Able to shoot for as long as power is available, electric laser weapons are an answer to threats like simple rockets and swarming boats that can overcome conventional defenses with limited magazines of cannon shells or interceptor missiles. But lasers need more power, efficiency and mobility to become practical weapons.

Lockheed Martin is to deliver a 60-kw ruggedized laser that will enable the U.S. Army and Boeing to demonstrate the lethal potential of the truck-mounted High-Energy Laser Mobile Demonstrator (HEL MD) in 2017, on the path to a 100-kw version planned to be tested by 2022.

The HEL MD shot down 60-mm mortar rounds and tactical unmanned aircraft using a 10-kw off-the-shelf industrial laser during six weeks of testing at White Sands Missile Range, N.M., that ended Dec. 12. This followed low-power testing with a surrogate laser in 2011.

Although the latest tests were successful, the short effective ranges and long lasing times required to disable targets mean a 10-kw laser is not militarily useful, says Terry Bauer, HEL PM program manager at Army Space and Missile Defense Command. The 60-kw laser from Lockheed “is what makes HEL MD feasible,” he says.

The higher-power laser is being developed by Lockheed company Aculight under the Pentagon's Reliable Electric Laser (RELI) program, a follow-on to the Joint High-Power Solid-State Laser (Jhpssl) program, under which Northrop Grumman in 2009 demonstrated the first electric laser to exceed 100 kw.

The goal of RELI is to develop more-efficient, compact and ruggedized high-power lasers that can be used in weapon systems. Aculight uses spectral beam combining to optically merge the beams from many fiber lasers, which are more efficient and compact than the diode lasers used in Jhpssl.

In late August, the Army announced its intent to award Lockheed a $23.8 million contract to deliver a 60-kw ruggedized laser module for integration into the HEL MD. Based on the 25-kw RELI laboratory laser, the system will combine additional 2-kw fiber laser modules to achieve the higher power.

Bauer says the RELI laser is slated to be ready in fiscal 2016, with integration into the HEL MD and testing against mortars, rockets and unmanned aircraft planned for fiscal 2017. A follow-on effort would increase power to 100 kw, further extending range and reducing lasing time to defeat targets.

In the latest tests, the HEL MD “killed a large number of 60-mm mortars,” says Mike Rinn, Boeing vice president for the Directed Energy Systems division. The 10-kw laser also demonstrated it could the blind the electro-optical sensors on UAVs and it brought down the aircraft by burning off their tails.

Because the off-the-shelf industrial laser, produced by IPG, has limited power, mortars were engaged at less than 2-km (1.2-mi.) range and UAVs at less than 5 km, says Bauer. Success for these tests was defined as putting laser energy on the target, but HEL MD went “above and beyond the criteria,” he says.

“A 60-mm mortar is the size of a football in length, at a range of 2,000-3,000 yards. We demonstrated we could rapidly acquire with radar a small, dim target and guide a beam the size of quarter to destroy that target in flight,” says Blaine Beardsley, Boeing HEL MD program manager. “It's remarkable we could do it over and over. That is what's unique compared with other demonstrations in the past.”

The kill mechanism against mortars is “deflagration, not detonation,” Bauer says. The laser energy heats up the high explosive in the round and causes a low-order explosion that disables the mortar. The round will still continue on its ballistic trajectory and hit its intended target, but not explode. “We turn it into a rock,” he says.

The HEL MD includes a beam director that provides 360-deg. coverage to below the horizon, the Army states. The White Sands tests used a surrogate radar to cue the laser system to targets, but the beam-control system includes its own illumination and ranging lasers. For future tests, the HEL MD's thermal and power subsystems will be upgraded to support the increasingly powerful solid-state lasers.

Operationally, a mobile high-energy electric laser could protect ground forces from rockets, artillery, mortars, cruise missiles and UAVs. The advantage over gun and missile systems is the deep magazine and low cost per shot. Each HEL MD engagement “consumed half a cup of diesel,” says Rinn.

Each laser system could engage only one target at time but, at higher power, engagement times would be just a few sec. “A laser is a serial killer; it takes out targets one at a time,” says Bauer. “We would not deploy one by itself, but a platoon with 3-5 systems would support a forward operating base.”