Hi, I'm new to the forums and I'd like to bounce an idea off of someone Although I've got a physics degree, I have successfully managed to forget a lot of it as people tend to do when not practicing, and I was wondering if someone would kindly pick some holes in an idea I've had. Firstly, I should imagine at least someone has heard of pumpjet propulsion for marine vehicles, as well as its nerdier cousin the magnetohydrodynamic drive. What I can't understand is why no one has mentioned a simple jet based on heating water using microwaves. It would not be necessary to boil the water, and in fact this would be unwise as it would cause cavitation, and the direction of flow could be controlled by simply shaping the tube so that it expands in the desirable direction. I think I'm right saying that microwave absorption would be very efficient if done correctly, and although it would not make for particularly responsive propulsion, it would be quiet and easy to maintain. The technology required is much more readily available than for MHD, and it would have the capacity for greater velocity. Can anyone see something I'm missing? I've got my suspicions you see :tongue2: Thanks!