EO/Lasers Laser Area Defense System to Provide Near-Term Tactical Defense Against Mortar, Artillery and Rocket Threats
To protect our warfighters and assets from mortar attacks while minimizing collateral damage, Raytheon is developing a laser system that will destroy incoming shells before they can cause harm. This solution, which is based on existing industrial fiber-laser technology, will be provided as a spiral upgrade to the Land-Based Phalanx Weapon System (LPWS). The current focus is on defeating mortar shells, but the ultimate goal is to destroy even more powerful projectiles — artillery shells and rockets.
To meet this critical force–asset protection need, Raytheon engineers challenged accepted premises about laser weapon system development. They, contrary to conventional thinking, assumed that close-range (1km~2km) engagements could be successfully performed by a laser with moderate power and relaxed (less-focused) beam quality.
Raytheon's modeling and simulation activities showed that the conventional approach of seeking near-diffraction-limited beam quality was not necessary for close-range tactical target engagements. To apply these insights, Raytheon engineers developed a system architecture based on the battlefield-proven LPWS system.
The LPWS high-value site defense system is automated and consists of:
A radar that detects and tracks incoming targets (such as rockets, artillery rounds or mortar shells)
A Gatling gun that fires high-power rounds at the targets
The gun's self-destructing rounds minimize collateral damage.
For the solution upgrade, Raytheon would integrate a laser telescope, power source and tracking system into LPWS, increasing the defended area beyond that currently protected by the gun system. Because the laser has a greater range than the gun, collateral damage from incoming projectiles is minimized. From early 2006 on, Raytheon engineers have taken a thorough, logical path to prove this laser concept through hardware development and field tests.
Little or no data existed on using a high-power, continuous-wave, multimode laser — such as the one specified in the solution architecture — to destroy incoming munitions. Therefore, in 2006 Raytheon, AFRL-DE (Air Force Research Laboratory–Directed Energy Directorate) and Sandia National Laboratory collaborated on the series of tests to obtain this knowledge. The Air Force provided its recently acquired 20kW fiber laser manufactured by IPG Photonics. This industrial laser delivered its power with an approximate beam quality of 30, which is far less exacting than anything previously considered for tactical weapon systems applications. (Generally, the beam quality adequacy threshold is 2. The closer the quality is to a value of 1, the more focused, and therefore more potent, the beam is.)
Preliminary tests were conducted to fully characterize the laser beam and understand its interaction with targets. The concept anchoring tests consisted of:
Measuring the reflectance of mortar paints and bare-steel surface treatments as a function of temperature at the laser wavelength
Measuring the laser-beam-induced rate of thermal conductance for mortar steels with varying surface treatments
Measuring the multimode, propagated laser spot size as a function of the beam director's aperture and range
Measuring (with Sandia National Laboratory) the destruction time and violence level of static and spinning mortars under ideal conditions in the lab and under realistic, severe field conditions
To research these results, Raytheon used its rapid prototype facilities and off-the-shelf hardware to fabricate a 60-centimeter, near-diffraction-limited telescope. This unit was packaged on a standard optical bed and integrated onto the Phalanx Gun 21 platform. The remote 20kW laser was fed into the beam director through a fiber.
This demo system was proven in the field by exposure to high temperatures (>90 degrees F), high winds (>80 mph) and rain. All systems survived and maintained boresight throughout the outdoor testing, which lasted a week and a half. Atmospheric conditions were monitored throughout the testing, and the turbulence and beam-propagation conditions on the more than 550-meter beam path represent severe tactical conditions (Cn2~10-13).
In June 2006, Raytheon completed a series of tests that proved the viability of a low-cost, solid-state, high-energy laser counter-rocket, -artillery and -mortar capability using existing industrial and military equipment. Within six months of project go-ahead, the AFRL's 20kW industrial fiber laser was integrated with a modified Phalanx mount and a low-cost beam director, and this unit was used to destroy live mortars at ranges of more than 550 meters in short (tactically useful) times.
These lab and field tests not only prove the technical viability of Raytheon's approach, but the rapid execution of this demonstration also shows that a tactical test bed can be developed in less than 24 months at low cost — several years earlier and at substantially lower development and recurring cost than existing alternative concepts. Lethality results from the tests provide the basis for moving forward to engage and defeat in-flight targets. Since these concept validation tests were completed, Raytheon has begun designing a beam director system to be incorporated onto the LPWS, providing a very near-term directed-energy augmentation to the gun-based system. (The laser can be added onto the current LPWS gun system or be provided as a laser-only LPWS variant.) The all-aluminum laser telescope is being developed at ELCAN, a wholly owned Raytheon subsidiary. Integration of the optical system will be done at the University of Arizona Optical Sciences Center, and we anticipate that the system will be delivered to the White Sands Missile Range High Energy Laser System Test Facility for field lethality testing in the late summer of this year.
