I doubt the first (civilian) drone assasination will be that sophisticated. Face recognition from a moving object at an unfortunate angle is not easy and it's even harder if you want to do it from a fixed-wing drone that can't hover like a quadcopter. I'd rather expect an assassination by a fixed-wing remote-controlled UAV targeted at someone speaking at a public event, some place where traditional methods (knives, rifles, car bombs) fail because line-of-sight access is heavily restricted.

Line of sight for rifles goes out to as much as 2,707 yards for .338 Lapua Magnum (in the very longest recorded sniper kill). 1,000 yards is a very standard range for long range target shooting.

What's more significant here is that people so exquisitely experienced just have no reason (today) to assassinate, and protection out to, oh, 500-600 yards is I suppose generally good enough.

I don't think a rifle would be a good anti-drone solution. The problem is you would be operating close to other people and missing a shot could end up killing someone else. Perhaps the solution could be in shooting a web over the drone and having the wires entangled in the rotors or maybe a tennis ball cannon could work.

How about something like a firehose? Water wouldn't be a threat to people, but a high pressure water cannon could probably down a drone within a reasonable range.

Lasers would be more effective. 1W and above lasers are readily available on the open market, and output more than enough power to fuse or burn out any optics that are not shielded.

Lasers are slow to impact (unless using an obscene amount of power) and require precise tracking of the target over time (because they're slow).

Conversely, it is far easier to hit a moving target with a laser than it is to hit a moving target with a projectile. With a projectile, you have to aim where the target is projected to be, whereas with a laser you aim where it is now.

CIWS systems and fighter cannon are gatling guns precisely because the probability of any single round hitting a small, moving target is low.

If all you need to do is overload the optical circuits of a drone, a 1W laser is sufficient. Whether you kill the drone by incinerating it in midair or kill it by causing it to crash due to loss of orientation, the result is the same.

A lot of CIWS systems are missle based: https://en.wikipedia.org/wiki/Close-in_weapon_system#Missile... And the US and Germany are moving from Gatling gun based ones to a "Rolling Airframe Missile" that as I read it is self-guided once fired: https://en.wikipedia.org/wiki/RIM-116_Rolling_Airframe_Missi... Needless to say, using blast fragmentation warheads near crowds is sub-optimal.

This really sounds like a job for Death Rays, err, the laser finally getting a serious workout as a kill mechanism.

Or hunter-killer drones that can close in and fire some sort of directed fragmentation / shaped charge warhead? That might be a viable alternative, especially once 3d fabrication reaches an acceptable maturity.

Including eyeballs. Using high-power lasers in crowded area seems even more dangerous than bullets - the latter at least don't reflect off surfaces.

No, but they follow ballistic trajectories and can ricochet. A laser is at least predictable, and given that most drones would fly above ground level for visibility, it would take a very unlucky reflection to injure someone on the ground.

A bullet is going to come down somewhere.

And we're likely talking about fairly low angles, i.e. less than 45 degrees up from horizontal. Straight up is fairly safe because air resistance slows the bullet on its way down. Less than 45 degrees, it's going to come down hard a long distance away.

Shotguns are another possible approach, but I'm pretty sure the shot size required would be big enough to cause harm to more than people's eyes. And for this sort of thing civilian shotguns would have an effective range of maybe 50 yards max, so it would be a CIWS.

The US Navy is moving from the 20mm Vulcan Gatling gun based Phalanx to a missile based CIWS ... that might be the most discriminating system after a laser, but still very problematic, you would have issues with the operators being very hesitant to set them to firing because there would likely be civilian casualties, and if it just turned out to be a paparazzi or otherwise non-dangerous drone, they'd get crucified.... And neither an effective laser nor an effective kinetic/explosive CIWS would be cheap.

I didn't do the math here, but my intuition tells me that as lasers scatter, if you point a 1MW beam at a rough surface, you'll have a lot of high-power reflections in every direction - even a laser pointer reflecting off a wall is annoying for the eyes. I'd love someone more knowledgable about high-powered lasers to chime in here.

Anyway, neither of those two options seem safe for drones flying just above people's heads. Maybe microwave lasers would be better? Also low-powered visible-light lasers could be enough to blind sensors and force the drone to rely on dead reckoning while not risking eye damage.