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Aviation Week & Space Technology:
July 8, 2002


Lasers Being Developed
For F-35 and AC-130

DAVID A. FULGHUM/WASHINGTON

Directed-energy devices are emerging from the 'black' world as weapons for manned and unmanned aircraft

Lockheed Martin is tailoring a laser for the F-35 Joint Strike Fighter that could be ready as early as 2010 for demonstration and the start of a full-scale development program.

AW2625
Lockheed Martin produced this artist's rendering of a laser-weapon-equipped F-35. Lasers will be put on manned aircraft, while the tougher to control high-power microwave weapons are slated for unmanned combat vehicles.
Variants of the solid-state laser, powered by a drive shaft from an aircraft's engine instead of batteries, also are being considered for use on AC-130 gunships and Lockheed Martin-designed unmanned aircraft. The high-energy laser system is being designed in a joint project with Raytheon.

An advantage of a directed-energy weapon is that it can shoot indefinitely and is limited only by the ability to cool it, and it's covert. "There's no huge explosion associated with its employment," a Lockheed Martin official said. "There are no pieces and parts left behind that someone can analyze to say, 'This came from the U.S.' The damage is very localized, and it's hard to tell where it came from and when it happened. It's all pretty mysterious."

A foe would be left largely clueless trying to analyze what happened and why. Planners envision scenarios where fires are set, electronic components are damaged and computer memories are erased with no collateral damage or injury to those near the target.

A Defense Science Board study last year said that several technology breakthroughs have moved high-energy lasers on fighters into the realm of the possible. Among them was increased electrical power-generation capability achieved under the "More-Electric Aircraft Project." The DSB contends that aircraft systems will be able to provide one megawatt of power in less than five years. Other rapidly developing technologies allow smaller packaging of systems. These include advanced solid-state lasers, chemical lasers with electro-regeneration of chemicals and fiber lasers.

The technical hurdles include compensating for vibrations and high g-forces that can punish the laser and beam-control system and turbulence around the aircraft. "The beam control system must be extremely dynamic to account for these fast transient processes occurring at kilohertz rates," the report said.

Lockheed Martin looked at laser concepts from TRW, Boeing and Textron, but Raytheon's appeared to be the most advanced, a company official said. Raytheon's solid-state design is "particularly suitable for JSF because it's very compact and shows promise for achieving the necessary power levels and beam quality," the Lockheed Martin official said. "The other companies don't appear to feel as confident in their ability to buy or develop a suitable laser." Company officials are also hoping that the Air Force Research Laboratory's directed-energy directorate at Kirtland AFB, N.M., or the Defense Advanced Research Projects Agency would fund some of the solid-state laser development.

A first-generation laser weapon would be able to engage aerial targets such as cruise missiles and enemy aircraft, as well as ground targets such as antiaircraft missile sites and ground vehicles. These capabilities would likely require laser power of 100 kw., analysts predict.

"That's about the minimum threshold to be a weapon," the Lockheed Martin official said. "Less than that and it's only useful against soft targets. One hundred kilowatts would also let targets be engaged at tactically significant ranges."

Except for self-defense, laser weapon designers think the minimum effective range is about 6 mi. for a fighter aircraft. As the power of solid-state lasers improves with the maturation of new technology, the range of directed-energy weapons would increase. Ideally, the laser-equipped aircraft would also carry conventional munitions. The F-35, for example, won't give up any weapon-carriage capability when the laser is installed, and it will allow a combination of effects. Lasers can provide low collateral damage and covert attack. Conventional weapons would provide longer range strike.

"Laser and HPM [high-power microwave] weapons are more like an avionics system," a company official said. "You don't go out, drop three and go home. It's always on the air vehicle, you use it when you want and, at least with solid-state technology, you're not going to run out of power."

The concept for F-35 is to have a turret, centered on the lift-fan cavity, which would extend when needed from the bottom of the aircraft. The system would be installed in the space just aft of the cockpit that was carved out to hold the vertical lift fan. With a single turret, the directed-energy weapon would be most effective against ground targets, low-flying airborne targets and for self-defense.

While conceptually the one-turret aircraft could be maneuvered to fire at other aircraft or air-to-air missiles, planners are dubious. "There's not always time to maneuver, especially in close-in self-defense situations, so you want multiple apertures," a Lockheed Martin official said. Therefore, company designers are considering a second turret that would extend from the top of the lift-fan space to cover the upper hemisphere around the aircraft. They don't yet know if they can make both turrets fit into the space that they must share with target trackers, laser, optics, power and cooling. "It will be a trade of coverage versus internal volume," he said. There also would be the option of flying a mix of aircraft, some specialized for air-to-air and others for ground attack. For demonstration purposes, the laser system would likely be installed first on a pod and later on an early model JSF airframe.

Lockheed Martin believes it has a distinct advantage in getting directed-energy weapons into the field because the F-35's unique design will allow it to supply a great deal of electrical power. Instead of having to rely on heavy, short-lived batteries to run the laser, it will be fed electrical power generated by a drive shaft run from the main engine. In the Marine Corps' short-takeoff, vertical-landing version of the F-35, the drive shaft will power the vertical lift fan. But for the Air Force and Navy versions, the empty spaces designed for the lift fan and cannon could be used for the laser weapon.

"The drive shaft has the [potential] of producing multi-megawatts of power in real time without hurting the aircraft's performance," the Lockheed Martin official said. The shaft from the engine can produce more than 27,000 shp. to drive a generator. But the rate of fire and recycle time for a laser weapon, particularly against targets at long range, may be limited by the need for thermal cooling. "You can't fire forever," he said. "The challenge is doing the cooling in near real time." What the duty cycle will be has still to be determined, but some specialists suggest that at least initially it might be a 4-sec. burst, followed by 4 sec. of cooling, then another 4-sec. burst and finally a 30-sec. cool-down before engaging two more targets.

Directed-energy, self-defense weapons with a fast recycle time for multiple shots (since two or more antiaircraft missiles are usually fired together) is considered a key concept for future warfare. By 2025, many U.S. Air Force planners believe multispectral sensor technology will overtake the ability of stealth designs to protect aircraft from air defenses.

Directed-energy weapons fall into two categories so far: high-energy lasers and HPM. Farther in the future is a plasma of ionized gas molecules that might resemble a bolt of lightning.

Lasers use thermal effects to quickly blow holes in targets, and they are being designed for use in manned aircraft, say Air Force and aerospace industry officials. A laser beam can be focused on a fuel tank to produce catastrophic damage, or it can be focused on a vehicle's engine to simply disable it. Generally, however, it is a lethal, longer range weapon.

HPM is most effective in attacking electronics, particularly computers where spikes of high power can damage components and erase computer memories. This kind of technology is seen as the weapon of choice for unmanned aircraft because spurious emissions might affect safety of flight.

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