Zapping rockets with 10 kW

At first glance, the demonstration of the Area Defense Anti-Munitions (ADAM) ground-based laser weapon by Lockheed Martin (Sunnyvale, CA) might sound like just another big aerospace company jumping into high-power solid-state laser systems to defend against rocket, artillery, and mortar attacks. Successful demonstration in March 2009 of the 100 kW Joint High Power Solid-State Laser (JHPSSL) by Northrop Grumman (Redondo Beach, CA) has led to a diverse family of tactical laser weapon projects.

But a close read of the press release shows something new and important. ADAM destroyed eight small-caliber rockets at a range of 1.5 km in March and April 2013 using a fiber laser emitting 10 kW, only 10% the power of the JHPSSL testbed. The laser is housed in a modest-sized trailer. A video shows the laser beam dwelling on the target for seconds until it explodes.

Reducing the power requirement a factor of 10 is a big deal. Pentagon planners had thought a minimum of 100 kW would be needed to destroy rockets, artillery, and mortars, and a review panel thought 400 kW would be a better bet. The JHPSSL program produced impressively compact 100 kW diode-pumped solid-state lasers, but they were well beyond the commercial state-of-the-art. You can buy 10 kW fiber lasers for industrial applications.

Reducing the power requirement also eases key concerns about trying to operate a laser in the field. A lower output power reduces the likelihood of damage to internal or output optics in a hostile field environment. It also reduces the amount of waste heat that must be dissipated, easing requirements on cooling equipment. And it reduces fuel requirements.

Lockheed did not announce the secret of its success, but presumably it had a lot to do with the optics for pointing, tracking, and beam delivery. Focusing the beam through 1.5 km of air and keeping it tightly concentrated on a target moving through a turbulent atmosphere are challenges. Yet the video shows detonation of a Qassam-type rocket like those used by insurgents less than 10 s after launch. Such rockets are considered easier targets than mortars, but even so, achieving that much with 10 kW is good news for laser-weapon developers.