One of the biggest challenges facing Lockheed Martin in its efforts to install a high-energy laser on the F-35 Joint Strike Fighter (JSF) is the question of what to do with all the excess heat generated by the system, according to the company's lead for directed energy programs.

Laser systems use electricity to produce highly focused beams of light, as well as considerable amounts of waste heat that must be dissipated. Lockheed Martin believes that a 100-kilowatt laser is the minimum power level needed to be an effective weapon for a fighter.

However, "to get 100 kilowatts of light out, you've got to put a megawatt of electrical power in, so somewhere along the way you've got to deal with 900 kilowatts of cooling," Tom Burris, lead for directed energy at Lockheed Martin Aeronautics, told The DAILY. "That's a ton, for a fighter that normally does tens of kilowatts of cooling."

To dissipate the heat, cooling loops will be employed to take heat from the laser system and transfer it into the aircraft's fuel tank, where it can be burned away.

"Just like a radiator in your car takes the heat from the cooling that goes into your engine and puts it into the air, this just puts it into the fuel," Burris said.

This process won't compromise the JSF's stealth, Burris said, because it will have no appreciable effect on its infrared signature.

"If you think about the amount of fuel onboard a jet aircraft, if you put all that heat in the fuel, you might raise it by a degree, something on that order," he said. "So in terms of signature, it has no impact."

Lockheed Martin plans to make space for the laser system by pulling out the Rolls-Royce-built shaft-driven lift fan in the Marine Corps short takeoff/vertical landing (STOVL) variant of the JSF (DAILY, Sept. 23). Within that 100-cubic-foot space, used largely for fuel storage in the other variants, the laser can draw wattage from a shaft connected directly to the aircraft's JSF119-611 engine.

Solid-state lasers, which use a solid material such as crystal or glass as the lasing medium, are the most mature and promising laser technology for this application, according to Lockheed Martin. Single-digit-wattage solid-state lasers already are commonplace on today's fighters, where they perform tasks such as rangefinding and target designation.

Over the summer, Lockheed Martin signed an agreement with the Air Force Research Laboratory's (AFRL) Directed Energy Directorate to cooperatively explore high-energy laser concepts for fighters (DAILY, June 6). AFRL will furnish the laser, while Lockheed Martin concentrates on integration into the aircraft.

Lockheed Martin anticipates the JSF using lasers against both air and ground targets, at a typical range of 10 kilometers (6.2 miles). The laser itself would be housed in a dome that would emerge from the aircraft when needed, Burris said.

"When you want to use it, you'll deploy the turret, so it'll pop out into the airstream," he said. "You'll get a target cue from somewhere, just like all weapons do. It'll slew over to where you think the target is, acquire the target, and then it'll start lasing it."

The earliest opportunity the company will have to place a high-energy laser system on the JSF will be beginning with the Block Four version around 2012, according to Burris.

Optics

The other major challenge in putting lasers on the JSF is keeping the laser beam focused properly as it passes through the turbulent air around the Mach 1 aircraft.

"That flow field around the aircraft will distort the laser beam," Burris said. "So you'll have to have some sort of system onboard ... that'll sense that distortion and then correct for it."

The solution is adaptive optics - a technology developed by AFRL that is already in use on the Airborne Laser (ABL) program and at many astronomical observatories around the world. An adaptive optics system performs real-time compensation for atmospheric distortion by using deformable mirrors that can "pre-distort" the beam in such a way that the atmosphere itself straightens it out.

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