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Flying laser (Part II)

Last time I talked about how the US Military ended up scrapping the so-called "Stars Wars" Project of the mid-1980s.

Last time I talked about how the US Military ended up scrapping the so-called "Stars Wars" Project of the mid-1980s. It was supposed to use big powerful lasers to destroy incoming nuclear missiles.

But after a while, they began work on smaller umbrella-type defence system, still using lasers.

In mid-January, 2000, a stripped-down 747-Freighter was flown to the Boeing Modification Center in Witchita, Kansas. This jumbo was the very first aircraft bought by the US Air Force in the new millennium, and so it was given the number, 00-0001. It deserved this cool number, because, if the plan worked, the Flying Laser would revolutionise warfare.

Lt. General Robert H. Foglesong, Commander of the US 12th Air Force, welcomed it to Witchita with the words, "It would not be smart to ever let our airmen enter a fair fight - the (AirBorne Laser) is another step toward ensuring we have an unfair advantage over our enemies".

Even so, as in the earlier failed Star Wars Project, the problems are still enormous.

Laser beams are generated by bouncing light back-and-forth, millions of times, along a very precise and exactly-controlled path. On the ground, powerful lasers are usually mounted on enormously heavy blocks of rigid concrete and steel, which in turn, are protected from all possible vibrations of the ground by very sophisticated isolation dampers.

But this 747-freighter jet is about 70 metres long, and made as light as possible, and the hull wobbles like jelly on a plate. So the engineers have developed a very sophisticated system that measures the flexing of the jet's hull, and compensates for it.

What about the turbulent atmosphere, which can distort and weaken the laser beam? Well, they have worked out a way to measure exactly what kind of turbulent air there is between the 747 and the target, by using a kilowatt-class laser.

They then compensate for the turbulence in the atmosphere by changing the shape of a mirror thousands of times per second, and then bounce the laser beam off that shape-changing mirror.

And did I say "mirror"? There are actually 127 separate sophisticated optical devices in the Flying Laser - devices such as mirrors, lenses and windows. They range in size from two centimetres to 150 centimetres across.

There are two kilowatt-class lasers, and one big megawatt-class laser - and they all run at different frequencies. It's difficult to coat mirrors, lenses and windows to let them deal with huge power at one specific frequency - and it's almost impossible to do it with three different frequencies at the same time.

But even so, they did it.

And how do they aim the megawatt laser at a quickly-moving target? They have a big mirror in the nose of the 747, that can quickly tilt up-and-down, and side-to-side. Of course, you need a window in front of it, to keep wildlife and airborne debris from hitting the mirror.

This window is like a giant contact lens, and is one of the largest transmissive optics ever coated. It had to be specially shaped to stop the beam from distorting, and specially coated to let the laser power through without reflecting or absorbing any of the power. Just to make this single "contact lens" took four-and-a-half years to shape and grind.

The megawatt-class laser is made from six separate modules, that combine their power to make one enormous killing beam. Each module is the size and weight of a large 4WD vehicle, standing on its nose. The laser runs on chemicals such as chlorine, iodine, potassium hydroxide and hydrogen peroxide. Each module carries enough fuel to fire off 30 laser shots, each lasting about 5 seconds. Each shot will use about $1,000 worth of chemicals.

The engineers built a two-tonne wall to keep the crew protected from any possible chemical leaks from the big laser.

Lockheed-Martin have come up with a clever way to find the target missile. They first look for the hot rocket exhaust, then "paint" the missile with kilowatt-class laser beams and analyse the reflected light to find the missile. Then they let off the big fat killer laser beam. It is supposed to land a spot of heat, the size of a basketball, and loaded with over a million watts of power, on a fast-moving missile hundreds of kilometers away.

By 2008, seven of these airborne fortresses should have been built, at a cost of around $US 5 billion. Light is made up of photons, so just like in Star Trek, the Captain will say, "Fire off the photon torpedos!"

But whether the Flying Laser proves to be any more useful than the original failed Star Wars Project - well, that remains to be seen...


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Published 09 November 2005

© 2015 Karl S. Kruszelnicki Pty Ltd