TNE HePlaR - Efficient???

[ColHut]

I would only add that a high ISP by itself does not equate to high acceleration. Just how many pounds of thrust a pound of propellant(s) will produce. Most of the High Isp stuff have motors producing very small acceleration which might be useful overlong periods outside gravity wells but that's about all. I guess if you need gravitics to make rockets work effficiently enough why not go the whole hog?

regards

 

[ColHut]

Ummm, 1 displacement ton has a mass of 1 ton - the density is irrelevant, so you don't need to multiply the impulse by 10 to get the same result.

So an average density of 70Kg per cubic metre...
including AV 14 BSD Hull and structural support. Thus TNE tried to include some mass calculations. It does all start to get a bit complicated at that point though.

regards

 

[Rikki Tikki Traveller]

Yep, that is why I just assumed that future spaceships were ABOUT the same density as the Space Shuttle.

The Space Shuttle has a density of about 8 tons per Dton, so using a number between 5 and 10 tons per Dton is probably "good enough" for a game.

Yes, you could assign density values to each component and then calculate a final density and get a final mass, and TNE does that. But personally, I think that is too much detail. I would rather use a reasonable number and move on.

 

[rinku]

I'm with Felonmarmer - the tonnage rating should be considered to be the mass, and any calculation of volume (usually using the 14 cubic metre per ton assumption) comes later. Mass and thrust are all that matters in free space, though surface area and density become very important when atmospheric operations are considered.

 

[simonh]

I'm with Felonmarmer - the tonnage rating should be considered to be the mass, and any calculation of volume (usually using the 14 cubic metre per ton assumption) comes later. Mass and thrust are all that matters in free space, though surface area and density become very important when atmospheric operations are considered.

For better or worse the Traveller Core Rulebook is quite explicit about this. The tons used in the design system are Displacement Tons which are a measure of volume, not mass.

Simon Hibbs

 

[rust]

For better or worse the Traveller Core Rulebook is quite explicit about this. The tons used in the design system are Displacement Tons which are a measure of volume, not mass.

By the way, this could also be one of those Age of Sail things in Traveller,
because the original "tun" (the predecessor of the "ton") was indeed a
measure of volume (a barrel holding 256 gallons, usually of wine) used
in sea trade.

 

[captainjack23]

For better or worse the Traveller Core Rulebook is quite explicit about this. The tons used in the design system are Displacement Tons which are a measure of volume, not mass.

By the way, this could also be one of those Age of Sail things in Traveller,
because the original "tun" (the predecessor of the "ton") was indeed a
measure of volume (a barrel holding 256 gallons, usually of wine) used
in sea trade.

Ding ! yes, thats so.

Now as to traveller......so, see, part of the way hyperspace works is that only volume is relevant, mass doesn't exist as a physical constraint, plus ability to exist in hyperspace is based on a quantized value...ie it goes up in jumps, not gradually.

So.....with the most important part of ship design (FTL travel) being mass independent, it has become much more convenient to measure ships by volume rather than mass, which while an issue in real space, is generally trivial considering the efficiency and power of the M drive.

Hows that ?

(I note that the above is entirely speculative fluff and not directly stated anywhere in The Real Rules)

 

[rust]

So.....with the most important part of ship design (FTL travel) being mass independent, it has become much more convenient to measure ships by volume rather than mass, which while an issue in real space, is generally trivial considering the efficiency and power of the M drive.

Hows that ?

Good.

Besides, despite what pilots, engineers and gunners may believe, the only
really important part of a ship is the cargo, which pays for the entire ope-
ration and creates wealth for its owner.

And the only way to reliably measure the "size" of the cargo in a universe
full of planets with different surface gravities, orbital starports and indus-
tries and thelike is the volume of the cargo - an attempt to use the mass
instead of the volume would be the way into howling madness.

 

[rinku]

And the only way to reliably measure the "size" of the cargo in a universe
full of planets with different surface gravities, orbital starports and indus-
tries and thelike is the volume of the cargo - an attempt to use the mass
instead of the volume would be the way into howling madness.

Err... you're confusing "mass" with "weight". Mass is invariant. Even if gravitic tech is being used to shift it and the weight being changed, the energy required to do work on a given mass should be the same.

The problem here is that you're thinking in oceanic shipping terms, where volume is much more important than mass.

Shipping stuff through space is more akin to air freight, where mass is more important than volume.

Traveller simplifies the mass/volume realtionship for ease of play, but in terms of lifting cargo off a planet, pushing it through space and landing it it IS the mass that matters most, just as it is for an airliner.

If a starship's cargo is overloaded (exceeding its rated mass), its thrust performance (and probably jump performance) should suffer.

 

[rust]

Err... you're confusing "mass" with "weight".

Oops ...

My only lame excuse is that I was thinking from the cargo owner's point
of view, who usually cannot measure mass directly, only weight. And the
weight of the same cargo would be widely different, depending on where
it is, making interstellar trade more difficult than using volume as the
measure.

 

[BP]

...
Shipping stuff through space is more akin to air freight, where mass is more important than volume.

Traveller simplifies the mass/volume realtionship for ease of play, but in terms of lifting cargo off a planet, pushing it through space and landing it it IS the mass that matters most, just as it is for an airliner.

If a starship's cargo is overloaded (exceeding its rated mass), its thrust performance (and probably jump performance) should suffer.

Most definitely, mass is of greater importance than volume when talking space travel.

Realistically.

But, gravitics based Traveller bypasses this reality and makes volume the limiting factor - with 'Thrust' given in acceleration, not force.

 

[Rikki Tikki Traveller]

UNLESS you postulate that gravitics works by reducing the mass of an object! Then mass becomes variable and Volume becomes your constant.

Another way to look at it is that Gravitics affects a volume of space; moving everything within it, regardless of mass. Combine that with the Captain's explanation of jumpspace and you have both an FTL and a sublight drive that are not dependent on mass, so volume becomes your scaling factor.

UNFORTUNATELY, that doesn't work if you want to use HePlaR... You need to know the MASS since you are using a conventional reaction-thrust propulsion system. For this drive, you have to figure out the mass of the ship. MANY ways to do that, taking a swag (Scientific Wild Ass Guess) is good enough for me and FF&S is out there for those masochists that have to do it the hard way...

 

[captainjack23]

No, not that Kiss.

Oh Geeeze. "Kiss alive 75 2005" . I think I suffered a mental misjump........


All else I'd add is that that kind of math can be fun, but only if the designer likes it; my experience (and I like math) is that the main impact on play of tracking more factors is that there are less ships to use in actual play -becuase they take too much time and are fiddly to customize...

Player: oh look. Another "x hundred ton fill in the blank"; don't traders ever use anything different ?
GM: asteroids fall. Everyone dies.

 

[BP]

For me, there are no 'realistic' solutions that meet Traveller's space mechanics. Without a totally fictional means like gravitics, the other 'real-world' approaches require even more outrageous fiction. When it comes to distances and time - the power and efficiencies for thrust become improbably un-realistic (like the examples used here for HePlaR). This compounds the lack of believability for me.

Since mass invariably becomes involved - things get even less believable - and more arbitrary. Consider, that mass depends on the density of a material which can range from aerogels to Osmium 'realistically' - and from sub-quark superstrings to collapsed matter (and beyond) on the fictional side. Given the realworld range of densities possible, SWAG doesn't even begin to cut it.

One just ends up building fiction upon fiction based on 'realworld' data. 'Hard science-fiction' just can't meet the needs of star faring or even solar system adventure, without slowed down aging/superbodies and other aspects that just aren't Traveller.

Me, I prefer the Clarke method - 'Any sufficiently advanced technology is indistinguishable from magic.' (Gravitics and Jump being Traveller's magic, IMHO!)

 

[rinku]

Well, my perspective is that Classic Trav always did deal in mass. The volume angle only comes up because people want to know "how big is my spaceship?" and draw deckplans. Later versions got sidetracked with the volume issue, but there was never any real reason to rate ships and their components in terms other than mass.

 

[rust]

Well, my perspective is that Classic Trav always did deal in mass.

All Classic Traveller ship designs I know mention the volume of the ship
as its most important data, but I am not aware of even a single Classic
Traveller ship design that mentioned its mass ?

 

[BP]

CT explicitly defined spaceship design in terms of mass displacement, i.e. dtons. The mass was never used anywhere.

 

[captainjack23]

CT explicitly defined spaceship design in terms of mass displacement, i.e. dtons. The mass was never used anywhere.

Correct. Even the trade rules were in displacement measured lots.

 

[BP]

Thanks - though I somehow edited out the 'IIRC' bit and I should never use never when spouting such things

CT did have a lot of stuff published for it - but, the gist of the post still should stand.

 

[rinku]

Well, I'll admit defeat. Sort of.

Book 1 (1977 1st edition) does rate everything in displacement tons... but no definition is given. It was impossible from the original 1977 rules to determine the volume of your ship.

The 1981 2nd edition is the first place that defines what a displacement ton is: "As a rough guide, one ton equals 14 cubic meters (the volume of one ton of liquid hydrogen)". This also states that when drawing up deckplans that a leeway of plus or minus 20% is acceptable.

Given that there is an acceptable variation in volume for a displacement ton is between about 12 to about 16 cubic metres, I'll stand by my opinion that the real rated mass is assumed to be the same as the displacement tonnage.