For a story I'm working on I'm designing a sattelite to take down infantry from orbit, but without the power to take down tanks or infrastructure. The goal would be to kill off a military base, or even an entire population, and then be able to claim all the territory and equipment intact.
I just need an idea on how this could be accomplished.
I also need a good acronym for this long-named weapon. Any idea's?
Let's suppose this satellite burns people like a magnifying glass kills ants. One satellite could keep switching between targets. A constellation of such satellites could help speed up the process.
If you are going to zap a person with a satellite, it has to be a real quick zap. A satellite on low Earth orbit will be moving at around eight kilometers per second in relation to the ground. Also the slightest movement from a target would remove them from the beam path.
Some sources cite the energy to vaporize a human in the vicinity of three gigajoules. But you don't need to completely vaporize a person in order to cause death. This article has a very good explanation on how to do so with much less energy. What matters most is how fast you deliver energy, though.
I think that vaporizing half the soft tissue of a body would already be lethal enough. That would take one hundred million joules. You could deliver that in one second with a one megawatt laser - add some 10% more power to compensate for losses due to atmosphere and body armor (I am totally eyeballing here).
Unfortunately for your goals, if you are able to output that much on a spot, you can cut through any metal. You can also melt concrete. So no, you can't have a laser weapon that is only able to kill humans. You may however limit what it can target through AI or other means.
A good acronym could be L.O.V.E. - Large Orbital Vaporizer Experiment, so you can say that you are killing your enemies with love.
Suggested theme: All Nightmare Long, by Metallica:
The light that is not light is here
To flush you out with your own fear
You hide, you hide
But will be found
Release your grip without a soundStill life,
Immolation...
Particle beam.
Stuff that kills people but not buildings is either a toxin/bioweapon, or mutagenic radiation. Not much prospect for gassing them from orbit so that leaves the radiation. Which might be doable.
As regards the neutron bomb, I like J. Frank Parnell explained it best. From the movie Repo Man
http://www.imdb.com/title/tt0087995/quotes
Otto: Lobotomy? Isn't that for loonies? Parnell: Not at all. Friend of mine had one. Designer of the neutron bomb. You ever hear of the neutron bomb? Destroys people - leaves buildings standing. Fits in a suitcase. It's so small, no one knows it's there until - BLAMMO. Eyes melt, skin explodes, everybody dead. So immoral, working on the thing can drive you mad. That's what happened to this friend of mine. So he had a lobotomy. Now he's well again.
Really, though, most people would die in a few weeks from radiation poisoning. As pointed out in the wikipedia article http://www.imdb.com/title/tt0087995/quotes the explosion necessary to generate a neutron radiation burst is big enough to cause lots of damage to stuff.
But not from space! And neutron are nifty because bombs generate them automatically. But they are not very heavy and air slows them down.
Essentially neutron radiation is a particle beam. If you want far punching particles, use heavier atoms. Gold, or iron. You could build your satellite into a captured asteroid for ammo then rain down super accelerated particles. Lots of trouble for biologicals. Not much for metal and other stuff.
What you want is a particle beam, specifically a hydrogen beam - also called proton beam.
More details on weaponized space particle beams here and here (from the always interesting ToughSF blog), but here are the elements that are important for the question:
Neutral particle beams accelerate ions and electrons before recombining them into neutral atoms. This last step is important because charged particle beams (like electron beams), while easier to produce, repel themselves and disperse rapidly, considerably decreasing their range. In addition, they are easier to protect from with magnetic fields, and create dangerous charges on the emitter. So neutral particle beams it is.
The problem is that particles are stopped by matter, and you want to fire through the atmosphere. Here is where things start being counter-intuitive. You would expect heavier particles to travel further before being stopped, but in fact the opposite is true: the lighter the atom nucleus, the further it will go for the same energy. And the lightest nucleus is a simple proton, from hydrogen atoms.
Intuitively, you would also expect how far particles go to continuously decrease the further you go, with more particles being stopped in the first 10cm than in the 10cm one meter past. however, most protons actually cross some distance unimpeded before being stopped en masse, something that is called a Bragg peak. Which is good for you, as you can fire with just the right energy so the Bragg peak is right in the middle of the squishy humans instead of in the atmosphere, building wall or tank armor.
With powerful enough emitters, you can even hit deep underground bunkers, though this require some hefty beams. At this point, you may even switch to antihydrogen beams to pack an extra punch - antiprotons beams seem to mostly work the same way than proton beams in that regard.
Hydrogen is better than neutrons for a few reasons: neutrons don't have a Bragg peak, so they aren't that good at penetrating hits. In addition, collimated neutron beams are very difficult to produce, and neutron activation will cause more material to become radioactive, which you do not want here.
What about the electron, one may ask. It is mostly negligible (beyond neutralizing the beam), as its mass (and thus the damage it will cause) is about a thousand times less than the mass of the proton.
Do note that while there have been some tests made for hydrogen beams as a space-to-space weapon, you would need much more energetic beams than could be put in orbit with today's tech for an orbit-to-surface weapon.
