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SPIE Professional April 2010

Lasers As Weapons

The laser's potential to defend against multiple threats at the same time has been a powerful lure for military research despite drawbacks.

By Kathy Sheehan

Airborne Laser Testbed

Despite doubtful political support, uncertain funding, and skepticism about feasibility issues, the U.S. military's research program on laser weapons continues to make strides in demonstrating the potential of directed energy to defend against missiles, artillery shells, and other explosives at the speed of light.

Within the last year, laser weapons have been used in test firings from the ground to successfully shoot down unmanned aerial vehicles (UAVs) and to destroy improvised explosive devices (IEDs) similar to those used against U.S. forces in Iraq and Afghanistan. In February, a heavily modified Boeing aircraft with a powerful chemical laser fired from its nose turret made history by demonstrating the lethal energy of an airborne laser when it destroyed a boosting ballistic test missile off the coast of California.

Several branches of the U.S. military have active R&D programs for laser weaponry using chemical, solid-state, and free-electron lasers, including the Airborne Laser Testbed (ALTB)'s chemical laser, said to be the most powerful mobile laser device in the world and the highest-energy laser ever fired from an aircraft.

U.S. Defense Secretary Robert Gates slashed the budget for the airborne laser program in 2009, however. While research tests on the airborne laser will continue, Gates cancelled plans to build a fleet of so-called flying laser cannons, calling the program's operational feasibility "highly questionable."

The controversial "Star Wars" program also remains in the realm of the distant future for the U.S. military. Yet several laser weapons programs are moving forward in research and development. Boeing estimates that a ground-based hybrid laser weapon it has developed independent of its military contracts, the Laser Avenger, could be ready for the battlefield within a year, if the funding is available.

Boeing's Laser Avenger took part in tests for the U.S. Air Force and the U.S. Army in 2009, successfully destroying one UAV and 50 IEDs. The Laser Avenger builds on an existing system used by the military that employs a lightweight 25-mm machine gun mounted on a HUMVEE. The new Laser Avenger system adds a solid-state laser.

Advantages for Defense

Laser weapons offer advantages in security and defense applications over kinetic weapons. Fired from the air in urban operations, a laser could disable both stationary and moving targets on the ground. For instance, a laser could burn a hole in the engine or wheels of a threatening vehicle with little or no collateral damage. The ultra-precise and speed-of-light nature of a laser could also protect commercial and military ships from small attack boats, again with little collateral damage.

One of the major benefits of lasers neutralizing IEDs is that soldiers do not have to get out of their armored vehicles or wait for a special team to disable the devices. "Laser Avenger provides the ultra-precision, stand-off capability our warfighters need today to safely neutralize those threats," according to Gary Fitzmire, vice president and program director of Boeing Missile Defense Systems' Directed Energy Systems unit.

Non-lethal laser weapons are already marketed to police agencies and private security forces for crowd control and similar applications. Such weapons use eye-safe lasers to temporarily affect a person's vision or balance or cause nausea.

A U.N. weapons convention bans the use of laser weaponry to permanently blind an adversary.

Serious Limitations

Ironically, beginning with Theodore Maiman's press conference 50 years ago announcing his successful operation of the first laser, the media was most focused on its potential use as a weapon. Maiman thought that was unlikely and preferred to focus on the laser's practical applications in space communications, medicine, and industry.

"The death ray label took a number of years to shake off," Maiman wrote in The Laser Odyssey, his 2000 book describing how the world changed on 16 May 1960 with his demonstration of the first working laser.

Maiman, who died in 2007, noted that lasers were extremely effective for precision guidance of other weapons. But as weapons of destruction, "They are huge monstrosities with severe practical limitations," he wrote.

Indeed, questions abound about the cost, size, thermal management, stability, and power requirements for a laser weapon to be practical. Some government officials have also raised concerns about the safety and logistics of transporting chemicals on planes or ships.

Dirt, dust, wind, clouds, rain, and inclement weather can also hamper a laser's range.

Still, the laser's potential to change the face and speed of warfare has been a powerful lure despite these and other drawbacks. Advances in adaptive optics, coating technologies, beam control, and output power have kept several test programs going.

In March 2009, for instance, Northrop Grumman announced it had successfully produced a 105-kW laser system as part of its contract with the Department of Defense on the Joint High Power Solid-State Laser (JHPSSL) program. The company reported the system continuously operated for five minutes, with very good efficiency and beam quality.

Some examples of laser weapons programs are outlined below.

Ground-Based Systems

MATRIX is the Mobile Active Targeting Resource for Integrated eXperiments. In tests for the U.S. Air Force in May 2009, a Boeing-made laser-weapon system mounted on a trailer in the California desert destroyed five UAVs. The successful test (pictured at left) demonstrated the system's ability at "ultra-precise and lethal acquisition, pointing, and tracking at long ranges using relatively low laser power," said Boeing's Fitzmire. "The Air Force and Boeing achieved a directed-energy breakthrough with these tests," he added.

laser weapon MATRIX
A Boeing-developed laser weapon called the MATRIX destroys a UAV with its high-energy laser beam in a May 2009 test. Photo courtesy of U.S. Air Force Research Laboratory.

MATRIX used a single-kilowatt-class, solid-state laser integrated with existing test-range radar to shoot down the UAVs at various distances.

As part of that demonstration, captured in dramatic pictures (above), Boeing also successfully shot down a sixth UAV with its Laser Avenger platform. Lasers from this separate, hybrid air-defense system successfully destroyed 50 IEDs in tests for the U.S. Army in September 2009.

Because the Laser Avenger is based on the existing Avenger system, already deployed by U.S. troops, a Boeing spokesman estimated that the hybrid Laser Avenger could be fielded within 12 months, if funded.

Mobile System

Another ground-based system being developed is the High Energy Laser Technology Demonstrator project (HEL TD), a three-phase U.S. Army program designed to build a weapon to counter incoming projectiles such as rockets, artillery shells, and mortars.

HEL TD prototype
An artist's rendering of a prototype for the HEL TD program.

The Army has awarded Boeing second-phase funding for this mobile, solid-state laser weapon and expects to begin testing of a truck-mounted laser system in 2011. The goal is to have a 100kW-class laser, but the initial tests will use a low-power surrogate.

In January, Boeing announced that the HEL TD is ready to be integrated into a test system that is expected to have a firing range of eight to 10 kilometers. The project officially moves into the fabrication phase this spring when Boeing begins integrating a beam control system (BCS) into an eight-wheel Oshkosh Defense military truck.

The control system will acquire, track, and select an aimpoint (vulnerable area) on a moving target, focus the laser beam on projectiles, and compensate for atmospheric turbulence. The HEL TD optical system includes high-speed sensors, mirrors, high-speed processors, and other optical equipment. (Read more about the HEL TD in a July 2010 feature story from Boeing.)

Airborne Lasers

The U.S. military has two so-called flying laser cannons under development, the Airborne Laser Testbed and the Advanced Tactical Laser (ATL), both using chemical lasers and adaptive optics systems.

Boeing, Northrop Grumman, and Lockheed are developing the ALTB for the Missile Defense Agency which calls the airborne laser program "a pathfinder" for the nation's directed energy program and for missile defense technology. Boeing is the prime contractor on the project, providing the aircraft and the battle management systems. Lockheed developed the beam control/fire control system which sits at the front of the aircraft, and Northrop is in charge of the megawatt-class chemical, oxygen, and iodine laser (COIL).

The successful test of the ALTB against a boosting missile target in February was the first directed energy lethal intercept demonstration against a liquid-fuel boosting ballistic missile target from an airborne platform. (See press release.)

The ALTB uses two solid-state lasers and the COIL on a modified Boeing 747-400 freighter with a 1.5-meter telescope in its nose turret.

Within seconds of the test missile's launch from a platform in the Pacific Ocean on 11 February, the ALTB used its six onboard IR sensors to detect the exhaust plume of the boosting missile.

Lockheed Martin turret ball
Lockheed Martin built the turret ball for the beam control/fire control system on the airborne laser. This photo shows a surrogate prepared for testing. The entire rotating turret weights nearly six tons and functions as a beam director.
Lockheed Martin chemical oxygen iodine laser
Lockheed Martin Space Systems engineer adjusts the beam control optics used to stabilize and shape the beam from the Chemical Oxygen Iodine Laser (COIL) on its way to the nose of the aircraft where it is pointed at a target.

One of the low-energy solid-state lasers tracked the target as it flew, and a second low-energy laser used an adaptive optics system to measure and compensate for atmospheric disturbances between the aircraft and the missile.

Onboard systems of the ALTB then accurately pointed and focused the high-energy laser at the missile's fuel tank, a pressurized area that is vulnerable to any disruptions of its "skin." When the COIL fired at the speed of light, the heat caused a stress fracture on the missile and caused it to break into multiple pieces. The entire engagement occurred within two minutes, while the missile's rocket motors were still thrusting.

Alignment in Flight

Tests of the airborne laser in 2009 validated the tracking and adaptive optics systems and the high-energy laser's ability to fire in an airborne environment.

IR images of Airborne Laser Testbed
Three images from an 11 February demonstration test of the Airborne Laser Testbed were taken from an IR camera. The first image shows an exhaust plume trailing behind a boosting missile (not pictured) climbing to the right. Yellow indicates the highest radiant intensity from the plume. Blue is the lowest. The middle picture shows burning pieces of the target missile above the plume, which is diminished and on its way to burning out. The image at right indicates the booster has stopped thrusting and hot burning debris coasts along ballistic trajectories as disintegration continues.

"Maintaining the precise alignment of optical components within the laser while in flight ranks among the program's notable accomplishments," according to Steve Hixson, vice president of Advanced Concepts - Space and Directed Energy Systems for Northrop Grumman's Aerospace Systems sector.

All of the powerful laser's optical components must be perfectly positioned as the aircraft vibrates and flexes during flight. "Since we were unable to fly the kind of large concrete pads used to hold a ground-based laser's optics in place, we had to isolate the COIL's optics from the structure but also maintain alignment," Hixson said. "So the team developed an optical bench isolation system that isolates disturbances caused by normal aircraft operations while maintaining alignment to the gain medium, or the source of a laser's optical power. It's like an automobile's 'smart suspension' that keeps the car riding smoothly at the same level over a bumpy road."

Boeing representatives involved with the ALTB said further testing is expected in April and May to explore the laser's range, pointing ability, etc.

The demonstration of the airborne laser's tactical strength in February was impressive from a technology standpoint but still doesn't overcome a major practical problem cited by Gates in curtailing the program. Because the system is designed to hit threatening missiles in their boost phase, the military would have to have a fleet of huge planes with lasers standing by in enemy air space to have a chance at detecting and hitting a target.

Tunable FEL at Sea

Advances in accelerator technology and the tunability of free electron lasers (FELs) have attracted the interest of the U.S. Navy for a FEL weapon system to thwart cruise missiles, pirates, small attack boats, and other threats to its warships. The Office of Naval Research awarded contracts in April 2009 to Boeing and Raytheon to develop prototypes for a weapons-grade FEL.

Still in the preliminary design phase, the goal of the program is to provide a future naval fleet with an onboard, speed-of-light defense capability using tunable, megawatt-power lasers. Such a FEL weapon system could only generate such powers, however, from a ship with adequate power generation, which does not yet exist.

The ONR said in a statement that the maximum power requirements for operation of FEL shipboard are estimated to be on the order of 15-20 mW. "When combined with the future electrical demands such as ship propulsion, advanced radars, Electromagnetic Rail Gun (EMRG), etc., the power requirement for FEL exceeds current shipboard capacity. Initial studies indicate that fielding the Next Generation Integrated Power System (NGIPS), currently under development, along with the weapon/sensor suite selection and shipboard power management, will meet the requisite FEL power requirements."

Both companies are working on the design of a 100-kW-class FEL device to demonstrate the scalability of a system and its advantages in the ocean air.

Boeing announced March 18 (after the print edition of this magazine was on the press) that it had successfully completed its preliminary design. "The Free Electron Laser will use a ship's electrical power to create, in effect, unlimited ammunition and provide the ultra-precise, speed-of-light capability required to defend U.S. naval forces against emerging threats, such as hyper-velocity cruise missiles," Fitzmire said. "The successful completion of this preliminary design review is an important milestone in developing a weapon system that will transform naval warfare."

Boeing Missile Defense Systems' Directed Energy Systems unit in Albuquerque and the Boeing Research & Technology group in Seattle support the FEL program. The company has partnered with U.S. Department of Energy laboratories, academia, and industry to design the laser.

ATL Scorches Target Vehicle

The Advanced Tactical Laser is one of two airborne chemical laser weapons under development. The Air Force wants to use this smaller weapon against stationary and moving targets on the ground.

The ATL is designed to destroy, damage, or disable targets on the battlefield and in urban operations with little to no collateral damage.

Boeing successfully tested the ATL in August and September 2009 from a C-130 Hercules aircraft, scorching holes in the target vehicles to disable them.

Intricate Beam Control

The beam control/fire control (BC/FC) system on the Missile Defense Agency's airborne laser testbed stretches from the rotatable turret on the front of the Boeing freighter to an area behind an airtight bulkhead that protects the crew from possible chemical leaks.

It tracks a target, measures range to the target, compensates for atmospheric turbulence, and points and focuses the megawatt-class laser beam.

Developed by Airborne Laser Testbed partner Lockheed Martin, the BC/FC system has 127 intricately coated mirrors, lenses, beam splitters, and other optical components. The optical elements range in size from one inch to the 67-inch-diameter gold-plated primary mirror. Each mirror in the adaptive optics system has 256 actuators capable of moving 5000 times a second to compensate for the atmospheric disturbance.

A 59-inch-diameter conformal window in the turret that took nearly four years of development protects the primary mirror and a 12.2-inch secondary mirror that form a large telescope.

SPIE Defense, Security, SensingFunding Outlook In Defense R&D

A special session on business and funding opportunities in defense, security, and sensing will be held at SPIE Defense, Security, and Sensing in Orlando, FL, 7 April.

Paul McManamon, formerly of the Air Force Research Lab in Ohio, will chair the session for companies, universities, national labs, and anyone interested in opportunities with the U.S. government. Representatives from several military research agencies will speak about the technical problems they are working on and present an overview of the R&D programs.

Zachary J. Lemnios, CTO for the Department of Defense, will also speak about 21st century challenges at a plenary session 6 April.

Technical Articles in SPIE Newsroom

Go to the SPIE Newsroom for the latest news and technical articles about lasers, defense, security, and other topics of interest to optics professionals. For instance, see: "Anti-aircraft laser introduced at UK air show" (20 July 2010).

The SPIE Newsroom offers video interviews with entrepreneurs and research innovators, industry technical reports, short research articles, updates on new products, and news feeds organized around lasers, security and defense, and 11 other technical areas.

Free technical articles are added to the Web site daily, and options are available to receive monthly e-mail alerts on specific topics.

The SPIE Newsroom also publishes a list of the most-downloaded technical articles from the previous month. See what your colleagues are reading.

Kathy Sheehan
is managing editor of SPIE Professional. 

Write to us at spieprofessional@spie.org

DOI: 10.1117/2.4201004.03

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