version has nearly 69,000 tons of cargo space. But this thread implies mass kind of doesn't matter? It's just about the volume?

No, it does not say that. Mass is unspecified, mass is within reason, something like 1 tonne per m³.

Ships are designed around volume, as that is simpler. It's a short-cut, a rule-of-thumb. And it makes deck plans much easier.

If you want to specify mass, volume, and surface area of a ship FF&S will let you do that.

If mass does matter, an alternate version has much larger engines, cutting the cargo space to 20,000 tons, but giving it an extra 200,000 tons of mass capacity, so it can haul denser cargoes like metals and radioactives.

MgT1 has no rules for that, so that is your house rules.

But, sure, if you want small, hi-mass cargo holds that seems reasonable. Something like what FF&S would let you do.

It seems like the bottom line is I am being told 'Forget physics, this is space magic, press the "I believe" button and do what the book says.'?

No, never forget physics, just remember that it's highly simplified view of physics.

Newton's laws with mass and thrust is the real background, ship design is simplified down for people who thinks calculating a percentage is too complicated, hence lettered drives.

If you want a ship design system closer to real physics, FF&S is available. It will just take longer time (or computer support) to design a ship.

 

[AnotherDilbert]

So, if reaction drives use normal physics, I think I actually know how to do this: I can build a vehicle with Supplement 6: Military Vehicles (I think the CT equivalent book may be CT Striker, but not sure) that tracks mass and volume separately. I can seal it against vacuum and put in life support and all that, and I can make a vehicle that can fly to, and in, space.

If it's anything like CT Striker (which it sounds like), sure you can.

That is somewhat close to what FF&S does, but FF&S has specialised rules for spacecraft. And simplified hulls, basically a sphere with some modifiers thrown in.

If you like designing spacecraft like that, you will love FF&S...

 

[AnotherDilbert]

77 mass displacement not defined, 1000kg of cargo is one ton
This infers a 100mdt ship is indeed 100tonnes.

Agreed.

81 mass displacement tonnage is defined as the 14 cubic metre volume of one ton of liquid hydrogen, 1000kg of cargo is still one ton - so cargo and fuel mass 1tonne per 1mdt.

If you follow an example in another section, that is unchanged since the 77 edition.
If you use the rules (in another book) from 1981:

Weight: Vehicle weight is determined by adding together the weights of all the components. The vehicle is assumed to be carrying a full load of ammunition and a full load of cargo, at 1 ton per m³.

That is not explicitly for spacecraft, but within reason.
A cargo density of ~0.07 tonnes per m³ is not within reason.

 

[AnotherDilbert]

And even in MT the gravitic/Thruster M-drives ignored mass, being only volume dependent. Mass was used fo rAgility and reaction M-drives (rockets), appearing in HT and Challenge under the name og One Small Step

Detailed mass, thrust, and power are used for grav drives, rockets, air-cushion vehicles, ground vehicles, everything but dedicated spacecraft. They used the exact same simplified system as LBB5.

And cargo is assumed to be 1 tonne per m³, not unlimited mass.

It's just a simplification...