|
Post by ross128 on Oct 5, 2016 23:47:45 GMT
Yeah, I think Earth-based observatories might actually be a good model for aiming large aperture lasers. Once you get to that scale a laser is essentially a telescope in reverse anyway, and our ships are quite large enough that any reaction from mechanically rotating our turrets would be negligible (barring an incredibly large turret on an incredibly small ship, but you should have thought about that when you built the thing), so the hull makes a perfectly acceptable reaction mass for our turret actuators (and as a bonus, it's a reaction mass that all our turrets can share). An observatory's ability to stay trained on a small patch of sky is directly applicable to a turret that needs to train a laser on a small patch of hull.
Reaction wheels are for drones.
|
|
|
Lasers
Oct 6, 2016 0:03:08 GMT
Post by apophys on Oct 6, 2016 0:03:08 GMT
To get your irradiance, I need a 9m aperture, which needs a 20m radius turret to hold it.
Can cut mass by using diamond reaction wheels (11 kt), but then they eat an entire 700MW of power themselves. Cadmium is more reasonable, but the mass becomes 26kt. Not great mass either way.
Even with diamond, ~90% of the thing's mass is reaction wheel, with ~10% being the 6cm boron armor. Everything else is drowned out.
What I really want to do is shove more than 1 GW into a laser.
|
|
|
Lasers
Oct 6, 2016 0:06:37 GMT
via mobile
Post by princesskibble on Oct 6, 2016 0:06:37 GMT
It would help to not have to mount the laser mirror in a turret at all, and steer it by rotating the entire spacecraft, like real space telescopes.
|
|
|
Post by tukuro on Oct 6, 2016 0:08:02 GMT
I've finally created a 1 GW laser that doesn't cost billions. I use it to test laser resistance on drones and missiles. It has an intensity of 79400 MW at 240 kmShip costs 190Mc with a mass of 21.1kt, meaning I could use it in the campaign if I wished. LaserModule 1.000 GW Nd:GGG Green Laser ArcLamp GasComposition Krypton EnvelopeComposition Fused Quartz PowerSupplied_W 1e+009 Radius_m 0.051 CavityWallComposition Silver CavityCoolantComposition Hydrogen CavitySemimajorAxis_m 1.7 CavitySemiminorAxis_m 1.6 GainMedium Nd:GGG OpticalNodes 20000000 LasingRodRadius_m 0.1 Mirror Composition Silver OutputCoupler Composition Fused Quartz CoolantTurbopump Composition Titanium PumpRadius_m 0.9 RotationalSpeed_RPM 470 CoolantInletTemperature_K 1200 FrequencyDoubler NonlinearOptic Composition Potassium Titanyl Phosphate OpticLength_m 0.0095 OpticRadius_m 0.0025 ApertureRadius_m 21 FocusingMirror Composition Silver Turret InnerRadius_m 45 ArmorComposition Magnesium ArmorThickness_m 0.0001 ReactionWheels Composition Magnesium RotationalSpeed_RPM 1 EngagementRange_km 250 TargetsShips true TargetsShots true I'm sure someone could improve this further.
|
|
|
Post by apophys on Oct 6, 2016 0:34:31 GMT
Ooh. Having zero armor certainly makes things easier... Nice find.
Hm... 23m aperture is the largest that fits on a turret, because turrets go up to 50m only... but apertures go to 100m... So can we do away with the turret entirely by undersizing it? Aim with the ship?
If so, I could hit 946,000 MW/m2 at 240 km for 1.07 kt and 26 Mc ... But wait a minute, it's only outputting 19.6 MW. That's 20 square millimeters. How much damage would that even do...
|
|
acatalepsy
Junior Member
Not Currently In Space
Posts: 97
|
Post by acatalepsy on Oct 6, 2016 0:52:35 GMT
Okay, now this is funny. Take one 50MW Titanium:Sapphire Laser, derived, as such things are, from tuna's design:
LaserModule 50.0 MW Titanium:Sapphire Violet Laser ArcLamp GasComposition Xenon EnvelopeComposition Fused Quartz PowerSupplied_W 5e+007 Radius_m 0.043 CavityWallComposition Silver CavityCoolantComposition Hydrogen CavitySemimajorAxis_m 1.9 CavitySemiminorAxis_m 1.8 GainMedium Titanium:Sapphire OpticalNodes 10000000 LasingRodRadius_m 0.083 Mirror Composition Silver OutputCoupler Composition Fused Quartz CoolantTurbopump Composition Copper PumpRadius_m 0.28 RotationalSpeed_RPM 56 CoolantInletTemperature_K 670 FrequencyDoubler NonlinearOptic Composition Lithium Niobate OpticLength_m 0.03 OpticRadius_m 0.0025 ApertureRadius_m 7.9 FocusingMirror Composition Aluminum Turret InnerRadius_m 17 ArmorComposition Graphite ArmorThickness_m 0.022 ReactionWheels Composition UHMWPE RotationalSpeed_RPM 13 EngagementRange_km 250 TargetsShips true TargetsShots true
Run the following experiment. Reduce the aperture to a set value. Then then reduce the size of the turret until it is just barely big enough to hold the laser. Record the mass of the laser turret, and its intensity at 200 km. Record the ratio between those two numbers. You'll get the following result:
aperture (m) mass (tons) intensity@200km (MW/m^2) ratio 0.5 7.86 6.34 0.806615776 1 12.8 25.4 1.984375 2 27.3 101 3.6996337 3 45.2 228 5.044247788 4 61.4 406 6.61237785 5 464 634 1.36637931 6 493 913 1.851926978 7 435 1240 2.850574713 7.8 1260 1540 1.222222222 7.9 774 1580 1.222222222 8 262 1620 6.183206107 9 3110 2050 0.659163987
Notice that something really weird is going on in the vicinity of the 8m aperture. As near as I can tell, what's happening is that the lens aperture and the reaction wheel for the turret are competing for space; if you increase the size of the aperture you will decrease the amount of mass in the reaction wheel. If the 8m aperture is a tighter 'fit' for the turret than the 7m aperture is for the smallest turret that will it it, the 7m one will be heavier even if it's smaller. You'll also lose turret speed, but you don't need a lot of turret speed to engage targets that are 200 km away. But this highlights what a big design problem the turrets themselves are, even independently from the laser.
In any case, my general finding would be that you want to make turrets in the range of 4m across, but that this is heavily dependent on the turret having the right "fit".
|
|
|
Lasers
Oct 6, 2016 1:02:26 GMT
Post by apophys on Oct 6, 2016 1:02:26 GMT
As near as I can tell, what's happening is that the lens aperture and the reaction wheel for the turret are competing for space; if you increase the size of the aperture you will decrease the amount of mass in the reaction wheel. If the 8m aperture is a tighter 'fit' for the turret than the 7m aperture is for the smallest turret that will fit it, the 7m one will be heavier even if it's smaller. You'll also lose turret speed, but you don't need a lot of turret speed to engage targets that are 200 km away. But this highlights what a big design problem the turrets themselves are, even independently from the laser. In any case, my general finding would be that you want to make turrets in the range of 4m across, but that this is heavily dependent on the turret having the right "fit". Yeah, that's the effect I was exploiting to make my ultralight 10.3m turret. It is an extremely close fit, so much so that I'm using iridium reaction wheels to get a decent power usage from them with the traverse speed I desire (45 degrees per second). The aperture for this point is 2.4 m. I noticed the effect when playing with gimballing thrusters earlier, in those the injector is competing for space with wheels.
|
|
|
Lasers
Oct 6, 2016 1:06:36 GMT
Post by tukuro on Oct 6, 2016 1:06:36 GMT
Nice find, sort of makes me wish we could do away with reaction wheel turrets for lasers like we can with the other weapons.
|
|
|
Lasers
Oct 6, 2016 1:08:33 GMT
Post by jakjakman on Oct 6, 2016 1:08:33 GMT
I'm seeing that the Titanium Sapphire lasers are great for intensity at range. Right now I'm using the 320MW Nd:YAG green laser from this post. After seeing here that intensity at range does better with a higher laser frequency I've been trying to convert my 320MW green laser over to sapphire violet but am not having any luck. Any thoughts on what to change to scale up a lower power laser like tuna 's optimized 60MW sapphire to a 320MW version?
|
|
|
Lasers
Oct 6, 2016 1:31:45 GMT
Post by apophys on Oct 6, 2016 1:31:45 GMT
To scale up a laser in power, just give it more power, and tweak the frequency doubler to get 100% again (and not melt). If anything else is melting, pump more coolant. Ah, you also will probably need to increase the Optical Nodes to bring M 2 back down to 3.00 Of course you can do the reverse to scale down any laser in power, like my 1GW to a 320MW.
|
|
acatalepsy
Junior Member
Not Currently In Space
Posts: 97
|
Lasers
Oct 6, 2016 1:47:55 GMT
Post by acatalepsy on Oct 6, 2016 1:47:55 GMT
I'm trying to see if I can get a Near Ultraviolet laser going - the advantage is that, for a give aperture, and output power, it seems to have a higher intensity at any given range. The catch is that it's less efficient overall. I don't really understand how the arc lamp spectra or pumping efficiency is calculated, so....
|
|
|
Lasers
Oct 6, 2016 1:52:30 GMT
Post by ross128 on Oct 6, 2016 1:52:30 GMT
Maybe we just need more materials (such as a wider selection of lasing media) to play with, before we can really start unlocking the potential of lasers. Though I also think it would be interesting if we could play around with pulse-width modulation...
|
|
|
Lasers
Oct 6, 2016 2:32:37 GMT
Post by apophys on Oct 6, 2016 2:32:37 GMT
I'm trying to see if I can get a Near Ultraviolet laser going - the advantage is that, for a give aperture, and output power, it seems to have a higher intensity at any given range. The catch is that it's less efficient overall. I don't really understand how the arc lamp spectra or pumping efficiency is calculated, so.... I'm not an expert in the field, but this is my take. The vertical red lines are the resonant frequencies of the gain medium. You want the green spectrum graph of the gas (the frequencies it naturally emits when blasted with electricity) to be high where at least one of those red lines intersect it. Ti:Sapphire matches well with xenon because the second red line hits a high point on the spectrum, and the first one is okay too. Krypton emits frequencies in a range that several materials match up with. Nd:YAG gets multiple nice intersections. Putting more power into a laser makes gas emit more high-frequency radiation, and since all the materials we have resonate in the very low end (except ruby), it makes the laser marginally less efficient. You can see the green graph sway. A larger radius of the gas tube makes pumping more efficient for some reason (but this worsens cavity shape, which you can otherwise compensate for). I find the minimum radius to be unequivocally best for Nd:YAG + krypton. Haven't tested others yet, because this combo makes a nice compact cavity with fine efficiency. None of this has anything to do with intensity at range. Higher frequency light simply carries more power, that's where the intensity is. But our high frequency options are currently quite poor.
|
|
|
Lasers
Oct 6, 2016 2:45:34 GMT
Post by nivik on Oct 6, 2016 2:45:34 GMT
So I have two contestants that are both reasonably effective. I guess I can get away with twice less power if I can afford just a bit larger turret... and the other way around. btw hellfire drones drop like flies if you target the gun... same with stingers... is it some kind of construction flaw or the game simulates explosion of the gun itself ? I believe the built-in ammo storage for the gun is detonating. You could fix that by making separate, internal ammo storage, but most drones are built around a single gun anyway, and if the gun is lost, the drone is pretty much pointless...so I don't really see a point in doing that.
|
|
|
Lasers
Oct 6, 2016 3:29:01 GMT
Post by RA2lover on Oct 6, 2016 3:29:01 GMT
It can potentially change the center of mass and moment of inertia enough to reduce the time required to change heading.
|
|