DIRECTED-ENERGY WEAPONS: Testing sets pace for solid-state laser weapons

Development of tactical solid-state laser weapons is settling into a slow but steady mode aimed at producing usable mobile systems in a few years. One example is the High-Energy Laser Mobile Demonstrator (HEL-MD) program at the Army Space and Missile Defense Command (Huntsville, AL).

“Our goal is to put together a pre-prototype system for an Army laser weapon system,” said Terry Bauer, manager of the program, at an Aug. 14, 2012, press briefing. He estimated the program was four to five years from demonstrating the readiness level required for a weapon system. On the same day, the Office of Naval Research (ONR; Arlington, VA) asked for industry proposals for a similar ship-based laser system.

Challenges for the HEL-MD program include developing power systems that can remove waste heat and ruggedizing the laser, power system, and support equipment to run reliably on the battlefield.

“Two things are pacing this program: the devices and robust testing,” says Mike Rinn, vice president of Boeing Directed Energy Systems (Albuquerque, NM), prime contractor on HEL-MD. “Testing takes time and money, but mostly time.” Targets will include rockets, artillery, mortars, and unmanned aerial vehicles (UAVs).

Truck-borne laser
In 2011, Boeing integrated the control system, beam-director assembly, an acquisition and tracking system, and other equipment on a standard Army battlefield vehicle—the Heavy Expanded Mobility Tactical Truck (HEMTT), an 8 × 8 truck able to carry a 16.5 ton payload. Boeing added a 100-W-class laser for low-power tests at the White Sands Missile Range in New Mexico that lasted from September through December 2011, demonstrating that the optical system worked with a low-power laser.

Now Boeing is installing a commercial 10 kW solid-state laser, which Bauer calls “on the low end of high power,” to test the 50-cm-diameter optical system at a higher laser flux. Tests starting in late 2012 and continuing through fiscal 2013 will assess how well the optics can deliver the beam to a range of potential targets.

“Ten kilowatts won’t have a lot of capability against mortars,” Bauer says, but that power is expected to be adequate against UAVs. Plans call for extensive testing on targets such as 122 mm rockets, mortars, and UAVs. Boeing is also developing adaptive optics to aid propagation of the 10 kW beam.

After those tests, the Army will select the design for a 50-kW-class laser to be used in a series of higher-power tests to verify that such lasers have reached the technology readiness level needed for a “program of record”—meaning an actual weapon system. The specific technology will be chosen later, but candidates include fiber lasers and coherent combination of outputs from an array of fiber amplifiers fed by a master oscillator, being developed by Northrop Grumman (Redondo Beach, CA) for the Pentagon’s Robust Electric Laser Initiative (RELI; see figure). The effective range of the laser weapon will depend on how well radar can pick up targets, whether they are visible to the laser, and the level of power delivered by the onboard laser.

An array of fiber amplifiers are fed by a master oscillator, forming a high-power laser weapon
An array of fiber amplifiers are fed by a master oscillator, forming a high-power laser weapon. The laser could attack mortars at 6 to 8 km, UAVs somewhat farther away, and at longer distances could help field commanders identify distant objects and decide how to engage them. (Courtesy of RELI)

Land, sea, and air

At the briefing, Rinn announced that Boeing and General Atomics (San Diego, CA) have received a DARPA contract to develop a laser weapon system module for use on land and sea, as well as in the air based on DARPA’s High-Energy Liquid Laser Area Defense System (HELLADS). That’s a big vote of confidence in the novel HELLADS design, aimed at producing 150 kW from a laser weighing less than 750 kg.

Last summer an initial module met program goals, and DARPA says that addition of a second module should reach 150 kW next spring. Then DARPA will ship it to White Sands for a year of tests starting next summer.

The new Solid-State Laser Technology Maturation (SSL-TM) program run by the ONR is aimed at producing lasers that can engage important Navy targets while operating on a ship in combat-like situations. The marine environment can be a tough one for optical systems, but even small Navy ships can handle equipment too large to haul in a fighter jet or on battlefield vehicles.

At the time of writing, the ONR was seeking lasers that could be connected to ship-based combat control and support systems, and could be powered and cooled by shipboard systems. The announcement sought plans for lasers with output of at least 30 kW but encouraged developers to offer higher powers, up to 150 kW, and required an optical system capable of handling at least 100 kW.

Plans call for assessing four initial designs and down-selecting to build two prototypes, each to go through a series of three demonstrations on land in 2014 and 2015 before both are demonstrated on ships at sea in 2016. The Navy has designated UAVs as the primary targets for the laser system, with small boats and rockets and missiles launched by patrol boats identified as secondary targets.

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