Can we vaporise space junk?
Colin says, "over here in Australia, I recently saw a news report about a new whizbang radio astronomy array that's in the desert. The astronomers were surprised and quite possibly also annoyed that they could detect and track space junk and satellites with exceptional accuracy with this apparatus. So my question is, could we possibly use this to target and destroy the junk with a powerful ground-based laser and zap it and destroy it?"
Matt - The answer is, hopefully. Space junk is a problem and it's only going to get worse. There's this positive feedback effect you have with space junk where if two bits of space junk crash together, they fragment and then suddenly you have a hundred bits of space junk that you didn't have before. And so if you cross a critical threshold, you can end up with so much space junk getting into orbit which could be really difficult. So we have to do something about it and part of the solution is going to be tracking it with these radio telescopes. I think you're talking about the square kilometre array in Australia, but there are different plans to get rid of the space junk and powerful space lasers are one of the top possible solutions. A slightly more popular option these days is to use a slightly less powerful laser to just heat the space junk until it changes its orbit, then burns up in the atmosphere. That's got the wonderful name - it's called a laser broom. I think the idea is to use the laser to sweep the orbits clear by making everything burn in the atmosphere.
Chris - That phenomenon of giving things a push with light also has a fantastic name, doesn't it? It's the YORP effect, which I learned about from a scientist who was studying how asteroids get pushed around by photon pressure from the sun. he said, Yarkovsky, O'Keefe, Radzievskii, Paddack effect, after the four blokes who discovered it. And I I said, I'm going to remember that because it's so fantastic. And here I am about 20 years later recalling that bit of information. But that's basically the same thing, isn't it? You give things a big burst of very powerful light, lots of photons, and they impart momentum and give it a push?