Northrop Grumman Announces the FIRESTRIKE(tm) Laser, World's First Weaponized Solid-State Laser for, page 1

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Laser Weapons Gain Momentum

Apr 21, 2008
Bill Sweetman/Defense Technology International

A U.S. Defense Science Board report on directed-energy weapons in late 2007 states: “Directed energy suffers from a history of overly optimistic expectations.” This may be the understatement of the century.

Northrop Grumman tested this laser module for the JHPSSL program in December 2007.Credit: NORTHROP GRUMMAN

The report cites canceled or delayed programs, and notes that the biggest U.S. directed-energy (DE) program—the Airborne Laser (ABL), which alone consumes more than half the Pentagon’s DE budget—was little or no closer to its crucial operational test than when the board last reported on DE in 2001.

Similar problems affect high-power microwave (HPM) and other radio-frequency weapons. For instance, the best-known RF weapon, the Area Denial System or “pain ray,” has been demonstrated in a Humvee-mounted configuration, but can’t operate at high ambient temperatures because the millimeter-wave RF source uses superconducting magnets that have to be cooled close to absolute zero. A system capable of operating on a hot day needs an 8 X 8 Oshkosh truck to haul it around.

None of this, though, has squelched the optimism of researchers. In the next 2-3 years, multiple teams and programs expect to demonstrate laser technology that will be practical and accomplish useful military tasks.

In the laser world, the most promising research is aimed at the lowest levels of lethal or damaging power—the 100-150-kw. realm—rather than the multi-megawatt world of the ABL. Two efforts appear to lead the field: the Defense Advanced Research Projects Agency’s (Darpa) High Energy Liquid Laser Area Defense System (Hellads) and the Army-led Joint High-Power Solid-State Laser (JHPSSL) project.

An important element of both is recognition that the size and cost of a system has to be proportional to its military usefulness, and that lasers are only likely to be accepted for use where a speed-of-light engagement is essential.

An important role for Hellads is aircraft self-defense—engaging and destroying incoming missiles. “It’s a game-changer,” says Program Manager Don Woodbury. “Put it on an aircraft, and it does not consume the aircraft—it can still do everything else that it can do—but now you can go anywhere without speed or stealth.”

A 100-150-kw. laser can engage a missile far enough out and disable it quickly enough to allow the system to defend against salvo attacks, given an attainable rate of fire.

Hellads started with the aim of using a liquid lasing medium due to its good thermal management characteristics, and for the first years of the program General Atomics’ Photonics unit was the prime contractor. In September 2007, though, Darpa contracted Textron Systems to supply an alternate laser module based on its “ThinZag” ceramic solid-state technology. The agency plans a “shoot-off in the next year or so,” Woodbury says, before proceeding to the outdoor testing of a weapon-power laser against tactical targets in 2010. The key issue, however, is to test the laser modules. “We’ll know in a year or two if it’s going to work.”

Woodbury is not specific about why Darpa brought Textron into Hellads. The program has been running for some years and was aimed at a full-scale firing in 2007. Woodbury says a big challenge has been the reliability of components as their designs transition from a laboratory to a weapon-type system. However, “the physics are working great.”

Hellads’ goals are written in practical numbers: 150-kw. output and a system mass of 5 kg./kw., leading to a weight of 1,650 lb. (750 kg.). The only inputs are energy—around 1 megawatt, from a shaft or electrically—and air for cooling.

Northrop Grumman and Textron Systems are involved in JHPSSL. The project is aimed at “stacking” eight 15-kw. laser modules into a single package with 100-kw.-plus output. Northrop Grumman claimed a milestone in December 2007, a full-power test on the first Phase 3 module. This represents the design to be used in the first eight-laser stack. The initial two-module test will follow soon, with an eight-module shot due later this year.

The laser modules are stacked like a filing cabinet, in two columns of four. A key to making JHPSSL work is good beam quality—i.e., a flat laser wavefront—in each module, so they form a high-quality beam when ganged together. Beam quality exceeded the specified requirement in the December test, and the laser also ran continuously for 300 sec.—50% better than the target. “Outside Northrop Grumman, I’m not surprised to hear people talk about the challenges of getting good beam quality,” says Dan Wildt, Northrop Grumman’s vice president of directed-energy systems.

A 100-kw.-class JHPSSL stack fits in a 1-meter cube, Wildt says, and with the expected 0.15 efficiency factor, needs 700-800 kw. of input power. The configuration of an operational system will vary by platform, he suggests. “On an all-electric ship, you’d just hook it up to power and cooling. On a smaller platform, you might not need long run times. You could use batteries and a phase-change cooling material, recharge the batteries and re-freeze the coolant between missions.”

The JHPSSL weapon might seem to be large for a short-range—“handfuls of kilometers”—weapon that is useful against smaller targets, but Wildt notes it has unique advantages. The cost per shot is extremely low at less than $1 per target, and the elimination of complex guidance simplifies operator training. In a counter-rocket, artillery and mortar (C-RAM) mission, particularly one that involves protecting a base in a populated area, the laser’s advantage is it kills the target by igniting the explosive fill, minimizing damage on the ground.

A non-chemical, 100-kw. laser could enable a mobile system for defense against rockets, or as a low-collateral-damage defense against UAVs.Credit: U.S. ARMY

Wildt argues that the laser could benefit ships. It is synergistic with kinetic weapons like guns and missiles. If the target weaves, as the Mach 2.8 rocket-powered kill vehicle of the 3M54 Klub missile is designed to, it exposes its side to the laser and is under g-loading, and more likely to break up when hit. “And if it doesn’t maneuver it gives the kinetic weapons an easier shot,” Wildt adds. For defense against small surface craft, the laser’s accuracy and adjustable lethality are an advantage; the laser can immobilize the engine or puncture the hull.

Northrop Grumman is one of several companies involved in the next step beyond JHPSSL, the High-Energy Laser Technology Demonstration. Under contracts awarded in the summer of 2007, Northrop Grumman and Boeing are developing beam-control systems—turret-mounted optical chains—compatible with a pre-production JHPSSL. The goal is to test a vehicle-mounted laser C-RAM system in 2013, capable of performing a military mission that would have required a chemical laser.

Northrop Grumman is advocating similar demonstration programs for airborne and shipboard applications. “We’d like to work toward full-up prototypes, testing and verifying commercial off-the-shelf batteries and building cooling systems,” Wildt says.

The laser team is “very much” working with Northrop Grumman’s Next-Generation Bomber team, as well.