Loaded vs. Unloaded M-ratings

[Sigtrygg]

Nope, its how the rules work.

Sorry to use the CT version but here goes.

The 200t free trader has a volume of 200 displacement tons. Of that 83 displacement tons is cargo space.

Unloaded the free trader has 1g acceleration.

Fill the hold with lead and it still has an acceleration of 1g.

The mass of the ship actually goes up by 83x14x11 = 12,782tonnes but it still accelerates by 1g.

Using your estimate the empty free trader has a mass of 2,800tonnes. Carrying a hold full of lead should reduce performance noticeably.

Reactionless thrusters move the volume of the ship, not the mass. Doesn't make sense with real world physics but there you go.

 

[CosmicGamer]

Except you are using magic reactionless thrusters that don't obey newtonian rules.

Because the drive's creating a gravity well, not directly applying a force of X newtons, your mass is supposedly irrelevant to the acceleration you get.

MgT, unlike MT, uses Grav creation (Gravity Maneuver Drives) for deep space drive.

And the apple accelerates at the same rate as a ball of lead. Newtonian laws.

I don't want my Sci-Fi to obviously break any laws of science. Some bending of the rules is ok because it's future tech we don't totally understand. If we could explain it we would be able to do it now and it would not be future tech. So a magical futuristic grav drive that moves a ship the same rate no mater the mass is ok to me.

 

[Wil Mireu]

Using your estimate the empty free trader has a mass of 28,000tonnes. Carrying a hold full of lead should reduce performance noticeably.

Exactly. That's how it should work. Obviously it's too much hassle to calculate the mass of the ship totally accurately, but drive performance should change as the mass changes. At the very least, calculate an unloaded and loaded mass (assuming bulk densities of ship and cargo) and then figure out how the acceleration is different for each.

Reactionless thrusters move the volume of the ship, not the mass. Doesn't make sense with real world physics but there you go.

Either way, it's still wrong, because if you had a reaction drive in CT then you would still have to calculate it using volume. It's as stupid as "the 100D limit is calculated by radius and not gravity". Honestly, I don't know why we're still calling this a science fiction game since there's barely any science in it.

TNE handled this much better because it *did* calculate the mass of the ship.

 

[Sigtrygg]

Exactly. That's how it should work. Obviously it's too much hassle to calculate the mass of the ship totally accurately, but drive performance should change as the mass changes. At the very least, calculate an unloaded and loaded mass (assuming bulk densities of ship and cargo) and then figure out how the acceleration is different for each.

Either way, it's still wrong, because if you had a reaction drive in CT then you would still have to calculate it using volume. It's as stupid as "the 100D limit is calculated by radius and not gravity". Honestly, I don't know why we're still calling this a science fiction game since there's barely any science in it.

TNE handled this much better because it *did* calculate the mass of the ship.

I agree with you completely. TNE got it right.

i you know in the '77 version of CT the maneuver drive was implied to be a reaction rive, and that 1st edition High Guard flat out stated that it is a fusion rocket and it can be use as a weapon at close range?
Also the trade rules in '77 implies that 1 displacement ton of cargo is usually no more than 1000kg in mass.

 

[hdan]

And the apple accelerates at the same rate as a ball of lead. Newtonian laws.

That's the crux of it. M-drives do not provide thrust, they provide acceleration. They do this by creating a gravity field in some way. The size of object they can accelerate and how much acceleration they can cause depends on their rating.

Trying to put F=MA into it is irrelevant. Gravity fields provide acceleration, not force.

You could possibly[1] compute the force with which your spaceship could push something if you knew its mass, but anything inside the acceleration field gets accelerated together.

[1] I say "possibly" because I don't know how the m-drive field would interact with the pushed object.

MegaTraveller and TNE had to deal with reaction drives, and thus cared about mass. MgT adding reaction drives without adding mass is problematic from a physics standpoint, but as a game simplification it's not a big deal.

Unless you're in a setting that uses reaction drives extensively, of course.

 

[Wil Mireu]

That's the crux of it. M-drives do not provide thrust, they provide acceleration. They do this by creating a gravity field in some way. The size of object they can accelerate and how much acceleration they can cause depends on their rating.

Trying to put F=MA into it is irrelevant. Gravity fields provide acceleration, not force.

I don't think you understand how this works at all.

You cannot simply "apply acceleration". You need a force to create the acceleration - the F in the equation - and that is what thrust is. If you apply a force (thrust), then it has to create an acceleration. That acceleration is equal to the force applied divided by the mass of the object it's applied to.

 

[F33D]

That acceleration is equal to the force applied divided by the mass of the object it's applied to.

Except, per the rules in MGT, the drives don't work that way. x amount of acceleration happens to x volume of ship. Regardless of the total mass involved. Ipso facto, they aren't the Drives you are thinking of.

 

[locarno24]

You cannot simply "apply acceleration". You need a force to create the acceleration - the F in the equation - and that is what thrust is. If you apply a force (thrust), then it has to create an acceleration. That acceleration is equal to the force applied divided by the mass of the object it's applied to.

Except that when the force is being generated by a gravity well, it's automatically proportional to the mass of the 'falling' object - hence the mass of the falling object drops out of the equation and the effect can be expressed directly as an acceleration.

 

[Wil Mireu]

Except that when the force is being generated by a gravity well, it's automatically proportional to the mass of the 'falling' object - hence the mass of the falling object drops out of the equation and the effect can be expressed directly as an acceleration.

That's right in that case ( http://www.grc.nasa.gov/WWW/k-12/airplane/ffall.html )... but that's not what is happening here. I've already explained why, twice.

The force is not being generated by "a gravity well in front of the ship" - it's being generated by the thruster plates. You put energy into the plates, you get thrust out that pushes the ship forward. So your entire line of argument is just wrong; the ship isn't falling towards anything - it's being pushed by "thrust", so its mass does matter.

 

[F33D]

That's right in that case ( http://www.grc.nasa.gov/WWW/k-12/airplane/ffall.html )... but that's not what is happening here. I've already explained why, twice.

In YOUR game perhaps. But, as has been explained to you numerous times, in MGT there is no change in accel due to mass of ship. Probably it would be good to list when you are talking about your house rules as opposed to the rules as written.

 

[Wil Mireu]

In YOUR game perhaps. But, as has been explained to you numerous times, in MGT there is no change in accel due to mass of ship. Probably it would be good to list when you are talking about your house rules as opposed to the rules as written.

I want to know exactly where it says in MGT that M-Drives create a gravity well in front of the ship that pulls it along, and I want an exact quote and page reference because so far nobody's provided that. I don't have my corebook to hand right now but there is nothing in the SRD that says anything like that.

But because I know you often can't be bothered to read what people say yourself (hello kettle, this is pot, you're black), I'll quote it again here:

That's the first I've heard of that explanation for how it works. As far as I can recall, gravitic M-Drives have not been very well explained anywhere except in TNE's Fire Fusion and Steel.

Artificial Gravity is described there (pg 73) as being a "force which could either push or pull and which acted on a gravitational field of a mass". Thruster plates are an extension of that, in which "the force generated by the drive pushed on the actual thruster plates of the ship itself". It's a reactionless drive though that just converts energy into thrust, and essentially it's like the ship is "pulling itself along with its bootstraps" (which doesn't really make any physical sense, but the text is honest enough to say that too).

Either way, there's no "mass or gravity well in front of the ship" involved at all, so your question simply doesn't apply.

What I quoted may have been from a previous edition, but if MGT does not actually state anything to the contrary then what I quoted stands. I'm not going to believe it until I see a direct reference and quote from MGT though.

 

[F33D]

What I quoted may have been from a previous edition, but if MGT does not actually state anything to the contrary then what I quoted stands. I'm not going to believe it until I see a direct reference and quote from MGT though.

LISTEN carefully. In MGT, the GRAVITY Maneuver Drive "delivers" the same Acceleration REGARDLESS of the mass of the ship. Exactly how the GRAVITY drive delivers that is unstated. We can only guess. (one guess is a grav well as that could explain it and explains why being near a planetary grav well doesn't matter) BUT, it (the Grav-M drive) doesn't perform as you have house ruled for your game.

If you have a better explanation that ALSO conforms to the rules in MGT lay it out. So far, no one has put out an idea that is as good or better. So, the BEST explanation is a created Grav well. That satisfies all the spacecraft performance rules in MGT.

 

[dragoner]

Traveller "ships" have always been magic carpets, their propulsion systems are just another facet.

 

[Ishmael]

I don't know whether this thread is making laugh or making me cry; I know it's make my dog cry
.....seriously?
a gravity well just in front of the ship that somehow ONLY affects the ship and not even its crew or cargo? if everyone/everything in he ship simply 'falls' towards the point source, then everything is in free fall and there is no need for inertial compensation except if you hit something...and everything nearby should be falling into your artifical gravity well too, perhaps for you to run into.

and its comparable to that of a planet's?..sure the inverse square law helps you when you get closer to the point source, but then you're going to have increasingly large tidal forces doing bad things to the ship.
The energy requirements are insane... check out Einstein's field equations.

Please explain what happens when the same energy input to the drives can give back significantly different levels of momentum depending on the mass of the cargo, or does conservation of momentum not matter with m-drive ( it doesn't )?

the reason the rules are like this, is that during the open playtest, people were fairly strident in their desire for a simple system as opposed to a hard sciece system; the system protects people from potentially scary maths.... and it had to follow CT's system reasonably close which also ignored mass. CT didn't ignore mass so much as it assumed that all ships had the same density.*

Why not just say grav-thrust is an offshoot of science's discoveries concerning the manipulation of the graviton/gravitational force. Non-grav reactionless thruster plates are an offshoot of science's manipulation of the strong and weak forces.... that's what DGP's Starhip Operating Manual did.

btw, the warped-space Albecuirre type of drive is mentioned in the SRD...as an alternate to jump drives as a FTL engine.
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* This is one of the primary reasons I do not use MgT or CT or T5.... I prefer a harder level of science than those rules provide. Even with MT and FFS1, I generally end up houseruling stuff to the point of being unrecognizable to the typical grognard.

 

[dragoner]

Say goodbye to every canonical trav ship.

 

[CosmicGamer]

What I quoted may have been from a previous edition, but if MGT does not actually state anything to the contrary then what I quoted stands. I'm not going to believe it until I see a direct reference and quote from MGT though.

Not for me. I don't own all the other versions of Traveller and don't consider MgT a sequel such that whatever came before, unless explicitly countered, needs to be part of my gaming. For me, MgT is it's own stand alone game and parts of other games like Star Trek, Warhammer, other versions of Traveleer, or anything else can all be brought into someones MgT game.

Perhaps MgT doesn't clearly state the science behind the M-drive. Why should it. Gravity in a ship. Jump drives. Magic. As I always say, if we completely understood it today it wouldn't be good future tech, it would be current tech. If MgT doesn't give an explanation how then some theory hatched (from previous versions or wherever else) which breaks the laws of science is what is wrong, not MgT. Use imagination. Grav tech, Pluto pseudo propulsion plasma pulses, or whatever else.

 

[F33D]

a gravity well just in front of the ship that somehow ONLY affects the ship and not even its crew or cargo? if everyone/everything in he ship simply 'falls' towards the point source, then everything is in free fall and there is no need for inertial compensation except if you hit something.

OBVIOUSLY it effects everything in the ship. Correct, no inertial comp. (probably why that isn't listed under ship design like it is in MT).

 

[CosmicGamer]

Why is the assumption you can't calculate mass and alter things if you are so inclined? Where do the MgT rules say you can't do so if you'd like?

Personally I don't have any interest in a game where I'd need to determine the mass of the ship, the gravity of the planet, air density, ships wind resistance, current weather and wind conditions, the orbital location of the moons and any other satellites and so on just to take off from a planet.

 

[Wil Mireu]

LISTEN carefully.

No, YOU listen for once.

So far absolutely nobody has quoted anything directly from MGT that says that is how it works. We know it's gravitic - big deal, Thruster Plates in previous editions were also gravitic, and the explanation for how they worked in those editions is absolutely nothing like how you and Locarno describe (which isn't explained in the MGT book anyway).

Exactly how the GRAVITY drive delivers that is unstated. We can only guess.

So everything you're saying is BS, since there is absolutely nothing in MGT to support your argument that it works by creating a gravity well in front of the ship. Thank you for admitting that.

If you have a better explanation that ALSO conforms to the rules in MGT lay it out. So far, no one has put out an idea that is as good or better. So, the BEST explanation is a created Grav well. That satisfies all the spacecraft performance rules in MGT.

Rubbish. I've quoted how they work in previous canon, and it's explicitly stated there. You've just pulled a method out of your arse and claimed that since MGT doesn't say anything different, your explanation must be the "best".

So I'm really not the one using "house rules" here. So stop claiming you're right and either start contributing something useful to the discussion or stay out of it.

 

[Wil Mireu]

Grav tech, Pluto pseudo propulsion plasma pulses, or whatever else.

Yeah but if one is going to make up a pretend-tech, one at least should make the effort to have it make some kind of sense. A gravity well pulling a ship along is nothing like what has been described elsewhere in Traveller's history, and it also would have effects on other objects nearby that obviously haven't existed previously.

But as I said, this whole "gravity well in front of the ship" argument seems to have been pulled out of thin air anyway and has no basis in the MGT rules.