July 07, 2015

Directed Energy Weapons from watts to gigawatts

After a nearly half-century quest, the U.S. military today is on the cusp finally fielding operationally relevant directed-energy weapons. While megawatt-class lasers to shoot down ballistic missiles remain, for now, a distant prospect, today’s tactical lasers are potentially useful, cost-effective approaches for countering threats such as low-cost drones and small boats. High-power microwaves open up new avenues for nonkinetic effects, a significant advantage for controlling escalation or limiting collateral damage. Perhaps the most significant benefit to fielding these nascent directed-energy capabilities, however, is that they will start the crucial process of integrating a new technology into operations.

Directed-energy (DE) weapons, including high-energy lasers (HEL), high-power microwaves (HPM) and related radiofrequency technologies, offer the prospect of cost-effective precision attack or enhanced point defense and can provide warfighters with flexible nonkinetic employment options.

Directed-energy weapons are not silver bullets, but rather one of a broader set of tools in the warfighter’s toolbox. Taken together, the parallel advances in directed energy, cybersecurity and electronic warfare could — if operated as a cohesive system — provide the nation an important, if dynamic, qualitative military edge.

The global electronic warfare market — which includes directed-energy (DE) technologies — continues to grow, from an estimated $7.72 billion in 2010 to roughly $12.15 billion in 2014. Even with downward pressure on defense spending in many countries, analysts anticipate a continued rise to $15.6 billion by 2020, a doubling of the global electronic warfare market in the span of a decade.

While per-system costs vary, a generalized per-shot cost for directed energy weapons is about $1 to $20. This is an affordable weapon option. Newer, electric systems can be charged on-station, allowing deep magazines. Because of that, multiple shots per engagement are inexpensive and have a credible probability of effect against susceptible targets. When used as part of a layered defense capacity alongside kinetic weapons, DE weapons can extend aggregate magazine depth and enhance platform survivability.

Many types of DE weapons have been developed or proposed over the past half-century. In the past two decades, HEL, HPM and millimeter wave technologies have proven of greatest interest to the Department of Defense. While the graphic below oversimplifies a complex technical area, it provides a useful framework for how to think about DE weapons.

• High-energy lasers have been the mainstay of DOD’s directed-energy weapon developments since the 1960s, affording the prospect of effects ranging from temporary sensor-dazzling through system destruction. Some chemical lasers, designed for strategic missile defense purposes, have demonstrated megawatt-level output. But the large footprint, complex logistics and various technical challenges associated with chemical lasers eventually led to their cancellation. Current developmental megawatt-class systems emphasize free-electron and diodepumped alkali laser technologies. More recent developments in solid-state and fiber lasers, designed primarily for tactical engagement, feature lower-power systems designed for forward-deployable platforms. Effectively meeting technical challenges including power-scaling, beam quality and thermal management — and packaging for use on appropriate operational platforms — are key to their future prospects.

• Radiofrequency weapons are principally counterelectronic weapons. Starfish Prime and other Cold War-era tests demonstrated the effects of nuclear EMP on electronics; the more modern explosively and electrically driven high-power microwave devices produce non-nuclear EMP effects. High-power microwave weapons have proven capable of gigawatt-class power output that can disrupt or even destroy modern electronics, but at comparatively short range. Radiofrequency weapons can also use millimeter waves for counterpersonnel applications such as crowd control or perimeter security.

Radiofrequency weapons are “devices that produce and emit electromagnetic energy for the purposes of intentionally disrupting or damaging the targeted electronics.” As early as the 1960s, atmospheric nuclear tests highlighted the downrange potential for electromagnetic pulse (EMP) effects on electronic systems. In the July 1962 Starfish Prime test, a 1.4-megaton nuclear device detonated about 400 kilometers above Johnston Island in the Pacific shut off street lights, triggered alarms and otherwise affected the electronic infrastructure of the Hawaiian Islands — more than 1,400 kilometers away — and damaged several satellites in low Earth orbit.

Over the past decade, the scientific community has made noteworthy progress on high-power microwave technologies. These include improvements in microwave sources, antenna design and other long-standing technical limiters to achieving operationally relevant size, weight and power configurations. Collectively, such developments serve to reduce an HPM system’s physical footprint, which expands the range of potential employment platforms. They increase a system’s power density and extend its effective range, which enhances its operational utility. They also improve a system’s ability to operate effectively at different frequencies and, therefore, improve performance against varied target types. Taken together, these improvements significantly enhance the probability of a system’s achieving the desired counterelectronic effect.

There are four general classes of EMP:
• High-altitude nuclear EMP, which results from a nuclear detonation typically 15 or more miles above the Earth’s surface and has the potential for wide geographic effects;

• Source region nuclear EMP, created when a nuclear weapon detonates at lower altitudes within the atmosphere and affecting a more limited geographic area;

• System-generated nuclear EMP, which originates from a nuclear weapon detonation above the atmosphere that sends out damaging X-rays that affect space systems (rather than Earth-based infrastructure); and

• Non-nuclear EMP, generated by explosively driven or electrically driven radiofrequency weapons with effects on electronic components, systems and networks.

The Air Force Research Laboratory characterizes four main types of electronic effects that can be generated by
radiofrequency systems:

• Upset is a temporary alteration of the electrical state of one or more nodes in such a way that they no longer function normally. Normal function resumes once a signal is removed. (For example: jamming.)

• Lockup produces comparable upset effects, but an electrical reset is required to regain functionality even after the signal ceases. (For example: computer reboot.)

• Latch-up is a greater form of lockup, in which the electric power to a node is cut off or the node ceases to function. (For example: a blown fuse.)

• Burnout is the physical destruction of a node. (For example: a melted circuit board.)

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