Airborne defense systems based on gas-dynamic lasers for the Russian Aerospace Forces
Active defense
The issue of the need to equip domestic aircraft and helicopters with combat and auxiliary equipment aviation on-board self-defense systems against attacking ammunition, missiles The author has repeatedly raised the issue of air-to-air (A-A) and anti-aircraft guided missiles (SAMs) of the enemy on the pages of Military Review.
In this case, we mean precisely the systems that ensure the physical destruction of attacking munitions, and not their suppression, for example, by means of electronic warfare (EW) or their diversion to the side using ejected or towed traps.
There are various ways to implement on-board self-defense systems for aircraft, for example, using small-sized air-to-air interceptors, which are essentially air-to-air missiles with reduced range and dimensions – we discussed this earlier in the article Air-to-air anti-missile missiles.
An image of the MSDM interceptor concept compared to short- and medium-range air-to-air missiles.
In principle, conventional air-to-air missiles with the necessary seeker sensitivity to lock on incoming enemy missiles could also be used as interceptors. However, it is more effective to develop air-to-air interceptors as a separate class of weapons due to the specific nature of the targets they engage and the need to intercept them at relatively short ranges. Interceptors can be made smaller and lighter than air-to-air missiles.
For heavy bomber, transport, and support aircraft, close-in defense systems based on rapid-fire automatic cannons and projectiles with remote detonation along the trajectory can be implemented – we also discussed this in an earlier article Return of the "heavenly fortresses": airborne air defense rifle and gun system.
The problem is that airborne self-defense systems based on rapid-fire automatic cannons can only be installed on large subsonic aircraft.
We also previously considered such a direction as active protection systems for aircraft equipment (KAZ AT), capable of defeating attacking enemy missiles using shrapnel munitions or unguided munitions detonated remotely along the trajectory. Potentially, the AT APS could be based on the aforementioned L-370 Vitebsk airborne defense system or on other APS systems for ground vehicles.
Active protection systems for aircraft are unlikely to be able to protect against heavy long-range SAMs, such as the 48N6 family of missiles of the S-400 system with their powerful warheads weighing 150-180 kilograms. At the expected operating range of the AT APS, the detonation of such SAMs will most likely still damage or destroy the protected aircraft. However, AT APS can be quite effective against SAMs and air-to-air missiles with small warheads or those attacking using the direct hit-to-kill method.
Northrop Grumman Corporation's concept for an integrated air defense system with guided munitions – possibly already implemented on the B-21 Raider strategic bomber
By the way, the KAZ AT would be especially useful now in the zone of the Russian special military operation (SVO) in Ukraine as a means of protecting combat helicopters from FPV-drones, man-portable air defense systems (MANPADS) and anti-tank guided missiles (ATGMs).
Finally, one of the most promising areas is the development of airborne laser defense systems (ALDS) – their main advantage is their relatively unlimited ammunition supply and the speed of light with which the laser beam reaches its target.
When they talk about laser weapons, they'll certainly think of bad weather—rain, snow, fog, and smoke screens. While it's undeniable that various atmospheric phenomena impede the propagation of laser radiation, their significance is greatly exaggerated. Just because something is invisible to the eye doesn't mean it's opaque to other wavelengths. There's a concept called an atmospheric transparency window, where the atmosphere's influence on a certain wavelength range is minimal.
As for aviation, high-altitude flights offer practically ideal conditions for laser weapons: on the one hand, there's high atmospheric transparency, and on the other, there's sufficient airflow to remove excess heat from the laser. It's especially important to consider that we plan to use laser weapons for self-defense against SAMs and air-to-air missiles, not to shoot down incoming ballistic missiles from a thousand kilometers away (and the US has even considered that).
The power of light
Experiments with mounting laser weapons on aircraft were conducted back in the 20th century. However, back then, these were heavy transport aircraft, as only they could accommodate the massive chemical or gas-dynamic lasers of the time. Even then, the possibility of destroying air-to-air missiles with lasers was confirmed. However, The deployment of powerful gas-dynamic combat lasers on heavy aircraft carriers is now fully justified for use against enemy personnel and equipment..
Image: Lasers and Laser Systems. Photonics, Vol. 14, No. 8, 2020
Gas-dynamic combustion CO2 lasers were developed back in the 70s and 80s. Megawatt-class laboratory gas-dynamic lasers developed in the USSR and the USA, as well as a 400 kW American laser of the same type, along with a beam steering system, installed on the ALL flying laboratory, made it possible for the first time to practically test and evaluate the scale and complexity of the technological challenges involved in creating laser weapons... Lasers and Laser Systems. Photonics, Vol. 14, No. 8, 2020.
However, by the early 21st century, advances in the development of powerful and compact lasers allowed consideration to be given to their installation on tactical aircraft and helicopters. Advances in laser weapons were primarily driven by the increased efficiency and power of solid-state and fiber lasers, which do not require expensive and fire-hazardous consumables like chemical lasers and are powered by electricity.
This is precisely the direction in which the world's leading powers are currently concentrating their efforts. The leaders here are the United States, China, Israel, the United Kingdom, and France. Some work is underway in Turkey, but the big question is who makes the laser modules themselves.
Contrary to the opinion of skeptics, progress in this direction is proceeding quite quickly. In particular, solid-state lasers with a power of tens of kilowatts, placed on the wheeled chassis of the Striker armored personnel carrier, are already being tested in the US Army, the Israeli Armed Forces (AF) announced the adoption of laser air defense systems, whose output power is expected to exceed 100 kW, and China presented the Laoxian-1 naval cannon, with an output power of 250 kW.
Regarding Russia's high-power solid-state and fiber laser programs, everything is shrouded in secrecy. Based on open-source development data in this area, it can be assumed that the power of Russian solid-state and fiber lasers, which will be used in advanced air defense systems in the near future, will be approximately 25-50 kW.
So far, the dimensions of laser systems only allow us to speak with confidence about the possibility of their deployment on strategic and transport aircraft, in particular, there is a possibility that onboard A laser self-defense system could be installed on the newest American strategic bomber, the B-21 Raider.Even if the B-21's current configuration does not include laser weapons, it is likely that space has been reserved for them in the design, and power takeoff devices and electric generators are installed on the turbojet engines.
However, it's only a matter of time; eventually, combat lasers are guaranteed to make their way onto tactical aircraft, and these could be either built-in solutions or fully autonomous modular systems mounted on external slings.
The problem of providing laser weapons with electrical energy must be mentioned separately.
Current strength
The efficiency of modern high-power solid-state lasers is on average about 25%, meaning that to power a 50 kW laser, 200 kW of electrical power is required.
In fact, generating such power in aircraft has long been a relatively simple task. For example, the generators mounted on the turbojet shafts of the American E-3 Sentry airborne early warning and control aircraft (AEW&C) produce approximately one megawatt of electrical power—and this aircraft is already several decades old. There's no doubt that a couple of hundred kilowatts could be squeezed out of the turbojet engines of tactical combat aircraft, had this been the original design goal, even if it meant slightly increasing the aircraft's overall weight.
Primary and secondary energy sources, as well as energy converters, have made significant progress in our time, thanks in large part to the rapidly developing electric vehicles. For example, the need to ensure fast charging of electric vehicles has driven the development of power electronics; in China, for example, charging stations with a capacity exceeding one megawatt have already appeared.
Some Tesla electric vehicles have a battery capacity of 100 kWh and weigh 900 kilograms, meaning such a battery would provide approximately half an hour of continuous operation for a 50 kW laser with an efficiency of 25%. The efficiency and power density (per unit mass) of electric motors and generators are gradually increasing—the latter are actively developing not only in electric vehicles and electric aircraft, but also in the context of "green energy," despite the criticisms leveled by proponents of traditional power generation methods.
Chain of transformations
There are two options for deploying combat lasers on aircraft carriers, the first of which is to place the laser emitter and batteries for its power on the external sling of existing aircraft carriers.
The second option is the deep integration of laser weapons, including power sources for them, into the design of promising, currently being developed and extensively modernized aviation systems. Moreover, batteries in such an integrated combat laser system will most likely still be present as a buffer between the generator and the laser emitter.
The second option will always have advantages in terms of power and operating time, while the first option will potentially cover a much wider range of aviation systems.
It should be noted that in the second option we have a chain of transformations with a loss of efficiency - the energy of the turbojet engine shaft is converted by the generator into electrical energy, after which it is stored in a buffer battery and only then converted into laser radiation, and if we are talking about a laser with an efficiency of 25%, then with an 80% efficiency of the electric generator and a total efficiency of 80% of the charge-discharge of the batteries (taking into account high currents and complex temperature conditions), the final efficiency will be only 16%.
On the other hand, the efficiency of promising solid-state lasers can exceed 70%, and the efficiency of generators and batteries can exceed 90%, in which case the total efficiency will already be over 60%, which is quite a lot.
However, taking into account possible Given the risks of our country falling behind in the development of combat laser systems based on solid-state lasers, as well as related products—compact and powerful electric generators and capacious high-current batteries—it is advisable to consider other options for equipping domestic combat aircraft with laser weapons, in particular, switching to the direct conversion of turbojet engine energy into laser radiation.
Direct transformation
One of the areas of laser weapon development in which our country achieved good results back in the Soviet era is the aforementioned gas-dynamic lasers, in which the energy of gases accelerated to supersonic speeds in a turbojet engine is directly converted into laser radiation.
Image Photonics Vol. 14, No. 8, 2020
Using such lasers on ground-based platforms is not very convenient due to the fact that each laser requires an expensive and difficult-to-maintain gas turbine. However, turbojet engines are installed "by default" on combat aircraft. Therefore, by capturing a portion of the exhaust gases from turbojet engines on combat and support aircraft, they can be used to generate laser radiation in integrated airborne laser defense systems.
This idea does not belong to the author of this material at all – the proposal for the implementation of on-board laser systems based on gas-dynamic lasers, by taking part of the turbojet engine power, was published in the publication Photonics, Volume 14, Issue 8, 2020.
...there are GDL variants that use ambient air supplied by the compressor of an aircraft gas turbine engine (GTE) as the oxidizer, with the majority (over 95%) of the fuel taken from the atmosphere. This allows for a significant reduction in component storage requirements, as the transported supply only includes fuel, which accounts for no more than 5% of the total consumption. This laser appears quite promising for deployment on aircraft... Lasers and Laser Systems. Photonics Vol. 14, No. 8, 2020.
Image: Lasers and Laser Systems. Photonics, Vol. 14, No. 8, 2020
...the output power characteristics of a gas dynamic laser using a kerosene-air fuel composition based on two AL-31F aircraft engines are presented. It is evident that, using two engines with a high pressure ratio and high flow rate, even with only 5% air extraction, a laser power of approximately 80 kW can be achieved in an uncooled nozzle block (laser prechamber temperature no higher than 1500 K). Using cooled nozzle vanes and a prechamber temperature of approximately 2000 K, the power can be increased to 135 kW... Lasers and Laser Systems. Photonics Vol. 14 No. 8 2020.
Conclusions
Of course, it's highly likely that electrically powered lasers will dominate combat lasers in the near future—these devices are the easiest to operate, relatively easy to scale, and can be deployed on a wide variety of platforms. At the same time, gas-dynamic lasers could well be in demand in aviation, where the working fluid needed to pump them is produced "naturally."
The topic of combat lasers in our country is quite closed, so it is difficult to reliably judge the state of affairs in this area. However, in the event that we do not have high-power solid-state combat lasers (on the order of hundreds of kilowatts) close to being adopted into service, we should return to the topic of gas-dynamic lasers with regard to their integration into existing, deeply modernized, and future aviation systems.
The main problem is that integration must occur at the earliest possible stage, and it must involve not only the developers of the aircraft or helicopters equipped with gas-dynamic laser weapons, but also the developers of the turbojet engines from which these lasers will receive pumping.
It is possible that somewhere here an ABLCO based on a gas-dynamic laser, receiving pumping from two turbojet engines of a fighter, could be located
Of course, no one wants any extra hassle, so the development of airborne laser defense systems based on deeply integrated gas-dynamic lasers is only possible with the active interest of the Russian Aerospace Forces.
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