Sandia LabNews

Directed-energy defense weapon tested at Sandia explosives facilities

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To enhance protection of military assets from mortar and small rocket attacks, Sandia, the Air Force Research Laboratory, and Raytheon Missile Systems Group successfully tested a prototype solid-state laser defense weapon built on the already-existing US Navy Phalanx platform.

The Phalanx close-in weapon system (CIWS – pronounced “sea-whiz”) is a fast-reaction Gatling gun deployed on Navy ships to protect against anti-ship missiles.

In the tests, the Laser Area Defense System (LADS) replaced the Gatling gun on the Phalanx with an off-the-shelf invisible-beam laser capable of destroying incoming targets. The tests were designed to determine if the weapon — based on a commercially available fiber-based laser system — could rapidly destroy mortar threats. The tests represented a major step in deploying a laser-based system to fill critical defensive military and homeland security needs, researchers say.

On the right track with fiber lasers

“Our simulation predicted that industrial fiber lasers with moderate power capabilities, simplified beam control, and limited beam quality could provide an initial near-term solution to the problem,” says Frank Brueckner, Raytheon program manager, “However conventional wisdom held that more power and a nearly perfect beam would be needed. These tests proved we are on the right track with the fiber laser.”

Sandia was contacted to perform experiments demonstrating the laser technology. Two rounds of testing were done in New Mexico. The first round occurred indoors, at the Labs’ Explosive Components Facility (Bldg. 905). The second round occurred outdoors, at the Terminal Ballistics Facility (Bldg. 6750 in Tech Area 3).

Marcia Cooper (2554), principal investigator for both phases of the project, says the tests helped researchers understand how the time required to destroy the mortar depended on the explosive material, the mortar spin rate, and the on-target laser energy.

“Ignition and burning of explosive,” Marcia says, “can vary from a somewhat benign reaction that just slightly ruptures the mortar’s case to complete fragmentation of the case and rapid burning of the bulk explosive.”

Ignition time and lethality

To determine if a laser-based system is effective, researchers care about both ignition time and target lethality, Marcia says. “The laser system must ignite the explosive within a munition quickly and must create a sufficiently violent reaction to minimize collateral harm,” she says. A defensive weapon cannot leave a nearly intact mortar round with a lot of explosive, Marcia says, because it could still successfully hit its target causing significant damage.

The Explosive Components Facility evaluated the laser firing on stationary and spinning mortars in a large test chamber. After those tests successfully demonstrated the laser’s effectiveness in destroying the mortars, the next step was to test the laser outdoors and at long ranges.

The team wanted to show that the LADS could destroy a mortar with sufficient destructiveness to negate its threat, so that it could then be deployed in a wider array of applications — potentially even in or near land-based assets near populated areas.

In the outdoor tests, Sandia technologist David Wackerbarth (2552) says that Raytheon researchers wanted to see if they could destroy an unfuzed, 60-mm round with the laser over a long distance, in such a way that the mortar would deflagrate (burn) rather than detonate. Deflagrating a mortar destroys the mortar without the concentrated energy release of detonated explosives. It could also mean fewer mortar fragments dropping down to earth.

Target mortar was 550 yards away

The tested Phalanx system replaced the normal 20-mm Gatling gun with a continuous-wave fiber laser, usually used in industrial welding applications. The laser, which required a 270-kW diesel generator, was fiber-optically linked to the Raytheon-developed beam director located on the Phalanx mount.

The target mortar was placed on a stand some 550 yards from the Phalanx mount. The beam director consisted of a series of mirrors that positioned and focused the beam downrange to the desired spot diameter onto the target mortar. After maintaining the beam positioned on the mortar, the explosive was heated sufficiently to cause complete destruction of the casing and burning of the explosive.

Sandia’s customer was pleased with the testing, according to Mike Booen, vice president of Advanced Missile Defense and Directed Energy Weapons at Raytheon Missile Systems in Tucson, Ariz.

“In just six short months,” Booen says, “Raytheon and government engineers went from an idea to operational field testing of a solid-state laser system that offers the potential of near-term protection for our troops.”

“Sandia’s Explosive Components Facility and the Terminal Ballistics Facility turned out to be the ideal places for these experiments,” says David Wackerbarth.

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