A SERIOUS flaw has emerged in the $1.1 billion US project to use
powerful airborne laser weapons to shoot down enemy missiles, says an Israeli
academic.
Nathan Kopeika of Ben-Gurion University told a conference in Florida last
week that he believes engineers working on the Airborne Laser (ABL) project have
overlooked the effect of tiny dust particles in the atmosphere, called aerosols.
These could scatter and weaken the laser beam, making it incapable of destroying
incoming missiles.
The ABL project, initiated by the US Air Force in 1996, plans to convert
Boeing 747 jets into flying laser cannons that would patrol the skies scanning
for enemy missiles.
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If Kopeika鈥檚 claim is correct then the atmosphere could throw a spanner in
the works and make the lasers all but useless. 鈥淲e found that, after a
propagation of 100 kilometres, aerosols can widen a laser beam up to a cross
section one kilometre wide鈥攕everal orders of magnitude worse than optical
turbulence,鈥� he says.
The widening causes a drastic reduction in the intensity of the laser beam.
What鈥檚 more, scattering doesn鈥檛 only occur in extreme atmospheric situations,
but can be caused by natural levels of aerosols鈥攖he density of which
changes with the weather and according to the seasons.
Richard Garcia, director of public affairs for the ABL project, is not
perturbed by the news. 鈥淭o compensate for the atmospheric effects, first a
lower-powered laser is bounced off the missile to tell us where the distortions
are, then we use an arrangement of oscillating mirrors to cancel out the effects
of the distortions,鈥� Garcia explains.
But Kopeika isn鈥檛 impressed. 鈥淭hat鈥檚 how you deal with optical turbulence,
not aerosols,鈥� he says. But he suggests one potential solution would be to use
data on aerosol density over several seasons to predict the altitude with the
lowest density on any particular day. The jumbo would then fly at this optimum
altitude, likely to be between 8 and 20 kilometres, and shoot horizontally at
the missile.
鈥淚f they don鈥檛 take note of this problem they are in for a nasty surprise,鈥�
says Kopeika.