Age of Wonders: Planetfall - Dev Diary #6: Combat Units 1

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BloodyBattleBrain

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We're still trying to figure out the exact balance of mods, and we recently increased the number of slots to three to give players more freedom to experiment with different combinations.

Without knowing how it works in practice, the idea of unlocking the 3rd mod through research (for Vanguard, presumably the same mechanic for the rest?) popped into my head.
 

Nikolai II

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So what are the Physics behind these pushing back lasers?
Erm... Photon momentum transfer?

Laser ablation.

Once the laser hits something it transfers energy so powerfully that parts of the target turn into plasma. The lasers will then instead hit this plasma and excite it further, turning it into an explosion which in turn propels the target further away from the laser.

For math on the topic I direct you to the end of this informative page by Randall Munroe:
https://what-if.xkcd.com/13/
 

Quark02

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Wouldn't laser ablation cook the "light" units to death before any 'push' effect came in? You'd get Kir'Ko invisible sniper assassin soup before you get them displaced out of the swarm.
 

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I like the assault bike, but designing the bike with literally no armour on the sides seems pretty cruel. Can't you add some glass panes (you can tell the driver they're bulletproof, I doubt hell check), 'cause I couldn't imagine there wouldn't be ANYTHING protecting his sides from shrapnel or space mosquitoes.
 

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Wouldn't laser ablation cook the "light" units to death before any 'push' effect came in? You'd get Kir'Ko invisible sniper assassin soup before you get them displaced out of the swarm.

Yes, it would.

I like the assault bike, but designing the bike with literally no armour on the sides seems pretty cruel. Can't you add some glass panes (you can tell the driver they're bulletproof, I doubt hell check), 'cause I couldn't imagine there wouldn't be ANYTHING protecting his sides from shrapnel or space mosquitoes.

Perhaps gives to much wind drag. If your strategy is being to fast to catch, you shouldn't need armor, right ?
 

Mulciber

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Laser ablation.

Once the laser hits something it transfers energy so powerfully that parts of the target turn into plasma. The lasers will then instead hit this plasma and excite it further, turning it into an explosion which in turn propels the target further away from the laser.

For math on the topic I direct you to the end of this informative page by Randall Munroe:
https://what-if.xkcd.com/13/

So, this can happen, although it depends on the intensity of the laser, the wavelength of the laser, the length of the pulse, and the surface of interaction. In general, the equation to determine the momentum (p) of a photon, given the energy (E) is p=E/c where c is the speed of light. The energy of a photon is given by E=h*c/λ, where λ is the wavelength of the laser. Assuming that the laser is 700 nm red (although any visible light will be different by less than an order of magnitude) this means that the energy per photon will be 2.84*10^-19 J, resulting in a momentum per photon of 9.48*10^-28 kg*m/s. This is small.

Next, we need to know how many photons are being emitted. Damage thresholds for many materials such as metals are in the kilowatt or higher range. As this laser is able to cut through armor, a few hundred kilowatts of continuous power seems a good start. Let's assume that Triumph will show the laser to fire for much more than a few microseconds, making it close enough to continuous for our needs. 100 kW of power means a lot of photons. To make the math simple, let's use 1 second as the time of the shot, resulting in an energy per shot of 100 kJ. This yields 3.5*10^23 photons per shot, and 3.34*10^-4 kg*m/s of momentum. This is not a lot of momentum.

If you want an appreciable momentum transfer, then the target needs to reflect almost all of the light, doubling the momentum transferred per photon and allowing for much higher damage lasers to be used. If the average target has a mass of 200 kg and needs to move 10 meters to get to the next space (I'm pulling numbers out of this air here) and will be slowed by friction, this would require at least 8*10^6 kg*m/s of momentum transfer, assuming that gravity is approximately that of Earth. Which means a shot providing 1.2*10^15 J. This is a lot of energy. That is 6,000,000 lightning bolts simultaneously. This is not the energy that the target receives (remember, it is now perfectly reflecting) but rather the energy produced by the laser. So, this seems unreasonable. The light produced by this would definitely blind everyone on the battlefield, get absorbed somewhere else (the bike itself is the most probable) vaporizing that target, and would likely blind everyone on the planet.

All of this becomes more complicated, however, if the target receives any damage at all. This is when the point about laser ablation comes into play. The write-up done by Randall Munroe is excellent (and hilarious) but seems to imply (to most laymen) that the target would necessarily be destroyed before it moved. This is not the case. Here is where I stop using math to explain. Having worked with ultra-short pulse lasers for a number of years, I have seen them shot at many things. My favorite is watching the interaction with Jell-o. Our ultra-short pulse laser produced about 1 millijoule of energy per shot, and was enough to make the jello wiggle. This is due to the plasma that it generates upon impact with both the Jell-o and the air. The target was less than a square millimeter, but was able to make a liter of Jell-o wiggle. The reason for this is that the energy was compressed in time down to 70 femtoseconds, or 70*10^-15 seconds. This gives a peak power of about 14 gigawatts. It is this enormous power, rather than the energy of the laser, which enables this sort of plasma generation

Jell-o wiggling is a far cry from a person in a suit of armor being pushed backwards, but the point is made clearly enough. The jell-o was still almost entirely intact after the laser. Much of the momentum transfer came from the plasma in the air, not the Jell-o. The point of this huge wall of text, which, admittedly is likely awful to read, is that if Triumph wants an explanation of the ability to push an object backwards via laser light, they should insist that it be a short pulse (just for animation purposes, as our eyes would still be able to see the after-image of the laser, this should last for just a few of frames, not even a second) and make sure to animate a purple (oxygen glows purple when ionized) glow around the point where the beam hits the target, due to the color of the plasma.

Also, don't ask how shields would interact with this because I do not know how they would physically work.

TL;DR Yes, this would work, even without destroying the unit, but could use an animation implying short plasma bursts.
 

Nikolai II

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Wouldn't laser ablation cook the "light" units to death before any 'push' effect came in? You'd get Kir'Ko invisible sniper assassin soup before you get them displaced out of the swarm.

No, Mulciber has a long post about it, but basically you get a lot of displacement effect from just a little vaporized matter since the pushy effect is so great. This is why laser ablation (with bigger lasers) is just about the most sensible way (doesn't mean a lot in the context for sure) to move entire planets if you want to control them like giant spaceships. (It's still preferable to not have anyone alive on the surface of the planet)
 

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No, Mulciber has a long post about it, but basically you get a lot of displacement effect from just a little vaporized matter since the pushy effect is so great. This is why laser ablation (with bigger lasers) is just about the most sensible way (doesn't mean a lot in the context for sure) to move entire planets if you want to control them like giant spaceships. (It's still preferable to not have anyone alive on the surface of the planet)

I assumed vaporizing that little matter would still cause considerable heat to be dispersed, cooking whoever is nearby (not disintegrating per se, just cooking to temperatures a Kir'Ko bug might not survive). I mean, vaporizing something still requires a massive amount of energy directed into a small area. Air-plasma wiggling jelly aside, this still may or may not be the case.

I also imagine aiming a laser at a distance through unknown (well, the light dispersal effects of it are unknown to us, known to whomever is firing the pew-pew) atmosphere at a potentially moving group of units isn't a straightforward task, a small slip of the hand could accidentally blind someone.

Having worked with ultra-short pulse lasers for a number of years, I have seen them shot at many things.

I'm guessing not everything was for 'scientific purposes'. Sounds like fun though, and I thank you for the interesting and illuminating write-up.
 

Gloweye

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I've worked with LIBS, blowing small holes in matter for analysis of what it's made off. The craters that makes are around 2 mm diameter, and that's a looong way off from inflicting any noticable momentum.

If you want to propel someone by laser ablation, you'll need to blow a fist sized crater in them at the least, and that might just stumble them (if they survive, that is.). And if you dont get your focus right, you'll just blow up some air. Your effective range will be a couple meters, probably. Adjusting that is possible, but requires rather delicate optics. A bit like a camera, but a bit higher demands on both the materials and the accuracy of the lenses. It's gonna be quite fragile.

Lets just give them the artistic license to have knockback lasers without all our pysics. Perhaps there's some residual magic in the air it utilizes that the people aren't even aware of.
 

Mulciber

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I assumed vaporizing that little matter would still cause considerable heat to be dispersed, cooking whoever is nearby (not disintegrating per se, just cooking to temperatures a Kir'Ko bug might not survive). I mean, vaporizing something still requires a massive amount of energy directed into a small area. Air-plasma wiggling jelly aside, this still may or may not be the case.

You aren't wrong in this. There's a lot of energy going into a small space, so there are very large temperatures. But at these scales, we are into the realm of statistical mechanics (yay?) where the concept of temperature gets a bit fuzzy. Temperature now ends up being the average kinetic energy of the molecule. So it's a matter of what direction the molecules move when they are ejected. It general, the answer is "out". This means that while the particles are "hot", they are not interacting with the surrounding medium to cause an appreciable transfer of energy, depending on the structure in question. You still have a lot of damage to the surface of the target, which does really cool things by itself, but below the surface (and by surface I mean the top few microns to as much as a few millimeters) everything stays cool for quite some time.

I also imagine aiming a laser at a distance through unknown (well, the light dispersal effects of it are unknown to us, known to whomever is firing the pew-pew) atmosphere at a potentially moving group of units isn't a straightforward task, a small slip of the hand could accidentally blind someone.

Moving targets become easier to hit when there is no time-of-flight delay or drop off, but the atmospheric effects are important. Whether or not the target is moving is not as important as the humidity and temperature gradient. The laser needs to be properly focused to work and atmospheric makeup is a huge part of that. And accidentally blinding someone is a real issue. This is why laser weapons are not employed as anti-personnel weapons. Killing someone with a laser is fine. Blinding them is illegal.

I'm guessing not everything was for 'scientific purposes'. Sounds like fun though, and I thank you for the interesting and illuminating write-up.

Well, it wasn't for a journal article, but ti's important to know what happens if you do x to y. Mostly though, this was for an outreach video explaining why physics is cool.

I've worked with LIBS, blowing small holes in matter for analysis of what it's made off. The craters that makes are around 2 mm diameter, and that's a looong way off from inflicting any noticable momentum.

If you want to propel someone by laser ablation, you'll need to blow a fist sized crater in them at the least, and that might just stumble them (if they survive, that is.). And if you dont get your focus right, you'll just blow up some air. Your effective range will be a couple meters, probably. Adjusting that is possible, but requires rather delicate optics. A bit like a camera, but a bit higher demands on both the materials and the accuracy of the lenses. It's gonna be quite fragile.

Lets just give them the artistic license to have knockback lasers without all our pysics. Perhaps there's some residual magic in the air it utilizes that the people aren't even aware of.

The effective range of this can be adjusted by variable optics, and a very good computer, which is not unreasonable to expect on a vehicle that also contains a laser this powerful. And blowing up the air can be of considerable help when trying to get momentum transfer without complete annihilation. Consider a laser creating a plasma filament (bullet shaped region about a few microns in size) in the air. The shockwave created by this plasma being created is moving around mach 3. If this shockwave is created a short distance from the target, the resulting force of the air against the target could conceivably be enough to move the target. In real life, the plasma created by the laser is in a very small area, and therefore a minimal amount of air is expanded (and it is quickly dissipated by the atmosphere), but with enough energy, it would not even be necessary to focus the laser by much to get the plasma to appear, therefore the effective size of the shockwave could be much larger.

I don't disagree that the idea is rather unfeasible, but so is alien psionic sniper rifles with today's technology. The physics holds, provided you can get enough energy. Slide side effects include instant radiation poisoning to all surrounding life, blindness, and deafness.
 

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I like the assault bike, but designing the bike with literally no armour on the sides seems pretty cruel. Can't you add some glass panes (you can tell the driver they're bulletproof, I doubt hell check), 'cause I couldn't imagine there wouldn't be ANYTHING protecting his sides from shrapnel or space mosquitoes.
He has to be able to lean out so he can see where he's going.
 

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Hrm, I used to try shooting past an enemy, at an enemy behind, to have a better chance of hitting something in AoW2. I didn't realise it was considered a little bit exploit.
But does it really make sense for a projectile to just stop at the desired distance and not have a chance to hit something behind?
Making it risky to surround the target with projectile weapons could be an interesting tactical consideration.

As for sideless bikes. The lack of side is increasing friction (its a complicated turbulence effect), but the reduced weight still helps with acceleration.
 

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The effective range of this can be adjusted by variable optics, and a very good computer, which is not unreasonable to expect on a vehicle that also contains a laser this powerful. And blowing up the air can be of considerable help when trying to get momentum transfer without complete annihilation. Consider a laser creating a plasma filament (bullet shaped region about a few microns in size) in the air. The shockwave created by this plasma being created is moving around mach 3. If this shockwave is created a short distance from the target, the resulting force of the air against the target could conceivably be enough to move the target. In real life, the plasma created by the laser is in a very small area, and therefore a minimal amount of air is expanded (and it is quickly dissipated by the atmosphere), but with enough energy, it would not even be necessary to focus the laser by much to get the plasma to appear, therefore the effective size of the shockwave could be much larger.

I don't disagree that the idea is rather unfeasible, but so is alien psionic sniper rifles with today's technology. The physics holds, provided you can get enough energy. Slide side effects include instant radiation poisoning to all surrounding life, blindness, and deafness.

A powerful computer could adept the optics fast enough - but variable optics like that is currently something avoided when possible - which is a lot easier if you're not in a combat situation, I admit.

The trouble is that it's hard to create a small focus with variable optics. On a camera, it doesn't really matter much if the focus gets a bit longer, or up to a couple cm a hundred meter away - you won't see the difference. But when focusing a laser, that's an order of magnitude reduction in power.


Also, force to knock back is about momentum. Even if the air goes Mach 3, it's mass is so ignorable that it'll blow back your hair and that's it.

I'd also like to contest about the knockback being the primary goal - damage would be the primary goal.

In specific this bit: "but with enough energy, it would not even be necessary to focus the laser by much to get the plasma to appear"

In the air, this simply isn't true. You need to achieve a certain photons/m^3 density to create a plasma in air, otherwise your laser will just pass through like the rest of the air. On (non-transperant) matter, you could do with just heating it up a lot.


@HousePet, I wouldn't consider that an exploit.
 

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Great to see these first units in detail. Already lots of new stuff compared to AoW3.
 

Mulciber

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A powerful computer could adept the optics fast enough - but variable optics like that is currently something avoided when possible - which is a lot easier if you're not in a combat situation, I admit.

The trouble is that it's hard to create a small focus with variable optics. On a camera, it doesn't really matter much if the focus gets a bit longer, or up to a couple cm a hundred meter away - you won't see the difference. But when focusing a laser, that's an order of magnitude reduction in power.


Also, force to knock back is about momentum. Even if the air goes Mach 3, it's mass is so ignorable that it'll blow back your hair and that's it.

I'd also like to contest about the knockback being the primary goal - damage would be the primary goal.

In specific this bit: "but with enough energy, it would not even be necessary to focus the laser by much to get the plasma to appear"

In the air, this simply isn't true. You need to achieve a certain photons/m^3 density to create a plasma in air, otherwise your laser will just pass through like the rest of the air. On (non-transperant) matter, you could do with just heating it up a lot.

I'm not trying to say that this is feasible, or even smart. This was an attempt to show that is was physically possible to have a laser with knockback potential. I think that the idea is silly and that the devs should probably just use missiles for knockback instead, but they want knockback lasers. Of course the primary goal of a laser should be to do damage, but if you want your laser to transfer momentum, you kind of need to make that your primary goal since it won't happen on it's own.

The optics used aren't really a concern; those can be chocked up to future technology to allow variable optics to work quickly to focus the light. But, the density of photons is a concern. For oxygen, that is somewhere around 10^17 photons/cm^3. That's a lot of photons, but it's not impossible even by today's standards. We do it all the time (all the time? well, with the right laser, yes.) These lasers also don't create a plasma only at the focal point. With a high enough intensity, both spatially and temporally, a process known as Kerr self-focusing takes over. This effect takes place when the beam is considerably larger that the beam waist limit, which is what's usually defined as the focus (at least in an ideal case.) After this, the laser is focused tightly enough to create a plasma, then the beam defocuses slightly due to multi-photon ionization. This process repeats itself until there is no longer enough energy in the reservoir.

10^17 photons/cm^3 is the photon density, which is enough to ionize about 1% of the air that the laser hits while focused, but this isn't what happens. Many photons are required to hit the same molecule to ionize it. This requires about 20 millijoules per cubic centimeter to ionize this small portion. 20 millijoules is not a large amount of energy, it just has to be compressed in time down to less than a few picoseconds, preferably a few femtoseconds, which is a bit tricky and there aren't many lasers that can do that.

The trouble at the moment is that the laser is unlikely to hit an air molecule and that most of the energy is left in the reservoir instead of being dumped into the filament. But those chances go up considerably with more energy, as this adds more photons. The density of air is about 10^19 molecules/cm^3. So, with enough energy, a few orders of magnitude, but still well within the sub kilojoule range, we could ionize a cubic centimeter of air. The shockwave created by this is also moving faster now as more energy has been dumped in, and there are more molecules moving faster. Yes, a 10 meter motion is still dificult, but it's a start.

But all of this has been in response to know how a laser could move something without turning it into soup. The much better answer is still laser ablation. Yeah, we might need to destroy a considerable portion of the target to move it, but imagine a fist size chunk being suddenly turned to plasma and ejected at super-sonic speeds. Your target will receive damage, which we know happens in the game, and trust me, it will move back a considerable distance. We've never really been concerned with whether or not the target survives before. We've hit units with lightning, fireballs, death-rays, explosions, bullets, all sorts of stuff. The laser doesn't need to do the pushing, it can just do the damage. The rapid destruction of the target, and resulting plasma expansion, can do the damage.

TL;DR Yes, it's possible, although missiles would be easier.
 

Gloweye

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Once you make a plasma, that plasma will absorb the rest of your laser pulse, thereby stopping the propagation of the beam. The rest of the pulse will just heat up the plasma some more (It's actually done, some LIBS setups use dual-pulsed plasma's, to increase signal strength.)

Attempting to reach plasma photon densities outside your focal point is a really, really bad idea. (it also requires a lot more energy than you'd naively think. Focal points of lasers we use to make plasma are really small.).

Actually, photons per m3 doesn't really give a good estimate - more important is energy per m3. A value often used is 10^8 W/cm2 (1). The setup I used had a focal point of about 0.6 mm3, and with a laser pulse length of 5 ns and around 65 mJ of energy per pulse, we started getting plasma's (used 150 mJ for better signal strength later, though).

Point is, if you get to intense away from the focal point, you're not really in control of anything anymore.


The only laser weapons currently that deal enough damage to have any military use work by just heating up the target a lot. The americans got one like that.



1) Volkov et al, Dependence of threshold for air breakdown by a focused laser beam on the geometry of the focal region. American Institute of Physics, (1976).
 

Quark02

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After all this, I wonder if they'll throw their hands up and remove knockback from the laser and substitute it with Blind (or remove the laser from the knockback and substitute it with projectiles).
 

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Once you make a plasma, that plasma will absorb the rest of your laser pulse, thereby stopping the propagation of the beam. The rest of the pulse will just heat up the plasma some more (It's actually done, some LIBS setups use dual-pulsed plasma's, to increase signal strength.)

Attempting to reach plasma photon densities outside your focal point is a really, really bad idea. (it also requires a lot more energy than you'd naively think. Focal points of lasers we use to make plasma are really small.).

Actually, photons per m3 doesn't really give a good estimate - more important is energy per m3. A value often used is 10^8 W/cm2 (1). The setup I used had a focal point of about 0.6 mm3, and with a laser pulse length of 5 ns and around 65 mJ of energy per pulse, we started getting plasma's (used 150 mJ for better signal strength later, though).

Point is, if you get to intense away from the focal point, you're not really in control of anything anymore.


The only laser weapons currently that deal enough damage to have any military use work by just heating up the target a lot. The americans got one like that.



1) Volkov et al, Dependence of threshold for air breakdown by a focused laser beam on the geometry of the focal region. American Institute of Physics, (1976).

I don't disagree with what you say, to a point. Your numbers look right, but they are for nanosecond lasers. I have no experience with nanosecond lasers, other than what I have read and heard from other people. So I will trust that you are correct in what you say. However, I am speaking specifically of femtosecond lasers, with which I have extensive experience. Femtosecond lasers have a pulse length (time) which is significantly shorter than the atomic response time. This means that the laser pulse has moved entirely through the plasma before the plasma is finished forming. The result of this is that the plasma does not absorb the laser pulse, allowing for plasma channels of up to a meter long. The length of the plasma is limited by the speed of light and recombination time. This channel, however, can move along the path of the laser; distances of up to a kilometer have been reported. If you like, I can provide references.

It is also possible to keep these channels open via a secondary pulse. This has been shown to work with a Ti:sapphire femtosecond laser coupled with a ND:YAG nanosecond laser. The plasma does not absorb the entire laser pulse as each photon is a separate interaction, so it boils down to probability densities.

In order to achieve breakdown via multiphoton ionization, what is important is energy per cubic meter, yes. But, as most ultrashort pulse lasers with high energy per pulse operate around 785 nm, it is frequently measured as photons per cubic meter, since the energy of the photons is a known quantity. The trouble with the idea that it is simply energy per cubic meter comes from the fact that an infinitely energetic photon (impossible, yes, I know, but bear with me) can only ionize one molecule. So yes, ionization requires energy per cubic meter, but the volume of the plasma channel is dependent upon the number of photons per cubic meter.

The lasers with which I have worked have been pulse energies around 1 millijoule, and times around 70 femtoseconds. This is a much lower energy than in most nanosecond lasers, but around 20,000 times as much power. This much power can result in one very long plasma channel or many smaller channels side by side, depending on the focal optic used. I do know how much power it takes to create plasmas a certain distance away from the classical focal point, having done it many times. To increase the effective diameter of the plasma channel requires that your intensity (power/unit area) increase quadratically.

Your point about the current military weapons, however, is not wrong (although that will likely change in the next few years) but it seems a bit irrelevant as we are talking about the distant future. Again, I am not saying that it is feasible with today's technology to use a laser to push something around, only that it is physically possible. If someone wants, I can always elaborate further on the ejection speeds and masses.

TL;DR Femtosecond lasers and nanosecond lasers are different.

After all this, I wonder if they'll throw their hands up and remove knockback from the laser and substitute it with Blind (or remove the laser from the knockback and substitute it with projectiles).

Either one would probably be better. Or, just don't call it a laser. Call it "hard light" or something equally nonsensical. That way fewer people will roll their eyes.
 

Gloweye

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Hm, plasma channels...that sounds nice. With such a surface, they'll probably last even shorter than the sphere (well, close enough) plasma's I've worked with. It makes a nice ticking sound to have a pulse laser creating them.

However, if you could make a long and stable plasma channel, you could use it for electrocution. But we're at the timeframes where electicity is kind of...really slow, so it's not really feasable without a big enough artistic license:physics. (drop a zero or six somewhere, probably)

Eh, anyway, we'll be playing with knockback lasers. I've wanted knockback for a while in AoW, so we'll see.