Starship Design and Drive Efficiency

[robject]

Efficiency is one of the most powerful elements of QREBS when selecting the powerplant, maneuver drive, and jump drive. It has facets that require thinking about and talking over. I'm going to try to write it down here.

Whenever you depart from the standard drives, and instead select something special along the research spectrum, you enter into quality differences. Some qualities are random. Efficiency, however, is not -- it is baked into the drive's stage. Coupled with the effect stage has on price, things can get complicated, so hang on.

Cost. Stage affects the cost of a drive.
Fuel. Stage affects fuel use.
Rating. Stage affects the rating of the drive itself via Efficiency.


Reference: page 338, "Drive Tech Level Efficiency", and page 500, "Variant Tonnages Using Tech Level Stage Effects".

THE STANDARD DRIVE

For example, let's take a 500 ton hull and put a Jump Drive K in it. The drive potential table (p.340) gives us Jump-4, and the drive table (p.338) says it's 55 tons, MCr1 per ton. Finally, we know that fuel usage is 10% hull per jump rating, which is 40% hull volume for Jump-4.

Hull: 500t.  Jump Drive K: J4, 55 tons, MCr55, fuel = 200 tons.

Fine. That's for the standard drive, and we're done. Walk away.


THE NON-STANDARD DRIVE

Oh, but wait, maybe you feel like tinkering with things. Can't leave it alone, eh? Fine, let's work thru a Stage Effect.

Being an Evil referee, you decide the drive is a Prototype, and hand its stats over to the players. Glancing at the table on p.500, you see that Prototype is Volume x 2, so that's 110 tons. Then from the table on p.338, you see that the cost is x 5, so that's MCr 5 per ton, or MCr 550.

That table also tells you that Efficiency is 80%, and Fuel is x1.2. Let's do those one at a time, Efficiency first.

Efficiency tells us what our actual drive performance is. To calculate it, multiply the rating we looked up in the drive potential table -- that's a 4 -- times the Efficiency, which is 80% or 0.8. The result is 3.2, and since we drop fractions, the result is 3.

This drive is only a Jump-3 drive.

If that's not bad enough, fuel consumption is also based on the rating in the drive potential table. As we know, fuel is 10% hull volume per jump number, and rating 4 jump drives need 40% of the hull volume for fuel. But now we multiply that rating by the Fuel multiple, which is 1.2. The result is 48%. So the drive requires more fuel than normal.

So the stats for our hull with a Prototype jump drive are:

Hull: 500t.  Prototype Jump Drive K: J3, 110 tons, MCr 550, fuel = 240 tons.

 

[atpollard]

Why would the drop in rating to 3.2 (rounded to 3), not change the standard fuel required to 30% ?

... which is then multiplied by 1.2 for a final Jump 3 fuel requirement of 36%.

 

[robject]

Why would the drop in rating to 3.2 (rounded to 3), not change the standard fuel required to 30% ?

... which is then multiplied by 1.2 for a final Jump 3 fuel requirement of 36%.

Both are treated independently; that is, both are calculated from the number in the Drive Potential Table.

But now you're going to ask me where that is in the book.

The Drive Potential Table provides performance for Standard (Base TL) drives and power systems. TL Stages alter Design Dive Potential to Usable Drive Potential.

and

Fuel requirements are based on Design Drive Potential regardless of the Usable Drive Potential.

Page 322 then provides this example:

For example, a Standard Drive-K in a 1000-ton Hull-K requires shows Design Drive Potential =2. Jump Drive-K could achieve Jump-2; Maneuver Drive-K can achieve 2G. Power Plant-K outputs Potential-2.

An Experimental Jump Drive-K shows 50% efficiency= Usable Drive Potential=1. It also shows Fuel Requirement 2.0 based on Design Drive Potential (= 2 x 2.0) = 4.

The Drive requires 4 units of fuel for every 2 units of fuel the Standard model requires, and the Usable Drive Potential is halved.

Standard Power Plant-K in Hull=D shows Design Drive Potential-5. Advanced Power Plant-K in Hull-D is 120% efficient and produces Usable Drive Potential-6. It requires 4 units of fuel as opposed to the Standard Power Plant’s 5.

 

[atpollard]

Thank you for the clarification.
I think that I will pass on T5 prototype drives.

[Since a Prototype J4 drive has the only J3 performance, is there any reason for a prototype to exist except as proof of concept for R&D?
In this specific case, the designer would obviously go with a standard J3 drive rather than a J4 Prototype with J3 performance.
Are all Prototype jump drives going to be pointless?]

(Confession, I don't own T5 ... it is on my to-do list, but I was waiting for the second edition CD. So these questions are just general curiosity.)

 

[SpaceBadger]

(Confession, I don't own T5 ... it is on my to-do list, but I was waiting for the second edition CD. So these questions are just general curiosity.)

Just as an aside, that was my plan, too, until Marc Miller told me that purchasers of the T5 CD now would receive free updates when errata is incorporated to update the CD. Now I have it waiting for me in my PO Box in town, and can hardly wait to check out the ship design stuff that I have been reading in Rob's ship posts.

 

[robject]

[Since a Prototype J4 drive has the only J3 performance, is there any reason for a prototype to exist except as proof of concept for R&D?

That is exactly the question to be asking.

Summary: Efficiency is not a candy store, and so stage effects are best used in edge cases only. This is a good thing, IMHO.

I'll say it more strongly:

Standard starships will not be using (most) stage effects with their drives. This is by design, and a good thing.

The reason it's a good thing is because stage effects can otherwise trump standard drives, and therefore must have tradeoffs to keep them non-standard. Efficiency restores balance to the universe.

Efficiency implicitly prevents "beyond your TL" performance ratings at any given tech level. Imperial R&D can have a Prototype TL17 Jump Drive theoretically rated at Jump 8, but it won't do better than Jump 6. And it has quality problems, to boot. This is to be expected and is by design. I, too, would pass on a Prototype Jump Drive unless that was all I had available and had to leave the system in a hurry. And I would be cursing the drive the whole time. In short, it's a good plot device, but I won't design a fleet around it. As expected with R&D projects.

The exception to this rule is in interplanetary drives. Here it is possible, for example, to have a TL10 culture that develops a Prototype TL12 Maneuver Drive that has a greater acceleration than standard. They're still going to have quality problems, and engineers will curse the prototypes, and fleets won't be designed around them, but they are still potentially useful.

To a lesser degree, Efficiency provides bonuses to older but high-rating technologies. An Xboat with an Ultimate Jump Drive B (buildable at TL17) can move at 5 parsecs per jump, for example.

 

[dalthor]

Probable errata item on this, and I'll use a generic drive as an example.

Generic drives are at 90% efficiency, and half the cost. This means there ain't no functional generic Jump-1 drive, by the standards discussed above.

I'd be inclined to allow it to make jump-1, but the tonnage it could MOVE would be reduced to 90% of the baseline. For example, a generic drive in a 100-ton hull would fail if the load exceeded 90 tons.

Of course, this is hard to enforce, since mass and volume are not truly segregated in T5. I'd adjust the cargo capacity in a case like this.

Either that, or allow minimum of Jump-1 for any viable drive.

"Grooowwwffff....shtill too heavy...tosh out dem Argulian mosh shamples, godda lighten de load!"


Am I firing blanks here, or is this food for errata and suggestion??

 

[atpollard]

Am I firing blanks here, or is this food for errata and suggestion??

No, I think that tossing out the 'Argulian mosh shamples' is the right move. :rofl:

 

[Spartan159]

Multiply Jump 1 drives by 1.11 rounding up to get the size you need then hit it with the .9 efficiency?

 

[whulorigan]

Standard starships will not be using (most) stage effects with their drives. This is by design, and a good thing.

The reason it's a good thing is because stage effects can otherwise trump standard drives, and therefore must have tradeoffs to keep them non-standard. Efficiency restores balance to the universe.

Probable errata item on this, and I'll use a generic drive as an example.

Generic drives are at 90% efficiency, and half the cost. This means there ain't no functional generic Jump-1 drive, by the standards discussed above.

I'd be inclined to allow it to make jump-1, but the tonnage it could MOVE would be reduced to 90% of the baseline. For example, a generic drive in a 100-ton hull would fail if the load exceeded 90 tons.

I think I would nuance it a little more.

For Below Standard TL:

EXPERIMENTAL Drives (and perhaps PROTOTYPE as well) would be found nowhere except at an Imperial (or Megacorporate) Research Station.

EARLY Drives would be found in limited use in the military/government for specialized purposes.


For Above Standard TL (IMPROVED thru ULTIMATE):

I would think what was produced at a given shipyard would be dependent upon the particular economic factors and cultural details of the world.

Typically one would expect the Shipyard to be able to produce the STANDARD or GENERIC version of the drive (which is cheaper). A poor economy might instead produce the BASIC version of the Drive.

An economic powerhouse or industrial center might produce the more efficient drives (IMPROVED thru ULTIMATE) as a standard option over STANDARD / GENERIC.


The above would not be limited to drives, but to all technology.

 

[robject]

Probable errata item on this, and I'll use a generic drive as an example.

Generic drives are at 90% efficiency, and half the cost. This means there ain't no functional generic Jump-1 drive, by the standards discussed above.
[...]
Am I firing blanks here, or is this food for errata and suggestion??

Think of it in terms of drive letter + hull, rather than potential. So a Jump Drive B is good for Jump-2 in a Beowulf, right? But, a Generic Jump Drive B is only good for Jump-1 in the Beowulf hull.

That is still an errata item, though. "Generic" doesn't show up in the Efficiency table on page 322, but it is in the one on page 338. There's an erratum.

 

[dalthor]

Think of it in terms of drive letter + hull, rather than potential. So a Jump Drive B is good for Jump-2 in a Beowulf, right? But, a Generic Jump Drive B is only good for Jump-1 in the Beowulf hull.

Thanks, fella. The original thought was good, I didn't follow it far enough.

Configuration matters.

That's what I get for doing this while distracted by the real world.

Also, to get REALLY picky, on page 322, under the Drive Efficiency section, in the Usable Drive Potential paragraph, it states

TL Stages alter Design Dive Potential to Usable Drive Potential.

 

[FrackinA]

Don't have a copy of T5, but I have some of the previous versions. Saw the heading on drive efficiency and was intrigued because Traveller seems to disregard basic science in coming up with power sources.

Classic Traveller kept this out of sight by not nailing down how much power was involved, until Striker came along and MegaTraveller pegged 1 ship energy point to 250 MW and then everything made no sense.

Okay, there were problems before. The robot rules based on hydrogen fuel cells (okay, hydrogen is the universal fuel and fuel skimming/refining is important to the universe - but can we think about how this works?) made little sense.

Fuel efficiency increases by fuel cell size (okay) but how does this key into the energy of the chemical reaction. Because current (TL 8 ) hydrogen fuel cells are about 75% efficient (meaning that 75% of the available energy is harvested and turned into working energy. But at TL 15, according to the rules, energy output for the same fuel consumption was trippled. hmm. they managed to figure out a way to get 225% of the energy from the chemical reaction. Well, we really didn't need that second law of thermodynamics anyway.

But I liked hydrogen fuel cells. A readily available fuel source for frontier refueling - but the technology matures at some point where you can perhaps make the fuel cell smaller and smaller but the fuel requirement just wouldn't change because there is only so much electricity you can get from combining hydrogen and oxygen. And it takes even more electricity to separate them again so you can have replacement hydrogen fuel. But that last part is irrelevant with fusion power as you have plenty of electricity to separate the atoms with electrolysis.

Lots of power from fusion power plants, but that is the problem. Too much. Because Traveller power plants went the wrong way - being way too inefficient. If 1 ship energy point is just 250 MWh (250 Megawatts produced continuously over the course of a period of time, such as an hour) then how much fuel is needed?

I can see that fusion of hydrogen atoms into helium (4 hydrogen atoms into one helium atom, which can then be fused with more hydrogen) could work reasonably well (not the easiest combination -but frontier refuelling is essential and supplies of deuterium and tritium aren't readily available).

But the energy from this reaction is horrendous. Really freaking big. By a rough estimate, 1 ton of hydrogen fuel should be able to keep the fusion power plant of a Scout ship, producing 500 MW continuously for about 4 years. The fuel consumption on Traveller power plants was set so high that either the harvesting of useable power from the reaction is very poor (in which case the most important component on a starship should be a large set of radiating wings turning heat energy into some continuous electromagnetic emissions from the ship to get shed heat before the ship melts (forget about stealth and black globe generators, you can't stop the emissions for long without baking your ship).

Maybe someone else has a better source on energy from a fusion reaction but 1000 Megawatts being generated for an entire year off 250 kg of fuel was what one of my sources indicated (not starting with hydrogen so I doubled the fuel mass in the equation above (though that may be unnecessary since the fusing of hydrogen produces energy on its own.)

Jump drives are fine because it is fantasy technology, they can handle and use however much fuel the game designer chooses. But if you are going to define energy in real world terms, a KW is a KW and a MW is a MW.

Does T5 fix this, or is it a choice of going with science or going with the rules?

 

[whulorigan]

But the energy from this reaction is horrendous. Really freaking big. By a rough estimate, 1 ton of hydrogen fuel should be able to keep the fusion power plant of a Scout ship, producing 500 MW continuously for about 4 years. The fuel consumption on Traveller power plants was set so high that either the harvesting of useable power from the reaction is very poor (in which case the most important component on a starship should be a large set of radiating wings turning heat energy into some continuous electromagnetic emissions from the ship to get shed heat before the ship melts (forget about stealth and black globe generators, you can't stop the emissions for long without baking your ship).

Maybe someone else has a better source on energy from a fusion reaction but 1000 Megawatts being generated for an entire year off 250 kg of fuel was what one of my sources indicated (not starting with hydrogen so I doubled the fuel mass in the equation above (though that may be unnecessary since the fusing of hydrogen produces energy on its own.).
.
.
.
Does T5 fix this, or is it a choice of going with science or going with the rules?

Both TNE and T4 adjusted the fuel consumption of Fusion plants to more realistic levels (rating them in kL per year).

T5 implies that ground-based Fusion Plants have realistic fuel consumption (dtons/year), but that in order to miniaturize the plant and still produce sufficient power for J-Drives and M-Drive, the Power Plant in question has the ability to "overclock", generating massive power in short time periods, but with the consequence that the P-Plant is always very fuel-inefficient, and thus consumes LHyd fuel at rates comparable to CT for starship-sized power plants.

However, stage-efficiency considerations modify these rates somewhat, based on P-Plant TL.

 

[FrackinA]

Interesting. I'll have to hunt for a copy of either to check this out.

The inefficient power plant, while explaining a higher fuel requirement, would seem to present other problems. The reaction is the reaction, whatever reactor it happens in. If the reactor is inefficient, this would mean capturing a smaller portion of the energy generated, so what happens to the rest of the energy generated?

Excess heat loss? That would be dangerous in a space craft as you would need a way to safely lose that heat into surrounding space? How? Venting plasma? How would you deal with the heat if operating on a planet's surface? I would expect most planets would frown on starships venting radioactive plasma.

For inefficiency of scaling down a fusion power plant it would be better to just put lower limits on how small a fusion drive can get.

 

[whulorigan]

Interesting. I'll have to hunt for a copy of either to check this out.

The inefficient power plant, while explaining a higher fuel requirement, would seem to present other problems. The reaction is the reaction, whatever reactor it happens in. If the reactor is inefficient, this would mean capturing a smaller portion of the energy generated, so what happens to the rest of the energy generated?

Excess heat loss? That would be dangerous in a space craft as you would need a way to safely lose that heat into surrounding space? How? Venting plasma? How would you deal with the heat if operating on a planet's surface? I would expect most planets would frown on starships venting radioactive plasma.

For inefficiency of scaling down a fusion power plant it would be better to just put lower limits on how small a fusion drive can get.

I personally prefer the house rule that overclock only comes into play when operating those drives that require the excess power (J-Drives and possibly M-Drives). Otherwise, the P-Plant consumes fuel at the low "kL per Year" rate.

In fact, you could argue that the T5 fuel rates are simply an average, if you include M-Drives as high-power components, since we do not typically calculate fuel usage when the M-Drive is operating versus when it is not.

 

[FrackinA]

I never liked the idea that regular power plants produce obscene amounts of power for the jump drive but cannot be overclocked to power maneuver drives at full along with a whole set of beam lasers.

Not wanting to mess with the balance of ship designs everyone was already using and familiar with, IMU the power plant did not power the jump drive. The jump drive was one big reaction chamber surrounded by a network of zuchai crystals and heat conductors. The power plant with a rating equivalent to the jump is needed to kickstart the system and maintain containment but the charging of the capacitors is purely from the reaction going on inside the jump drive.

I also interpreted the "lanthanum coil" to be a network of lanthanum embedded in the hull of the ship - it needing to be on the outside of the ship to define the jump bubble that protects the ship from jumpspace.

This made doing an emergency jump with hull damage a risky prospect as you wonder how much of your ship just won't make it into the jump bubble.

I just shook my head at the whole jump torpedo-autopilot jump debates where people envisioned a cruiser sized ship accelerated up to a significant fraction of light-speed and then jumped to another system to collide with a planet. The vacuum of space is not empty (a few million atoms per cubic meter, mostly hydrogen) and the collision with matter involves exponentially greater kinetic energy as velocity increases. Before a ship can get up to even .05 light speed (about 3 days constant acceleration at 6G) it will have to deal with the cumulative impact of these atoms. Not that the collisions are necessarily penetrating bonded superdense armor, but they still impart heat which won't be dissipating faster than it accumulates. At some point the robot kinetic kill vehicle tries to jump with the lanthanum coils boiled off the hull. Nasty.

Okay, it is possible to put maneuver drives on a really big asteroid which can clear a path with the kinetic kill vehicle accelerating in its wake. but this is just getting more expensive. But even if the genocidal inclined government can get this kinetic kill cruiser accelerated up to a horrifying speed and get it to jump..... well jump drives are precise (within 5,000 km plotted destination) in relation to the star system, but arrival time is plus/minus an hour. Trying to hit Earth, with it's 12,700 km diameter.? If you plot for the center your +/- 5,000 km radius of emergence will overlap the planet's position IFF you arrive within 3.5 minutes of the 1 week You have to arrive +/- 3 minutes of the 168 hour jump time, and even then there is a greater than 50% chance of missing. Of course the range of arrival time is +/- 60 minutes so that hyper-expensive cruiser you intend to jump in and hit the planet at high velocity will only hit 2% of the time.

As for jump torpedoes, I accepted them for purposes of jumping out a black box (shielded communications beacon to transmit a distress call with some detail/video/audio) that can survive the jump while pretty much nothing else of the torpedo does because you can't make a stable jump field at less than 100 tons. GMing the old Leviathan adventure I explained it to players as a 100 kg missile (would have liked it to be larger like the torpedoes in Mongoose Traveller) which consisted of a 2 kg black box surrounded by (expensive) 10 kg of lanthanum shielding with 88 kg of Jump 4 drive. In a typical jump the outer lanthanum coil survives long enough to execute the jump after which the jump drive is lost into jumpspace (before it completely overheats and melts the rest of the missile - ingenious design). Much of the shielding on the black box is boiled away but it only needs to survive the one jump. The black box itself is recyclable but it is actually the least expensive component in the missile.

Want to try this trick to put jump drives on a 10 ton fighter, well after adding 40 tons of shielding and perhaps 5-10 tons of jump drive to make a one-use jump drive it seems to make more sense to add another 40 tons of fuel and make a stable 100 ton starship that can jump multiple times that is capable of launching a fighter as a "ship's boat". I liked that Traveller established rules for what would commonly be encountered but allowed variations in technology such as Annic Nova and the jump torpedoes in Leviathan that worked outside of normal parameters - just less effective than the standard equipment. I did some of this myself, such as laser rifles that did 16dice damage but burned themselves out after 5 shots (disposable weapons used by TL 10 forces against enemies in battle dress).

 

[whulorigan]

Ganged Maneuver-Drives

I had a thought while looking over Robject's ship-designs ported over to T5. Since we now have the ability to make "ganged" drives under the T5 ruleset, why not (when installing maneuver-drives) make the number of individual drive-units used equal the number of drive units shown in the standard illustration of the ship?

For example, both the Patrol Corvette and Yacht are typically portrayed as having two thrust-nozzles/thruster plates. Why not install a ganged x2 maneuver drive that meets the maneuver specifications of the class, instead of a single maneuver drive?

So if a given design requires a 400EP drive for its maneuver engines, but is depicted in artwork as having two maneuver engines, instead of giving it a single D-Drive, give it a B2-Drive (or if depicted with 4 engines, give it an A4-Drive, or a 2A2-drive [i.e. an A2 on the Port side and an A2 on the Starboard side]).

That would nicely showcase the new ganged-drive rules in T5.

 

[robject]

Since we now have the ability to make "ganged" drives under the T5 ruleset, why not (when installing maneuver-drives) make the number of individual drive-units used equal the number of drive units shown in the standard illustration of the ship?

For example, both the Patrol Corvette and Yacht are typically portrayed as having two thrust-nozzles/thruster plates. Why not install a ganged x2 maneuver drive that meets the maneuver specifications of the class, instead of a single maneuver drive?

I think I've said something along these lines to Marc: "CT deckplans quite often show the maneuver drive split in two (or more) locations; that indicates a possible grouped drive configuration to me".