Posted on 09/26/2002 2:58:56 PM PDT by green team 1999
Aerospace Daily: Keeping Cool A Big Challenge For JSF Laser, Lockheed Martin Says
By Jefferson Morris/Aerospace Daily
26-Sep-2002 11:44 AM U.S. EDT
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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Turn the excess energy into a power source. Presumedly, after firing, the platform should get out of the area. Carry along a supply of some material with a high specific heat capacity and use it to flush the excess heat away from the electronic coils. Water comes to mind. By flushing water over the by now very hot coils, the water flashes to steam, and if ducted to the exhaust discharge, can provide an ample boost to the jet blast, providing the effect of an afterburner.
Of course they have. They finally reverse-engineered the dilithium crystals from the flying saucer that crashed in Roswell back in 1947.
TWA 800 Reference? Do we now have engineers conflicting with the NTSB?
What kind of problem are they trying to solve with a laser weapon? How much would all of that equipment to feed the laser, and cool the laser weigh? How much would a gun with a 20 mile range weigh?
I don't think a 155MM howitzer is going to fit on the airplane.
I would lay odds that this will be the solution, at least for the first generation. I don't see any way to radiate or convect this amount of heat away without adding too much weight. The working-fluid approach you suggest converts the heat reject problem into an expendable, like water. Still has a lot of weight, though.
My question is: how are they going to generate a megawatt of electrical energy? I have no doubt they can generate that much mechanical energy out of the engine, but how do they convert that mechanical energy into electricity within reasonable weight and size constraints? An off-hand guess would be that it will involve high-temperature superconductors in some way. Wow.
I don't see how they can "turn the excess energy into a power source" because of the thermodynamics. The only good use for a lot of heat on a fighter jet would be do dump it into the exhaust for use as an afterburner, in effect. The problem here is that the entropy of the waste heat will probably be too high to do any good; IOW the temperature of the rejected heat flow won't be enough to add anything to the thrust of the engine. The engine's exhaust will almost certainly be hotter than the heat being rejected by the electronics.
(steely)
In effect becoming a turbo hydro-ram jet.
The engine generates several megawatts of mechanical energy. Generators today operate at very nice efficiency levels. The rest is merely detailed engineering.
I might be able to tell you more. But if I did tell you, I'd have to kill you :o)
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