…in the theoretical sense, anyway. I’m aware that this isn’t exactly off the shelf hardware.
But, say I wanted to build a Death Ray Satellite™ in low-Earth orbit (~250 miles), intended primary for attacking surface targets—specifically, delivering the equivalent of 1 ton of TNT (4.184 gigajoules) onto a sedan-sized target per shot. All else being equal, what’s the most efficient type of directed energy device to accomplish this? That is, what would waste the least amount of energy (shooting through the atmosphere, etc) to destroy a target?
And before you ask, kinetic bombardment is off the table. For purely aesthetic reasons.
If we’re looking at efficiency, how big of a parabolic reflector would you have to use to reflect the sun’s rays and fry a tank like an ant under a magnifying glass?
I’m thinking something along the lines of a high intensity maser (a microwave laser), that can store up huge amounts of solar power in on board batteries, between blasts.
Light and heat diminish at the inverse square from its distance, so something about 100 miles up in orbit, would have to be huge. Not only that, but for maximum intensity at the focal point, it’d have to be built to crazy precision and this isn’t factoring in a moving target or cloud cover (let alone, time of day and angle of incidence).
If you look at it from the point of view of the target, the absolute best you can do, with perfect efficiency, is to make your entire device look like the surface of the Sun (corollary: you can never use a sun-reflector to heat anything to hotter than the surface temperature of the Sun). To the ant, the size of a magnifying glass looms quite large in its field of view. To anything on the Earth, though, any sane-sized satellite will take up a very small field of view, far smaller than the Sun itself (which isn’t enough to zorch things).
Also, how tight a spot you can make is limited by the angular size of the Sun. If your optics were in orbit, then you’d get a bright spot on Earth that was of order a kilometer across (again, assuming perfect optics).
Say we’re able to build an adequate energy weapon to blow up a tank on the ground or and ICBM en route from orbit.*
Wouldn’t counter-counter-tactics easily give rise to shield such things from said orbiting energy weapons?
*yes we nuke them from orbit, as it’s well… you know.
The range seems like it’s about there “Tougher solid-fueled ICBM destruction range would likely be limited to 300 km…” but does it have the destructive power of 1 ton of TNT? doesn’t sound like it from the Wiki article "The ABL does not burn through or disintegrate its target. It heats the missile skin, weakening it, causing failure from high speed flight stress. "
Would it even destroy an ordinary passenger car with a direct hit from orbit or just make it very hot inside?
The inverse square law is true for spherical waves, but for a laser within its Rayleigh range, the intensity doesn’t fall off as the inverse square. Of course, virtually all lasers are used beyond their Rayleigh range, and outside that range the limiting case is an inverse squsare law, but it’s still a tighter beam and greater intensity than you get from a body radiating in all directions, or veven in a beam with greater divergence than a laser. Lasers beat searchlights.
Nevertheles, it’s true that you’d need a huge amount of power to do damage on the earth from an orbiting laser. Even ignoring the spread of the beam with distance, the interaction of a powerful beam with the atmosphere will cause the air to heat up and expand the beam, reducing its intensity. This is called “thermal blooming”, and is considered a serious problem. It’s a big reason that people who want to build SDI systems want to put their beams in orbit and shoot at targets that are outside the atmosphere – nobody has to worry about thermal blooming effects.
If you really want to destroy a target on the ground, it’s a helluva lot easier and cheaper to use a weapon closer to the ground.
