Microwave Thermal Rockets
Ah microwave beamed rockets. Such a wonderful sounding idea, and yet so difficult to pull off. For those of you who know Keith Hensen his Solar Power Satellites are best launched into orbit with laser powered (or more generally ground powered) rockets. And the concept is mathematically sound, just the notion of having a multi-gigawatt laser pointed up at things in orbit is so destabilizing.<p>The summary for this link and for ground powered rockets in general, is that the amount of energy you can get out of an Hydrogen&#x2F;Oxygen reduction reaction is about about it as far as chemicals go, but you can combine a lot of energy sources into a single transmission beam and if you can transfer that energy to your propellent you can do much better in terms of rocket efficiency.<p>The diplomatic challenge is that you need to be able to create a large directed beam of energy that you can steer at orbital (or near orbital) velocities that can reach into space. And while it is great when you&#x27;re pointing it at some heat exchanger which is converting heat to thrust, its rather unfortunate if the target is a satellite just going by overhead taking pictures perhaps.<p>So really, in the current political climate, it&#x27;s a non-starter. Not from a physics point of view but from a stir up the rest of the world point of view.