Comment by hbd-investor | Hacker News Reader

Comment by hbd-investor | Hacker News Reader

Parent Full thread

You are wrong MiroslavPokorny

The physics change entirely when its Air to Air laser defense vs Ship to air laser defense.

There are numerous things that shift the math

1. Speed difference

The Stealth fighter is moving at mach 2 The Ship is moving at 40 mph

A fleeing stealth fighter will be able to fire at the incoming missile far longer

2. Atmospheric difference

At sea level, humidity, salt spray, and atmospheric thermal turbulence absorb beam energy, causing thermal blooming

At Sea Level: Air density is 100%. A 100 kW laser beam diverges quickly and may struggle to keep a tight focal point beyond 3 to 5 km.

At 45,000 Feet: Air density drops by 80% down to roughly 20% and water vapor is almost zero.

3. Missile types and threat profiles

The missile likely to take down a stealth fighter is a infrared air to air missile. They have glass domes that allow light and heat to enter. Thus vulnerable to getting blinded

The missile likely to take down a ship is a hypersonic antiship missile, is likely using a AESA seeker and sporting a extremely tough and heat resistant ceramic dome. You cannot blind a AESA seeker, a ship would need a hard kill and to try to burn through a missile body designed to survive the extreme heat and force of moving at hypersonic speeds at low altitudes.

------------------------------------------------------

The physics change entirely, it makes tons of sense from a physics standpoint to have a defensive laser on a fighter jet to defend from air to air missiles. A laser system would prevent infrared missiles from hitting your stealth jets.

While for ships it makes no sense, A laser system can't burn through a hypersonic antiship missile fast enough and will just be a waste.

And before you bring up, muh power the J-36 has 3 engines this is why the chinese put in a 3rd engine inside their 6th gen fighter, the intent of the design was always to install a defensive laser

> The Stealth fighter is moving at mach 2 The Ship is moving at 40 mph

Irrelevant, lasers move at the speed of light.

> At sea level, humidity, salt spray, and atmospheric thermal turbulence absorb beam energy, causing thermal blooming

> At Sea Level: Air density is 100%. A 100 kW laser beam diverges quickly and may struggle to keep a tight focal point beyond 3 to 5 km.

> At 45,000 Feet: Air density drops by 80% down to roughly 20% and water vapor is almost zero.

THis may all be true, but the problems of heating dynamics remain. A laser cannot requires cooling times for both plane and ship because of heat, which limits the frequency it can be used.

> The missile likely to take down a stealth fighter is a infrared air to air missile. They have glass domes that allow light and heat to enter. Thus vulnerable to getting blinded

> The missile likely to take down a ship is a hypersonic antiship missile, is likely using a AESA seeker and sporting a extremely tough and heat resistant ceramic dome. You cannot blind a AESA seeker, a ship would need a hard kill and to try to burn through a missile body designed to survive the extreme heat and force of moving at hypersonic speeds at low altitudes.

Dont tell me, tell the he navies of the world who have tried and failed to create lasers mounted on ships.

>Irrelevant, lasers move at the speed of light.

I don't think you understand the setup

Setup number 1 = Fighter is fleeing at mach 2 from a mach 5 missile

Setup number 2 = Ship is fleeing at 40mph from a mach 5 missile

Lasers moving at the speed of light is irrelevant, what matters is the engagement time and dwell time

engagement time = time it takes missile to hit target from 10km range (estimated range of laser effectiveness)

Dwell time = How long the laser needs to shine on a target before cooking it China's J-36 will be moving at mach 2 and blasting the missile with the defensive laser.

The ship will be doing the same. What this means is that China's J-36 will have around a 12 second window to blast the missile. The ship only has around 5 seconds before it impacts!

>THis may all be true, but the problems of heating dynamics remain. A laser cannot requires cooling times for both plane and ship because of heat, which limits the frequency it can be used.

The laser is only for defensive applications, its not going to be blasting for 10 minutes straight. It only needs around 3 seconds of dwell time to cook air to air missiles that are fired at it. The J-36 can handle this by using the heat from the laser to dump to heat into preheating its fuel.

>Dont tell me, tell the he navies of the world who have tried and failed to create lasers mounted on ships.

Because they don't work on sea - The laser is too weak, the target profile is designed to resist heat, and the engagement times are too short. While in a plane vs missile, the laser is stronger (less atmosphere and vapor), The target profile is vulnerable (Primary method to hit a stealth fighter is to use a heatseeking missile and not using a radar seeker), and engagement time is longer (Fighter is fleeing at mach 2)

Let me throw up some numbers for the 2 scenarios

1. Naval Ship vs. Inbound Hypersonic Missile

Missile: Mach 6 (1,950 m/s at sea level) carrying a UHTC ceramic matrix nose cone (2.5 cm thick) protecting an active millimeter-wave radar seeker.

Laser: 300 kW class Naval Solid-State Laser (SSL).

Engagement Envelope: Starts tracking at 15 km; laser fires at 10 km (optical line-of-sight window).

Time required to disable missile: 1.5s (tracking) + 3.8s (dwell) = 5.3 seconds

Time for Hypersonic missile to hit : 5.12 seconds

2. J-36 vs. Air to Air Missile

Missile: Mach 5 (1,475 m/s at 35,000 ft) tail-chasing the jet. Carrying a toughened Sapphire/Yttria optical dome covering a dual-band Infrared Search & Track (IRST) seeker.

Fighter Jet: J-36 fleeing at Mach 2 (590 m/s at 35,000 ft).

Laser: 100 kW class internal pulse-burst laser.

Engagement Envelope: Laser fires rearward at 10 km distance.

Time required to disable missile: 1.2s (tracking) + 1.6s (dwell) = 2.8seconds.

Total time before impact: Because the J-36 is fleeing at Mach 2, it takes the missile 11.3 seconds to catch up and hit the J-36.

Conclusion

The ship with a 300kw laser, will take 5.3 seconds to disable a hypersonic anti ship missile. The hypersonic antiship missile will take 5.12 seconds to hit the ship.

The J-36 with a 100kw laser, will take 2.8 seconds to disable a Air to Air Infrared missile. The air to air missile will take 11.3 seconds to hit the J-36.

*Adding a note the 1.6 seconds dwell is how long it takes to cook the air to air missile. But within .2 seconds it is already blinded.

So my analysis is biased

For the ship scenario the ship needs to completely cook the missile, the missile is protected by ceramics and seeing with AESA

For the J-36 scenario the missile has a glass dome and is using a heat seeker. .2 seconds of direct laser is enough to blind it and destroy detector elements.

To add, it is entirely about target profile.

Larger airborne lasers have been tried and failed, i.e YAL1 needed magnitude more power, but that was to intercept ICBMs shielded to survive rentry.

100 kW and 10s dwelling in atmosphere theoretically works for AA intercepts.

What's slept on is it lasers also potentially like scifi tier infinite ammo laser gun vs subsonic targets... like drones and cruise missiles. You don't have to line up gun runs (which J36 doesn't even have). The limit is basically how fast heat exchange dumps laser heat into fuel burn, but lazy llm math suggest like... multiple targets per minute with off boresight engagement - i.e. all targets within 10km cone/swath. This absolute game changer / flips economics against any budget drone precision complex adversaries.

Reply on news.ycombinator.com