At 1:43 AM +0300 7/24/01, Sampo Syreeni wrote:

...

But I also think the question Choate posed is a valid one: what happens when the target is *not* a ballistic missile, but people, equipment and vehicles on the ground, normal aircraft, or air-to-air missiles? One would think that the lower velocity differentials and expected distance-to-target make aiming much easier, and that effective counter-measures would be significantly more difficult to erect, considering that such conventional targets have properties very different from those of ballistic missiles (e.g. aircraft raise questions of aerodynamics and payload efficiency, wearable materials with albedos high enough are difficult to come up with, rotation and aerodynamic engineering cannot be used to dissipate the heat generated by a hit, people/cars/tanks/whathaveyou often need to be difficult to spot using aerial and satellite imaging, and so on).

Such weapons capability could be *quite* useful, especially if the 747 can be effectively defended against anti-aircraft missiles, and the laser has a range and targeting capability on par with anti-ballistic missile applications. Hits on critical infrastructure, control over a nation's airspace, death-from-above FUD, that sort of thing.

IANALS (laser specialist), but I am given to understand that with the high energy demands of these types of lasers, and the problems with getting good energy levels through airborne dust, clouds, etc (and especially in combat areas where dust and other airborne particles are rather common) make lasers less than ideal against ground or low flying targets.

========================= From US Pat 5,345,238, Satellite signature suppression shield If a high energy laser (HEL) is being used to attack the shield, the laser must irradiate the cone with an energy above 10 watts per square centimeter normal for more than two minutes continuously to damage the gold coating. Occasional short term hits will do no damage except by lasers with a much higher energy than currently considered practical. Higher laser energy levels will do damage in less time, but the signature suppression levels are low enough, that closed loop tracking of the satellite is impractical at altitudes above 100 km. FIG. 6 shows the time required for vaporization of the metal film over the balloon skin as a function of the aspect angle. Direct irradiation with a 10 W/cm.sup.2 laser beam was used. The dotted line in the figure represents a 10 micron gold film over a 0.5 mm Kapton skin. The solid line represents a 10 micron aluminum film over a 0.5 mm Mylar skin. ========================== So if the exterior of the missile had characteristics similar to the shield above it might deter direct damage from a HEL. I haven't done the path loss calculations but suffice it to say acquiring and maintaining beam lock and delivering several Watts/cm at distances of 100 km is a daunting challenge. Due to Raleigh scattering some pretty big aperture mirrors are needed to keep beam divergence sufficiently small (non-Gaussian optics, for example second order Bessel, could also help but complicate optical design and efficiency.) steve