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Post by spacemancraig on Mar 13, 2019 18:24:57 GMT
Can someone help me understand why the lasers in game are so inefficient? According to a presentation by theAmerican Society of Naval Engineers (http://apps.dtic.mil/dtic/tr/fulltext/u2/a582998.pdf) and other sources I've skimmed, proposed military laser technology could have the below efficiencies
- Free Electron Lasers are supposedly 10% - Fiber lasers are potentially 30% - Solid state slab lasers potentially 20%
Yet the lasers in game seem to have efficiencies of around 3% to 5%. Does the game take into account factors that the ASNE presentation doesn't?
Please be kind, I'm new to the game and am a functional moron when it comes to science. I just want to build spaceships and blow stuff up
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Post by bigbombr on Mar 13, 2019 19:09:24 GMT
Can someone help me understand why the lasers in game are so inefficient? According to a presentation by theAmerican Society of Naval Engineers (http://apps.dtic.mil/dtic/tr/fulltext/u2/a582998.pdf) and other sources I've skimmed, proposed military laser technology could have the below efficiencies - Free Electron Lasers are supposedly 10% - Fiber lasers are potentially 30% - Solid state slab lasers potentially 20% Yet the lasers in game seem to have efficiencies of around 3% to 5%. Does the game take into account factors that the ASNE presentation doesn't? Please be kind, I'm new to the game and am a functional moron when it comes to science. I just want to build spaceships and blow stuff up The game deviates from reality in more than a few ways, because the math/models/information is flawed. Combustion rockets, lasers and conventional cannons underperform compared to their real life counterparts, while resistojets achieve efficiencies in excess of 10 000%. With materials from the community materials mod pack, 40+% efficient lasers are possible.
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Post by AtomHeartDragon on Mar 13, 2019 19:48:25 GMT
To play devil's advocate, I'm not sure how well would those super efficient lasers scale to very high powers and operating temperatures we have in CDE.
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Post by dragon on Mar 14, 2019 17:21:15 GMT
What we have in game are solid state lasers operating at a very high temperature. It's not an error in the model (the author is a physicist whose expertise involves lasers), but rather a consequence of what we're doing with them. We're also not able to use any of the precision-tuning and other tricks used to get high-efficiency lasers, but IMO it's OK, given the lore. TBH, if anything, the game underestimates the problems with actually constructing lasers and optics of the physical dimensions we're working with in game.
While we're at it, conventional cannons don't really underperform, as far as I've seen (though again, we're limited in design options for them). I was even able to replicate Yamato's naval gun pretty closely, given the stock materials available. The only thing that didn't work out was the turret. The real model issues are found in coilguns.
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Post by spacemancraig on Mar 14, 2019 17:23:25 GMT
THank you all for the feedback. My computer is old and overheats so until I get a new one, I'm limited in the amount of time I can spend tinkering and learning.
My ultimate goal is to eventually design ships that exist in an alternate near future alternate history where US and Soviets expanded into space, with their own unique combat doctrines, so the technology and ships would need to be within parameters of what we could maybe achieve by 2050, assuming space race never ended in the 1970s.
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Post by L5Resident on Apr 18, 2019 9:05:20 GMT
What we have in game are solid state lasers operating at a very high temperature. It's not an error in the model (the author is a physicist whose expertise involves lasers), but rather a consequence of what we're doing with them. We're also not able to use any of the precision-tuning and other tricks used to get high-efficiency lasers, but IMO it's OK, given the lore. TBH, if anything, the game underestimates the problems with actually constructing lasers and optics of the physical dimensions we're working with in game. While we're at it, conventional cannons don't really underperform, as far as I've seen (though again, we're limited in design options for them). I was even able to replicate Yamato's naval gun pretty closely, given the stock materials available. The only thing that didn't work out was the turret. The real model issues are found in coilguns. Well the “Solid state” lasers are crude arc lamp pumped lasers compared to the diode pumped/fiber lasers. Having sub 5-10% efficiency lasers is kind of Silly IMO when the current lasers used as directed energy weapons have a demonstrated minimum efficiency of 30%.
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Post by dragon on Apr 18, 2019 21:38:47 GMT
I'm not sure if a diode or fiber laser could handle 1100 degrees or more. Arc lamps are crude, but robust. Remember, if you can get a high output temperature at the price of thermodynamic efficiency, the overall system tends to end up lighter, due to radiators being by far the most massive component (higher temp, smaller radiator). Current military lasers don't run nearly as hot as COADE's, because cooling is far less of an issue in atmosphere.
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Post by AtomHeartDragon on Apr 20, 2019 10:21:29 GMT
I'm going to give qswitched benefit of doubt on this one. He seems highly knowledgable in this area and lasers operating in the atmosphere can afford much lower operating temperatures due to not having to be radiation cooled. Do mind that: - Semiconductors generally don't like high operating temperatures due to thermal runaway (which is a one time off failure mode)
- Thermodynamics seems to be working against high temperature lasers in terms of efficiency
- High temperature lasers are going to suffer additional beam quality issues
Given two 4MW (output) lasers, one 4% efficient and the other 40%, I would rather be dumping tens of megawatts waste heat at several thousand K than megawatts at several hundred K.
Also, COADE lasers seem to perform unreasonably well in terms of frequency doubling and quadrupling, and generally don't work like pure CW lasers due to lack of threshold below which armour simply re-radiates everything without ablation and laser does nothing, so it's not like qswitched erred everywhere towards the side of "lasers suck".
Anyway, so far lasers, at least of non-strategic kind (as in vast, orbit- or surface-bound arrays that aren't going anywhere), seem to be beaten by missile swarms and dakkaistic kinetics (which suffer their own issues in regards to feasibility of extreme velocity guns and destructive power of low calibre sandblasters against realistic modules) as primary weapons. It's still a good idea to pack a bunch as one of PD layers and for precision strikes, of course.
We really need particle beams and radiation damage model in game.
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Post by airc777 on Apr 20, 2019 15:32:09 GMT
We really need particle beams and radiation damage model in game. I second this.
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Post by jageriv on Nov 9, 2019 15:50:23 GMT
The general consensus has been for a long time that lasers tend to be very inefficient. To quote Atomic Rocket: www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Laser_Cannon--EfficiencySo, really high efficiency lasers are a product of about the last 10-20 years, and most of those are still somewhat labitory systems, or do very different things than what we want lasers to do in the game. For what the laser weapons currently need to do, the current state of the art (at least up to what Atomic Rocket Mentions) do not perform that task yet: Also notice the scale that current laser weapons are struggling at, even with all the temperature benefits having an atmosphere allows: about 30 KW for the 2014 AN/SEQ-3 system, the weakest laser in the game by default is a 1 MW laser, about 10-20x as powerful as the best systems we currently use. Also noteworthy is to look at these graphs of the performance of the high efficiency options currently available. This is where you get stuff like the 80-70% efficient laser. But look at the temperature range necessary to do so: Remember that freezing is about 273 kelvin. Room tempurature is in the range of about 300 kelvin. Which means everying on that chart is basically over an actively cooled range, and we see that efficiency starts going down about 10 percentage points every 100 degrees after 200. The ruby laser has an output/operating temperature of about 1,000 kelvin. So, assuming a linear relation, since I don't have any sources describing laser efficiency at 1,000 degrees, but guestimating based on the above trendline, this diode laser measured/modeled above would have an efficiency of about 0% at 1,000k. Which is close, but meaningfully different, from the 3% modeled in game. Given you can actually do something with 3%. Of course, the heat issue on the effect of lasers does not seem to be directly modeled as far as I can tell: other issues are what's reducing laser efficiency. But, the lack of efficiency at the modeled tempuratures isn't necessarily unrealistic.
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Post by dragon on Nov 28, 2019 2:30:36 GMT
Arc lamps don't really have the problem with high temperatures, semiconductors do. This is why arc lamps are good for space usage. At 200K, you're going to need gigantic radiators, sacrificing thermodynamic efficiency for higher output temperature is generally a bargain in COADE (and I wouldn't be surprised real space warship engineering was about pushing temperature limits, as well).
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Post by jageriv on Nov 28, 2019 3:36:18 GMT
Arc lamps don't really have the problem with high temperatures, semiconductors do. This is why arc lamps are good for space usage. At 200K, you're going to need gigantic radiators, sacrificing thermodynamic efficiency for higher output temperature is generally a bargain in COADE (and I wouldn't be surprised real space warship engineering was about pushing temperature limits, as well). Now, heat pumps are a thing, which is the complicating issue. This gives a forumula for calculating a theoretical maximum heat pump efficiency. www.engineeringtoolbox.com/heat-pump-efficiency-ratings-d_1117.htmlFor cooling, you take the cold side, divided by the temperature difference, to see how many watts of heat you can move per watt of power supplied. So, say you had a chilled laser in the 250 kelvin range, and you wanted heat pumps to get it up to a 1,000 degree range. A perfectly efficient heat pump would be able to move .333 watts per watt. Or, removing one watt of energy at 250 degrees to 1,000 degrees would take about 3 watts. So, say your laser had a 75% efficiency at 250 degrees, in line with my earlier chart. Assume a 1 Megawatt laser. 750 kw of the laser go "downstream", 250 kw is produced as heat. Moving those 250 kw to 1,000 degrees would take the input of 750 watts of power into the heat pump. Thus, assuming a perfect heat pump, you would put out 750 kw and have to consume about 1,750 kw. This would be an efficiency of about 42% overall. Which is of course much better than the 3-5% currently modeled in game. Such efficiency also means that you could do what a 1 MW laser can do in game (about 3 Kw downrange) with only a 7 KW laser. Which is a major variation. Of course, "perfect" heat pumps are not something your going to get, and lasing power tends to undermine efficiency, so the advantage might not be nearly as great as it looks there. For example, the heat pump being 80% perfect increases the watts required per watt removed to about 4-1, so the above laser goes down from about 42% efficient to 37% efficient. And if the laser in a high power situation is only 50% efficient, it falls to 16% efficient. Which of course is still some 3-4x as efficient as CODE lasers. But it does show how accumulating inefficiencies can bring down the overall efficiency.
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Post by dragon on Nov 28, 2019 17:32:33 GMT
Actually, heat pump efficiency is going to be way lower than 80%. Heat pumps are, essentially, heat engines working in reverse. The link you gave gives a theoretical "maximum" efficiency, but in a physical system, the absolute limit is Carnot efficiency, which, for the temperature gradient you gave, is about 33%. Put that into your equations and it turns out you really don't gain much.
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Post by jageriv on Dec 8, 2019 5:41:57 GMT
Actually, heat pump efficiency is going to be way lower than 80%. Heat pumps are, essentially, heat engines working in reverse. The link you gave gives a theoretical "maximum" efficiency, but in a physical system, the absolute limit is Carnot efficiency, which, for the temperature gradient you gave, is about 33%. Put that into your equations and it turns out you really don't gain much. Well, that 33% is I think the initial 3-1 watts I described initially. The .3333 watts per watt. The 80% I was describing was how close it got to that "perfect" 33% efficiency. The way a 33% efficient heat pump produces a 42% efficient laser is because the heat pump doesn't have to remove all the heat from the laser, only the "waste" heat. And since the laser in that example was 75% efficient, only 25% of the energy had to be boosted up from 250 k to 1,000 k at 33% efficiency. Assuming you can get heat pumps operating close to their Carnot efficiency, which is the 33%, and keeping them cool gets you lasers that are more efficient, the greater share of energy going out the laser instead of being converted to heat greatly reduces the amount of energy you need to run through the heat pumps. Of course, having efficient heat pumps over such a large range can be challenging. Most seem to operate over a couple of dozen degrees, not a couple hundred. I'm also not sure how well they scale, both with their power draw (the below example assumes a 750 kw heat pump) and with surface area (if you need to remove 250 kw of heat a second from the laser, how many square meters of coolant surfaces do you need to actually handle that heat? Since you can rely on convection, its faster than the black body radiation figures would suggest, but if your trying to keep the whole things cold I think that suggests relatively low heat transfer: hell if your keeping the laser colder than the rest of the ship, heat is going to be trying to get into it from anywhere it can. Plus, an energetic gas with kilowatts or megawatts of electricity running through it is just not naturally going to be inclined to staying cool. Assuming your still using a gas of course. But, just wanted to clear up that potential misconception.
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