I tend to think in volume only for the M-Drive, but TNE introduced the wrinkle of HEPlaR which is a reaction drive, so mass needs (or should) to be accounted for in g-turns of thrust available (can't remember the exact rules around it but it did send me off an a learning adventure to learn 'rocket science stuff' which in my as usual convoluted mental processes way leads to some of the stuff behind designs in Pioneer).

And Merchants is classic Traveller or do you not consider it canon
Show me where in Merchant Prince it defines the mass of a cargo? The word is never mentioned.
The only rules for breaking down a cargo ton are in LBB2 where 1 ton of cargo is 1000kg.

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Where in MT does it define the mass of a cargo ton? Genuine question.

A 70kg mass still has a mass of 70kg on the moon. It has a mass of 70kg anywhere in the universe. It is its weight that changes due to local gravity, its mass remains constant. I would recommend remedial physics at this point.

It is obvious you want to pick fault, good luck with that. I still don't understand why you wanted do go back to a post from 8 months ago to pick a fight, especially when you are wrong.

I definitely should not jump in, but tytalan, you are wrong, and Sigtrygg is right. I will have a go at trying to explain what Sigtrygg means and we will see if my explanation gets across any better.

Mass is a property of all matter, and it does not change due to gravity. Weight is mass x gravity, but it is better to disregard weight for this discussion. If you fly your 1000 ton spacecraft to a 2G planet, suddenly it weighs 2000 tons, but the mass is still 1000 tons. Since it is variable in this context, hereinafter, I am not using the concept of weight.

Mass is what matters for determining, for example, how much force a spacecraft will need to exert to accelerate a given amount, and this is the case even in zero gravity. Even if there is no gravity, objects with more mass will require more force to accelerate than objects with less mass. So a 1 G M drive on a 1000 ton (mass) spacecraft becomes a .5 G M drive on a 2000 ton (mass) spacecraft (tons meaning tons of mass). This is because mass has inertia: force is required to overcome this inertia and the amount of force is proportional to the mass of the object, and this is the case both inside and outside a gravity field.

(This is confusing because experientially we only have ever to deal with objects in a 1G gravity field - usually they ARE "harder" to move in gravity except of course downward when it is easier)

If you have a gravity control based engine, it does not affect or remove objects' mass. Rather, it affects the effect of gravity on the objects - if you have a grav sled, with massive objects stacked on it, you can push it more easily because 1) gravity is not creating friction with the ground 2) you can accelerate the mass little by little instead of needing to continually overcome gravity with constant pushing. The mass is still there, though. If you get your massive sled going fast and it runs into something, all that inertia is still there.

In addition to nullifying the effect of gravity on the spacecraft, the Traveller M drive engines provide thrust, which we know because the rulebooks tell us so, and because it is measured in G forces, which is a measure of thrust. The mass of the spacecraft would be important for this reason, and technically the mass of the cargo in the ships should definitely affect the ships' performance if we want to be realistic. A cargo of cottonballs with the same volume as a cargo of gold bricks could both fit in the hold but one MASSES more that the other, and physics tells us this will affect ship performance - not in terms of ability to take off, since we can nullify gravity - but in the ship's G rating certainly.

This way lies madness, however, so we handwave the issue and just leave that can of worms tightly shut when playing the game.

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I definitely should not jump in, but tytalan, you are wrong, and Sigtrygg is right. I will have a go at trying to explain what Sigtrygg means and we will see if my explanation gets across any better.

Mass is a property of all matter, and it does not change due to gravity. Weight is mass x gravity, but it is better to disregard weight for this discussion. If you fly your 1000 ton spacecraft to a 2G planet, suddenly it weighs 2000 tons, but the mass is still 1000 tons. Since it is variable in this context, hereinafter, I am not using the concept of weight.

Mass is what matters for determining, for example, how much force a spacecraft will need to exert to accelerate a given amount, and this is the case even in zero gravity. Even if there is no gravity, objects with more mass will require more force to accelerate than objects with less mass. So a 1 G M drive on a 1000 ton (mass) spacecraft becomes a .5 G M drive on a 2000 ton (mass) spacecraft (tons meaning tons of mass). This is because mass has inertia: force is required to overcome this inertia and the amount of force is proportional to the mass of the object, and this is the case both inside and outside a gravity field.

(This is confusing because experientially we only have ever to deal with objects in a 1G gravity field - usually they ARE "harder" to move in gravity except of course downward when it is easier)

If you have a gravity control based engine, it does not affect or remove objects' mass. Rather, it affects the effect of gravity on the objects - if you have a grav sled, with massive objects stacked on it, you can push it more easily because 1) gravity is not creating friction with the ground 2) you can accelerate the mass little by little instead of needing to continually overcome gravity with constant pushing. The mass is still there, though. If you get your massive sled going fast and it runs into something, all that inertia is still there.

In addition to nullifying the effect of gravity on the spacecraft, the Traveller M drive engines provide thrust, which we know because the rulebooks tell us so, and because it is measured in G forces, which is a measure of thrust. The mass of the spacecraft would be important for this reason, and technically the weight of the cargo in the ships should definitely affect the ships' performance if we want to be realistic. A cargo of cottonballs with the same volume as a cargo of gold bricks could both fit in the hold but one MASSES more that the other, and physics tells us this will affect ship performance - not in terms of ability to take off, since we can nullify gravity - but in the ship's G rating certainly.

This way lies madness, however, so we handwave the issue and just leave that can of worms tightly shut when playing the game.
I’m going to point out the fact that M-Drive already are stated as having inertia compensation so inertia is not an issue. But I’m done with this argument you both can run thing how you want but I’ll give you a hint from someone who know. With your way there should be little if any trade.

I’m going to point out the fact that M-Drive already are stated as having inertia compensation so inertia is not an issue. But I’m done with this argument you both can run thing how you want but I’ll give you a hint from someone who know. With your way there should be little if any trade.
Inertia clearly is an issue. If it were not, any thrust at all would immediately result in infinite velocity - i.e. instantly take the spacecraft to the speed of light.

The reality I describe isn't "my way". If you have a problem with it, take it up with physics. It is not clear to me how using the terms "weight" and "mass" incorrectly interchangeably means there will be less trade. The two things have nothing to do with each other.

Let me see if I can simplify the issue:

Does mass/weight effect game mechanics in Mongoose Second, and thereby spacecraft performance.

No, it doesn't.
But it should

Ok I am kidding, but the only explanation that makes sense to me is that the m-drive produces its effects based on the volume it (a field? a bubble?)can extend to, rather than the mass of whatever is inside.

Let me see if I can simplify the issue:

Does mass/weight effect game mechanics in Mongoose Second, and thereby spacecraft performance.
Doesn't really simplify the issue. Weight is not relevant to the discussion, and using the term only creates confusion.

Tons in this context is a measure of mass, and the more of it a spacecraft has the bigger drives it needs, so yes it does affect game mechanics and spacecraft performance. The relationship of mass to volume in spaceship design is simplified because otherwise deckplans would be much harder to make. The effect of cargo's mass on ship performance is handwaved, so that mass doesn't need to be constantly recalculated. However, for many things - like dropping off pods and stuff, there is an assumption in the rules that mass matters for ship performance. There is still the assumption that the mass of determines the amount of thrust needed to move it at a given acceleration.

Buffered planetoids have thirty five percent of their volume taken up by nickel iron, and that's before you added gravitationally crushed super bonded hull armour.

For starships, fuel consumption would ensure that that what went in one hole, has a different mass coming out the other, disregarding drop tanks.

As game mechanics stand now, there's more cost in exporting pillows than smuggling gold, calculated by volume.

Buffered planetoids have thirty five percent of their volume taken up by nickel iron, and that's before you added gravitationally crushed super bonded hull armour.

For starships, fuel consumption would ensure that that what went in one hole, has a different mass coming out the other, disregarding drop tanks.

As game mechanics stand now, there's more cost in exporting pillows than smuggling gold, calculated by volume.
A good pillow is definitely worth its weight in gold.

If you want to ignore inertia, GURPS Lensman is right over there.

Traveller already ignores inertia.

Ship displacement is the metric used for drive performance, and the magic of gravitics also gives us acceleration compensators...

just a thought but in some places Traveller calls them inertial compensators, in others acceleration compensators, anyone else notice the difference...
Acceleration compensators are also usually installed, to negate the effects of high acceleration and lateral G forces while maneuvering. A ship's passengers would be unable to tell whether they were moving through space or grounded on a planet without looking out a viewscreen.

Traveller already ignores inertia.

Ship displacement is the metric used for drive performance, and the magic of gravitics also gives us acceleration compensators...

just a thought but in some places Traveller calls them inertial compensators, in others acceleration compensators, anyone else notice the difference...
And we are back to my original statement in Traveller Mass doesn’t matter only volume does. . Thank you for proving my point after arguing against it for so long.

In MegaTraveller a ton or lot of goods (Freight, Mail, Cargo, etc) is defined as 1 dton or 13.5 Kiloliters. Pg 46 Referee’s Manual.

Mongoose says cargo comes in Ton lots but never defines if it’s Tons of Displacement or Mass.

T5 defines it the same as MegaTraveller

In the LBBs while b2 explicitly tells us a 1000kg figure Merchant Prince doesn’t directly counters in this many of the trade rules and charts do run counter to LBB2.

Inertia clearly is an issue. If it were not, any thrust at all would immediately result in infinite velocity - i.e. instantly take the spacecraft to the speed of light.

The reality I describe isn't "my way". If you have a problem with it, take it up with physics. It is not clear to me how using the terms "weight" and "mass" incorrectly interchangeably means there will be less trade. The two things have nothing to do with each other.
See here’s the thing in Traveller inertia compensation is rated like in many sci-fi (David Webers Homer Harrington has a good example). So no we don’t get an infinite velocity.

I'm guessing here, but since Merchant Prince was brought up.

Since that covers the more mercantile aspect of Traveller, goods are priced by weight, since that's known, rather than volume, where packaging plays a factor, and the exact volume taken up is unknown.

See here’s the thing in Traveller inertia compensation is rated like in many sci-fi (David Webers Homer Harrington has a good example). So no we don’t get an infinite velocity.

Mass always has inertia, so if something doesn't have inertia that means it doesn't have mass. That's not what I see happening in Honor Harrington books or Traveller with the "inertial compensation". What seems to happen there is that objects have mass and inertia, even when there is "inertial compensation" going on. That is to say, inertial compensation seems to mean that there is a field which keeps the inside of the ship in a gravity field at the passengers' preferred gravity, regardless of how the ship accelerates. This does not mean that objects do not have mass or inertia. If an object has 0 mass it does not exist, or it can be light - that is to say something moving at the speed of light because only a thing with zero mass can move at the speed of light. This is just how the math works.

Of course, this is sci fi and lots of things can happen, but things becoming 0 mass/inertia is just not what happens when antigravity/inertial compensators get turned on in the fiction you mention. Spacecraft still require thrust to move, and they move in exactly the same way a spacecraft without inertial compensators with a torch drive of the same G rating would move them. This is the case in Traveller, and, albeit with a lot more Gs, in the Honor Harrington books. If inertia was being ignored, then we would not need different size drives for different size ships. So mass is there; it is just being approximated for some aspects of the Traveller ship design process and cargo business because it is easier to do it that way.

The Honor Harrington universe use the inertial compensator as a way to cancel out the hundreds of Gs that the ships accelerate at. From memory total mass of the vessel determined compensator efficiency and that determined how fast the ship could safely accelerate.

This may have changed since I last followed the discussions, especially after the ship density issue.

Lol, your usual aggressive style.
LBB2
When determining the contents of a cargo, the players and referee must be
certain to correlate the established price of goods with the cost per ton. For example,
the base price of a shotgun is Cr150, while a ton of firearms as trade goods
has a base price of Cr30,OOO. A strict weight extension of the shotgun (3.75 kg per
shotgun) would indicate 266 shotguns.
Extension should be instead based on
price, with weight as a limiting factor. Thus one ton of shotguns would contain 200
guns, at Cr150 each. The extra weight can be considered packing and crates. Similar
calculations should be made to keep prices in line on other trade goods.

So 1 cargo ton is 1000kg, I won't wait for your apology.

Just so you know 77 CT didn't mention displacement tons, they came in with the 81 revised rules.

Try again.
This is actually a GOOD example of the rules being written without accounting for any of this stuff works. And while, yes, it's in the rulebook, for a game that prides itself on the quote "In MY Traveller universe", it's also a GREAT example of a rule that should have been changed in one of the many updates to the rules. However, from a company that refused to fix their canonical errors for decades (Ex - The Gazelle with it's drop tank and tonnage/turret error) it's par for the course.

What they SHOULD have done would have been to correct the sample through a very simple rule change. In the shotgun example, they are entirely correct that using the base price for a shotgun, the base price for a ton of firearms as trade goods, and then extrapolating the total number does NOT give you anywhere near an exact number of items in a ton of trade goods. Plus Traveller doesn't care about mass, just displacement. A TON of trade goods does not necessarily correlate to a Dton (unless we are talking water). Here's what I see as a better explanation that would generate much less IMTU:

When determining the contents of a cargo, the type of cargo, how it's transported and ultimately used should be considered to determ oods. For example, the base price of a shotgun is Cr150, while a ton of firearms as trade goods has a base price of Cr30,000. A strict weight extension of the shotgun (3.75kg per shotgun) would indicate 266 shotguns. Shotguns are typically packaged and sold individually, so 20% wastage (.75Kg per shotgun) is added, giving an individual shotgun a shipping weight of of 4.5kg). 222 shotguns would be possible within 1,000 kg. To keep the bookeeping simple, a referee can round the total count down to 200. A Dton of gold is not equivalent in mass to a Dton of consumer goods, so referees should keep that in mind. In the above example 1Dton of firearms would mass 1,000Kg and contain 200 shotguns and have a base price of Cr30,000. A lot of precious metals costs Cr50,000 but would not consume 1Dton and would not mass 1,000Kg. Referees should try to balance these conflicts when considering bulk trade items.

In the real world of shipping many other things are taken into consideration (pallets have a general maximum weight, trucks have a maximum height and width for loads, and containers have a maximum cargo weight that can be added to their own empty weight) for mass. The loading/unloading of cargo also factors in a maximum weight since cargo moving equipment has its own limitations. All of these realities bog a game down but consideration of them should be used when creating the gaming universe - at least where practical. This is where updates/corrections to patch the rules and justify buying the new version come into play. Changing rules withoug fixing the potholes just to sell a new version of the game is great business, but bad service.

Mass always has inertia, so if something doesn't have inertia that means it doesn't have mass. That's not what I see happening in Honor Harrington books or Traveller with the "inertial compensation". What seems to happen there is that objects have mass and inertia, even when there is "inertial compensation" going on. That is to say, inertial compensation seems to mean that there is a field which keeps the inside of the ship in a gravity field at the passengers' preferred gravity, regardless of how the ship accelerates. This does not mean that objects do not have mass or inertia. If an object has 0 mass it does not exist, or it can be light - that is to say something moving at the speed of light because only a thing with zero mass can move at the speed of light. This is just how the math works.

Of course, this is sci fi and lots of things can happen, but things becoming 0 mass/inertia is just not what happens when antigravity/inertial compensators get turned on in the fiction you mention. Spacecraft still require thrust to move, and they move in exactly the same way a spacecraft without inertial compensators with a torch drive of the same G rating would move them. This is the case in Traveller, and, albeit with a lot more Gs, in the Honor Harrington books. If inertia was being ignored, then we would not need different size drives for different size ships. So mass is there; it is just being approximated for some aspects of the Traveller ship design process and cargo business because it is easier to do it that way.
In the HH books, the inertial compensator is used so that the crew of the ship aren't turned to paste with their massive accelerations. There are a couple of examples of compensator failure and the pasting the crew can get. Traveller pretty much ignores the mass rule, but Weber does make reference to it and how it puts limits on armor and overall ship size. Plus as size increases he does reference that the accelerations and top speeds decrease (don't recall if it's true in the hyperwaves and when they go FTL, or just in N-space).

I haven't quite figured out how the references to their ship tonnage are supposed to correlate to their size and/or displacement. And Weber doesn't go too far down that rabbit hole to really explain the physics of the HH universe. Traveller sidesteps the mass and displacement question (GT did try to take some into consideration) in its entirety.

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