directed energy weapons
TRANSCRIPT
Anthony F. Hillen
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Directed Energy Weapons
Technology Overview
Research into directed energy devices was conducted as early as World War II, when the
Nazis experimented with sonic weaponry. However, since the Hollywood sensation, Star Wars
was released in 1977; the public’s perception of directed energy weapons (often dubbed “ray-
guns” or “death rays”) has been fundamentally ill-informed. For the sake of parsimony, this
paper will focus solely on weapons that directly cause damage. While certain technologies could
be considered “directed energy devices” in the strictly technical sense of the term, this discussion
will exclude technologies that do not cause physical harm to their targets such as electronic
countermeasures, designed for communications interference. Two classes of directed energy
weapons sit on the threshold of practical military significance: systems that employ laser-based
technology and those that utilize radio frequencies (commonly known as high-power
microwaves, or HPMs).
Laser-based systems are by far the most publicized, as well as the most promising of
directed energy technologies. By exciting atoms, lasers generate powerful bursts of single-
frequency, single-phase photons capable of being focused and directed using mirrors.
Weaponized lasers are typically gas dynamic and use fuel or a turbine to propel the lasing media
through a circuit or sequential orifices. Due to the intense heat and pressure, the medium forms a
plasma and lases, the beam can then be aimed in any direction.
Despite several fruitless decades of development efforts, laser weapons have recently
become a technological reality. Nevertheless, the technology is still plagued by operational
drawbacks and various developmental obstacles. Fielding a reliable laser weapon has proven
exceedingly challenging, primarily due to the difficulty in maintaining the impeccability of the
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high-precision mirrors and windows in its resonating cavity, in addition to their inherent
vulnerability to environmental obscurants like dust and water vapor. Secondly, attacking a target
behind cover or shielding requires the use of gravity, but gravity’s effect on light is practically
non-existent, revealing another inherent operational drawback: lasers cannot be used for indirect
fire.
Lasers have typically suffered from three developmental problems that have significantly
contributed to the delay in fielding an effective system. An effect known as “blooming” causes
the laser to defocus and lose energy due to the atmospheric plasma breakdown that occurs when
energy densities reach approximately 1 mega-joule per cm2. A second problem is that when the
laser strikes its intended surface area, evaporated material can effectively shade the target, thus
mitigating the weapon’s effect. The final, but probably most developmentally prohibitive issue,
is the high energy requirements associated with laser weapons. The technologies currently being
used for storing, conducting, and directing energy are incapable of powering a mobile weapon
for combat purposes. This lack of portability is primarily due to the bulky nature of the
equipment needed to power and cool modern lasers, which emit as much heat as they do energy.
Parallel to that of lasers, another promising research track involves the use of radio-
frequencies, specifically microwaves. Operating in the low-frequency, long-wavelength section
of the electromagnetic spectrum, high-power microwaves (HPMs) are capable of rendering
electronic systems ineffectual. HPMs might not possess the strategic flexibility offered by lasers,
but they do share similar qualities (like light-speed transmission), and even possess certain
operational advantages (such as requiring very little in the way of logistical support and being
able to propagate in adverse weather). Like radio transmitters on a swivel, HPMs can be aimed to
disable or destroy electronic systems and cause explosions by generating intense electromagnetic
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bursts of energy. It is worth pointing out, however, that in the strictly technically sense, the term
“microwave” only applies to the highest radio wave frequencies, typically in the gigahertz range.
Nevertheless, it has become commonplace to hear of all radio frequency-based directed energy
weapons being referred to as “high-power microwaves” in daily parlance.
Development Status
Directed energy has made substantial advancements thanks to innovative new research
efforts by Boeing, TRW, Lockheed-Martin and the United States Air Force, under the auspices
of the Missile Defense Agency. The airborne laser (ABL) was designed to detect the launch of
ballistic missiles and destroy them in flight. The ABL is currently undergoing a long-term test
phase at Edwards AFB. The ABL’s tracking system successfully demonstrated its accuracy when
a modified Boeing 747-400F, known as the “YAL-1A Airborne Laser” test fired its target
illuminator several times off the California coast on March 15th
2007. The program’s next phase
will involve integrating the targeting system with a chemical oxygen iodine laser (COIL), a high-
energy device designed to destroy missiles in flight. The COIL is intended to be fired through the
plane’s nose turret and produce enough energy in a five second burst to power a typical
household for over an hour.
Another promising research endeavor currently underway concerns the Tactical High
Energy Laser (THEL). THEL is a promising new defense system that has been proven to be
capable of ballistic missile and battlefield rocket interception. THEL has successfully intercepted
over twenty BM-21/Fajr-3 rockets (also known as Katyushas), in addition to intercepting and
destroying artillery shells and multiple rockets launched in a single salvo. THEL’s operational
flexibility prompted an on-going effort to develop a mobile THEL (MTHEL), a vehicle-borne
system capable of air transport.
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Significant advancements have also been made in the development of infrared
countermeasure (IRCM) devices, particularly by the US Army and Air Force. IRCMs are
intended to use directed energy to destroy inbound missiles. The Air Force program aims to
develop an IRCM to protect transport aircraft from man-portable anti-aircraft missiles
(MANPADs) like Stingers, Chinese Anzas or Iranian Misagh missiles. The Army’s research
initiative is intended to create IRCMs to counter air and ground-launched anti-tank missiles.
However, one should note that such IRCMs would most likely be ineffective against anti-aircraft
systems that utilize multiple kinetic sub-munitions like the recently fielded British Starstreak
missile.
Solid-state laser technology has made significant advances in recent years, but the
ultimate goal of 100kw output levels remains out of reach (the current standard being
approximately 10kw). It is, as yet, unclear how soon an order-of-magnitude improvement can be
made to the performance of solid-state lasers. HPM weapons have also experienced some recent
development, but efforts to produce a first generation weapon have not focused on directed
energy. Instead, current research efforts are oriented around the concept of explosively-driven
HPM generators, something akin to electromagnetic pulse bombs.
Security Implications
Directed energy technology has myriad security implications. In continuum mechanics, a
laser-based directed energy weapon’s primary effect on its target is known as plastic shear: a
“non-fracturing, physical deformation”. In other words, the target’s surface area is explosively
evaporated. A million joules of energy delivered as a laser pulse would have the same effect as
200 grams of high explosives.
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ABL’s operational concept is not dissimilar to that of other airborne electronic-warfare
and intelligence platforms. Theoretically, a squadron of three ABLs, supported by an aerial
refueling plane like the Boeing KC-767 would establish a patrol pattern in friendly airspace yet
still within range of known or suspected missile launch facilities. Orbiting a given area in this
manner could provide defensive coverage of approximately 60,000 square kilometers.
The security implications of laser-based missile defense systems are staggering, but
directed energy weapons possess several tactical advantages over conventional offensive systems
as well. Unlike projectile weapons, laser beams are unencumbered by the constraints of gravity
or atmospheric drag and travel at the speed of light, so it is unnecessary to compensate for target
movement once the shot has been fired. In addition to being highly precise, their versatility
means that directed energy devices can be employed as both sensing devices as well as kill
mechanisms. Assuming the power source problem can be solved; their reliance on electricity
obviates the costly need for regularly re-supplying ammunition. Another inherent benefit is
light’s nugatory ratio of momentum to energy; this means that laser weapons fire completely
without recoil. Laser-based weapon’s ability to inhibit attacks by missiles and artillery implies
that those in possession of such systems will have achieved a strategic advantage in ground, air,
and space combat against an adversary that lacks them.
The ABL and other tactical lasers are not the only directed energy weapons capable of
suppression of enemy air defense (SEAD) operations. HPM devices could be used against area
and point targets, potentially revolutionizing C4ISR denial, air defense suppression, as well as
ground vehicle interdiction. An HPM weapon attached to an unmanned combat aerial vehicle
(UCAV) could well prove to be the ultimate SEAD weapon. A microwave-armed UCAV would
be capable of flying along penetration corridors and taking radar and missile sites offline in
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preparation for the ingress of cruise missile or manned aircraft. This type of SEAD capability
would essentially obviate the need for dangerous “wild-weasel” attacks with costly HARM
missiles, or with even more expensive cruise-missiles strikes.
HPM weapons possess several military advantages over lasers. First, because HPMs can
have a wide-area effect, (depending on the power of the pulse generator and the specific
frequency being generated) everything within range will be attacked simultaneously; a
characteristic that can be particularly useful against imprecisely located targets. Second, HPMs
have the ability to make “system kills” by causing critical damage to electronic circuits,
components, and sub-systems, even when those systems have been turned off. Third, completely
isolating the target from conducting energy is the only effective countermeasure to HPMs, an
action that would probably result in a mission kill, effectively serving the attacker’s interests.
Finally, by their very nature, HPM weapons allow for reduced collateral damage, and since they
are inherently tunable, their intended effects can be graduated.
Future Outlook
Directed energy weapons technology stands to dramatically alter the conduct of warfare.
Nevertheless, it is more appropriately viewed as just one facet of the wider “Revolution in
Military Affairs” currently underway in the United States and several other countries. The advent
of digital technology significantly enhanced the speed and accuracy in the acquisition and
transmission of military information, in very much the same way that directed energy weapons
could potentially increase the speed and accuracy with which targets are engaged and destroyed.
For example, the primary limiting factor in contemporary air combat is an aircrafts armament
payload. Directed energy weapons have the potential to eliminate that restriction by replacing
cannons, and eventually, missiles as well. It would allow aircraft armed with such weapons to
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engage their targets more rapidly, in addition to providing greater engagement opportunities
against maneuvering aircraft and low-altitude, high-velocity, terrain-masking cruise missiles.
Although the effect of directed energy-armed aircraft on the battle-space might well be similar to
the advent of jet propulsion, prudence dictates that equipping aircraft with a combination of
missiles and directed energy weapons would be the best course of action for the foreseeable
future.
Militaries seeking to integrate directed energy weapons into their current force structures
and operational concepts will face significant challenges. First, coordinating directed energy
operations with those of conventional forces on what could very well be a crowded battlefield
will not be simple. Given its intensive use of information technology, weapons deconfliction and
battle-space management will prove particularly daunting for the United States. Another problem
concerns the risk of friendly fire casualties. Although lasers are highly accurate, “HPM bombs”
are indiscriminate within their area of effect. Nevertheless, their relative technological simplicity
means that microwave bombs will likely be the first directed energy weapons to be fully
developed and fielded. Thus, the creation of appropriate procedures and guidelines governing the
use of HPM weapons is critical to ensuring the safety of friendly forces.
Directed energy weapons have been on the brink of technological feasibility for years,
but never have they been more critical to defense and national security as they are in today’s
information age. It is a reasonable assumption that the military importance of this technology
will only increase with time, and according to military history, success is not achieved by those
who first acquire a new technology, rather by those who realize its importance and learn to wield
it effectively.