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Power systems, thermal management and cooling technologies are critical for wide employment of directed energy weapons

A directed-energy weapons (DEW) are ranged weapon systems that inflicts damage at a target by emission of highly focused energy, including laser, microwaves and particle beams. Potential applications of this technology include anti-personnel weapon systems, missile defense system, and the disabling of lightly armored vehicles or mounted optical devices

 

Laser weapons use high power lasers to damage or destroy adversary equipment, facilities, and personnel. The technology provides major advantages for military applications due to High precision and rapid on-target effect, precise and scalable effects, Avoidance of collateral damage caused by fragmenting ammunition, Low logistics overhead and minimum costs per firing. Laser weapons have already been employed on warships and military trucks. After warships US has plans to employ laser weapon on airborne platforms.

 

Earlier this year, NAVSEA released its latest Naval Power & Energy Systems Technology Roadmap led by the Electric Ship Office, which stated that the US Navy was “on the cusp of revolutionary changes” that will take the form of “high-power pulsed mission systems”. “These include directed energy weapons such as lasers and stochastic electronic warfare systems, radiated energy systems such as the air and missile defense radar, and advances in kinetic energy weapons, including electro-magnetic railguns,” said Stephen Markle, the director and program manager of PMS 320.

 

The development of laser weapons requires many critical technologies, first is development of lasers capable of generating powers in kilowatts to megawatts range to be able to produce useful damage effects on the target. For instance, to destroy anti-ship cruise missiles would require a beam of 500 kilowatts and demand megawatts of power.

 

Laser weapons require  energy storage technologies that will allow a ship to fire multiple shots from a high-powered laser without taxing the ship’s electrical system. Future all-electric ships may generate enough power that additional
energy considerations are not necessary but older ships may need to be back fitted with these weapons as well. If the ship’s power generation system is unable to directly power the laser, then energy storage methods must be considered. These “energy magazines” would provide the necessary power for multiple engagements, and then be recharged during downtime.The four candidates are Lead acid batteries, lithium ion batteries, supercapacitors, and flywheels.

 

Existing lasers generally dissipate two-thirds to three-quarters of the energy as heat, requiring still-bulky cooling equipment to avoid overheating damage. If an laser  is 25% efficient, then for every kilowatt of energy leaving the weapon there are 3 kW worth of heat to be removed from the system. Scaled to hundreds of kilowatts  this results in massive new loads on the ship’s cooling system. Air cooling can yield an unacceptable delay between shots.

Powering  High power Microwave directed energy Weapons

High power microwave systems emit concentrated microwave energy to jam, disrupt or destroy the electronics of wide range of Air and ground targets including command and control systems, UAVs, military vehicles etc. Recent technical advances may allow high power microwave (HPM) directed energy weapons (DEW) for deployment on aircraft soon. Heat production, is an important issue in high power microwave directed energy weapons due to high repetition rate multi gigawatt sources and pulse power systems. A small, light-weight cooling/thermal management system is required for integration into a HPM DEW system, which integrates into, military vehicles. A thermal management, cooling system is also needed for integration with each of the high power microwave source.

 

Major obstacles in their application will require effective solutions in high heat flux thermal management and reducing the mass of the components. An innovative lightweight thermal management concept providing high heat flux capability for HPM source devices for DEW systems is proposed.

 

The thermal approach utilizes enhanced cooling mechanisms (subcooled nucleate flow-boiling cooling) coupled with an optimized cooling channel geometry that can be integrated within the HPM structure. The concept provides both improved thermal performance (capability up to 500 W/cm2) and a low mass thermal management system for projected aircraft DEW applications. The enhanced heat transfer allows much higher heat flux operation yet maintains the structure’s temperature. The overall design concept provides a mass efficient and highly effective thermal control approach that will provide necessary enabling technology for successful deployment of advanced HPM directed energy weapon systems.

 

 

Energy Storage

Few power systems onboard ships can support sustained usage of a highpowered laser without additional energy storage. This magazine stores energy for on-demand usage by the laser. It can be made up of batteries, capacitors, or flywheels, and would recharge between laser pulses. The energy magazine should allow for sustained usage against a swarm of targets in an engagement lasting up to twenty minutes. Ideally, it would charge up as fast as it discharges, allowing for indefinite use (as long as there is ship’s fuel to expend). Low maintenance, high safety, and long lifespan are other desirable characteristics.

 

Typical lead-acid batteries have changed little in the last hundred years. They are readily available and come in many varieties and sizes but share similar construction. Two metal plates, one lead and one lead-oxide, are immersed in a
sulfuric acid solution. This creates one cell, which typically produces 2.1 volts.

 

Lithium ion batteries work similar to lead acid, but with different elements. A typical construction consists of a sheet of Lithium-cobalt-oxide and a sheet of carbon separated by an insulator. These sheets can be rolled and immersed in
an electrolyte, allowing for the passage of charges between the cathode (Lithium) sheet and the anode (carbon) sheet. The layers of lithium and carbon constitutes a cell that has a potential charge of 3.7 volts,12 making them more compact than the lead acid cell that stores only 2.1 volts.

 

Advantages and disadvantages are similar for all batteries. Batteries have high energy density and specific energy. They maintain their charge for many hours or even days in a stable, readily available form. The construction of
individual cells allows for modular design, making their additions, subtractions, and replacements onboard ships simple. Many different designs and manufacturers are available for all types of batteries. Lithium based batteries
continue to advance in design due to their extensive use in consumer products.

 

Batteries have some drawbacks. Their discharge rate is limited and they produce large amounts of heat during heavy use, which may affect their performance. Their charge rates are much slower than their discharge rates. A given amount of energy taken out of the battery in 15 minutes can take hours to put back in. Over time, less than ideal charge and discharge rates and depth of discharge can lead to a loss of capacity.

 

Capacitors are a mature technology that has risen as a competitive energy storage option with the development of supercapacitors. The latest advance in capacitor technology is the supercapacitor. In a supercapacitor, a carbon electrode coated with a porous material (usually activated charcoal) is inserted into an electrolytic solution. The walls of the pores provide the charge surfaces for the storing charge and the electrolyte connects them in series. The discharge rate for the supercapacitor is slower than for a regular capacitor, a trade-off for higher energy storage. Supercapacitors are still limited to ~2.7 volts and a specific energy density of 30Wh/kg. This is one fifth of that for a lithium ion battery. The voltage limitation can be overcome by adding cells in series.

 

Advantages of capacitors include a very high cycle life and charge rates that nearly match discharge rates. Also, super capacitors can be “floated” for long lengths of time. This means that they will hold their charge (potential energy)
for a long period without a large residual decay. Shelf life is comparable to batteries and depends upon the type and design of the capacitor

 

Flywheels are an old technology being used in a new way. Storing energy in the form of inertia avoids many of the disadvantages of batteries and capacitors. The technology is relatively simple. Flywheels use motor-generators attached to spinning discs and convert mechanical energy to electrical energy and back again at >95% efficiency.23 Increasing either the rotational speed or the mass of a flywheel allows it to store more energy.

 

Flywheels have a very high efficiency during cyclic operation. With magnetic bearings there are no wear parts that require replacement. Unlike batteries and capacitors, there are no chemicals or gassing issues. One of the largest advantages is that the flywheel can be charged almost as quickly as it can be discharged at the power levels required by high-energy lasers.

 

Capacitors traditionally have a very low capacity to hold energy but release it very quickly, similar to a spark. Batteries are very high in energy density, but much slower when releasing that energy. Flywheels and supercapacitors fall in between.

 

UK’s DSTL from F1 to laser weapons

The UK’s Defence Science and Technology Laboratory is working with UK industry and the US Navy to explore advanced energy storage options for British warships. The UK’s DSTL is working closely with British aerospace and automotive component specialists GKN to explore this technology. DSTL and GKN have come up with the Flywheel energy storage system (FESS), which uses high-speed and lightweight flywheels to provide high-power electric pulses.

 

In 2009, Formula 1 engineering (F1) introduced the kinetic energy recovery system, or KERS, which allowed a power boost of 80bhp for 6.6 seconds using energy generated under braking that was then stored in a motor generator unit or electric flywheel. Later F1 had effectively entered the hybrid age, utilising electric power along with the standard internal combustion engine.  Defence industry, is now adapting this technology to new equipment that will require intensive energy loads, such as directed energy weapons.

 

As well as working closely with UK industry, DSTL has partnered with research organisations within the US Navy to test the FESS for naval applications. This bilateral testing has been “fundamental to the success of the project”, according to the UK MoD, and carried out under what is known as the Advanced Electric Power and Propulsion Project Arrangement.

 

He added: “Legacy power systems found on all existing ships do not possess the inherent electrical ‘inertia’ to withstand the ramp-up/down (on/off), or ripple (pulsation) effects of complex power profiles of these advanced mission systems.”

 

For the UK-US testing of FESS, the teams involved have used an approach known as power hardware in-the-loop, which sees the integration of a real FESS system into a virtual ship power architecture that emulates a Royal Navy operating in real time. This was initially carried out at Florida State University, and was then brought to the Power Networks Demonstration Centre in Scotland to advance the UK’s PHIL capabilities.

 

“This project gave us a great opportunity to showcase the PHIL test-bed that we’ve developed at PNDC,” said Kyle Jennett, the PNDC MOD programme technical lead, in a UK MoD statement. “This test bed lets us connect real-world hardware, like the FESS, to simulated naval platforms to evaluate the impact on the ship during different operational scenarios.”

 

In the future, this technology could ease the integration of next-generation weaponry onto naval vessels, including the UK Dragonfire, which is being developed by DSTL and UK industry as part of the laser directed energy weapon capability demonstrator programme. It is hoped that in the future UK DragonFire will drastically reduce the cost of engagements, as well as providing crews with a range of options for defeating incoming vessels, drones and indirect-fire attacks. In the US, there is also a flurry of activity on directed energy weapons, as well as electromagnetic railguns that can propel solid projectiles at hypersonic velocities.

 

Rolls-Royce unveils hybrid power system for laser weapons

Rolls-Royce has developed   an integral system required to operate laser weapons on the battlefield. The system is also considered hybrid as it combines a battery with the engine. That technology is an integrated power and thermal management system capable of powering a 100-kilowatt-class laser weapon, according to Mark Wilson, LibertyWorks’ chief operating officer.

 

The system uses the company’s well-known M250 helicopter engine — that was used in the OH-58D Kiowa Warrior helicopter and is also found in the Little Bird and the AH-6i helicopters — which allows the system to generate roughly 300 kilowatts of electrical power and 200 kilowatts of thermal management capacity, Wilson said.

 

The engine “allows us to have continuous operations as long as you have fuel available,” which leads to an endless magazine of laser shots, he said. The battery allows “instantaneous power, so you don’t have to have the engine running all the time,” Wilson said. “You can start running on the battery and then switch over to the turbine engine once it’s up to speed.” And the engine, when it’s running, can recharge the battery, he added.

 

The system is designed to fit inside the same vehicle as the laser weapon itself. Up until now, demonstrations of laser systems have focused on scaling and building up the technology of the weapon itself and so the services have used commercial off-the-shelf diesel generators and cooling systems that require a separate trailer.

 

“Our idea here is we want to package it in a size that can fit along with the laser system onto a vehicle, a type of a truck or eventually a ship or even eventually airborne, so the focus of our research is on developing that kind of capability that can go on an actual platform,” Wilson said.

 

To date, Rolls-Royce has done “quite a bit of work” in terms of designing, testing and modeling the system. The company plans to go through another round of testing beginning soon and lasting through the end of May and possibly into June. That testing is in preparation for sending the system down to be field-tested this year with Lockheed Martin’s laser weapon system.

 

Lockheed Martin, partnered with Dynetics, is competing — head-to-head with Raytheon — to build a powerful 100-kilowatt laser for the U.S. Army, which pushes the envelope on directed-energy capability development.

 

The winner of the competition will integrate its laser system onto the Family of Medium Tactical Vehicles (FMTV). And that is the size of truck that Rolls-Royce has its eye on for fitting its own power and thermal system.

 

But the company believes its technology is scaleable when it comes to powering different laser weapons and when it comes to the platform on which a laser weapon might find itself, Wilson said. That could be an Army vehicle, a naval vessel or a medium transport airlifter. The Army, for instance, is testing laser weapons on a Stryker combat vehicle.

 

The goal is for the services to see the utility of such a system because it will allow “customers to move past current low-power, low duty-cycle demonstrations by solving many of the difficult issues integrating high-power output with matching levels of thermal management,” Wilson said in a May 10 statement.

 

 

 

 

 

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