An English inventor, Roger Shawyer, has been developing a microwave-powered thruster which uses absolutely no propellant!
Voices in the scientific community are expressing doubts and questions - along the lines of 'How can this possibly be true?' This is because, as we have understood the universe since the time of Sir Isaac Newton, if something pushes one way, there must be something pushing the other way. In a rocket motor, for example, tons of burning fuel shoot out the back which pushes the rocket in the opposite direction. Ion thrusters in satellites use electric fields to push ionised gas and move the satellite. But in this new device, nothing moves! Just microwaves. And microwaves have no mass.
Roger Shawyer proposes that the microwave radiation pressure difference inside the tapered chamber produces the thrust. The Chinese scientists who have both verified Shawyer's results have a different way of explaining it, and when NASA repeated the experiment recently they declined to propose a theoretical explanation.
Honestly, I'm fascinated. Will this prove to be another let-down, like cold fusion? Or will this be the 'dawning of a new age in the history of space travel', in the style of some of the recent journalism? Time will tell.
What could this lead to, if it's true? Certainly it might be put to good use in satellite station-keeping - maintaining a satellite's precise orbit against the slight but constant drag of the outer fringe of Earth's atmosphere.
If it can work efficiently on a large scale, in a vacuum, it might prove practical to power interplanetary probes and crewed craft on missions to Mars and elsewhere. If mission planners are suddenly told 'You don't need to take fuel anymore', everything will change. The need for fuel to accelerate and decelerate, to change orbits, is the big limitation on all space missions.
The force produced by this microwave drive looks small so far, but it can be maintained for as long as there's electrical power to generate it. So use nuclear power, perhaps, or lots of solar power, and a spacecraft could accelerate gradually, steadily, over a long period, to build up a truly impressive speed. The transit time to Mars, for example, might be reduced to weeks instead of months.
The eventual result, though, will be closer to home for me: I think that science fiction writers will have to change gears! Usually a writer has to 'invent' a space drive like this to allow easier travel to the planets, and eventually the stars, and it's tricky to make it believable. Perhaps, if there's a real space drive in use, it will make our new microwave-powered spaceships look realistic. Perhaps we'll still be inventing the next generation of drives. What next? Bio-fuel starships?