Could an orbiting laser platform be used to destroy space junk? I would expect not since it seems like a really obvious solution. What are the technical problems?
Thanks,
Rob
First, lasers aren’t necessarily that powerful. If you blast something so it falls apart, you simply create 10 pieces of junk where there was 1. A hot piece of junk is just a piece of junk. The “light pressure” is not going to have much effect - even if it did, hitting from below could be counterproductive. the ideal would be vaporizing it - but the amount of laser light needed to create iron vapour is pretty high.
Also note a laser tends to be incredibly inefficient - about 2% or 3% of the energy used to power a laser comes out as the beam.
Maybe a more effcient method might be to hit thing with a particle beam. collisions with high speed particles could help - but that would have to happen from above the atmosphere, meaning the need to lift a powerful beam weapon into space. Weapons in space are kind of discouraged right now.
And spitting out particles from a satellite would screw up the orbit of the satellite as well as what ever it was shooting at. Perhaps if it shot at several different pieces in several different directions, the momentum would average out. Would such a cannon necessarily qualify as a weapon?
Rob
P.S. I was also thinking of a satellite-based laser.
I blame the pope.
The biggest technical problem is generating a powerful enough beam. As a point of comparison, the Boeing YAL-1 project involved mounting a megawatt laser in a 747, and was designed to shoot down ballistic missiles. There were a couple successful tests, but it destroyed the missiles by heating them enough to cause structural failure under aerodynamic stress, not by melting through it’s skin. Such a laser would be completely ineffective against space junk. The cost of the program was about $5 billion.
Lasers are power intensive, but electricity doesn’t cost much. Say they had something crazy, like a 100 megawatt laser that pulsed for 1 second, 2% efficiency. Thats 1400 kwh, or around $200 in power costs.
Remember, they don’t have to or want to destroy the fragment, or melt it, or anything. They want to superheat a surface to vaporize some material, which will push the fragment in another direction and cause it to change orbits. This is known as ablative propulsion. This will either steer it away from something in orbit, or lower its perigee to a point in the upper atmosphere so its orbit can decay.
But the most powerful lasers are not powered by electricity. The YAL-1 mentioned above uses a chemical oxygen iodine laser which needs to be fed with “gaseous chlorine, molecular iodine, and an aqueous mixture of hydrogen peroxide and potassium hydroxide.”
Obligatory what if.
Very good point. 
Let’s say you had some kind of magic snot cannon that could deploy huge balls of fibrous mucus, like dozens of meters across. More and more junk would get embedded until the whole thing came crashing back to earth like a fiery space booger of justice.
Since lasers are not miracle “make shit not exist anymore” like on movies and tv, no they can’t “destroy” space debris.
Or maybe it would turn into a star of its very own consisting of paper clips, cruise ships, and unfortunate poodles.
The idea of using space lasers to de-orbit orbital junk has been around for a while now. I dobn’t know if anyone’s done a numerical analysis (probably they have), but the idea is to use laser light pressure (and possibly laser ablation, which is a lot bigger and more impressive – we speaks from experience) to slow down small objects in orbit to the point where they start encountering more atmospheric friction, where they will slow down even more, and so on, until they get so low that they fall into the atmosphere. Laser pressure is good for this application because, even though it’s a small push, it can be applied for long periods of time and from long distances, and there’s no satmospheric attenuation or thermal blooming to mess up the beam. It’s the perfect environment for using laser light pressure.
Obvuiously this would require lasers that coukld provide continuous push, so this doesn’t seem like a good application for chemical lasersw, which would exhaust their constituent gases.
And if you question the ability of lasers to provide the oomph to do this, observe that Leik Myrabo, Arthur Kantrowitz, Jordin Kare, and others have been advocating using laser propulsion from the ground to put objects into orbit. Using lasers to change orbits is trivial by comparison.
Then I vote 
YES! on Proposal Space Booger.
I’ve heard of proposals to deploy a kind of very wispy foam or gel to do exactly this. Well, actually I think the idea isn’t to trap the junk, but to slow it down as it punches through the “cloud” of space booger, so it falls out of orbit faster.
Another idea I’ve toyed around with: Does anyone remember the old arcade game Xevious with the flying indestructable plates? Maybe we could set up some large iron plates in space, and angle them so any space junk that hits them would be deflected towards the atmosphere.
Laser propulsion usually involves using a laser to heat up the propellant (reaction mass) carried on the projectile/spacecraft. It’s not photon pressure that provides thrust. Using this method to deorbit space junk would require enough power density to heat up and vaporize the surface of the space junk. That means a very powerful laser and a large aperture optical system.
I’ve worked on laser propulsion, and , as my post indicates, it doesn’t use photon pressure, but gives more oomph. People have suggested using both photon pressure and photon ablation.
cc
As an aside…man that sounds scary…now I know why someone referred to that laser as a rocket engine with mirrors on each end.