Newbie question - Jump travel and fuel consumption.

[DPSteve]

I don't agree that it boils down to those two options. It boils down to playability vs realism.

If you want realism, then throw the whole "two weeks of fuel for the powerplant" idea out of the window - realistically, one ton of liquid hydrogen will run the power plant for years (if not decades). That being the case, the only reason you'd use hydrogen in large amounts over very short timescales must be because the Jump Drive itself requires it (to create and maintain the jump bubble for example).

There's been some discussion on the SJG boards about this: http://forums.sjgames.com/showthread.php?t=44453

Correct, which is why I made the point of balancing gameplay to realism. It works better from a gameplay standpoint to have fuel consumed at an accelerated rate. It provides situations for encounters and obstacles that a truly realistic scenario may not provide.

My point wasn't to ask for realism, it was to argue that the situation wasn't binary and was predicated more on the balance of gameplay to realism than it was anything else.

I personally don't want pure realism, but I also don't want pure fiction either. A balance is my preference, as I imagine it is for most people. The discussion arises from the differences of what I think is a good balance versus what you think is a good balance.

 

[GypsyComet]

There's been some discussion on the SJG boards about this: http://forums.sjgames.com/showthread.php?t=44453

Not to mention other fora. The question was addressed a few times on the TML even before TNE came along and dropped powerplant fuel usage by two orders of magnitude (in light of better available information on nuclear fusion than 15 years prior).

Bottom line is that its been discussed, and fixed, before. And broken again. If you have enough fuel to run the powerplant for a year, a few megawatts difference in jumpspace really drops off of the "things to care about" list.

 

[Gee4orce]

Yeah, I'm with EDG here - fusion fuel consumption rates are huge - but if you ignore them for starships, what about small craft and vehicles - suddenly you have vehicles that can operate for years without a topup.


Possible solutions:

- the endurance is more limited by consumables for life support than fuel, eg. food, water, O2 etc.

- Traveller M-drives and A/G aren't totally reactionless, and require some small amount of reaction mass to operate. This solves the problem for vehicles and small craft too, though it does mean you only need to count maneuvering time towards endurance - if you're just coasting, you get it for 'free'.

- hardwave it as being a combination of these factors :-/

 

[GypsyComet]

what about small craft and vehicles - suddenly you have vehicles that can operate for years without a topup.

While the sorts of vehicles you would normally buy as a ship subcraft could be running on fusion, I suspect a lot of smaller vehicles are not. The standard air/raft is a borderline case, being (when you get down to it) a surprisingly large utility barge/jeep that floats and is a popular starship accessory. Other types of civilian grav are more likely battery or fuel cell powered, simply on a cost basis. Flatlanders aren't going to need a MCr0.6 monstrosity all that often when the little MCr0.03 grav sedan with five hours of endurance is all they really need.

 

[EDG]

Yeah, I'm with EDG here - fusion fuel consumption rates are huge - but if you ignore them for starships, what about small craft and vehicles - suddenly you have vehicles that can operate for years without a topup.

I just say that the reactor needs monthly maintenance or things will break down, so it the ships aren't completely independent.

 

[Jeff Hopper]

A real world engineering problem that may have been skipped is the fact that the conversion of thermal energy to electrical power is never 100% efficient. Even with MHD turbines and 'magical' heat exchangers that have no loses in enthalpy, waste heat is going to occur. So if your fusion power plant is 5% efficient in converting the energy from fusing hydrogen to electrical power, you are doing pretty damn good. That alone could probably account for the excess fuel usage.

 

[EDG]

I'm no engineer, but 5% efficiency is really crappy isn't it? If you convert the energy directly to electricity (using some kind of really beefy solar-panel type thing that directly absorbs photons or whatever from the fusion reaction) then you should be able to get much higher efficiencies than that, even with our current level of technology on Earth.

The waste heat is a whole other can of worms though - Traveller ships don't have the required heat sinks/radiators, and most people just armwave it as being dumped into jump space or something (which doesn't really explain it either).

 

[Infojunky]

Yeah, I'm with EDG here - fusion fuel consumption rates are huge - but if you ignore them for starships, what about small craft and vehicles - suddenly you have vehicles that can operate for years without a topup.

I just say that the reactor needs monthly maintenance or things will break down, so it the ships aren't completely independent.

At a yard? I have a hard time with that.

As part of the normal operations cycle as preformed by the ships engineer, with the associated parts requirement, then... well at least that is how it works in my universe.

 

[Infojunky]

A real world engineering problem that may have been skipped is the fact that the conversion of thermal energy to electrical power is never 100% efficient.

Who says that Traveller Fusion reactors need to a Thermal loop to take power off of the reaction?

 

[Jeff Hopper]

A real world engineering problem that may have been skipped is the fact that the conversion of thermal energy to electrical power is never 100% efficient.

Who says that Traveller Fusion reactors need to a Thermal loop to take power off of the reaction?

I was giving a possible explanantion for the excess fuel use. If there is another way you use in YTU to convert the thermal energy of the fusing hydrogen to electrical power, then I'm all ears. The fusion plants in MTU use MHD turbines and heat exchangers in steps on a loop of the plasma but it still isn't 100% efficient.

 

[kristof65]

I'm no engineer, but 5% efficiency is really crappy isn't it? If you convert the energy directly to electricity (using some kind of really beefy solar-panel type thing that directly absorbs photons or whatever from the fusion reaction) then you should be able to get much higher efficiencies than that, even with our current level of technology on Earth.

It's probably dependant upon how you're calculating it. But 5% does sound a little low, when I know that under current tech, companies are working hard to break the 20% barrier in solar panels being able to convert sunlight to electricity.

 

[Jeff Hopper]

I'm no engineer, but 5% efficiency is really crappy isn't it? If you convert the energy directly to electricity (using some kind of really beefy solar-panel type thing that directly absorbs photons or whatever from the fusion reaction) then you should be able to get much higher efficiencies than that, even with our current level of technology on Earth.

By todays standards, 5% conversion efficiency is beyond our technology. IIRC, when I was a nuke in teh Navy, our reactors operated with a 0.03% efficiency converting the energy of nuclear fission into electrical power or propulsive power. Again IIRC, a gasoline fueled internal combustion egine is 0.0002% 0.0006% efficient at converting the gasoline combustion energy to propulsive power or electrical power.

A really beefy solar panel inside of the fusion reaction chamber would have problems similar to placing one in the photosphere of a star. I don't think it is possible to create a solar panel capable of functioning in that kind of environment with the high temperature and high magnetic field.

Now a thermocouple might possibly work, but the power created from a thermocouple is dependant on the temperature difference between its hot and cold endpoints - again creating problems with the extremes of environments there.

 

[Jeff Hopper]

I'm no engineer, but 5% efficiency is really crappy isn't it? If you convert the energy directly to electricity (using some kind of really beefy solar-panel type thing that directly absorbs photons or whatever from the fusion reaction) then you should be able to get much higher efficiencies than that, even with our current level of technology on Earth.

It's probably dependant upon how you're calculating it. But 5% does sound a little low, when I know that under current tech, companies are working hard to break the 20% barrier in solar panels being able to convert sunlight to electricity.

But what kind of electricity? Every photovoltaic solar cell known creates DC electrical power, which then must be converted in AC electrical power, which will be inefficient in the conversion. It is almost like comparing apples to oranges (not to mention that even with a 100% efficient photovoltaic solar panel,one that would create a similar power output as a fusion power plant would have an enourmous and fragile surface area which is hard to accomodate on a 1G or more thrusting starship).

The electrical plant on Navy ships that I am familiar with use 3 seperate levels of alternating current. 120 volt, 60 hertz, 3-phase AC for small power applications. 440 volt, 60 hertz, 3-phase AC for most pumps and other rotating machinery (which sometimes proved to be more efficently powered by steam than electricity). Finally there was 400 hertz, 3-phase AC (and I forgot the voltage) for radars and similar electronics (which was achieved by powering a motor-generator from the 440-volt line).

Now if you could somehow directly convert the energy of your hydrogen fusion to electrical power, you are still going to have losses while you transmit the electrical power throughout your ship along the power lines (not to mention some pretty entertaining electromagnetic effects that would create sensor 'ghosts' and interfere with communications if it was unshielded and the ship's avionics weren't programmed to account for it).

Having a fuel consumption that appears too high for the fusion power plant doesn't seem at all wrong to me. That extra hydrogen could be used as a heat sink or reaction mass for the M-Drive, or to just make up for the losses in a realistic fusion plant. Plus, its just a game, and as long as it is not using Star Trek style science then I'm OK with it (then again, I try for a balance between the science and the fiction in my science fiction). YMMV.

 

[kristof65]

By todays standards, 5% conversion efficiency is beyond our technology.

Umm, I think we're lacking a common frame of reference as far as conversion efficiency is calculated.

I distinctly recall reading an article last year that said solar panels were about 17% efficient at converting sunlight to electricity, and that companies were trying hard to break the 20% barrier. I went looking for that article today, and I can't find it, but instead, find this:

The most expensive, carefully designed, and complicated solar panels in the world operate at about 40% efficiency. That means that, for every bit of sunlight that hits the panel, only 40% of it is turned into electricity.

Scientists think that this is just about as good as silicon panels can do and are now looking at ways to make it cheaper, instead of making them more efficient.

Now, I know that solar panel efficiencies didn't suddenly double in the last year, so the other than me misremembering the first article, the only other thing I can assume is that the base calculation is different.

Still, whether solar panels are 17% or 40%, that's a lot higher than a 5% conversion efficiency. Which leads me back to thinking we don't have a common frame of reference here.

 

[Jeff Hopper]

Now, I know that solar panel efficiencies didn't suddenly double in the last year, so the other than me misremembering the first article, the only other thing I can assume is that the base calculation is different.

Still, whether solar panels are 17% or 40%, that's a lot higher than a 5% conversion efficiency. Which leads me back to thinking we don't have a common frame of reference here.

I'm talking heat engine conversion efficiencies, which is probably the source of confusion. There is also the problem of the type of electricity created, which is DC for photovoltaic solar cells - which then has to be converted to AC for most electrical power applications.

 

[Pyromancer]

I'm talking heat engine conversion efficiencies, which is probably the source of confusion.

Even really simple heat engines have efficiencies in the double digits.
What you are probably refering to is the matter-to-energy-conversion. 0.0something% for modern nuclear fisson seems the right order of magnitude.

 

[kristof65]

Even really simple heat engines have efficiencies in the double digits.
What you are probably refering to is the matter-to-energy-conversion. 0.0something% for modern nuclear fisson seems the right order of magnitude.

That makes more sense, since solar cells are basically converting heat to electricity.

 

[Infojunky]

A real world engineering problem that may have been skipped is the fact that the conversion of thermal energy to electrical power is never 100% efficient.

Who says that Traveller Fusion reactors need to a Thermal loop to take power off of the reaction?

I was giving a possible explanantion for the excess fuel use.

Cool. Just looking for base assumptions, a lot of

If there is another way you use in YTU to convert the thermal energy of the fusing hydrogen to electrical power, then I'm all ears. The fusion plants in MTU use MHD turbines and heat exchangers in steps on a loop of the plasma but it still isn't 100% efficient.

There a couple of ideas out the about using the electron flux from the chamber as the power take-off. Which might be just playing around with ideas, but I tend to run a solid state sorta universe so I try to keep my techno-babble within that for at least the internals of things like Power plants.

As a side question for the general populace, is fusion power the densest power source in your universe? Or do other high energy sources exist?

 

[EDG]

That makes more sense, since solar cells are basically converting heat to electricity.

You mean light to electricity, surely?

 

[kristof65]

That makes more sense, since solar cells are basically converting heat to electricity.

You mean light to electricity, surely?

Yes, I did. That's my mind playing tricks on me when I answered too quickly, because for some reason I'm stuck on Infrared=heat, when in fact it's just another frequency spectrum of light. Since most solar cells operate in the infrared spectrum...well, you get the idea.