Extracted from Aviation Week..
DEW TECHNOLOGY HAS BEEN gathering momentum with the construction of powerful solid-state lasers that can be used in the development of small weapons. Solid-state technology also offers fewer environmental concerns than chemical lasers like those in the U.S. Air Force's YAL-1A airborne laser aircraft which requires a Boeing 747 to carry the long-range laser device and huge amounts of toxic chemicals aloft.
However, there is interest in larger, non-airborne directed energy weapons that can fire repeatedly in short periods of intense combat against, for example, a wave of low-flying, high-speed cruise missiles. The Navy's new ship design, DD-X, which was awarded to Raytheon, will have an electric drive capable of producing the massive power necessary to run a self-defense system that can shoot down aircraft, large numbers of very-high-speed surface-skimming cruise missiles and, eventually, ballistic missiles. Electric drive ships are the perfect platform for weapons that must fire quickly and repeatedly. But, for the aviation community, the necessity for small payload packages for both laser and HPM weapons that may only need to produce a few pulses of energy during each mission as it attacks other aircraft, missiles or ground targets, will remain.
Boeing is working with U.S. Special Operations Command on the Advanced Tactical Laser to develop a medium-power laser using uncooled optics on a CV-22 tiltrotor, AC-130 gunship or MH-47 helicopter. The device is intended for attacking targets with lethal and non-lethal forces at ranges of up to 10 mi.
Another near-term project is development of a laser weapon envisioned for the F-35 Joint Strike Fighter. Some of the problems of a small payload are reduced because the aircraft already has a drive shaft from the engine to the bay just behind the cockpit that could be used to produce the electrical energy needed to power a directed energy device. When needed, the area holds a lift fan used for vertical flight. But for other versions of the manned aircraft, the space can be used for a laser weapon using shaft-generated electrical power.
Raytheon has to complete the solutions to two technology problems as they create a powerful laser weapon for the F-35.
First, they have to scale up the power output of their solid-state lasers from about 10 kw. to about 100 kw. in order to kill targets at a tactically significant range. Some analysts set the mark at about 10 km. (6.2 mi.). A solid-state laser is needed for the F-35 "because its going to be sold in large numbers, it has to be easily maintainable and it must operate without a chemical farm going in and lots of toxic residue coming out," a Lockheed Martin official said. "Right now solid-state lasers don't exist at the power level and beam quality [needed]."
Second, they have to keep the laser beam focused over those long distances.
"The air around a fighter is pretty disturbed because you're trying to operate at around Mach 1," he said. "That, in turn, will disturb the laser beam as you fire it to the target. The air density and the shocks coming off the air vehicle will distort the beam. As part of our laser concept, we will employ adaptive optics to sense what the distortion is and use a conformal mirror. The mirror will predistort the beam so that as it goes through the disturbed air it corrects itself." Mirror technology is being developed in the airborne laser project which uses deformable mirrors to limit defraction of the laser over its 250-mi. range.
HPM (which produce spikes of power much like energy generated by radars) is primarily thought of as an anti-electronics weapon. While a laser is a low-frequency weapon requiring perhaps 4 sec. to inflict the necessary damage, HPM consists of high-frequency energy pulses that need only milliseconds to create the needed effect.
An advantage of HPM is that the technology is more mature than solid-state, high-energy lasers. "HPM will proceed the solid-state lasers by a few years," a senior Raytheon official said. "We have focused a lot of new people and dollars on the technology. But the race is between directed energy technologies and the platforms. If we had a DEW available today, we couldn't fly it because [the Air Force and Navy] don't have a UCAV.
"But the intersection of DEW and UCAVs is a perfect marriage and a growth area. That's how you can prosecute the war in a heavily defended area. Look at the missions for UCAV. Suppression of air defense is number one. You don't want your pilots shot down. You can speculate on what an antielectronics weapon could do to electronics on a SAM battery or an air operations center."
THE AIR FORCE'S UCAV that will evolve from Boeing's X-45 program will have the added problem of providing a large enough power supply to drive an HPM device. Part of the solution is achieved by putting the DE weapon on an unmanned aircraft that can fly very close to a well-defended target before loosing its pulse of microwaves, without endangering an aircrew. The effectiveness of an HPM weapon decreases by the square of its distance from the target.
"Where we can pull power off the engine we will," Booen said. Lockheed Martin intends to use that strategy with its UCAV designs. "But in many configurations, we do plan on using batteries. You will see HPM applications within the next 4-5 years."
