Comment by fuoqi | Hacker News Reader

Comment by fuoqi | Hacker News Reader

It's hard to take his praise for laser interception of hypersonic weapons seriously.

For intercepting swarms of cheap drones? It's a great fit! Space-based lasers for intercepting ICBMs? Maybe? But true hypersonic weapons (which Kinzhal is not) fly only in air (after all, they use oxygen in it to fly), while being covered in a plasma shield which is really good at absorbing all kinds of electromagnetic radiation.

Meanwhile, with high enough laser power you get instabilities in air which act as a natural diverging lens for your beam, drastically reducing effective range of your system. Push power even further to compensate for it and you will get plasma, which does even better job at dispersing energy of your beam. So in the end, you get a very short range interception system with a minuscule time frame to perform interception of a hypersonic target.

This reference [1] tends to support what you are saying:

> For this thesis, an atmospheric propagation code named ANCHOR (Atmospheric NPS Code for High Energy Laser Optical pRopagation) was developed and utilized to study the propagation of high energy lasers in various atmospheric conditions and for numerous laser configurations. The ANCHOR code accesses existing industry databases to obtain relevant optical properties for various atmospheres and then uses scaling laws to simulate laser propagation through the defined environments. ANCHOR accounts for the effects of atmospheric diffraction, turbulence, platform jitter and thermal blooming on the laser beam, and outputs on-target irradiance and power-in-the-bucket profiles for a wide range of laser wavelengths. Several known physical trends associated with laser propagation will be reproduced, and the results will be compared to the industry accepted propagation code Wavetrain. The results of ANCHOR studies will indicate that the 100 kW-class high energy laser can effectively engage slow-moving targets at ranges greater than five kilometers in clear weather by delivering enough energy to melt 0.1 liters of one millimeter-thick aluminum aircraft skin in five seconds. For hazy, turbulent, and rainy conditions, the laser can effectively engage targets from ranges closer than three kilometers, but reasonable dwell times are only achieved for ranges closer than two kilometers.

[1] https://core.ac.uk/download/pdf/36734846.pdf

That sounds like a lot of caveats. Five seconds sounds like a long time to track a target like that precisely enough to melt the skin.

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