DIRECTED-ENERGY WEAPONS, THE ONCOMING REVOLUTION IN WEAPONRY

By Jerome Bilet, PhD

As a preamble to this article, we are endorsing the premise that conventional weapons are nearing their peak technical capability and that, unless we invest in the development of directed-energy weapons (DEWs), time and loads of money are going to be spent in pursuing the so-called “next generation” of kinetic everything, from aircrafts, missiles, vehicles, to combat ships ... all of them prone to be zapped by DEWs. It is predicted that DEWs will pose a drastic and unprecedented threat to future military assets in the next 5 to 10 years.

Introduction

Technological innovation has not only altered the course of warfare, but also created an endless race since each progress is generating a countermeasure, leading to further progress, leading to new countermeasures1, and so forth.

Ever since gunpowder was invented in China around the 9th century, weapons efficiency no longer depended on the physical strength of the warrior handling them, but on the chemical energy of their propellant or explosive. Although the power of these compounds improved, the fundamental operating principle of these chemical-powered weapons is unchanged2 and they still exhibit substantial shortcomings. To overthrow targets, conventional weapons depend on the kinetic/chemical energy of a projectile – which must travel a tangible distance (taking a certain time) – as a result a lot of energy released by these weapons is wasted. Missile systems are also reaching their apex and there are inherent limitations to traditional global strike systems (e.g. bombers or ICBMs/SLBMs).

The race progress/countermeasure sent the cost of conventional weapon systems skyrocketing. As a result, the cost of defending assets may be disproportionate when compared to the cost sustained by the attacker. It has been estimated that if China were to launch a salvo of 30 ballistic missiles at US forward bases and assuming the US uses two interceptors (e.g. PAC-3, THAAD or SM-3) at each incoming missile, the US would spend approximately $700 million (against a cost of $70-105 million for the attacker). The cost-exchange ratio is clearly not viable on the long run and must be fixed3.This is well illustrated by the famous statement of Norman Augustine when he was explaining that defence budgets grow linearly but the unit cost of a new military aircraft grows exponentially “in the year 2054, the entire defence budget will purchase just one aircraft. This aircraft will have to be shared by the Air Force and Navy 3-1/2 days each per week except for leap year, when it will be made available to the Marines for the extra day”.4

Henceforth, we are now facing a very genuine interrogation: can the “blast and fragmentation” kinetic weapon technology advance any further? The answer is “maybe”, but not without limits as we are already reaching the kinematic and aerodynamic boundaries set by Newtonian physics, and even though they may move a little bit further, their incremental cost will surge drastically. We are reaching the practical limit of chemical propellants for guns; extracting more power demands some as yet unpredicted breakthrough in chemistry.

Directed-Energy Weapons (DEWs)

DEWs use non-kinetic directed energy primarily as a straight means to damage or destroy (with either lethal or non-lethal effects) equipment, facilities and personnel. In their Electronic Warfare publication, the US Department of Defense (DOD) defines a directed-energy weapon as “an umbrella term covering technologies that produce a beam of concentrated EM energy or atomic or subatomic particles”.

1 An example was presented by M. Gunzinger (see footnote 3): today, the US sophisticated reconnaissance-strike complex (RSC) is challenged by competing RSC, such as the Chinese anti-access/area-denial (A2/AD) strategy or the Iranian one (the latter leveraging the geography of the Persian Gulf, using anti-ship cruise missiles-ASCMs and a swarm of fast attack boats). 2 Kochems, Alane and Gudgel, Andrew. “The Viability of Directed-Energy Weapons” The Heritage Foundation, 28 April 2006 3 Gunzinger, Mark. “Changing the Game, the Promise of Directed-Energy Weapons”. CSBA, 2012 4 Norman Augustine was the US Under Secretary of the Army between 1975 and 1977

The concept of DEW is said to have originated in 212 BC in Greece, when Archimedes allegedly used polished parabolic mirrors to direct sunlight on the sails of Roman ships while defending the city of Syracuse; fact or fiction? … most likely the latter. The notion of “heat ray” was revived by HG Wells in his book “The War of the Worlds” published in 1898, and was the subject of extensive researches by the visionary Nikola Tesla in the 1930s.

The theory behind DEWs is fairly evident since Einstein conceived his mythical equation, e = mc2. On its most basic level, this equation states that energy and mass are interchangeable; in other words, they are different forms of the same thing. This means that under the correct settings, energy can turn into mass and vice versa. This equation allows conceptualising why electromagnetic energy, a fundamental force of the Universe, can be turned into practical energy weapons.

Electromagnetic energy (EM) is present everywhere and, contrarily to nuclear energy, is clean, rather malleable and able to be directed. DEWs use EM waves and also subatomic particles (particles with mass) to attack targets at, or near, the speed of light. The first application of the fact that atoms can be stimulated to emit directed-energy was the laser. Other sources of directed-energy include microwaves (MW), radio frequency (RF) or high-energy radio frequency (HERF), particle beam and plasma.

DEWs Distinctive Features

DEWs display several distinctive features5.

Speed of Light Engagement As EM energy travels at the speed of light, DEWs reach their targets at or at near the speed of light

Repetitive/Deep Clip Capacity DEWs have a virtually unlimited magazine capacity, which allows repetitive engagements (as long as consumables, like power, are available)

Cost Effective

Even though their initial development cost may be high, DEWs offer a minimal cost of engagement (low cost per use and maintenance). As an example, circa $1 per shot vs. $3.3m for a PAC-3, Patriot Advanced Capability-3 missile

High Penetration Power & Long Range

Some DEWs emit energy that can pass through walls at distances of hundreds of metres or even kilometres. Some can pass through most unshielded structures. DEWs have long distance projection in the tens of kilometres (e.g. the ABL demonstrated on the Boeing testbed aircraft had a destructive range in excess of 100 kilometres)

Precision/Accuracy

DEWs are extremely precise, even at very long distances. They have pinpoint accuracy (they undergo diffraction-limited propagation along a geodesic6); you shoot what you see, this allows also to follow manoeuvring targets

Simplified Pointing & Tracking DEWs are simple to track, aim and shoot. No need to compute ballistic trajectories, just direct the beam at the target

Multiple Target Engagement DEWs can engage multiple targets

Rheostatic (Tuneable/Scalable)

Operators can tune/scale the amount of energy (power) or the wavelength (frequency) emitted by DEWs, thus producing a beam with non-lethal to lethal, or from disruptive to destructive, effects

Stealth DEWs are silent and almost undetectable through casual observation

5See also: “Directed-Energy Weapons – Technologies, Applications and Implications”. The Lexington Institute, 2003 6 Harris, Stephen. “Laser Weapons”, the Engineer, 9 May 2013

Immune to Environment

Beams are indifferent to gravity and atmospheric drag (they have no mass). Some DEWs can operate in all weather conditions

Versatile DEWs, such as lasers, can also work as sensing devices

Challenges & Countermeasures

The remarkable distinctive features of DEWs should not hide the fact that their development (long, intensive and expensive) and operation face challenges primarily linked to power, temperature and the environment in which they operate.

DEWs need a lot of power and require the development of very powerful energy sources. DEWs generate masses of heat (they have low electrical efficiency) and thermal management/cooling is still a critical issue. But let’s not fail to recall that these concerns also apply to the development of future kinetic weapons.

The energy propagation of DEWs must cope with atmospheric propagation loss, absorption, scattering, turbulence, thermal blooming and diffraction7. Under adverse weather conditions, lasers can be prevented from operating with efficiency and precision as their beam can be disturbed or scattered by turbulences, clouds, rain, smoke and dust. Microwaves devices are much less vulnerable to atmospheric interferences. Conversely, diffraction can be used as an advantage when high-powered microwaves (e.g. e-bombs) are meant to irradiate a large area. Particle beams do not propagate efficiently in the atmosphere.

Once operational, DEWs can only shoot targets within their line of sight (LOS) – they cannot use indirect fire outside visual range. They also need to focus the beam on the target for a certain period of time.

Countermeasures are physical devices or technologies that result in the decreased effectiveness of DEWs; these are divided in three sub-groups: materials (e.g. certain materials and coatings may be used to reflect laser energy, but only for certain wavelengths8), hardening (e.g. reducing the number of conductive paths) and obscurants (e.g. using smoke or water to create unfavourable atmospheric conditions for lasers and radio frequency weapons).

Types of DEWs

In this article we will only deal with two types of DEWs: the high-energy lasers (HELs)9 and the high-power microwaves (HPMs), and ignore emerging technologies (e.g. particles with mass) or certain applications (e.g. electromagnetic launch).

High Energy Lasers (HELs)

Laser is the acronym for “light amplification by the stimulated10 emission of radiation”. A product of quantum electronics, the laser is an energy conversion medium, which transforms electrical or chemical energy into coherent radiation11. It is a source of a narrow beam of monochromatic, coherent light in the visible, IR or UV parts of the EM spectrum. The laser medium can be a gas, liquid, glass, crystalline solid or semiconductor crystal12.

Three broad categories of lasers are currently under development for military applications: solid state lasers (SSLs), chemical lasers (CLs) and free electron lasers (FELs). Within the SSLs, the US DOD is developing fibre SSLs and slab SSLs.

7 Shorter wavelengths (like lasers) experience less diffraction than longer ones (like microwaves) 8 These coatings will add weight to the target and will not deflect lasers of different wavelengths 9 We will not consider in this article low-energy lasers, which can be used to disrupt vision 10 “Stimulated” as opposed to “spontaneous” emission, such as the light from the sun or from fires 11 Gvozdich, Grant Gregory. “Modelling the Effect of Transient High Energy Weapon Subsystems on High-Performance Aerospace Systems” Virginia Polytechnic Institute, 2011 12 Hecht, Jeff. “The Laser Guidebook” McGraw Hill, Second Edition,1992

Solid State Lasers (SSLs)

A solid-state laser uses a solid (e.g. a neodymium-doped crystal) as an active gain medium. SSLs are optically pumped with flash lamps or arc lamps, or for more efficiency with laser diodes. The United States have been testing these lasers for many years (e.g. the Maritime Laser Demonstration or MLD, a 100 kW slab SSL, and the Tactical Laser System or TLS). Since December 2014, the most “famous” SSL is the Laser Weapon System (LaWS).

Laser Weapon System (LaWS)

The US Navy has deployed aboard the USS Ponce a state-of-the-art SSL, the so-called LaWS (Laser Weapon System). The LaWS is a 30-kilowatt fibre SSL (light wavelength of 1.064 microns) consisting of two sub-systems: a high-energy solid state IR laser and a tracking/targeting computer. LaWS can also be directed onto targets from the radar track acquired from a MK 15 Phalanx Close-In Weapon System (CIWS).

The beam director installed in the turret is linked to the lasers' power source via fibre-optic cables. LaWS operators are using machine vision to lock onto particularly distant

targets and track them through the air or water. The 33-kilowatt discharge hits the target with six highly convergent focussed beams (forming one spot with a BQ of 17), and burns through the target very rapidly.

The LaWS13 is designed to counter UAVs, UCAVs, EO guided missiles, rockets, artillery shells, mortars (C-RAM), ASCMs, and high speed boats (“swarm boats”), or augmenting radar tracking or imaging.

As the first ever deployed sea-based DEW, the LaWS is now being fired in operational scenarios. The results are so favourable that, on 10 December 2014, US Central Command has given the USS Ponce's commander permission to use the LaWS in a defensive capacity. The personnel who tested LaWS reported that it worked well even in high winds, heat and humidity. The Navy estimates that firing the LaWS is significantly less expensive than firing a SAM – one dollar per shot, compared to several hundred thousand dollars. Another positive point was that the LaWS was operating flawlessly with existing ship defence systems.

Chemical Lasers (CLs)

Chemical lasers acquire their energy from a chemical reaction and are capable of reaching continuous wave (CW) output in the multi-megawatt range. Examples of CLs are hydrogen fluoride (HF) lasers, chemical oxygen iodine lasers (COIL) and deuterium fluoride (DF) lasers. The United States launched several programmes around CLs (e.g. the Airborne/Advanced Tactical Laser or ATL, the Tactical High Energy Laser or THEL, the Airborne Laser or ABL, and the Mid-Infrared Advanced Chemical Laser or (MIRACL).

Mid-Infrared Advanced Chemical Laser (MIRACL)

MIRACL is a deuterium fluoride laser, CW operating at 3.8 microns, with an output of 1 Megawatt, and lasing for over 70 seconds. Developed by the US Navy, it became operational in 1980, cancelled in 1983, but since 1990 maintained by the US Army Space and Strategic Defense Command.

13 In order to attack most of the targets listed, the power level of the LaWS will have to be significantly increased. As a matter of fact, the US Office of Naval Research (ONR) is reportedly to have plans to deploy a much more powerful laser (100 to 150-kilowatts) by 2016.

Free-Electron Lasers (FELs)

Free-electron lasers (FELs) do not use molecular or atomic states for the lasing medium, but a relativistic electron beam (e-beam) as an alternative. The e-beam is produced by a superconducting electron accelerator and then shoot up into the undulator (a periodic structure of dipole magnets). FELs can achieve a wider range of frequencies/wavelengths than other laser types, and can be scaled up to megawatt power levels. Furthermore, the wavelengths can be tuned to match precisely atmospheric transmission “sweet spots”. The US Office of Naval Research (ONR) is assessing the FEL technology and a 14.7kW demonstrator has been built14.

HELs-Target Interaction

A laser emits photons, which interact with a target from the outside-in. The energy transferred through the beam is absorbed by the target’s skin. Subject to a set of variables such as atmospheric absorption, scattering, level of reflection and absorption, the laser beam will inflict damages to the target as a burn through, not as a quick outburst. However, the beam can also cause structural weakening of the target by the buildup of energy.

To impair a target, the laser must deliver energy in sufficient quantity, but likewise this energy must be delivered over a small area of the target (density of energy measured in Joules per square centimetre or “fluence”) and in a short time (rate of delivery of the energy measured in Joules/second or Watts)15.

A laser “kill” involves the calculation of “F” the amount of fluence to impact the material and then the amount of fluence over time16.

𝐹 = 𝜌 ∗ ℎ ∗ (𝐶𝑝 ∗ (𝑇𝑚𝑒𝑙𝑡 − 𝑇𝑎𝑚𝑏𝑖𝑒𝑛𝑡) + ∆𝐻𝑓𝑢𝑠𝑖𝑜𝑛) ∗ (1

1 − 𝑅𝑓

)

Where 𝜌 is the target’s density (g/cm3); h the target’s thickness (cm); Cp specific heat (J/g-K); K melting

temperature (K); ambient temperature (K), Rf reflectivity (%) and ΔH heat of fusion (J/g)17.

High Power Microwaves (HPMs)

HPMs refer to a particular range of frequencies that can transfer large quantities of EM energy to conductive objects at a distance. One of the HPMs main technical challenges is to generate a pulse directed enough to concentrate on a specific target and with sufficient power until it reaches that target. HPMs weapons are essentially divided into two key technologies: millimetre-wave (MMW) devices and electromagnetic bombs (e-bombs).

14 O’Rourke Donald. “Navy Shipboard Lasers for Surface, Air, and Missile Defense: Background and Issues for Congress”. US Congressional Research Service. December 2014 15 Nielsen, Philip. “Effects of Directed Energy Weapons”, National Defense University, Washington DC, 1994 16 Team Bravo Cohort 19. “Viable Short-Term Directed Energy Weapon Naval Solutions: A Systems Analysis of Current Prototypes” Naval Postgraduate School. Monterey, California. June 2013 17 For a more detailed approach to laser interaction with targets: Dr Schmitt, Rudiger “Physics of laser interaction in military and homeland security applications” French-German Institute of Saint-Louis, February 2012

Active Denial System (ADS)

The ADS is a HPM which transmits high-frequency waves at 95 GHz (a wavelength of 3.2 mm) at a certain effective distance (classified). The ADS is comparable in its physical design, build and operation to a radar system, apart from its operating frequency. The MMW beam, once focused on a target, stimulates water and fat molecules in the body, instantly heating them and causing excruciating pain. Higher frequency microwaves would penetrate human tissue and create extensive tissue injury, but the MMW used by the ADS are stopped by cell density and only go through the top layers of skin. In operation, the ADS prevents people from approaching a restricted area within several hundred metres.

E-bomb

An electromagnetic bomb (e-bomb) produces a non-nuclear EM explosion (pulse) which diffuses a concentrated microwave beam of energy enabling to transmit EM energy to distant electrical or electronic devices. This enables to destroy, disable, disrupt or damage electronic systems, circuitry, communications networks, and injure organic matter at a certain distance. The bearing on the target is similar to an electromagnetic pulse (EMP) effect caused by a high altitude explosion of a nuclear weapon.

HPMs-Target Interaction

Microwaves inflict damages to a target through thermal heating or electrical inductance. The MW intensity is given by:

𝐼 = 𝑃𝑝𝑒𝑎𝑘 ∗ 𝐺 ∗ 𝑇

4 ∗ 𝜋 ∗ 𝑅2

Where P is the power transmitted by the MW; G the MW weapon antenna power again; T atmospheric transmittance (%) and R distance from target.

Conclusion

Besides the United States, several countries are working on the development of DEWs (e.g. Russia, China, India, Israel, UK, France and South Korea). In addition to defence research agencies, several companies (e.g. Raytheon and MBDA) are currently actively developing DEWs (e.g. Lockheed Martin’s Area Defense Anti-Munitions or ADAM system, a laser weapon designed to defeat improvised rockets, UAVs and small boats). Some defence specialists already see HELs as the natural successors of kinetic systems when it comes to practical applications such as air defence systems. HELs can attack more airborne targets, more rapidly (at the speed of light), more precisely and ostensibly more cost-effectively, than kinetic defence systems such as AA missiles or Phalanx CIWS18. It is evident that a trend has now been set and the coming of DEWs is inevitable, although some technical challenges remain to be addressed, such as scaling up beam power, while respecting beam quality and managing thermal issues, and turning laser demonstrators and prototypes into production-ready series19. Future warfare will be dominated by technological advance, and every modern nation must place the development of DEWs as a top priority on their defence agenda.

18 Crane, David. “Rheinmetall 50kW Anti-Aircraft/Mortar/Rocket Laser Weapon System: The Future of Air Defense?” Defense Review, 23 January 2013 19 O’Rourke Donald. “Navy Shipboard Lasers for Surface, Air, and Missile Defense: Background and Issues for Congress”. US Congressional Research Service. December 2014